抄録
The adhesive ability of diamond film deposited on nitric-acid treated Co-cemented tungsten carbide was evaluated using ultrasonic cavitation tests. Without nitric acid treatment, the diamond film surface roughness is high, but its adhesive ability is quite low. During nitric acid treatment lasting longer than five minutes, Co is eluted from the Co-cemented carbide and fine pores are formed on the surface. The adhesion strength depends on the nitric acid treatment time: strength after treatment for five minutes and over ten minutes is significantly different. Neither the surface morphology nor its chemical composition changed, but ultrasonic microscopy revealed a lowered ultrasonic surface-wave velocity after nitric acid treatment. A deformation layer of 5 μm or less was formed when the substrate was polished. Furthermore, acid-affected layers of 5-18 μm were formed during nitric acid treatment. Longer nitric acid treatment duration yields a thicker acid-affected layer. The low ultrasonic surface-wave velocity indicates that the Co is eluted and that the conjugation between WC particles weakened and that the apparent Young's modulus of the acid affected layer decreased. The layer with the low apparent Young's modulus is thought to absorb the thermal residual stress of CVD diamond deposition. Presumably, the difference in results obtained at five minutes and at more than ten minutes is attributable to their different acid-affected layer thickness.
