1

LTPÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE

Powder Technology

From Landslides and Avalanches to Concrete

and Chocolate

Prof. P. Bowen (EPFL), Dr. P. Derlet (PSI)

WEEK 13

Sintering Mechanisms & New Technologies- (3)

Processing – Forming - Shaping

Teaching plan 2017

Files of lectures and notes to be found on LTP website : http://ltp.epfl.ch/Teaching

Week-DATE File.

no.

Powder Technology – Wednesday 10.15-12.00 – MXG 110

1- sept 20 1 Introduction - PB

2 – sept 27 2 Powder packing and compaction - 1- PB -

3 – oct 4 3 Powder packing and compaction - 2-PB- and guest lecturer - MS

4 – oct 11 4 Powder packing and compaction -3- PD

5 – oct 18 4 Powder packing and compaction - 4 – PD

6 – oct 25 5 Particle – Particle Interactions 1 - PB

7 – nov1 6 Particle – Particle Interactions 2- PB

8 – nov 8 7 Particle – Particle Interactions - 3-PB

9 – nov -15 8 Introduction to atomistic scale simulations PD

10 – nov 22 9 Compaction, Sintering & Defects in metals at atomistic scale - PD

11 -nov-29 11 Sintering Mechanisms (& New Technologies) - 1 – PD

12 - dec 6 11 Sintering Mechanisms (& New Technologies) - 2 – PD

13 – dec 13 10 New Technologies (& Sintering Mechanisms) -3 PB

14 – dec 20 12 New Technologies (& Sintering Mechanisms) and exam 4 – PB

PB – Prof. Paul Bowen (EPFL), PD – Dr. Peter Derlet (PSI)

MS- Dr. Mark Sawley (EPFL)

Today’s Objectives

This Week

• Standard forming methods…..ceramics and metals

– Dry Pressing…(Generalities from 3rd year & summary PT compaction

courses – weeks 4&5 file PowderTech 4)

– Wet methods – overview - slip casting, tape casting, injection moulding

– Limitations …additive manufacturing approach

– General intro to additive manufacturing…video…importance of dispersion!!!

– Green bodies…Sintering…standard procedures (next week)…

• Additive manufacturing and sintering combined – SLS

– Introduction…..Video…..

– Detailed study thesis Cedric André importance of particle packing …..

Next week …

• Summary of standard sintering methods and procedures

• New sintering processes, SPS, flash sintering, cold sintering…

• Typical questions, Powder Technology – Learning outcomes,

• Exam….

4

Standard forming methods – Dry pressing ceramics

• Dry pressing – Compaction – Ceramics (3rd year* p.209 & TP2)

• Ceramics – powders granulated (PT week 3 – Neural network –

particle packing) with

• Binder (e.g. polyvinyl alcohol PVA) and

• Plasticizer (e.g. polyethylene glycol PEG [-CH2-CH2-O-]n)

• 3- stages of compaction

– i) rearrangement →RCP of granules

– ii) deformation → plastic…PEG/PVA

– iii) granule fracture/densification

– Ceramic particle density ~ 60% →RCP

• Limitations L/D – density gradients - friction

4

*Les Traité des Matér, Vol. 16 « Les Céramiques » J. Barton, P. Bowen, C. Carry & J.M. Haussonne, PPUR, 2005

Grey – C, Red – O, White- H

PVA

Standard forming methods – Compaction metals

• Dry pressing – Compaction – Metals (PT weeks 4&5) – higher plasticity cf

ceramics…also 3 stages …

– Stage 0 – packing…. rearrangement → RCP ….

– Stage 1 – deformation – increase in contact area -connected pores (60%-80%)

– Stage 2 – sealing off of pores between particles (80%-90%) - porous solid

• Density variations as L/D increases…lubrication walls vs powder

• Four major mechanisms controlling densification are

– rearrangement, plastic deformation, power-law creep and diffusional flow

5

DEM modellingDrucker-Prager-Cap

(DPC) model

Limitations – compaction

• Generally shapes have to be symetrical and simple in 2D i.e.

small orthogonal features not possible

• Ceramics limited in size…few cm..

• Length to diamter ratio…> 2 start getting density gradients

• Ceramics max force 150-200 MPa – otherwise elastic rebound

leading to defects..

• For cylinders and tubes – isostatic pressing (10’s cm)

• Metals …work hardening can limit compact density

• Sizes higher – cars 9-25 kg compacted & sintered steel parts..

