Graded cemented carbides are functionally graded materials where the composition of tungsten carbide and metallic binder such as cobalt is varied from the surface to the interior of the material in order to provide both high hardness and wear resistance on the surface with high toughness in the core. These materials are produced using powder metallurgy techniques to create composition gradients and are then consolidated using liquid phase sintering or microwave sintering to achieve full density. Graded cemented carbides have applications in cutting tools, mining, and construction due to their improved mechanical properties over traditional cemented carbides with a uniform composition.

1. Studies on Graded Cemented
Carbides
Rahul Mitra

2. Contents
•Introduction
•Graded cemented carbides over cemented carbides
•Graded cemented carbide materials
•Production of cemented carbides
•Co-Free cemented carbides
•Conclusion
•References

3. Introduction
• Materials obtained by continuously grading their constituent elements
(metals, ceramics, etc.) to match the usage conditions and by optimally
controlling the coefficient of thermal expansion and coefficient of thermal
conductivity are known as functionally graded materials (FGM ).
• The functionally graded materials possesses an unique combination of
various properties, which cannot be achieved in bulk materials.
• They play a key role in production of ultra hard components capable to
sustain in high wear environment such as cutting, machining, mining and
drilling operations

4. • Different failure mechanisms of Cemented carbides include micro
spalling, abrasion wear, WC grain pull-out etc.
• The main requirement is to have surface very hard and good wear
resistant whereas the centre of it should have a high toughness .
• Functionally graded cemented carbides provide a viable solution,
providing wear resistance and toughness by grading the binder metal
composition from the surfaces to the interior and compressive residual
stress is introduced to the material surface providing restricted crack
propagation .
Graded Cemented Carbides Over
Cemented Carbides

5. Graded Cemented Carbide materials
• Cemented carbides are metal matrix composites where carbide particles act
as the aggregate and a metallic binder serves as the matrix.
• Different carbides: WC, TaC, (Ta, Nb)C, TiC, HfC, Cr3C2, VC etc.
• Different binder metals: Co, Ni, Al, Cu

6. Porosity and pore-size
gradients
Volume content of
phases and grain size
gradients in two or
multiphase materials
Chemical composition of
single phase materials
Types of Gradient
The manufacturing process of functionally graded cemented carbide can, usually, be
divided into two process-
1. Gradation.
2. Consolidation.
Mainly done by Powder metallurgical processes
Production of Graded cemented carbides

7. Types of functionally graded materials (a) Gradient with Fraction (b) Gradient with Size, (c)
Gradient with Orientation, (d) Gradient with Shape.
A Typical Graphical Representation

8. Deposition Of Powder Mixtures With
Gradient In Composition
• Continuous dry deposition of layers:
In this process continuous deposition of powder with various composition is done
using a conveyor belt. Such sequential deposition results in a stepped gradient.

9. Sheet lamination: Thin sheets of different
composition made by powder rolling or gel
casting are joined to form a stepped gradient.
Die Compaction
• Die compaction:
Gradient is formed by the deposition of powder
layers with varying compositions in the compacting
die.

10. Wet powder spraying:
Mainly 2 processes are involve-
1. Mixing.
2. Multi-layered spraying.
Mixing Multilayered spraying
Slurry dipping method:
Sequential dipping of a substrate into
slurries with various powder
composition results
such stepped gradient .

11. Jet solidification:
• Also known as Solid freeform process.
• A hot powder-binder mixture is deposited
with an extrusion jet moved in two
dimensions.
• If the powder composition is varied from
layer to layer three dimensional graded
bodies can be formed.

12. Deposition Of Powders With Continuous
Changes In The Mixture
Gravity sedimentation:
During sedimentation inside a column, different
particle velocity caused by different density or size of
the powder particles lead to de-mixing of the
different particle types. As a result, a pore size or
composition gradient is produced.
Centrifugal sedimentation:
The formation of a graded structure by de-mixing of suspension of a powder with varying
particle size, can be achieved for finer particles using centrifugation. Only thin layers can
be produced due to limited concentration in suspension.

