SiAlON Ceramics Hasan Mandal Sabanc University, Istanbul, TURKEY - PowerPoint PPT Presentation

Grain Boundary Engineering for Improved Mechanical Properties in SiAlON Ceramics Hasan Mandal Sabancı University, Istanbul, TURKEY MDA Advanced Ceramics Ltd, Eskisehir, TURKEY

Si 3 N 4 and SiAlON s  -Si3N4  -Si3N4 a= 7.76 Ǻ c=5.62 Ǻ a= 7.61 Ǻ c= 2.91 Ǻ Si +4 Al +3 Si +4 Al +3 N -3 O -2 N -3 O -2 Si 6-z Al z O z N 8-z Me m/val Si 12-(m+n) Al m+n O n N 16-n

SiAlON s α -Si 3 N 4 +AlN/Al 2 O 3 + Sintering additives (Y 2 O 3 , rare earths) α - β SiAlON* α -SiAlON β -SiAlON + Grain Boundary phase *Reversible α→β SiAlON Transformation in Heat-Treated Sialon Ceramics Mandal et al, 1993, Journal of European Ceramic Society

SiAlON s α - β SiAlON α -SiAlON β -SiAlON Tough Hard Hard & Tough

Application Areas of Si 3 N 4 and SiAlON s Cutting Inserts image courtesy of CeramTec Germany Turbochargers image Courtesy of NGK/NTK Spark Plug Co Swirl Chamber Bearing Applications image courtesy of Kyocera company

Potential Application Areas of Si 3 N 4 and SiAlONs Diesel particulate filters mineral processing tiles Wind Turbine Parts Cutting blades for wood machining paper processing dewatering tiles Sand Blast Nozzle Liners

DESIRE Wider mechanical, chemical and refractory applications CHALLENGES Properties in severe conditions Cost of powders and processing DEVELOPMENT STRATEGIES Phase relationships and grain boundary chemistry

SiAlON Cocktail Al O N Si  50-200 nm Triple Junction Yb +2/+3 Ca Er Y Phases (TJs) α -SiAlON Sm +2/+3 Ce +3/+4 Crystalline ? β -SiAlON Fe +2/+3 Amorphous ? β -Si 3 N 4 Film Thickness  1-5 nm Lattice parameters are different!!! > 10 nm Reinforcing Additives (SiC, TiN)

EFFECT OF INTERGRANULAR PHASE CHEMISTRY

Crystalline Grain Boundary Phases La 3+ High Absorption La 3+ La 3+ La 3+ La 3+ High Anisotropy La 3+ La 3+ La 3+ La 3+ Low Interfacial La 3+ La 3+ Strength Si 2 ON 2 Low Absorption Lu 3+ Low Anisotropy Lu 3+ High Interfacial Lu 3+ Strength Lu 2 Si 2 O 7 Hoffmann, M.J. and Satet R., “Impact of Intergranular Film Properties on Microstructure and Mechanical Behavior of Silicon nitride”, Key Eng. Mater. Vols. 264-268, (2004), 775-780. Shibata, N., Pennycook S., Gosnell, T.R., Painter, G.S., Shelton W.A. and Becher P.F.”Observation of rare earth segregation i n silicon nitride ceramics at subnanometre dimensions”, Nature, Vol 428, (2004), 730 -733

SINTERING ADDITIVES FOR  /  SiAlON CERAMICS DEVELOPED by MDA •CaO (To avoid  SiAlON transformation) • Y 2 O 3 and/or Re 2 O 3 (where Z Re  62) (To increase the stability and hardness of  -SiAlON) • Re 2 O 3 (where Z Re <62) (To develope elongated  -SiAlON grains and increase fracture toughness) US Patent No: US 7,064,095 B2 EP Patent No: 1 414 580 B1 2002

PROCESSING • Powder: – α -Si3N4 (SN E-10, UBE/Japan) • Composition: Y Total additive content: 6.5 vol% :Sm:Ca Er Yb Designed phase composition: 25% α -SiAlON - 75% β -SiAlON (x:0.42, m=1.25, n=1.3) (z = 0.2) Heat treatment above eutectic (AET) to enable crystallisation of sintering additives

