IIM, Trivandrum chapter – List of Award Winners

The first Prof. Brahm Prakash Best Ph.D. Thesis Award of the IIM, Trivandrum Chapter is conferred to Dr. Rohit Kumar Gupta, Scientist F, MPA/MME, VSSC, Trivandrum for the Ph.D. thesis entitled “Deformation Studies of + 2 Titanium Aluminides processed through Reaction Synthesis”. Dr. Gupta had received the Ph.D. degree from IIT Roorkee under the guidance of Prof. Vijaya Agarwala, IIT-Roorkee and Dr. P.P. Sinha, VSSC, Trivandrum.

Prof. Brahm Prakash Metals and Materials Quiz conducted by IIM Trivandrum Chapter - Mr. Vamsee Krishna and Mr. Aravind J Students of Arya Central School, Pattom, Trivandrum

IIM, Trivandrum chapter – Honouring Award Winning Members

S No Name Award/Fellowship

1. Dr. Koshy M George, Deputy Director, VSSC

"Lifetime achievement award "of Society of Aerospace Manufacturing Engineers (SAME).

2. Dr. K.G.K. Warrier CSIR Emeritus Scientist, Materials Science and Technology Division, CSIR-NIIST

Two life time achievement awards… 1. Indian Society for Analytical Chemistry Award

2012 2. Sri Kishan Modi Memorial Award by Indian

Ceramic Society 2013

3. Sri. Niraj Nayan, VSSC

(Co-Authors-Dr. SVSN Murty, Dr. Koshy M George)

Received the GS Tendulkar Best paper award during NMD-ATM 2013 at Varanasi

4. Dr. Thomas Tharian (LPSC, Tvm) & Team

(1. K.Kumar , MME/LPSC- New member 2. Joby Thomas MME/LPSC- New member 3. Anoop CR MME/LPSC- New member 4. Vartha Venkateasrlu SRQA/LPSC- New member 5. VMJ Sarma VSSC 6. G. Sudarsana Rao VSSC)

ISRO Team Excellence Award for indigenisation of VIKAS Engine materials.

5. Mr. E. Jeyakumar, CSIR-NIIST

(Co-authors: Praveen A.P., K.K. Ravikumar, T.P.D. Rajan, B.C. Pai and V.R. Rajeev)

ISRS Best Paper award for the paper presented in the International Symposium for Research Scholars on Metallurgy, Materials Science and Engineering

(ISRS-2012), December 13-15, IIT- Madras, Chennai

6. Mrs. Laksmi V, CSIR-NIIST

(Co-authors: Annu Raju, Resmi V.G., Deepa J.P., T.P.D. Rajan, C. Pavithran, B.C. Pai)

Best Paper award in the National Conference on Materials Science and Technology (NCMST-2013),

July 10-12, 2013, IIST, Trivandrum

IIM, Trivandrum chapter – List of Award Winners

The first Prof. Brahm Prakash Best Ph.D. Thesis Award of the IIM, Trivandrum Chapter is conferred to Dr. Rohit Kumar Gupta, Scientist F, MPA/MME, VSSC, Trivandrum for the Ph.D. thesis entitled “Deformation Studies of + 2 Titanium Aluminides processed through Reaction Synthesis”. Dr. Gupta had received the Ph.D. degree from IIT Roorkee under the guidance of Prof. Vijaya Agarwala, IIT-Roorkee and Dr. P.P. Sinha, VSSC, Trivandrum.

Prof. Brahm Prakash Metals and Materials Quiz conducted by IIM Trivandrum Chapter - Mr. Vamsee Krishna and Mr. Aravind J Students of Arya Central School, Pattom, Trivandrum

IIM, Trivandrum chapter – Honouring Award Winning Members

S No Name Award/Fellowship

1. Dr. Koshy M George, Deputy Director, VSSC

"Lifetime achievement award "of Society of Aerospace Manufacturing Engineers (SAME).

2. Dr. K.G.K. Warrier CSIR Emeritus Scientist, Materials Science and Technology Division, CSIR-NIIST

Two life time achievement awards… 1. Indian Society for Analytical Chemistry Award

2012 2. Sri Kishan Modi Memorial Award by Indian

Ceramic Society 2013

3. Sri. Niraj Nayan, VSSC

(Co-Authors-Dr. SVSN Murty, Dr. Koshy M George)

Received the GS Tendulkar Best paper award during NMD-ATM 2013 at Varanasi

4. Dr. Thomas Tharian (LPSC, Tvm) & Team

(1. K.Kumar , MME/LPSC- New member 2. Joby Thomas MME/LPSC- New member 3. Anoop CR MME/LPSC- New member 4. Vartha Venkateasrlu SRQA/LPSC- New member 5. VMJ Sarma VSSC 6. G. Sudarsana Rao VSSC)

ISRO Team Excellence Award for indigenisation of VIKAS Engine materials.

5. Mr. E. Jeyakumar, CSIR-NIIST

(Co-authors: Praveen A.P., K.K. Ravikumar, T.P.D. Rajan, B.C. Pai and V.R. Rajeev)

ISRS Best Paper award for the paper presented in the International Symposium for Research Scholars on Metallurgy, Materials Science and Engineering

(ISRS-2012), December 13-15, IIT- Madras, Chennai

6. Mrs. Laksmi V, CSIR-NIIST

(Co-authors: Annu Raju, Resmi V.G., Deepa J.P., T.P.D. Rajan, C. Pavithran, B.C. Pai)

Best Paper award in the National Conference on Materials Science and Technology (NCMST-2013),

July 10-12, 2013, IIST, Trivandrum

3

Hot Isostatic Press (HIP)-An over view DineshrajS ,Girikumar S

Materials and Metallurgy Group(MMG), MME Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram- 695 022

Introduction

Advances in materials development lead to new inventions in engineering field.Materials related technologies play key role in such critical areas such as high temperature materials for thermal protection system of reusable launch vehicle, high performance cast components of cryogenic engines working under extreme conditions etc.

Aerospace manufacturing sector deals with variety of material processing activities such as Investment casting, diffusion bonding, powder metallurgy processing etc to produce components with functional criticality. Safety is the first priority for man-rating of space crafts/airplanes. We need high reliability in these functionally critical components to ensure safety. These functionally critical components demand special processing techniques to obtain defect free products/ components. High quality and reliability of these products are essential to succeed in any mission. This demands cutting edge technology for realization.

Hot Isostatic Pressing (HIPping) technology is a state-of-the-art manufacturing process which can be utilized effectively for catering to the above mentioned. It can be used for making components of very high quality and complexity. It subjects the materials to a combination of high pressure and temperature in a specially designed vessel. The pressure applied here is isostatic in nature, where pressure is equal in all directions, aiding in the production of near net shape components using powders. Under these extreme conditions the internal voids present in the material are eliminated. Theoretical density of 100 percent can be achieved in HIPpedmaterials.

HIPping provides metallurgical advantages say, uniform microstructure, isotropic properties, improved

mechanical properties with reduced Scattering[1]inturn helping the designer toutilize high proportion of physical strength of the material and to design the product with higher safety factor. The reliability and

service life are also significantly increased by HIP process.