• 10’s cm ..but again… too big get density gradients

• E.g. http://www.perrytool.com/ precision gears, pulleys, bearings,

• cams, sprockets, fasteners, soft magnetic components and

• complex multi-level, close tolerance mechanical parts

6

3cm

2cm

http://www.perrytool.com/products_gears.shtmlhttp://www.perrytool.com/products_pulleys.shtmlhttp://www.perrytool.com/products_bearings.shtmlhttp://www.perrytool.com/products_magnetics.shtmlhttp://www.perrytool.com/products_mechanical.shtml

7

Wet Ceramic Slip Casting technique

Suspension forming method

Prepare suspension – called slip

Slip = concentrated suspension

Need adequate viscosity to pour into

the mould

Want a minimum of liquid

Give us a minimum shrinkage during

drying

Porous mould – cappilary suction Pc

Deposit thickness α t 0.5

Can also use to make films – tape

casting - 10-250 mm thickness

Suspension

Filter 0.2 mm

Mould - Silicone

Porous Support

rP lvc

cos2

8

Slip casting – cups or solid forms

empty mouldfilled with suspension

drained of excess suspension

taken from mould for drying

empty mould filled with suspension

pressure or slurry suppliment

final green solid form - for drying

drain casting

– par vidange

solid casting

- forme remplit

9

Application Traditional Ceramics

Porcelaine – hand basin, toilets

Complex shape and big!!!

Slip casting 45% vol solids - 80 minutes per

mould

Pressure casting – add gas pressure

2 minutes!! 40 times quicker

Modern plants semi-automatic

1week to mix and mill powders before using

the « slip »

High green densities (before firing) of 69%

can be reached with optimum dispersion and

particle size distribution

LAUFEN - Switzerland

P. Bowen, EPFL. 13/12/2017 10

Wet methods – injection moulding – metals & ceramics

Small precision pieces –very complex forms - precise… 1-2 microns without machining

Mixture of ceramic or metal powder – polymers (20% wt, 50% vol)

Heat to 150 - 200°C – plastic injection

Limitations – expensive tooling (80,000 €) - size limited – cm…

Very good for large series, thousands of pieces

Binder burnout… slow 1-3 days…new technology BASF – 2-4 hrs

HNO3 at 120°C (limited to BASF powder quality…no control)

http://www.pim-international.com/metal-injection-molding/binders-and-binder-removal-techniques/

SPT Roth SA- Ceramic injection moulding (CIM) of small complex & precise

components in micron tolerances. Materials include Alumina, Zirconia, Zirconia-toughened

Alumina and polycrystalline Ruby. Limitation size max cm….

•Medical tools & implants - Dental applications - Industrial and Electronic components

•Nozzles with hole diameter less than 15µm - http://www.smallprecisiontools.com/

Nozzles

https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_1.html

http://www.smallprecisiontools.com/products-and-solutions/fine-ceramics-solutions/ceramic-materials-table/?oid=439&lang=enhttp://www.smallprecisiontools.com/products-and-solutions/fine-ceramics-solutions/custom-engineered-ceramic-parts-application-examples/medical-tools-and-implants-bioceramic-biocompatible-ceramic/?oid=522&lang=enhttp://www.smallprecisiontools.com/products-and-solutions/fine-ceramics-solutions/custom-engineered-ceramic-parts-application-examples/dental-applications-anatomical-shape-translucent-ceramics/?oid=523&lang=enhttp://www.smallprecisiontools.com/products-and-solutions/fine-ceramics-solutions/custom-engineered-ceramic-parts-application-examples/industrial-components-wear-resistance-high-precision/?oid=524&lang=enhttp://www.smallprecisiontools.com/products-and-solutions/fine-ceramics-solutions/custom-engineered-ceramic-parts-application-examples/electronic-applications-high-complexity-wear-resistance/?oid=677&lang=enhttp://www.smallprecisiontools.com/products-and-solutions/fine-ceramics-solutions/custom-engineered-ceramic-parts-application-examples/ceramic-and-metallic-nozzles-with-small-precision-holes/?oid=891&lang=en

Wet methods - general limitations

• Slip casting slow…can speed up with – addition of pressure but complexity

of form still limited

• Drying – slow – days…

• Limited thickness…cm’s

• Injection moulding – high cost of tooling...need to test proof of concept

before making expensive tools…

• Additive manufacturing – initially called rapid prototyping – proof of

concept…for complex pieces...then perhaps use injection moulding…

• Much work over past 20 years …become interesting for pieces…

• improved resolution, improved green body homogeneity

• Giving comparable sintered densities to standard techniques

• New Horizons are promising – even more complex pieces…..

