��������������� ������� ��������������������

������������ �������������� �����������������������

������������� !��"� ��#$�%��&�� '���"��(��� ����� ��)��"� ��#$�%��&�� '��

�*� ������+'�,!'���

����� ��+'�,!'���

��(,������+'�,!'��

��������� "���,-� .� ����� �� �� /��� ��� ���� �'�� �)��(����� �0� �� 1 ��-�� ���� �'�������(�� �')�����-��� � ��

�

���������Due the rapid heating rate combined with high pressure by the Spark Plasma Sintering

(SPS) technologies possible manufacture a wide range of novel materials with exceptional properties

that cannot be achieved using conventional sintering techniques. Hard metals are, from a technical

point of view, one of the most successful composite materials. An overview of the metallurgical

reactions during the SPS sintering process of powder mixtures for the manufacture of hard metals is

presented. The relatively complex phase reactions in the multi-component system TiC-Mo-W-Ni are

discussed. There were elaborated a new technology for the fabrication of nanocrystalline hard metals

of a new class assigned for the production of articles with high different characteristics. Elaborated

materials are characterized by high melting temperature, hardness, wear-resistance, and satisfactory

strength at high temperature and corrosive resistance. Through the use of developed technology and

the appropriate structural condition gives possibility to achieve high physical-mechanical

characteristics. Obtaining of composite materials via elaborated technology is available from the

corresponding complex compounds and directly consisting elements too. In this case

High-temperature Self-propagation Synthesis (SHS) and spark plasma sintering/synthesis (SPS)

process are united and during a single operation it is possible to get not only the powder materials but

at the same time obtain required details.

���� �������

Development of nanostructured hard metals is a task of great importance. Diouf and Molinari [1]

investigated densification mechanisms in spark plasma sintering using commercial copper powder.

They found that under low initial pressure, densification was due to particle rearrangement, localized

deformation, bulk deformation, and neck growth. Nevertheless, in spite of some “euphoria” with

respect to nanograined hard metals, their potential application ranges are yet not clear. In some works,

near-nano and nano hard metals are believed can potentially substitute conventional medium- and

coarse-grained WC–Co grades [2].

The properties of nano WC/Co hard metals prepared by different Spark Plasma Sintering processes

were measured. A 4-layer Functionally Graded Materials (FGM) was also obtained by Spark Plasma

Sintering technology (SPS), starting from powders of nano WC/10%Co, nano WC/12%Co, micro

WC/15%Co and stainless steel disk [3].

The development of new hardmetals during the past 10 years has focused strongly on fine, ultrafine

and nano-structured materials. Significant innovations have occurred and the move towards

'nano'-grained hard metals is attracting ever more attention. These developments, the improved

performance achieved in service applications and other trends are briefly reviewed [4].

Investigations have been made on obtaining of nanosized powders of titanium carbide (TiC) by

carbothermal reduction of a precursor prepared by sol-gel process. Two methods of precursor gels

fabrication of TiC were used. The resulting xerogels are calcined under flowing argon at different

temperatures. TiC nanopowders were obtained with crystallites of 40 nm – 45 nm [5].

We show here that novel nanomaterials can be fabricated by an ancient casting technology.

Titanium carbide (TiC) nanowires have been synthesized by casting NiTi alloys containing a little

amount of carbon. The morphology and structure of the TiC nanowires have been investigated using

Applied Mechanics and Materials Vol. 376 (2013) pp 38-41Online available since 2013/Aug/30 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.376.38

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 130.207.50.37, Georgia Tech Library, Atlanta, USA-16/11/14,14:26:04)

X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The TiC

nanowires have a single crystalline structure and grow along the <100> direction. The diameters of

the TiC nanowires range from 50 to 500 nm, and their lengths vary from 10 to 100 µm [6].

The chemical formation of advanced ceramics from organometallic precursors is promising with

respect to structural design and tailormade properties. There were synthesized nanocrystalline

titanium carbonitride materials at different pyrolysis temperatures via the polymer-to-ceramic

transformation of synthesized poly(titanylcarbodiimides) and their structural and nanochemical

characterization using high-resolution and analytical electron microscopy, in combination with

quantummechanical calculations [7].