II ABOUT HOT ISOSTATICPRESS(HIP)

The word HIP denotes,HOT–(using heating from 500°C to 2000°C), ISOSTATIC–(Pascal’s Law: In a fluid, pressure is transmittedequally in all directions.fluid used: Argon.) PRESSING –using high pressure up to 2,000 bar.

Inert gas like Argon is most commonly used as the pressure transmitting medium. By applying combined action of both pressure and temperature, defects like porosity or internalvoids present in the material are eliminated and near 100 percent theoretical density is achieved.Further, due to isostatic behavior, only photographic reduction takes place.So that there is no shape change.

For ease of comparing, the pressure used in HIP is roughly two times (2000bar) the pressure available (1000bar) at the Ocean’s deepest trench- Mariana Trench, having the depth of 10.29Km.

Commonly,many types of Pressure vessel designs are available. Monolithic with threaded end-closures, Monolithic with non-threaded end-closures and a separate yoke frame and Pre -stressed wire-wound with non-threaded end-closures and a separate yoke frame.This development involves many challenges like Engineering Design, Forging of Heavy pressure vessel, Safety measures due to high pressure operation, High temperature furnace fabrication etc.

A. Working principle of HIP

At the starting of each HIP cycle, the chamber is evacuated to remove all the dust particles and gas particles. Argon gas is filled into the pressure vessel at near room temperature using gas compressors to a pre-determined pressure value. After that the heater is switched on. Due to that the temperature inside the furnace is slowly increased and the expansion of gas as

a result of heating is used to increase the pressure to desired value. Pressure and temperature will be maintained for required duration depending upon the developed HIP cycle for each material.Fig 1 a & b shows lab scale and world’s largest HIP(Giga HIP) respectively.

Fig.1 (a)Lab scale &( b)-world’s largest HIP (Giga HIP )[22]

HIP -Temperature is normally 50 to 70% of the melting point of the lowest-temperature material in the system. A relatively high temperature during HIPping is necessary to lower yield strength and to raise the diffusivities in the material sufficiently for pore closure to occur in a reasonable time. HIP- Pressure should be sufficient to close all internal pores and pores created by interdiffusional pores. Plastic deformation, Dislocation Creep, Diffusional Creep are flow mechanisms occurring during HIPping. [5]

Products like castings are usually HIPped directly without using any special container. But, a special container is used for manufacturing near net shape component through powder metallurgy route. The container is designed according to the shape of the component and fabricated by welding of steel sheets and tubes .Weld seam of the container is examined with respect to leakages using Helium detectors for maintaining effective sealing during HIP operation.Glass can be used as a container material when HIP processing temperature is higher.

In HIP cycle I, the temperature can be increased, after pressure reaches to certain values. Finally, both pressure and temperature reach their peak at the same time as shown in fig.2.a.The pressure raise in later stage is obtained by increasing temperature. This is useful when castings are HIPped [1,2]. Fig. 2.b shows the example of another type, HIP cycle-II where the pressure is applied aftertemperature has reached some desired value for avoiding the crack of glass encapsulation, where HIPping the encapsulated powders.The cycle-III is for reducing time & cost the simultaneous increase of pressure and temperature is used normally

B. Basic Mechanisms

The driving force for shrinkage of pore is calculated as mentioned in Eq.1

P = 2γ / r ………………..…..[1]

where, P is pressure in MPa, γ is the specific energy of the internal surface of the pore (2.1 Joule/m2 ) r is theradius of pore. This is for spherical pore. It is calculated that for 1micron pore size, the driving force is typically 4MPa. The driving force for the removal of larger pores is lesser than smaller pores.If irregular

Fig.3 Pores inside the castings and Powder particles with pores when in contact

pores are present, then the surface is divided into many regions with different radius. Radiusis positive if surface is concave into the pore and is negative if the surface in convex as shown in the fig.3

Pumping to a pre-determined value

Pressure

Fig. 2(b)- HIP Cycle – II

Temperature

Time

Pressure

Time

Fig. 2(a)- HIP Cycle1

Temperature

4

Hot Isostatic Press (HIP)-An over view DineshrajS ,Girikumar S

Materials and Metallurgy Group(MMG), MME Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram- 695 022

Introduction

Advances in materials development lead to new inventions in engineering field.Materials related technologies play key role in such critical areas such as high temperature materials for thermal protection system of reusable launch vehicle, high performance cast components of cryogenic engines working under extreme conditions etc.

Aerospace manufacturing sector deals with variety of material processing activities such as Investment casting, diffusion bonding, powder metallurgy processing etc to produce components with functional criticality. Safety is the first priority for man-rating of space crafts/airplanes. We need high reliability in these functionally critical components to ensure safety. These functionally critical components demand special processing techniques to obtain defect free products/ components. High quality and reliability of these products are essential to succeed in any mission. This demands cutting edge technology for realization.

Hot Isostatic Pressing (HIPping) technology is a state-of-the-art manufacturing process which can be utilized effectively for catering to the above mentioned. It can be used for making components of very high quality and complexity. It subjects the materials to a combination of high pressure and temperature in a specially designed vessel. The pressure applied here is isostatic in nature, where pressure is equal in all directions, aiding in the production of near net shape components using powders. Under these extreme conditions the internal voids present in the material are eliminated. Theoretical density of 100 percent can be achieved in HIPpedmaterials.

HIPping provides metallurgical advantages say, uniform microstructure, isotropic properties, improved

mechanical properties with reduced Scattering[1]inturn helping the designer toutilize high proportion of physical strength of the material and to design the product with higher safety factor. The reliability and

service life are also significantly increased by HIP process.

II ABOUT HOT ISOSTATICPRESS(HIP)

The word HIP denotes,HOT–(using heating from 500°C to 2000°C), ISOSTATIC–(Pascal’s Law: In a fluid, pressure is transmittedequally in all directions.fluid used: Argon.) PRESSING –using high pressure up to 2,000 bar.

Inert gas like Argon is most commonly used as the pressure transmitting medium. By applying combined action of both pressure and temperature, defects like porosity or internalvoids present in the material are eliminated and near 100 percent theoretical density is achieved.Further, due to isostatic behavior, only photographic reduction takes place.So that there is no shape change.

For ease of comparing, the pressure used in HIP is roughly two times (2000bar) the pressure available (1000bar) at the Ocean’s deepest trench- Mariana Trench, having the depth of 10.29Km.

Commonly,many types of Pressure vessel designs are available. Monolithic with threaded end-closures, Monolithic with non-threaded end-closures and a separate yoke frame and Pre -stressed wire-wound with non-threaded end-closures and a separate yoke frame.This development involves many challenges like Engineering Design, Forging of Heavy pressure vessel, Safety measures due to high pressure operation, High temperature furnace fabrication etc.

A. Working principle of HIP

At the starting of each HIP cycle, the chamber is evacuated to remove all the dust particles and gas particles. Argon gas is filled into the pressure vessel at near room temperature using gas compressors to a pre-determined pressure value. After that the heater is switched on. Due to that the temperature inside the furnace is slowly increased and the expansion of gas as

a result of heating is used to increase the pressure to desired value. Pressure and temperature will be maintained for required duration depending upon the developed HIP cycle for each material.Fig 1 a & b shows lab scale and world’s largest HIP(Giga HIP) respectively.

