The transverse-rupture strength of WC-Co cemented carbides which were HIP-treated and then coated with titanium nitride by the physical vapor deposition (PVD) process was investigated in relation (923-1273 K) of annealing after PVD. The PVD temperature was fixed at 773K. It was found that the strength of coated specimens in the as-PVD state decreased as a rule with increasing thickness of the deposited layer and with increasing Co content, demonstrating that the adhesion between the layer and

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... bstrate was sufficient. A sharp decrease in the strength was caused by the annealing of specimens and it became more remarkable, as the annealing temperature increased. The strength obtained after annealing at temperatures above 1073 K was almost equal to that of specimens coated by the chemical vapor deposition (CVD) process. The strength of coated specimens, which is a function of thickness, annealing temperature and so on, has been explained in terms of the fracture mechanism. In the cemented carbide industry, much attention has recently been given to tools coated with hard materials by means of the PVD (physical vapor deposition) process. This is because PVD-coated tools are more precise in dimension and seem to be tougher than those coated by C VD (chemical vapor deposition) process which is now widely used(1). However, so far as the strength of PVD-coated cemented carbides are concerned, detailed studies have not yet been reported. Therefore, a study on the subject was undertaken for WC-Co alloys coated with titanium nitride. WC-(5-20)%Co medium carbon alloys were used as a substrate. These alloys were HIPtreated in Ar of 100 MPa at 1623 K, and six surfaces of each compact were ground with a diamond wheel of #150 to get a JIS specimen K after Ar bombardment, using an ion plating equipment (ULVAC Co., Japan, Model IPB-30, hollow cathode type), in which the partial pressure of nitrogen and the growth rate of the titanium nitride layer were 0.13 Pa and At first, the room-temperature transverserupture strength (span, 20 mm) of the coated specimens was measured as a function of d and Co content of the substrate. Next, optical and SEM microstructures and X-ray diffraction profiles near the interface between the deposited layer and the substrate were examined for each specimen. According to the results of strength test, the strength level of the PVD * This paper is a summary of the papers which were published in Japanese in J. Japan Inst. Metals, 48 ( 1984), 214 and J. Japan Soc. Powder and Powder Metallurgy, 31 (1984), 94.