Titanium carbide is one of the main constituents of hard metals. Main disadvantage of hard metals

based on titanium carbide is lack of elasticity though we think that this problem can be solved if the

hard metals are of nanocrystalline level, because physical-mechanical properties of nanocrystalline

materials are much better than of those with crystalline structure. Nanocrystalline carbides are

characterized with excellent catalytic properties [8].

Chemical-mechanical methods for the production of nanocrystalline materials in attritory mills are

also far from perfect because long-term milling contaminates the charge with oxygen and contacts of

carbide particles are more extensive. Better results were achieved by using chemical methods

developed at the University of Rutgers for the synthesis of nanocrystalline WC-Co hard metals [9].

Nanocrystalline tungsten or molybdenum carbides made by ultrasound chemical method, where local

pressures and temperatures as well as rates of overcooling are incommensurably high, can be

considered at the level of the Pt group elements by their catalytic properties [10].

�������������

Carbides and hard metals are synthesized by the following method:

Mixture of TiCl3, WCl4, MoCl5 and CaCl2 with mass ratio X:Y:Z:Q is placed in the autoclave.

After evacuation, the autoclave is heated up to 400oC (1 h.), then cooled and opened in order to add

0.5 l of water oxidated with HCl. Content of the autoclave is stirred for 30 min., then the reaction

mixture is filtered and washed in water. Then it is dried in a warm flow of air (400oC). Nickel chloride

is added to the carbide mixture. The obtained mass is brought into a quartz tube and heated in

hydrogen flow up to 850-900 oC during 3h with formed mass forms (Ti, W, Mo)C-Ni. Elimination of

excessive C is carried out at transmission of CO/CO2 (1:1) mixture through the obtained carbides at

750oC (120 min).

For sintering carbide and hard metal nanocrystalline powder materials was used developed SPS

device. This device was equipped with low -voltage pulsed AC current generators. Low voltage was

capable for regulation and it was changed within the limits of 20 V; AC current was up to 5000Amp.

Was designed and prepared Ultrasonic excitation unit with 3 kW power and 22-25 kHz frequency.

Magnetostrictive and generator was constructed ourselves. Second ultrasonic unit for the bottom

punch of the mold in addition was increase conducting of plasma processing and reduce of porosity.

���������� � �����������

For the preparation of nanocrystalline carbides it is necessary to prepare metal-organic or complex

compounds of appropriate elements by using chemical synthesis and the follow up thermo-synthesis.

Fig.1 shows diffraction patterns of titanium carbide obtained from the complex compounds of

Ti(CH2)6N4Cl3 and TiCl3C6H6 after thermo-synthesis at 800

оС. These compounds were synthesized

through interaction of aqua-free titanium trichloride with urotropin (CH2)6N4 and benzol C6H6,

respectively. Broadening of the diffraction maxima indicates to nanocrystallinity of the obtained

carbides. Nanocrystalline titanium carbide was also synthesized from the products of interaction of

titanium hydride - TiH2 and iodoform - CHI3. Sintering of the synthesized powder at 1450оС leads to

growth of crystallites but crystals remain of nano size. The investigations showed that no compound is

formed upon interaction of titanium hydride and urotropin at low temperatures and we could not

Applied Mechanics and Materials Vol. 376 39

manage to obtain titanium carbide. Adding of the mixture of titanium hydride as well as of urotropin

of chlorides of nickel, molybdenum and tungsten allowed preparing nanocrystalline powders of

model hard alloys of TiC-Ni, TiC-Ni-Mo, TiC-Ni-W and TiC-Ni-Mo-W. After the sintering of

abovementioned compacted powder at 1450оС we are having a finished hard alloy. Structure can be

read as made of two phases (titanium carbide and nickel). Nanocrystallinity is kept after sintering.

Fig.1 X-ray diffraction patterns of TiC synthesized from a)Ti(CH2)6N4Cl3, b) TiCl3

C6H6.

We have managed to fabricate appropriate nanocrystalline carbides through interaction of aniline

C6H5NH2 with titanium tetrachloride TiCl4, tungsten hexachloride WCl6 and molybdenum

pentachloride. By adding in the reaction mixture of chlorides of nickel and cobalt it is possible to

obtain appropriate hard alloys. Using of the TiH2-NiCl2-WO3-MoO3-C system for the synthesis of

titanium carbide-based hard metal charges gives better results if compared to other systems.