Fig.1 (a)Lab scale &( b)-world’s largest HIP (Giga HIP )[22]

HIP -Temperature is normally 50 to 70% of the melting point of the lowest-temperature material in the system. A relatively high temperature during HIPping is necessary to lower yield strength and to raise the diffusivities in the material sufficiently for pore closure to occur in a reasonable time. HIP- Pressure should be sufficient to close all internal pores and pores created by interdiffusional pores. Plastic deformation, Dislocation Creep, Diffusional Creep are flow mechanisms occurring during HIPping. [5]

Products like castings are usually HIPped directly without using any special container. But, a special container is used for manufacturing near net shape component through powder metallurgy route. The container is designed according to the shape of the component and fabricated by welding of steel sheets and tubes .Weld seam of the container is examined with respect to leakages using Helium detectors for maintaining effective sealing during HIP operation.Glass can be used as a container material when HIP processing temperature is higher.

In HIP cycle I, the temperature can be increased, after pressure reaches to certain values. Finally, both pressure and temperature reach their peak at the same time as shown in fig.2.a.The pressure raise in later stage is obtained by increasing temperature. This is useful when castings are HIPped [1,2]. Fig. 2.b shows the example of another type, HIP cycle-II where the pressure is applied aftertemperature has reached some desired value for avoiding the crack of glass encapsulation, where HIPping the encapsulated powders.The cycle-III is for reducing time & cost the simultaneous increase of pressure and temperature is used normally

B. Basic Mechanisms

The driving force for shrinkage of pore is calculated as mentioned in Eq.1

P = 2γ / r ………………..…..[1]

where, P is pressure in MPa, γ is the specific energy of the internal surface of the pore (2.1 Joule/m2 ) r is theradius of pore. This is for spherical pore. It is calculated that for 1micron pore size, the driving force is typically 4MPa. The driving force for the removal of larger pores is lesser than smaller pores.If irregular

Fig.3 Pores inside the castings and Powder particles with pores when in contact

pores are present, then the surface is divided into many regions with different radius. Radiusis positive if surface is concave into the pore and is negative if the surface in convex as shown in the fig.3

Pumping to a pre-determined value

Pressure

Fig. 2(b)- HIP Cycle – II

Temperature

Time

Pressure

Time

Fig. 2(a)- HIP Cycle1

Temperature

5

III APPLICATIONS OF HIP

HIP has the advantages of healing the defects in the castings made up of different materials which are widely used in aerospace applications such as turbines and cryogenic engines, Diffusion bonding of similar and dissimilar materials , Processing of powders metallurgy products like thrust chambers and super alloy rotor disk in near net shape , Processing of ultra high temperature ceramic materials.

A. Healing of Castings using HIP.

Casting is widely used method for the manufacturing of products with very complex shapes made up of different materials like stainless steel, Ni base and Ni-Fe base Super alloys, Titanium alloys, Aluminum alloys mainly for aerospace applications involving high temperature to Cryo applications.

In spite of the advances in casting technology, it is still prone for residual internal defects due to shrinkage, trapped gases and generation of gases by reaction which reduces the mechanical propertiesof the product. Also it is not possible to cover 100 percentage of component’s surface by radiography during NonDestructive Testing (NDT) due its complex shape which reduces the reliability of the product.HIPping ensures the absence of defects in the areas which are difficult to analysis as above mentioned.Reduction in scattering of mechanical properties are observed by using HIP as shown in fig.4.Significant reduction in amount of pores present in A356 Aluminum alloy castings was noticed [8] in HIPped specimen compared to non-HIPpedspecimen which contributes

towards the improvement is mechanical properties when HIPped at 520C and 100MPa for 2 hours[8].Fig.5 shows the removal of porosities due to Hipping of Al alloy casting.[8]

Ti castings are difficult to cast in to shape without defects due its fluidity problems. HIP procedure typically uses 1000 bar pressure in an inert atmosphere at about 900-980 C. At these conditions material can creep without adversely affecting macroscopic dimensional stability. In the final phase of the process, the walls of the former cavity join together by diffusion welding. The high fatigue results shows that the average stress at the same cycle(107 cycles) is increased to 500MPa from 400MPa [9]. Also Hipping improves the product quality by enhancing the microstructure and avoiding coring in super alloy castings.[6]

B. Near-net Shape Products by HIP –Powder metallurgy route.

Near net shape is an industrial manufacturing technique where initial item in production route is very close to final shape of the product. Powder metallurgy is used as one of the manufacturing tools for this method.

Fig.6.Micro structures of as cast(a),Forged(b) ,HIPped(c) material with same magnification.[12]

But still HIP-Powder metallurgy route is beneficial than conventional powder metallurgy route. Because it provides homogeneous material with isotropic properties.(ref fig 6). Also it is possible to achieve 100 percent theoretical density with the possibility of producing complex components. The rate of densification of powder during HIPping is controlled by particle re-arrangement, Plasticity, power law creep

Fig.4Reduction in scattering of mechanical properties

As cast

As Forged

As HIPped

Fig.5 Microstructure of A356-T6 Al alloy-(a)Non-HIPped Specimen and (b) HIPped specimen[8]

(b)

(a)

(c)

Fig. 8 Schematic picture of HIP-Diffusion bonding

&grain boundarydiffusion.[10,11].Separate capsule preparations are needed for producing near net shape

Fig.7a) Near net shape products made by HIPfor Large Hadron collider [18]and b) method of Hipping (i)Encapsulated powders(ii)HIPped part,(iii) final machined part

by HIPping of metal and ceramic powders. Fig.7a shows the end covers of dipole magnet of Large Hadron Collider(world's largest and highest-energy particle accelerator,Switzerland.)made by HIP route using powders (Stainless steel AISI 316LN) [18]and Fig 7 b shows the sequence in HIP –Powder metallurgy route. The required shape is obtained by making the shape material with sheets by joining, evacuating the capsule and filling of powders. Therefore proper design of capsule is necessary. Also gas tight weld joints are essential. So, encapsulation is a special technique which is the preliminary step for making near net shape products.[3,12,14,16]

C. HIP- Diffusion bonding

Diffusion bonding is the process of joining similar and dissimilar materials by applying pressure uni-axially and heating to high a temperature.

But, In HIP diffusion bonding pressure is applies in all directions when compared to uni-axial loading in conventional diffusion bonding as shown in fig.8.

Compared to conventional diffusion bonding, HIP diffusion bonding offers several advantages to make metallurgical bonding with many re-entrant angles and complex shapes, without any stringent surface preparation needed for bonding. Powders and porous bodies can be simultaneously diffusion bonded and metal-ceramic bonding is also possible.

The refined microstructures with fine precipitates were found compared to conventional diffusion bonding process.[12,13,14]

The major challenge is the joining interface area of two materials, which should be free from pressurizing medium of HIP equipment for obtaining good bonding strength. In HIP diffusion bonding of complex shaped components can be made Fig.9 shows good examples for joining different materials with shape constraints.High value of joint strength is obtained due to the diffusion of alloying elements. The microstructure is finer than casted or forged Ti alloy. Experimental trial of HIP diffusion bonding of Fe-Al alloy and Cr-/Mo steelshows that growth rate of columnar grain is lesser in the case of HIP-diffusion bonded specimens than in conventional diffusion bonded specimens[14].