13. Electrophoretic deposition:
• The gradation is done on the basis of
differences in the electrophoretic mobility
of different powders.
• An external mixing system supplies
suspensions with the variable
concentrations of the components or the
second component is added with time in
calculated proportions.
• The velocity of ceramic particles in
suspensions ν depends on the
electrophoretic mobility μ and the electric
field strength E,
ν = μE

14. Transformation Of Graded Structure Into A
Bulk Material (Consolidation).
After the gradation, consolidation is done via Liquid phase sintering and in
many cases Microwave sintering process .
• Liquid phase sintering (LPS)
I. Cemented carbides are based on tungsten carbide and other additions
(TaC, VC, TiC as examples) with cobalt used to form a liquid phase.
II. The mainstay compositions are based on WC-Co, mostly with 6 to 12
wt. % Co.
III. The LPS are ideal for densifying those hard materials that can’t be
fabricated using other manufacturing approaches.

15. •A schematic of the microstructure changes during LPS, starting with mixed powders
and pores between the particles.

16. Advantages:
Several advantages include-
• volumetric heating
• non-thermal effect
• selective heating over the conventional
method
• accelerated heating rate
• shortened processing cycle
• high energy efficiency
• environmentally friendly
Microwave Sintering (MS)
The microstructures can be improved greatly in terms of fine grain size, uniform
cobalt distribution for WC-Co alloys for enhancing the mechanical properties
The carbon activity in the microwave furnace chamber is expected to be extremely
sensitive because of many factors such as moisture level, purity of the protective
atmosphere, the oxygen content in raw materials .

17. Co-free Cemented Carbide
Binders of cemented carbides are first to encounter corrosion, thus finding
alternatives to binders should be well emphasized.
• Ni based cemented carbide: Nickel is a promising substitute of cobalt for being
cheaper and as it possesses FCC structure, good ductility and higher wettability
towards carbide grains. Though Ni-bonded carbide possess inferior strength and
hardness compared to Co-bonded carbides.
• Carbon/Oxide-bonded cemented carbides: Sometimes TiC, Mo2C, VC etc are
used instead of metallic binders. Metallic Binders generally offers good toughness
but performs poorly in chemical regime. TiC offers a lower sintering temperature,
along with good resistance to oxidation and corrosion, But lesser hardness and
toughness compared to WC-Co. Fractures easily occur in surface due to
segregation of Carbon in boundary of Ti-C/WC.
Applications involve sliding parts and Mechanical Seals .

18. Application areas

19. Conclusion
• Potential application of graded cemented carbides in the field of
geo engineering, mining, cutting tools, construction materials over
past decades.
• Graded carbides provide better strength, high hardness as well as
good toughness and higher wear resistance, thus improving the
service life of the products.
• The fracture toughness being an interesting property of graded
cemented carbides, further improvement in
this area is very much necessary. The design of functionally graded
cemented carbide with an
optimized gradient is also of interest in further.

20. References
[1]. Material design method for the functionally graded cemented carbide tool, ToshioNomuraa,
HidekiMoriguchia, KeiichiTsudaa, KazutakaIsobea, AkihikoIkegayaa, KiyokoMoriyama, International
Journal of Refractory Metals and Hard Materials,Volume 17, Issue 6, November 1999, Pages 397-404.
[2].Phase composition, transition and structure stability of functionally graded cemented carbide with dual
phase structure, ZHANG Li , CHEN Shu , XIONG Xiang-jun , HE Yue-hui , HUANG Bai-yun , ZHANG
Chuan-fu, J. Cent. South Univ. Technol. (2007)02-0149-04.
[3]. A review of cemented carbides for rock drilling: An old but still tough challenge in geoengineering,
Xiaoyong Ren, Hezhuo Miao, Zhijian Peng, Int. Journal of Refractory Metals and Hard Materials 39
(2013) 61–77.
[4]. Processing techniques for functionally graded materials, B. Kieback, A. Neubrand, H. Riedel, Materials
Science and Engineering A362 (2003) 81–105.
[5]. Sintering: From Empirical Observations to Scientific Principles, Randall M. German