11

Additive manufacturing

• Ceramics –

• The most difficult thing for ceramic processing is to make a

complex shape with high reliability!

• The most critical part for ceramic processing is particles, not

sintering…

• Once forming done to best possible packing and best

homogeneity and uniformity (densities, pore sizes) then

advanced sintering techniques can be useful

• If not always limited by heterogeneities…weak points for

mechanical properties or optical properties…

• Slides 46-79 week 1……

• Metals

• …complex shapes …and sintering at same time

• Selective Laser Sintering…

12

Additive manufacturing – 3D printing techniques for

ceramics* - direct technologies

13

DIWDIPFDC

3DP SLSDLP/SLA

Lewsi et al J. Am. Ceram. Soc., 89 [12] 3599 (2006)

Ceramic particles in appropriate

thermoplastic binders

Ink is continuously

extruded through a fine

cylindrical nozzle

Direct ink-jet printing

Ink-jet printing of material

in the form of droplets

in a desired pattern via a

layer-by-layer build

sequence

Lous et al J. Am. Ceram. Soc., 83 [1] 124 (2000)

*Franks et al. J Am Ceram Soc 2017; 1–33

*Zocca et al. J. Am. Ceram. Soc., 98 [7] 1983–2001 (2015)

Suspension/ink

Additive manufacturing – 3D printing techniques for

ceramics – powder beds – indirect technologies

14

3DP SLSDLP/SLA

Stereolithography

https://www.youtube.com/watch?v=NM55ct5KwiI

Stereolithography (SLA) and

Digital light processing (DLP)

-similar principles – different possible

outputs.

Both use UV or light curable resins

SLA - laser that travels over the cross

sectional area of each layer of the part

DLP uses digital light projector screen to

flash a single image of each layer all at once

Powder bed Powder bed

binder

Powder-Based 3D Printing –

an inkjet printing head spits

a binding

liquid onto a powder bed,

thus defining the cross

section

of the object in that layer.

Selective Laser Sintering local densification of the powders by directly sintering. Direct laser sintering of ceramics

is complicated by the poor resistance of this class of materials to thermal shock. But good with metals

European leaders

15

Lift-up DLP

Common Strategy: flocculated ceramic resin with very high viscosity!

Top-Down SLA

What can it do?

- - Shanghai (China) (Prof. Zhao Zhe)

20

Low shrinkage during printing, the thin sheet of 300mm can be sintered

without noticeable deformation

Low viscosity which lead to potential applications with desk-top machines

Easy to be burned resin design which is critical for fast processing and also

low post-processing cost

Top-Down DLP and SLA；

Low Viscosity dispersion-type ceramic resins

3D Printing Ceramic Materials

• Practical Properties：

– Shelf life-time：6 months with re-dispersability

– Continuous Work Time：2 weeks

– Smallest channel size：200mm

– Thinnest wall thickness：300mm

– Smallest support size：200mm

– Viscosity at 30s-1: 800-3000cps

– Exposure time：3-30sec (DLP), >1500mm/sec (SLA)

– Penetration thickness：>100-300mm

21

• Density after sintering: 3.93g/cm3 for 99.99% pure

alumina and 6.03g/cm3 for zirconia 3Y-TZP

• Printing time: 50mm layer thickness, each layer

20sec, almost 1cm/hour

• The principles for printing materials development:

surface modification of powder is the key!

Still defects observed….cf standard processing

22

Reality: inter-layer defects, incomplete edges and fringes of layer thickness….

Reduced Defects By Better Power Dispersion

23

Inter-layer can be reduced but still some small pores need to be removed! Further development of slurry is necessary。

3Y-TZP，1600°C

3Y-TZP，1600°C

Topological Design For Structure And Functions

• Light-weight design；truss-like cellar/lattice structure design; Biomimiticstructure and functions.

• It is very promising that 3D printing ceramics can break the bottle-neck limits

for ceramic material applications…open new avenues….

24

The Intrinsic Benefits from 3D Printing

25

• Built through layer-by-layer mode, limited thickness and volume of elastic

ceramic materials will decrease the residual stress during the forming and

sintering stages.

• It is expected that 3D printed Ceramics can be better than traditional processing

products if material design can be good enough.

• Material design golden rule: low shrinkage during the layer

stacking/solidification.

• This will improve the binding strength between layers and also reduce all

structural defects which severely affect the reliability of ceramics.

• Key for Success：good powder dispersion and good material design

• Commercialization：focus on Sterolithography but with solid consideration with precision and size.