D. Rejuvenation of cast parts by HIP

Gas turbine components are made up of super alloys such as turbine blades and disks which are used in aircrafts and also in many critical applications[1,15] The efficiency of gas turbine engine depends upon the operating temperature. Therefore it is normally operated at maximum possible operating temperature range. After several hours of working, it will be replaced with new one, even though safe operating hours left, to avoid the failure of turbine which happens due to the microstructural damages and

Fig.9(a)HIP-Diffusionbonded Ti-6Al-4V (1)with stainless steel -1Cr18Ni9Ti (2)with bonding interface(3)[13]& (b) bonding of Copper and stainless

l [18]

(b) (a)

6

III APPLICATIONS OF HIP

HIP has the advantages of healing the defects in the castings made up of different materials which are widely used in aerospace applications such as turbines and cryogenic engines, Diffusion bonding of similar and dissimilar materials , Processing of powders metallurgy products like thrust chambers and super alloy rotor disk in near net shape , Processing of ultra high temperature ceramic materials.

A. Healing of Castings using HIP.

Casting is widely used method for the manufacturing of products with very complex shapes made up of different materials like stainless steel, Ni base and Ni-Fe base Super alloys, Titanium alloys, Aluminum alloys mainly for aerospace applications involving high temperature to Cryo applications.

In spite of the advances in casting technology, it is still prone for residual internal defects due to shrinkage, trapped gases and generation of gases by reaction which reduces the mechanical propertiesof the product. Also it is not possible to cover 100 percentage of component’s surface by radiography during NonDestructive Testing (NDT) due its complex shape which reduces the reliability of the product.HIPping ensures the absence of defects in the areas which are difficult to analysis as above mentioned.Reduction in scattering of mechanical properties are observed by using HIP as shown in fig.4.Significant reduction in amount of pores present in A356 Aluminum alloy castings was noticed [8] in HIPped specimen compared to non-HIPpedspecimen which contributes

towards the improvement is mechanical properties when HIPped at 520C and 100MPa for 2 hours[8].Fig.5 shows the removal of porosities due to Hipping of Al alloy casting.[8]

Ti castings are difficult to cast in to shape without defects due its fluidity problems. HIP procedure typically uses 1000 bar pressure in an inert atmosphere at about 900-980 C. At these conditions material can creep without adversely affecting macroscopic dimensional stability. In the final phase of the process, the walls of the former cavity join together by diffusion welding. The high fatigue results shows that the average stress at the same cycle(107 cycles) is increased to 500MPa from 400MPa [9]. Also Hipping improves the product quality by enhancing the microstructure and avoiding coring in super alloy castings.[6]

B. Near-net Shape Products by HIP –Powder metallurgy route.

Near net shape is an industrial manufacturing technique where initial item in production route is very close to final shape of the product. Powder metallurgy is used as one of the manufacturing tools for this method.

Fig.6.Micro structures of as cast(a),Forged(b) ,HIPped(c) material with same magnification.[12]

But still HIP-Powder metallurgy route is beneficial than conventional powder metallurgy route. Because it provides homogeneous material with isotropic properties.(ref fig 6). Also it is possible to achieve 100 percent theoretical density with the possibility of producing complex components. The rate of densification of powder during HIPping is controlled by particle re-arrangement, Plasticity, power law creep

Fig.4Reduction in scattering of mechanical properties

As cast

As Forged

As HIPped

Fig.5 Microstructure of A356-T6 Al alloy-(a)Non-HIPped Specimen and (b) HIPped specimen[8]

(b)

(a)

(c)

Fig. 8 Schematic picture of HIP-Diffusion bonding

&grain boundarydiffusion.[10,11].Separate capsule preparations are needed for producing near net shape

Fig.7a) Near net shape products made by HIPfor Large Hadron collider [18]and b) method of Hipping (i)Encapsulated powders(ii)HIPped part,(iii) final machined part

by HIPping of metal and ceramic powders. Fig.7a shows the end covers of dipole magnet of Large Hadron Collider(world's largest and highest-energy particle accelerator,Switzerland.)made by HIP route using powders (Stainless steel AISI 316LN) [18]and Fig 7 b shows the sequence in HIP –Powder metallurgy route. The required shape is obtained by making the shape material with sheets by joining, evacuating the capsule and filling of powders. Therefore proper design of capsule is necessary. Also gas tight weld joints are essential. So, encapsulation is a special technique which is the preliminary step for making near net shape products.[3,12,14,16]

C. HIP- Diffusion bonding

Diffusion bonding is the process of joining similar and dissimilar materials by applying pressure uni-axially and heating to high a temperature.

But, In HIP diffusion bonding pressure is applies in all directions when compared to uni-axial loading in conventional diffusion bonding as shown in fig.8.

Compared to conventional diffusion bonding, HIP diffusion bonding offers several advantages to make metallurgical bonding with many re-entrant angles and complex shapes, without any stringent surface preparation needed for bonding. Powders and porous bodies can be simultaneously diffusion bonded and metal-ceramic bonding is also possible.

The refined microstructures with fine precipitates were found compared to conventional diffusion bonding process.[12,13,14]

The major challenge is the joining interface area of two materials, which should be free from pressurizing medium of HIP equipment for obtaining good bonding strength. In HIP diffusion bonding of complex shaped components can be made Fig.9 shows good examples for joining different materials with shape constraints.High value of joint strength is obtained due to the diffusion of alloying elements. The microstructure is finer than casted or forged Ti alloy. Experimental trial of HIP diffusion bonding of Fe-Al alloy and Cr-/Mo steelshows that growth rate of columnar grain is lesser in the case of HIP-diffusion bonded specimens than in conventional diffusion bonded specimens[14].

D. Rejuvenation of cast parts by HIP

Gas turbine components are made up of super alloys such as turbine blades and disks which are used in aircrafts and also in many critical applications[1,15] The efficiency of gas turbine engine depends upon the operating temperature. Therefore it is normally operated at maximum possible operating temperature range. After several hours of working, it will be replaced with new one, even though safe operating hours left, to avoid the failure of turbine which happens due to the microstructural damages and

Fig.9(a)HIP-Diffusionbonded Ti-6Al-4V (1)with stainless steel -1Cr18Ni9Ti (2)with bonding interface(3)[13]& (b) bonding of Copper and stainless

l [18]

(b) (a)

7

structural discontinuities.Fig.10 shows the micro voids and micro cracks.

Precipitates are the strengthening factors for super alloys which could become coarsen when exposed to high temperature, leading to void formations on grain boundaries.

Fig.11Microstructures(a)before and (b)after HIP treatment [15]

This leads to reduction in safe life time of the component. HIP process heals these above mentioned cracks and voids which were generated during service. Also the dispersion of fine gamma prime precipitates are very uniform compared to service parts after HIPping treatment [15].Fig.11 shows the difference in microstructures due to Hipping. The applied pressure and temperature aids more diffusion to take place across the interface for local yielding and creep which can increase the real area of contact.[1]

E. Processing of High temperature materials

Nose cone, leading edges, thrust diverters and. as shown in fig.12 typical applications where high temperature materials such as SiC, HfB2, ZrB2,TiB2 and Carbon/carbon composites are used.[1,3]Silicon carbide and silicon nitride are important structural materials for high temperature applications because of their excellent mechanical properties. The metallic thermal protection system is also under development by where Titanium Aluminide is used which can be processed by HIP.

