Temperature dependence of W metallic coatings synthesized by double glow plasma surface alloying technology on CVD diamond films

Abstract

W metallic coatings were synthesized on free-standing chemical vapor deposition (CVD) diamond films using double glow plasma surface alloying (DGPSA) technology. The influence of varying metalizing temperatures on the microstructures, phase composition and adhesion of the W metallic coatings were investigated. Likewise, the effectiveness of the W metallic coatings was preliminary evaluated via examining the shear strength of the brazing joints between W-metalized diamond films and commercial cemented carbide (WC–Co) inserts. The results showed that continuous and compact W metallic coatings were formed on the diamond films in the temperature range of 750–800°C, while cracks or cavities presented at the W/diamond interface at 700°C, 850°C and 900°C. Inter-diffusion of W and C atoms preformed, and WC and W2C were formed at the W/diamond interfaces at all temperatures except 700°C, at which only W2C was formed. Moreover, etched cavities appeared at the W/diamond interface when the temperature exceeded 850°C. The critical loads for coating delamination, as measured with the scratch test, increased as the temperature rose from 700°C to 800°C, while decreased with further increasing temperature. The maximum load was obtained at 800°C with a value of 17.1N. Besides, the shear strength of the brazing joints depicted the similar trend with the critical load. The highest shear strength (249MPa) was also obtained at 800°C.