P. Bowen, EPFL,CdP 13/12/2017 26

Steric -polymer adsorption – layer thickness

Dispersion – Colloidal Stability - IMPORTANT

Repulsive

Electrostatic, ion adsorption, dissociation, polyelectrolyte

h

(a)

(b)

++

+

+

++

+

+

+

++

++

+

+

++

+

+

+

++

(distance h between particles)

hak al

r = ( h + 2a )

*U. Aschauer, et al J. Dispersion Science Technology, 32(4), 470 – 479 (2011).

( ), , 212k lha a h

aF A

h 2 k l

k l

a aa

a a

Harmonic average radius

2

2

0 22

1

h L

ES h L

eF a

e

Electrostatic potential

From zeta potential)

1/ Electricaldouble layer thickness

5

3

2

3 2, 2 1

5

B adsster k l

k T LF a a a

s h

Lads - Adsorbed layer thickness, s - Spacing of adsorbed molecules

In mushroom configuration – geometry important

Attractive - dispersion or Van der Waals forces – A(h) – Hamaker constant

(dielectric properties)

26

L – charge/zeta plane

Dispersion – Colloidal Stability - IMPORTANT

♦ Net potential/force is algebraic sum of

repulsive and attractive forces

#Robert J. Flatt, Paul Bowen, J. Am. Ceram. Soc., 89 [4] 1244–1256 (2006)

0

Inte

rac

tio

n E

ne

rgy

charge

polymer

Attraction - VdW

h

(-)

(+)

1-4 nm

Repulsion total

,htotal VdW ES SterhaF F F F

Total Interaction

VT = VA + VR

Maximum Energy Barrier, VT = VVdW + VE (+ VS )

27

2 k l

k l

a aa

a a

Harmonic average radius

hak al

r = ( h + 2a )

Selective Laser Sintering - ExampleTHESE N◦ 3716 (2006)

PRESENTEE A L’ INSTITUT DE PRODUCTION ET ROBOTIQUE (IPR)

ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE

POUR L’OBTENTION DU GRADE DE DOCTEUR ̀ ES SCIENCES

PAR

CEDRIC ANDRE

EPFL

Laboratoire de Gestion et Procédés de Production (LGPP)

Institut de Production et Robotique (IPR)

CH-1015 Lausanne

Switzerland

acceptée sur proposition du jury :

Prof. R. Glardon, directeur de thèse

Dr. E. Boillat, directeur de thèse

Prof. N. Boudeau, rapporteur

Dr. P. Bowen, rapporteur

Dr. C. Martin, rapporteur

Lausanne, EPFL, 2006

Selective Laser Sintering (SLS)

Applications....2017...

- Stainless steel - automotive industry

- Heat exchangers (SS)

- T- Blade Aerospace (thermal barrier support)(Ti)

- Laminar flow reversers (Al) (plant engineering)

- Dental crowns and bridges, Sensor element - CoCr (Medical)

https://www.youtube.com/watch?v=te9OaSZ0kf8

VIDEO _ https://www.youtube.com/watch?v=rEfdO4p4SFc

METHOD

1. First layer

2. Laser sweeps surface

-partial melting of particles

- consolidation on cooling

3. Reservoir descends

– second layer sintered

4. Repeat steps 1-3…

UT Austin, 1995Advantages

1. Metals, polymers,

ceramics(mixed with polymers)

2. Rapid fabrication – CAD file

3. Recycle non-used powder

4. Complex geometries…possible

5. Graded layers or gradients

https://www.youtube.com/watch?v=rEfdO4p4SFc

Powder technology related questions

• Powder bed density (particle arrangement)

• Heat transport in a powder bed

• Mass transport in a powder bed

• Sintering, surface quality....

P0 - power (w)

f - pulse frequency kHz)

h – distance de ratser (mm)

v – speed of sweep (mm/s9

ecouche - layer thickness (mm)(200-700 mm)

rbed - layer density before

sintering (g/cm3)

tp- pulse duration (nsecs)

Parameters Microstructure

Density

Roughness

Mechanical

Hardnes

Precision…

Properties

Key Parameters for SLS

31

• How energy is supplied to the powder ?

• How much energy is supplied to the powder ?

• To what is this energy brought?