Very strong interatomic bonds generally characterize high temperature ceramics. A consequence of the strong bond characteristic is that the ceramic components are often very difficult to fully densify and machine to required shape. Due to high melting

point, the manufacturing of these materials is a challenging task . The application of pressure during sintering accelerates the kinetics of densification.Normally hot pressing is used for processing where stress is applied uni-axially.

But,HIP is the one of the best routes for processing such materials. So,HIPping provides faster rate of densification. The faster rate of densification also has the advantage of maintaining a smaller grain size in the UHTC,which enhances its high-temperature mechanical and thermal properties. Also inHIPping it is possible to produce near net-shape products[11] due to three dimensionally applied force which is not possible in conventional hot press.

IV. THE RECENT TRENDS IN HIP

A. Usage of HIP in different applications

Super alloy billet making is becoming effective root for processing compared to melting route.HIP route avoids severe segregation and produces homogeneous microstructure with good hot workability for further operation.Also processing of medical implants with high quality, HIP -brazing without any porosities, Sputtering targets and composites (Metal Matrix Composites,C-C composites) are other different and new areas where HIP technology is utilized .

HIPping of Beryllium has been developed which is light weight and stable at cryogenic temperatures. Beryllium was chosen over SiC as the substrate for James Webb Space Telescope’s (as shown in fig 13and 14) primary mirror of the Advanced Mirror Systems Demonstrator Program (AMSD) which will be launched in 2018 by NASA[16]. HIP increases the

Fig. 10Microvoidsand micro cracks[15]

Fig. 13 HIPping of Beryllium blanks in desired shape.[16]

(1) (2)

(a) (b)

Fig. 12 Nose cap(1) and leading Edges(2)

dimensional stability of Beryllium parts by making the material more isotropic in bulk .

B. Advancements in HIP equipments

Due to the advancements in the engineering field, the HIP-pressure vessel size, operating temperature and operating pressure are constantly increasing. Recent development of vessel size of dia 3m and height 4.2 m with operating temperature of maximum 1350C and pressure of 2100 bar is reported [17].

In-situ dilatometers are developed, which provide continuous measurement of dimensions duringHIPping. By doing so actual consolidation of materials can be studied which is useful in developing optimized HIP running cycles.HIP quenching is another trend, which enables densification and heat treatment to be combined into one operation for reducing total cycle time.[1]

V. CONCLUSION

Healing of cast parts is the main process carried out by industries running HIP. Manufacturing of the near net shaped products of PM components with high quality and complexity is also developing in industries. Further it can also be used effectively for repairing serviced parts of a aircraft engines microscopically for avoiding failures. The applications of HIP is getting wider and wider in all sectors. HIP also helps to overcome the limitations of processing high temperature materials.

Other than high capital cost, HIP is an effective technique for processing advanced materials for high end applications. Undoubtedly HIP is a wonderful tool for developing newer materials and for doing cutting edge research. In future, HIP will mainly focus on areas like advanced systems for faster cooling and heating rates, computer modeling to reduce trials needed for optimizing HIP process cycles.

REFERENCES [1] H V Atkinson B A Rickinson.“Hot Isostatic Processing” -Adam HilgerBristol,Phildelphia and New York p 1-93 [2]M.Koizumi,M.Nishihara,“Isostatic Pressing Technology” Elsevier Applied Science1992p100-p 110 [3]“Powder Metal Technologies & Applications’.Volume-7-ASM Hand book,ASM INTERNATIONAL 1998 [4] F.B. Swinkles D.S. Wilkinson, E.Arzt and F.Ashby,“Mechanisms of Hot –Isostatic pressing” –Acta metal Vol.31 No.11 pp-1829 -1840- 1983 [5]GeorgeE.Dieter,“ Mechanical etallurgy”-Metric Editions Materials science & Metallurgy, McGraw –Hill Book Company1988 -page no 445-452 [6]Shih-Chin Lee,Shih-HsienChang,Tzu-PiaoTang,Hsin-Hung Ho and Jhewn-Kuang Chen “Improvement in the Microstructure and Tensile Properties of Inconel 718 Superalloy by HIP Treatment”- Materials Transactions ,Vol.47,No.11 (2006)pp.2877 to 2881 [7]MinHaLee,JaeJooong,Kim,KyungHoonKim,Nackj.Kim,SunghakLee,EuiW.Lee, “Effects of HIPping on High cycle fatigue properties of investment cast A356 Aluminum alloys” –Materails science and Engineering A340(2003) 123-129 [8]Guang Ran, Jing` en Zhou, Q.G. Wang.“ Effect on the microstructure and tensile properties of an unmodified A356-T6 cast aluminum alloy”- Journal of Alloys and Compounds 421 (2006) 80–86 [9]ChristophLeyens, Manfred Peters,“Titanium and Titanium Alloys - Fundamentals and Applications” WILEY-VCH Verlag GmbH & Co Page.No 265-269 [10]ChristophBroeckmann, “Hot isostatic pressing of near net shape components-Process fundamentals and future challenges”- Powder Metallurgy 2012 vol 55 No 3 pp 176 [11]Hans T.larker ,Robert Lundberg, “Near net shape production of Monolithic and composite High Temperature ceramics by Hot isostatic pressing”. –Journal of European ceramic society 19-(1999) 2367-2373 [12]Uiz. H. D. Crestana – Engenheiro de Aplicaes, “Experience and references of Powder Metallurgy parts produced by HIP in offshore applications for O&G industry” - Sandvik Materials Technology doBrasil [13]LANG Ze-bao, WANG Liang, ZHANG Xu-hu.“HIP diffusion bonding of P/M titanium alloy Ti-6Al-4Vand stainless steel 1Cr18Ni9Ti”- Trans. Nonferrous Met. Soc. China 17(2007) s79-s83. [14]Naoyamasahashi ,ShujiHanada, “Effect of pressure application by HIP on microstructure evolution during diffusion bonding”. Materials Transactions ,Vol.46,No.7(2005) pp. 1651 to 1655. [15]WangyaoP ,PolsilapaS,Nisaratanaporn, “The application of Hot isostatic pressing process to rejuvenate serviced cast super alloys turbine blades”- ActaMetallurgicaSlovaca 11,2005,2(196-206) [16]http://www.jwst.nasa.gov/ [17]http://www.avure.com [18]http://www.kinzoku.co.jp/english/eng/hip.html [19]http://www.metsomaterialstechnology.com

Fig.14 James Webb Space Telescope[16]

8

structural discontinuities.Fig.10 shows the micro voids and micro cracks.

Precipitates are the strengthening factors for super alloys which could become coarsen when exposed to high temperature, leading to void formations on grain boundaries.

Fig.11Microstructures(a)before and (b)after HIP treatment [15]

This leads to reduction in safe life time of the component. HIP process heals these above mentioned cracks and voids which were generated during service. Also the dispersion of fine gamma prime precipitates are very uniform compared to service parts after HIPping treatment [15].Fig.11 shows the difference in microstructures due to Hipping. The applied pressure and temperature aids more diffusion to take place across the interface for local yielding and creep which can increase the real area of contact.[1]

E. Processing of High temperature materials

Nose cone, leading edges, thrust diverters and. as shown in fig.12 typical applications where high temperature materials such as SiC, HfB2, ZrB2,TiB2 and Carbon/carbon composites are used.[1,3]Silicon carbide and silicon nitride are important structural materials for high temperature applications because of their excellent mechanical properties. The metallic thermal protection system is also under development by where Titanium Aluminide is used which can be processed by HIP.