We have developed a new device for sintering of nanocrystalline hard metals. Principle of working

of the device was based on plasma-sparkling sintering method. Passing of pulse current through the

powder provides the process of sintering due to creating a sparkle and the followed up plasma

between contact points of hard metal particles. High interfacial contact temperature promotes

sintering of the sample and due to low integral temperature - prevents the process of grain growing

thus providing for maintenance of nanocrystalline structure.

The developed device also solves problems of excessive free carbon creating at fabricating of

titanium carbide based nanocrystalline hard metals. The solution is analogous: in this case it is also

necessary to bring an excessive amount of free carbon into the charge for fabricating nanopowders

with normal structure. This excessive free carbon further makes obstacles to the alloys to be normally

sintered. If carbon introduced into the charge is of less amount, then there is detected presence of new

structure compounds besides the main phase in nanopowders. From the nanopowders with rather

defective structure (Fig. 2a) can be easily fabricated alloys with normal structure (Fig. 2b) if the SPS

method and the developed device are applied. Too large amount of carbon introduced into the initial

charge intended for preparing nanopowders makes obstacles to complete sintering of powders though

the structure of nanopowder and the sintered alloy is normal.

40 Materials and Diverse Technologies in Industry and Manufacture

Fig.2. X-ray diffraction patterns of hard metal TiC-Ni-Mo-W: a- nanopowder with W/Mo,

W2G/Mo2C, NiTi, b- sintered alloys with normal structure.

��������

The technology for manufacturing of titanium carbide based nanocrystalline hard metals was

developed. It was realized through selection of compositions based on the research results of hard

metals fabricated by a conventional technology. Hard constituent of titanium carbide alloys and

bonding materials – Ti, Mo, W and Ni was taken in different ratio. There were also selected salts of

the above-mentioned metals and their common oxygen-free organic solvents. Complex and

metal-organic compounds of transition metals were prepared by chemical synthesis of the salt

solutions. For the formation of hard metal charge, the complex and metal-organic compounds were

subjected to pyrolysis at 800-900oC in hydrogen flow and/or without it. Interaction of titanium

hydride with oxygen-free organic at 700-800oC for the fabrication of hard metal charge was also

provided. The hard metal charge was subjected to and was sintering by standard technology and by

Spark Plasma Synthesis (SPS) method. Technological modes by all cycles of fabrication of titanium

carbide and hard alloys based on this material were developed.

�����������

[1]� S. Diouf and A.Molinari, Densification mechanisms in spark plasma sintering: effect of particle

size and pressure, Powder Technology, 221 (2012) 220–227.

[2]� I. Konyashin, B. Ries, F. Lachmann, International Journal of Refractory Metals and Hard

Materials, 28 (2010) 489–497.

[3]� Xinglong Tan, Shaoyu Qiu, Wenyan He, Daifu Lei, Journal of Metastable and Nanocrystalline

Materials 23, (2005) 179-182.

[4]� van den Berg, Henk, Powder Metallurgy, 50 (2007), 7-10.

[5]� I. Zalite, A. Letlena, MATERIALS SCIENCE, 18 (2012) 75-78.

[6]� Z. Zhang, Y. Wang and J. Frenzel, CrystEngComm, 12 (2010) 2835-2840.

[7]� O. Lichtenberger, E. Pippel, J. Woltersdorf, R. Riedel, Materials Chemistry and Physics 81

(2003) 195–201.

[8]� T. Hyoen, M. Fang, and K. S. Suslick, J. Am. Chem. Soc., 118 (1996) 5492-5493.

[9]� Z. Yao, J. J. Stiglich and T. S. Sudarashan, Materials Modification, Inc, 27, (1997).

[10]�K. S. Suslick and G.J. Price, Annu. Rev. Mater. Sci., 29 (1999) 295-326.

Applied Mechanics and Materials Vol. 376 41

Materials and Diverse Technologies in Industry and Manufacture 10.4028/www.scientific.net/AMM.376 SPS Method for Manufacturing Carbide Materials 10.4028/www.scientific.net/AMM.376.38