Microscopic properties of the powder and bed

• Stainless steeel – model powder

• Follows log-normal distribution

• Low agglomeration factor 1.4

• Apparent density (RLP) – 4.4 g/cm3 (56%)

• Tapped density (RCP) – 5.2 g/cm3 (67%)

• Bed density varied from 4.3 to 4.6 g/cm3

32

DEM – modelling (C. Martin – Grenoble)

• Gas – compressed – particle coordination number (Z) and density (rbed)

33

o DEM results between RLP and

RCP found experimentally

o Apparent density - 56%

o Tapped density - 67%

m - coefficient of friction

w energy of adhesion (J/m2)

DEM

conditions

Properties

m w r bed Z

0 0 65.2 5.4

0.2 0 58.3 4.7

0.2 1 57.4 5.6?

SLS – control of microstructures

Statistical analysis and simulation (DEM)

• 39 points – statistical experimental hybrid design – looking for

• Relationship – microstrcrural parameter - h = h(tP, Er, rbed).

34

rb

ed

g.c

m-3

[]

Er [J.mm-2]

tP [ns]

tP [ns]

Er

[J.m

m-2

]

h

X1 ≡ tP

X2 ≡ Er

X3 ≡ rlit

Microstructural Parameter* - h

• From solid area ( = total area-pore area) – Fs

• Perimeter of pore-solid interface – p

• And equivalent perimeter of powder bed before sintering – pFs

• pFs = dv50 nFs , where nFs the number of particles to cover analysis area)

• From image analysis….get binary image ….

• Can describe the fineness and denisty of the sintered layer

35

Original grey scale Binary image

*Thesis Cedric Andre , EPFL, N◦ 3716 (2006)

Microstructural Parameter* - h

36*Thesis Cedric Andre , EPFL, N◦ 3716 (2006)

h = 0.35 0.5 0.7

Classe 1 :

fine

heterogeneous

Classe 2 :

fine

homogeneous

Classe 3 :

large

oriented

Classe 4 :

Large melted

Affinement de la structure

• 4 – classes of microstructure…according to h

0.9

Energy Density

37

sample a03, h = 0.87sample m074, h = 0.80

P0 = 11W, v = 40mm.s-1, h = 45mm, P = 2 kW

^

Er = 6.1 J.mm-2

tP = 550 ns

rlit = 4.3 g.cm-3

P0 = 6W, v = 22.2mm.s-1, h = 45mm, P = 0.5 kW

^

• Same energy density but different power and velocities….

• Similar if slightly different features…according to h

Influence of powder bed

thickness

Concrete!!!!

• https://www.youtube.com/watch?v=WzmCnzA7hnE

39

• ETHZ – NCCR

• Digital

Fabrication

Today’s Objectives

This Week

• Standard forming methods…..ceramics and metals

– Dry Pressing…(Generalities from 3rd year & summary PT compaction

courses – weeks 4&5 file PowderTech 4)

– Wet methods – overview - slip casting, tape casting, injection moulding

– Limitations …additive manufacturing approach

– General intro to additive manufacturing…video…importance of dispersion!!!

– Green bodies…Sintering…standard procedures (next week)…

• Additive manufacturing and sintering combined – SLS

– Introduction…..Video…..

– Detailed study thesis Cedric André importance of particle packing …..

Next week …

• Summary of standard sintering methods and procedures

• New sintering processes, SPS, flash sintering, cold sintering…

• Typical questions, Powder Technology – Learning outcomes,

• Exam….

4

Teaching plan 2017

Files of lectures and notes to be found on LTP website : http://ltp.epfl.ch/Teaching

Week-DATE File.

no.

Powder Technology – Wednesday 10.15-12.00 – MXG 110

1- sept 20 1 Introduction - PB

2 – sept 27 2 Powder packing and compaction - 1- PB -

3 – oct 4 3 Powder packing and compaction - 2-PB- and guest lecturer - MS

4 – oct 11 4 Powder packing and compaction -3- PD

5 – oct 18 4 Powder packing and compaction - 4 – PD

6 – oct 25 5 Particle – Particle Interactions 1 - PB

7 – nov1 6 Particle – Particle Interactions 2- PB

8 – nov 8 7 Particle – Particle Interactions - 3-PB

9 – nov -15 8 Introduction to atomistic scale simulations PD

10 – nov 22 9 Compaction, Sintering & Defects in metals at atomistic scale - PD

11 -nov-29 11 Sintering Mechanisms& New Technologies - 1 – PD

12 - dec 6 11 Sintering Mechanisms & New Technologies - 2 - PD

13 – dec 13 10 Sintering Mechanisms &New Technologies -3 PB

14 – dec 20 12 Sintering Mechanisms & New Technologies- and exam 4 – PB

PB – Prof. Paul Bowen (EPFL), PD – Dr. Peter Derlet (PSI)

MS- Dr. Mark Sawley (EPFL)