Influence of brazing atmosphere on the characteristics, mechanical and thermal stress damage properties of diamond interface by molten Ni-Cr filler alloy

Ni-Cr-Si-B active filler alloy was used to braze diamond on 40CrMo steel in vacuum and argon atmosphere, respectively. Scanning electron microscopy, X-ray diffraction, Raman spectroscopy and Transmission electron microscope were applied to characterize the surface morphology, interfacial microstructure, elemental diffusion properties and thermal damage of brazed diamond. Further, the characteristics of brazed molten alloy specimens were evaluated by experiments of hardness and wear resistance. The results showed that a good metallurgical bonding on brazed diamond interface was occurred, forming a Cr-C phase compound with fibrous columnar structure. Besides, the brazing diamond did not appear explicit surface graphitization phenomenon, but the thermal damage of diamond suffered from high temperature brazed process in argon atmosphere was lower at 52.1% than that in vacuum. Moreover, the hard point phase compound like chromium-boron and nickel-boron were not generated in molten alloy in argon atmosphere, which contributed to the reduction of residual stresses around diamond interface. In addition, frictional wear experiment of molten brazed alloy was designed, which indicated that the wear rate in argon atmosphere was reduced by 12.3%. This fact implied that it was beneficial to reduce thermal damage of diamond and improve wear resistance of molten alloy during brazing process in argon atmosphere.