CRYSTALLISATION-AFFECTING FACTORS (i) EFFECT OF DOPANTS CATION SYSTEMS Yb 1Yb:1Ce Ce Yb:Sm:Ca Y:Sm:Ca Y:Ce:Ca Sintering S s /Y s - - - M W M S (ii) EFFECT OF HEAT TREATMENT CATION SYSTEMS Yb Yb:Sm Yb:Sm:Ca Y:Sm:Ca Y:Ce:Ca Sintering S s /Y s - - M W M S HT-1500 S s /Y s S s /Y s S w /Y w , M w HT-1600 S s /Y s M w M s M vs Y: Ln 4 SiAlO 8 N ; S: Ln 2 Si 2 O 7 ; M: Ln 2 Si 3-x Al x O 3+x N 4-x EP12185237, OZ12031EP-Q2/BR, 20 September 2012

Good or Bad Crystallinity! Desired crystalline triple pocket Crsytalline Triple Pockets Amorphous Undesirable crystalline Intergranular Films triple pocket tip Amorphous Mini Triple Pockets EP12185237, OZ12031EP-Q2/BR, 20 September 2012

Good or Bad Crystallinity! SiAlON Grain SiAlON Grain SiAlON Grain Triple pocket (Fully crystalline) Amorphous regions Triple pocket (Partially crystalline) SiAlON Grain Good Crystallisation Insufficient Crystallisation

Y -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET) Crystalline Secondary Phase    

Y -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)  Amorphous Secondary Phase   

Y -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)     Amorphous Mini Triple Pocket

Er -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)   Crystallization Degree of Mini Triple Pockets  

Er -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)    

Er -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)   Crystallization Degree of Triple Pockets  

Er -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)    Crystallization Degree of Triple Pockets 

Er -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)   Crystallization Degree of  Triple Pockets 

Yb -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)   Crystallization Degree of Secondary Phases  

Yb -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET) Crystallization Degree of Mini Triple Pockets  

Yb -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)  Crystallization Degree of Mini Triple Pockets  Crystallization Degree of Mini Triple Pockets

Yb -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET) Crystallization Degree of Secondary Phases  

Yb -Sm-Ca Added  /  -SiAlON System (1990 o C sintered and AET)  Crystallization Degree of Secondary Phases 

Comparison of Creep Behavior of Si 3 N 4 and α/β -SiAlONs @ 1400 ° C & 100 MPa Si 3 N 4

Yb versus Er Yb Flexural strain % Er Time (h)

Effect of Crystallinity on the Performance Less wear 40% improvement in life time

DESIRE Wider mechanical, chemical and refractory applications CHALLENGES Properties in severe conditions Cost of powders and processing DEVELOPMENT STRATEGIES Phase relationships and grain boundary chemistry

α - β SiAlON from  -Si 3 N 4 powder containing impurities 2  m D 50 = 5 µm Al2O3 MgO CaO Fe2O3 TiO2 β -Si 3 N 4 ≤0,05 1,4 0,40 0,60 0,07

Microstructures of SiAlON from different particles size β – Si 3 N 4 powders 1µm 0.5µm 2µm As-sintered Heat treated

Impurity/dopant incorporation into β -SiAlON STEM-HAADF Image LG10002 1000 900 N Al 800 LG1 LG1 Si 700 O 600 Counts 500 1.0 µm 1.0 µm 1.0 µm 1.0 µm 1.0 µm 400 Cu Cu 300 Fe Fe Fe Cu 200 Cr 100 0 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 keV Si6-z(Al,Fe)zOzN8-z

Improved grain boundary crystallization Transient liquid phase sintering Impurity incorporation to enable Cost reduction • Use of coarse and/or impure and/or  -Si 3 N 4 powders • Increased amount of (crystallizable) liquid phase • Lower temperature and/or pressureless sintering

Conclusion Opportunities are present to increase the applications of SiAlON based ceramics by chemistry and process improvement . • BETTER PROPERTIES MARKET • COST SIZE