Very strong interatomic bonds generally characterize high temperature ceramics. A consequence of the strong bond characteristic is that the ceramic components are often very difficult to fully densify and machine to required shape. Due to high melting

point, the manufacturing of these materials is a challenging task . The application of pressure during sintering accelerates the kinetics of densification.Normally hot pressing is used for processing where stress is applied uni-axially.

But,HIP is the one of the best routes for processing such materials. So,HIPping provides faster rate of densification. The faster rate of densification also has the advantage of maintaining a smaller grain size in the UHTC,which enhances its high-temperature mechanical and thermal properties. Also inHIPping it is possible to produce near net-shape products[11] due to three dimensionally applied force which is not possible in conventional hot press.

IV. THE RECENT TRENDS IN HIP

A. Usage of HIP in different applications

Super alloy billet making is becoming effective root for processing compared to melting route.HIP route avoids severe segregation and produces homogeneous microstructure with good hot workability for further operation.Also processing of medical implants with high quality, HIP -brazing without any porosities, Sputtering targets and composites (Metal Matrix Composites,C-C composites) are other different and new areas where HIP technology is utilized .

HIPping of Beryllium has been developed which is light weight and stable at cryogenic temperatures. Beryllium was chosen over SiC as the substrate for James Webb Space Telescope’s (as shown in fig 13and 14) primary mirror of the Advanced Mirror Systems Demonstrator Program (AMSD) which will be launched in 2018 by NASA[16]. HIP increases the

Fig. 10Microvoidsand micro cracks[15]

Fig. 13 HIPping of Beryllium blanks in desired shape.[16]

(1) (2)

(a) (b)

Fig. 12 Nose cap(1) and leading Edges(2)

dimensional stability of Beryllium parts by making the material more isotropic in bulk .

B. Advancements in HIP equipments

Due to the advancements in the engineering field, the HIP-pressure vessel size, operating temperature and operating pressure are constantly increasing. Recent development of vessel size of dia 3m and height 4.2 m with operating temperature of maximum 1350C and pressure of 2100 bar is reported [17].

In-situ dilatometers are developed, which provide continuous measurement of dimensions duringHIPping. By doing so actual consolidation of materials can be studied which is useful in developing optimized HIP running cycles.HIP quenching is another trend, which enables densification and heat treatment to be combined into one operation for reducing total cycle time.[1]

V. CONCLUSION

Healing of cast parts is the main process carried out by industries running HIP. Manufacturing of the near net shaped products of PM components with high quality and complexity is also developing in industries. Further it can also be used effectively for repairing serviced parts of a aircraft engines microscopically for avoiding failures. The applications of HIP is getting wider and wider in all sectors. HIP also helps to overcome the limitations of processing high temperature materials.

Other than high capital cost, HIP is an effective technique for processing advanced materials for high end applications. Undoubtedly HIP is a wonderful tool for developing newer materials and for doing cutting edge research. In future, HIP will mainly focus on areas like advanced systems for faster cooling and heating rates, computer modeling to reduce trials needed for optimizing HIP process cycles.

REFERENCES [1] H V Atkinson B A Rickinson.“Hot Isostatic Processing” -Adam HilgerBristol,Phildelphia and New York p 1-93 [2]M.Koizumi,M.Nishihara,“Isostatic Pressing Technology” Elsevier Applied Science1992p100-p 110 [3]“Powder Metal Technologies & Applications’.Volume-7-ASM Hand book,ASM INTERNATIONAL 1998 [4] F.B. Swinkles D.S. Wilkinson, E.Arzt and F.Ashby,“Mechanisms of Hot –Isostatic pressing” –Acta metal Vol.31 No.11 pp-1829 -1840- 1983 [5]GeorgeE.Dieter,“ Mechanical etallurgy”-Metric Editions Materials science & Metallurgy, McGraw –Hill Book Company1988 -page no 445-452 [6]Shih-Chin Lee,Shih-HsienChang,Tzu-PiaoTang,Hsin-Hung Ho and Jhewn-Kuang Chen “Improvement in the Microstructure and Tensile Properties of Inconel 718 Superalloy by HIP Treatment”- Materials Transactions ,Vol.47,No.11 (2006)pp.2877 to 2881 [7]MinHaLee,JaeJooong,Kim,KyungHoonKim,Nackj.Kim,SunghakLee,EuiW.Lee, “Effects of HIPping on High cycle fatigue properties of investment cast A356 Aluminum alloys” –Materails science and Engineering A340(2003) 123-129 [8]Guang Ran, Jing` en Zhou, Q.G. Wang.“ Effect on the microstructure and tensile properties of an unmodified A356-T6 cast aluminum alloy”- Journal of Alloys and Compounds 421 (2006) 80–86 [9]ChristophLeyens, Manfred Peters,“Titanium and Titanium Alloys - Fundamentals and Applications” WILEY-VCH Verlag GmbH & Co Page.No 265-269 [10]ChristophBroeckmann, “Hot isostatic pressing of near net shape components-Process fundamentals and future challenges”- Powder Metallurgy 2012 vol 55 No 3 pp 176 [11]Hans T.larker ,Robert Lundberg, “Near net shape production of Monolithic and composite High Temperature ceramics by Hot isostatic pressing”. –Journal of European ceramic society 19-(1999) 2367-2373 [12]Uiz. H. D. Crestana – Engenheiro de Aplicaes, “Experience and references of Powder Metallurgy parts produced by HIP in offshore applications for O&G industry” - Sandvik Materials Technology doBrasil [13]LANG Ze-bao, WANG Liang, ZHANG Xu-hu.“HIP diffusion bonding of P/M titanium alloy Ti-6Al-4Vand stainless steel 1Cr18Ni9Ti”- Trans. Nonferrous Met. Soc. China 17(2007) s79-s83. [14]Naoyamasahashi ,ShujiHanada, “Effect of pressure application by HIP on microstructure evolution during diffusion bonding”. Materials Transactions ,Vol.46,No.7(2005) pp. 1651 to 1655. [15]WangyaoP ,PolsilapaS,Nisaratanaporn, “The application of Hot isostatic pressing process to rejuvenate serviced cast super alloys turbine blades”- ActaMetallurgicaSlovaca 11,2005,2(196-206) [16]http://www.jwst.nasa.gov/ [17]http://www.avure.com [18]http://www.kinzoku.co.jp/english/eng/hip.html [19]http://www.metsomaterialstechnology.com

Fig.14 James Webb Space Telescope[16]

