1. cermets
Presented by :-
Anurup Sarker
Arpan Das
Sumedh Dasgupta

2. Composite materials composed of ceramic (cer)and metal(met)
WHAT ARE CERMETS
Composite materials composed of ceramic (cer)and metal(met)
Cermets deliver the benefits of both metal and ceramic in engineering material which cant be obtained from either one material.

3. Development of cermets can be traced back to post World War II
HISTORY OF CERMETS
Development of cermets can be traced back to post World War II
First tungsten- free hard metal cermet ( TiC. Mo2C.Ni[Co,Cr]) developed in by P. Schwarzcopf and J. Hirschl
German scientists first developed oxide based cermets as a substitute to alloys for jet engines and high temperature turbine blades

4. Ohio state university first developed alumina based cermets
HISTORY CONTD…
First developed cermets used magnesia , alumina and beryllia as ceramic part
Ohio state university first developed alumina based cermets
Silicon carbide and silicon nitride anticipated as good ceramic part in early 1960’s

5. TYPeS OF CERMET OXIDE BASED CERMETS Combination of Al2O3 with TiC
Eg. Al2O3-Cr
Carbide based cermets
Eg. WC-Co, TiC-Ni
TiC based cermets are wear resistant
SiC, B4C cermets are corrosion resistant

6. TYPES CONTD…. Carbonitride based cermets
Generally produced by addition of Mo2C
Eg. TiC/TiN ; MoC/MoN
Nitride based cermet
Eg. TiN, cubical BN & ZrN based cermets

7. TYPES CONTD…. Boride based cermets
Eg. CrB-Mo, CrB-Cr.Mo Alloy, CrB-Ni, TiB- Fe/Ni/Co ; combination of ZrB2/Sic excellent corrosion resistant

8. ADVANTAGES OF CERMETS
Ceramic part of cermets deliver beneficial properties like high abrasion resistance, creep resistance, greater chemical stability and high refractoriness
Main disadvantage of ceramic part brittleness
Metal part delivers ductility, high thermal conductivity, high thermal and mechanical shock resistance but less resistant to higher temperature
Cermets club all above mentioned properties

9. CERMET PREPARATION:CONTROLLING PARAMETERS
Degree of wetting between ceramic and metal phase
Degree of alteration of either metal or ceramic to ensure proper wetting
Degree of phase interaction

10. CERMET PREPARATION:CONTROLLING PARAMETERS
Mutual solubility
Chemical inertness of the interface bond
Relative thermal expansion of the two phases
Inherent strength of each components
Inherent conductivity of each component

11. Morphology of Cermets
Mostly developed cermets contain of carbide ceramic particles imbedded in a metallic binder
Classified as metal matrix composites because the metallic binder is the matrix which holds the bulk material together
However, the carbide particles constitute the largest proportion of the composite material, normally between 80% and 95% by volume

12. MORPHOLOGY OF CERMETS Usual proportion of binder metal is 4% up to 20%
The carbide powders must be sintered with a metal binder to provide a strong and pore‑free part
Cobalt works best with WC, while nickel is better with TiC and Cr3C2

13. GENERAL METHODS OF CERMET FABRICATION
Static cold pressing
prismatic shapes
Hydrostatic cold pressing
Simple/complex shapes
Powder rolling
flat & thin shapes

14. GENERAL METHODS OF CERMET FABRICATION
Warm extrusion
long piece with uniform cross section
Powder injection moulding
complex shapes with undercuts
Hot isostatic pressing
simple/complex shapes

15. CARBIDE CERMETS:FABRICATION
Powders of carbide and binder metal are thoroughly mixed wet in a ball mill to form a homogeneous sludge
The sludge is then dried in a vacuum or controlled atmosphere to prevent oxidation in preparation for compaction

16. FABRICATION CONTD…
Most common process is cold pressing, used for high production of cemented carbide parts such as cutting tool inserts
Dies must be oversized to account for shrinkage during sintering (shrinkage can be 20% or more)

17. FABRICATION CONTD…..
For high production, the dies are made with WC‑Co liners to reduce wear
For smaller quantities, large flat sections may be pressed and then cut into smaller pieces
Other methods: isostatic pressing and hot pressing

