Hisashi Suzuki1 and Kozi Hayashi1
1Department of Metallurgy and Materials Science, Faculty of Engineering, University of Tokyo, Tokyo
The effects of surface-grinding, i.e., γ→ε' transformation and residual compressive stress ( σ r), on the mechanical properties of WC-(6∼30)%Co alloy were investigated in detail. The specimen almost free from the ε' phase and the residual stress was prepared by sufficiently polishing the ground specimen so as to remove the surface-layer containing ε' and σ r (the thickness is about 30 μ ).
The results obtained were as follows: (1) The hardness of the alloy and in particular that of the binder phase were increased by grinding. (2) The binder phase contracts by a small amount due to the γ→ε' transformation, whereas the residual compressive stress was formed in the surface layer by grinding. (3) One set of crack length around Vickers indentation and frequency of crack path in the binder phase were larger in the orientation perpendicular to the grinding direction than in the orientation parallel to it. These were considered to be due to the anisotropy in the formation of a plate-shaped ε' phase in relation to the grinding direction. (4) The contribution of σ r to the transverse-rupture strength appeared to be neglected in common alloys, but it became considerably large in high-strength alloys. The amount of the contribution was considered to depend on the perfection of specimens, the surface state and distribution of σ r, etc.
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