9

Transparent Ceramics Dr. U. S. Hareesh, MSTD, CSIR-NIIST,

Thiruvananthapuram, hareesh@niist.res.in

Transparent ceramics has in recent years emerged as an advanced class of functional material owing to a multitude of applications in the area of laser optics, thermal imaging and lighting. The materials by virtue of its transparency, in the spectral regime of 400nm to 10 microns, coupled with appreciable mechanical properties are essential requirements for strategic applications also. The advancements in processing techniques and the cost affordability have lead to the dominance of polycrystalline materials over single crystal variety.Presently, the most widely employed transparent ceramic material is zinc sulphide (ZnS), obtained by the process of chemical vapour deposition (CVD) involving the reaction of zinc and hydrogen sulphide at temperatures of 600-700°C. The CVD process proceeding through a layer by layer deposition process at deposition rates of 50-100 microns/hour ensures compositional and optical homogeneity and provides densities close to 99.5% TD. The zinc sulphide thus obtained display infra red transmission levels up to 76% in the wavelength region of 2-10 microns. A post CVD hot isostatic processing step imparts nearly full densification (99.95%TD) and improved transmission in the 400-900nm range. The mechanical properties of zinc sulphide transparent ceramics is not appreciable as compared to their oxide counterparts of alumina, magnesium aluminate spinel and aluminium oxynitride. The following table summarises the optical and mechanical properties of state of the art transparent ceramic materials

Table1 Optical and mechanical properties of transparent ceramic materials

It is evident from the table that, of the materials listed sintered sub-micrometer alumina (polycrystalline aluminium oxide with sintered grain sizes averaging less than a micron) possesses the highest mechanical properties. However, being hexagonal in structure exhibits birefringence and there is a dependency on the sample thickness on visible transparency. The transparency level drastically decreases with thickness beyond 1mm. In view of this,

Property AlON Spinel Sapphire Sintered Sub m alumina

ZnS

Transmission 3-5 m400-900 nm

~85% ~85% ~85% ~85%70 %

76%

Density (g/cc)

3.67 3.58 3.984 3.986 4.09

Elastic Modulus (GPa)

315 277 386 390 75

Flexural Strength (MPa)

228 241 350 700 103

KIc(MPa. m1/2)

2.4+0.11 1.7+ 0.06 3.5 3.5 0.8

Hardness(GPa)

13.8+0.3 12.1+0.2 16-17 20-23 2.5

Weibull Modulus 8.7 19.5 - 30 -

10

presentl(AlON)oxynitri

Figure:transparsample

Polycrycastingdried uattainintreatmepressingthere isgrindingaroundmicrostfigure b

Figure:emergin(right) a

Note: THyderab

ly the mate). Due to thide, efforts

Photograprent ceramiis a produc

ystalline oxiwherein a

under controng densitiesent stage shg (HIPing) s complete g and polis

1300-135tructure andbelow

Typical mng applicatiaesthetic de

The work onbad during

erials of hihe relative eare now bei

phs of ZnS c materials

ct of IKTS, D

ide ceramicslurry of reolled condis greater thould ensureto be succeelimination

shing. The 0°C whiled emerging

microstructuions like (m

ental braces

n zinc sulphthe period 2

igh potentiaease of procing made in

(left), sint(ZnS and a

Dresden, Ge

s are develoelatively higitions. Thishan 95%TDe the removessful. Durinn of pore dsintered su

e spinel aapplication

ure of tramiddle) lam[www.Dr d

hide and tra2004-2011

al are spinecessing magn the comme

tered sub-malumina are ermany)

oped by colgh solid loa

s is followeD with mival of open ng HIPing tdue to whiub-micromeattains denns of polyc

ansparent smp envelopedroser.de]

ansparent al

el (MgAl2Ognesium aluercialisation

micrometer products of

lloidal formading (75-8ed by a preinimum sin

pores for tthe densificich the sameter aluminnsification crystalline o

sintered subes [G. C. W

lumina cera

O4) and aluuminate spinn of spinel

alumina (mf ARCI, Hy

ming process80 wt%) is essureless sntered grainthe post sin

cation levelsmples appeaa is obtainat T>170

oxide ceram

b-micrometWei, J.Eur.C

amic was ca

uminium oxnel over alu

middle) andyderabad an

ses like slipcast in mousintering inn sizes. Thntering hot s reach 99.9ar transpare

ned at temp0°C. The

mic is prese

ter aluminaCer. Soc 20

arried out a

xynitride uminium

d spinel nd spinel

p and gel ulds and n air for his heat isostatic

95% and ent after peratures

typicalented in

a (left), 008] and

at ARCI,

presentl(AlON)oxynitri

Figure:transparsample

Polycrycastingdried uattainintreatmepressingthere isgrindingaroundmicrostfigure b

Figure:emergin(right) a

Note: THyderab

ly the mate). Due to thide, efforts

Photograprent ceramiis a produc

ystalline oxiwherein a

under controng densitiesent stage shg (HIPing) s complete g and polis

1300-135tructure andbelow

Typical mng applicatiaesthetic de

The work onbad during

erials of hihe relative eare now bei

phs of ZnS c materials

ct of IKTS, D

ide ceramicslurry of reolled condis greater thould ensureto be succeelimination

shing. The 0°C whiled emerging

microstructuions like (m

ental braces

n zinc sulphthe period 2

igh potentiaease of procing made in

(left), sint(ZnS and a

Dresden, Ge

s are develoelatively higitions. Thishan 95%TDe the removessful. Durinn of pore dsintered su

e spinel aapplication

ure of tramiddle) lam[www.Dr d

hide and tra2004-2011

al are spinecessing magn the comme

tered sub-malumina are ermany)

oped by colgh solid loa

s is followeD with mival of open ng HIPing tdue to whiub-micromeattains denns of polyc

ansparent smp envelopedroser.de]

ansparent al

el (MgAl2Ognesium aluercialisation

micrometer products of

lloidal formading (75-8ed by a preinimum sin

pores for tthe densificich the sameter aluminnsification crystalline o

sintered subes [G. C. W

lumina cera

O4) and aluuminate spinn of spinel

alumina (mf ARCI, Hy

ming process80 wt%) is essureless sntered grainthe post sin

cation levelsmples appeaa is obtainat T>170

oxide ceram

b-micrometWei, J.Eur.C

amic was ca

uminium oxnel over alu

middle) andyderabad an

ses like slipcast in mousintering inn sizes. Thntering hot s reach 99.9ar transpare

ned at temp0°C. The

mic is prese

ter aluminaCer. Soc 20

arried out a

xynitride uminium

d spinel nd spinel

p and gel ulds and n air for his heat isostatic

95% and ent after peratures

typicalented in

a (left), 008] and

at ARCI,

11

Flash Bainite Processing

Agilan M Materials processing Research Group(MPCG), MME

Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram- 695 022

Flash Bainite processing is an advanced heat treatment process to produce steel microstructure with high strength and ductility. As the name pronounces, heating and cooling cycle is done in a short period of time (< 10 seconds). Flash processing of 0.15%C plain carbon steel results in very high yield strength (>1200 MPa), tensile strength (>1500 MPa) and appreciable ductility (7%). Also, this process is considered as alternate route for conventional high strength steel production process and this process shows atleast 7 % increase in UTS and 30% increase in ductility than conventional high strength steels.

The flash processing assembly consists of heating and cooling stage. Heating is done by electric induction or oxy-propane flame. Cooling trough is placed just below the heating stage. Normally water is used as coolant. Water in the trough is continuously agitated and the temperature of water is maintained by a chiller. Pairs of roller are kept at top and bottom of the stages to feed the material at controlled speed.