18. Sintering of WC-Co
It is possible to sinter WC (and TiC) without a metal binder, but the resulting material is less than 100% of true density
Using a binder yields a structure virtually free of porosity
Sintering of WC‑Co involves liquid phase sintering

19. WC-Co SINTERING CONTD…
The usual sintering temperatures for cemented carbides are 1700‑2200C
Thus, the pure binder metal melt at the sintering temperature

20. WC-Co SINTERING CONTD…
However, WC dissolves in Co in the solid state so WC is gradually dissolved during the heat treatment, and its melting point is reduced so melting occurs
As the liquid phase forms, it flows and wets the WC particles, further dissolving the solid
Presence of molten metal also serves to remove gases from the internal regions of the compact
These mechanisms cause a rearrangement of the remaining WC particles

21. Process occurring during heat treatment
Metals ions diffuse into the crystal lattice of the ceramic matrix
Sintering occurs causing grain to grain coalition

22. METALS THAT CAN BE USED AS METAL PARTS IN CERMETS
Transition metals like Fe, Ni, Ti, Co
Co is used because
Higher melting point – 1495oC
High temperature strength
Forms an eutectic at 1325oC

23. PHASE DIAGRAM OF W-C-Co
Fixing the cobalt composition gives F=C- P+2 F=2 (2-2+2 = 2)
Melting point of WC = C
Melting point of Co = 1495oC
Forms a eutectic at 1325oC

24. PHASE DIAGRAM OF W-Fe-C
Melting point of WC = 2776oC
Melting point of Fe = 1538oC
Eutectic at 1275oC

25. PHASES PRESENT IN CARBIDE CERMETS
Pure grains of carbide
Grains of carbide doped with metal which forms a solid solution of metal with carbide
Metal as the binder phase

26. HUME – ROTHERY RULE FOR SOLID SOLUTIONS FORMATION
Same crystal structure
Relative size of atomic radii
Chemical affininity factor
Relative valence factor

27. Structure of tungsten carbide
Hexagonal closed pack
Tungsten – tungsten bond length – 291 pm
Tungsten – carbon bond length = 220 pm
Distance between two layers 209 pm

28. Structure of cobalt
Cobalt has a hcp structure
Atomic radius = 125 pm

29. Structure of WC – Co CERMET
Interstitial solid solution is formed by penetration of the Co molecules into the crystal lattice of the tungsten carbide

30. Property development due to formation of cermets
Diffusion of metal ions inside the crystal structure of the cermets induces strain inside the structure
Strain improves the toughness and wear resistance of the materials

31. Properties of cermets contd…….
Electrical conductivity
Thermal conductivity
Presence of free metallic atoms inside the structure

32. NUCLEAR WASTE UTILIZATION: STEEL-UO2 CERMET

33. UO2 BASED CERMETS… UO2 and steel powder thoroughly mixed
Placed between clean of steels
Sandwich is heated
Sandwich is rolled
UO2 cermets used as nuclear fuels
Non uranium cermets used as brake pad, cutting tools, and similar applications

34. APPLICATION OF CERMETS
Used as cutting tool materials involving titanium carbide or titanium carbonitrides as the hard refractory phase
Cermets based on SiC & B4C used in wear and corrosion resistance or antifriction applications and also in nuclear reactor applications

35. APPLICATION OF CERMETS CONTD…
TiN & ZrN bonded with their respective metallic elements developed for special heat and corrosion resistant purposes
UO2 or ThO2 based cermets found application as a major fission component in nuclear reactor fuel elements
Combinations of Al2O3 with TiC are suitable for hot machining tools

36. APPLICATION OF CERMETS CONTD…
Combination of ZrB2 and SiC is resistant to erosion from the propulsion gases of chemical rockets
ZrB based cermets used in liq. Metal pumping system and also thermocouple sheathes

37. SUGGESTIVE CONCLUSION
Coke oven wall silica bricks can be replaced by a cermet brick since the operation temparature is below 1000 deg C
Cermet has good thermal conductivity
Cermet therefore may ensure better heat transfer to coal
Cost effectiveness is a basic question

38. Suggestive conclusion
Cermet may be used in blast furnace regenarator
Carbide or oxide based cermet may be used
Manganese steel beaters coluld be replaced by WC-Co cermet for better toughness
Feasibility needs to be studied

39. Thank you