It has been known for the past three decades that 80% martensite plus 20% bainite is stronger and tougher than 100% martensite. Since the process is so fast with rapid heating and cooling, the carbides don't get a chance to dissolve completely within austenite at high temperature, so they remain in the steel and make this unique microstructure containing bainite, martensite and carbides

Flash processed products are used in high performance armour for military and civilian applications, high performance vehicle structures and crash member applications

References:1. U.S Patent No: 8480824, Method and apparatus for micro-treating iron-based alloy,

and the material resulting therefrom, Cola, Jr. ,et al. July 9, 2013. 2. Development of rapid heating and cooling (Flash processing) process to produce

advanced high strength steel microstructures, Material Science and Technology, July 2011

Conventional process

Glass-Ceramics VENKATESWARAN C

Materials and Metallurgy Group(MMG), MME Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram- 695 022

Glass-Ceramics (GC) area new breed of materials having a great importance among researchers due to their combination of physical properties not available with other class of materials. They are polycrystalline materials produced by the controlled crystallization of host glass with controlled microstructure and properties. GC can also be produced by sintering and cerammingthe powdered glass. The basis of controlled internal crystallization lies in efficient nucleation with higher nuclei per unit volume that allows the development of fine, randomly oriented or alighted crystals in desired phase assemblage.

Despite their higher prices than glasses they have been commercially successful due to their impressive variety of properties. In last six decades, these partially devitrified materials found its place in variety of exotic applications including wavelength up-conversion devices, tunable & infrared lasers, waveguide grating, solid state lighting, magnetic media disks for hard disk drives. Few important applications are discussed here.

Transparent visible GCs can be produced by growing crystals of any following characteristics a) crystal size less than wavelength of visible light, b) negligible difference in refractive indices of residual glass and crystal c) very low birefringence.

Lithium aluminosilicate (LAS) GCs have gained considerable commercial importance due to their very lowthermal expansion, their transparency, high chemical durabilityand strength, and widely being employed in telescope mirrorblanks,ring-laser gyroscopes, optically stable platforms, andcooktop panels. Cook top panels established a market for several million US$ in the world.

For optical applications,GCs are always preferred than their single crystal counter parts due to their cost effective manufacturing process. Lightweight bullet proof vest and transparent visible armor for automobile and aircraft cockpits can be made fromGCs.

12

Flash Bainite Processing

Agilan M Materials processing Research Group(MPCG), MME

Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram- 695 022

Flash Bainite processing is an advanced heat treatment process to produce steel microstructure with high strength and ductility. As the name pronounces, heating and cooling cycle is done in a short period of time (< 10 seconds). Flash processing of 0.15%C plain carbon steel results in very high yield strength (>1200 MPa), tensile strength (>1500 MPa) and appreciable ductility (7%). Also, this process is considered as alternate route for conventional high strength steel production process and this process shows atleast 7 % increase in UTS and 30% increase in ductility than conventional high strength steels.

The flash processing assembly consists of heating and cooling stage. Heating is done by electric induction or oxy-propane flame. Cooling trough is placed just below the heating stage. Normally water is used as coolant. Water in the trough is continuously agitated and the temperature of water is maintained by a chiller. Pairs of roller are kept at top and bottom of the stages to feed the material at controlled speed.

It has been known for the past three decades that 80% martensite plus 20% bainite is stronger and tougher than 100% martensite. Since the process is so fast with rapid heating and cooling, the carbides don't get a chance to dissolve completely within austenite at high temperature, so they remain in the steel and make this unique microstructure containing bainite, martensite and carbides

Flash processed products are used in high performance armour for military and civilian applications, high performance vehicle structures and crash member applications

References:1. U.S Patent No: 8480824, Method and apparatus for micro-treating iron-based alloy,

and the material resulting therefrom, Cola, Jr. ,et al. July 9, 2013. 2. Development of rapid heating and cooling (Flash processing) process to produce

advanced high strength steel microstructures, Material Science and Technology, July 2011

Conventional process

Glass-Ceramics VENKATESWARAN C

Materials and Metallurgy Group(MMG), MME Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram- 695 022

Glass-Ceramics (GC) area new breed of materials having a great importance among researchers due to their combination of physical properties not available with other class of materials. They are polycrystalline materials produced by the controlled crystallization of host glass with controlled microstructure and properties. GC can also be produced by sintering and cerammingthe powdered glass. The basis of controlled internal crystallization lies in efficient nucleation with higher nuclei per unit volume that allows the development of fine, randomly oriented or alighted crystals in desired phase assemblage.

Despite their higher prices than glasses they have been commercially successful due to their impressive variety of properties. In last six decades, these partially devitrified materials found its place in variety of exotic applications including wavelength up-conversion devices, tunable & infrared lasers, waveguide grating, solid state lighting, magnetic media disks for hard disk drives. Few important applications are discussed here.

Transparent visible GCs can be produced by growing crystals of any following characteristics a) crystal size less than wavelength of visible light, b) negligible difference in refractive indices of residual glass and crystal c) very low birefringence.

Lithium aluminosilicate (LAS) GCs have gained considerable commercial importance due to their very lowthermal expansion, their transparency, high chemical durabilityand strength, and widely being employed in telescope mirrorblanks,ring-laser gyroscopes, optically stable platforms, andcooktop panels. Cook top panels established a market for several million US$ in the world.

For optical applications,GCs are always preferred than their single crystal counter parts due to their cost effective manufacturing process. Lightweight bullet proof vest and transparent visible armor for automobile and aircraft cockpits can be made fromGCs.

13

Besides requiring biocompatibility and natural looking aesthetics, dental implant calls for high strength and fracture toughness. Ivoclar’s IPS e.max made from lithium disilicate composition GC has been reported with 350-400 MPa Strength and 2.3 to 2.9 MPa√m toughness.

Substitution of trivalent cation for Ti4+ in LiT2(PO4)3 system generates positive charge deficiency, which is an essential characteristic for lithium ion conducting solid electrolytes for Li-ion battery. Making these materials through glass-ceramic route creates reduced porosity.

Modern era started yielding products withhigh dielectric strength (~40kV/nm), super conductivity, super capacitance & QEO effect (high Kerr). New processes like photothermo induced and laser pulsed crystallization are emerging.

It is really a surprise that a serendipitous invention fills many engineering bills. Principally 1052 possible glass compositions can be made by varying 1 mole% all 80 friendly elements; same could be crystallized to form glass-ceramic.

‘There's Plenty of Room at the Bottom’.

14

Besides requiring biocompatibility and natural looking aesthetics, dental implant calls for high strength and fracture toughness. Ivoclar’s IPS e.max made from lithium disilicate composition GC has been reported with 350-400 MPa Strength and 2.3 to 2.9 MPa√m toughness.

Substitution of trivalent cation for Ti4+ in LiT2(PO4)3 system generates positive charge deficiency, which is an essential characteristic for lithium ion conducting solid electrolytes for Li-ion battery. Making these materials through glass-ceramic route creates reduced porosity.

Modern era started yielding products withhigh dielectric strength (~40kV/nm), super conductivity, super capacitance & QEO effect (high Kerr). New processes like photothermo induced and laser pulsed crystallization are emerging.

It is really a surprise that a serendipitous invention fills many engineering bills. Principally 1052 possible glass compositions can be made by varying 1 mole% all 80 friendly elements; same could be crystallized to form glass-ceramic.

‘There's Plenty of Room at the Bottom’.