Performance of brazed diamond wheels fabricated in hydrogen/methane plasmas or a vacuum

The ambience in which brazed diamond wheels are fabricated has an important effect on the sharpness of the brazed diamond grits and on the hold of the filler alloy on these grits. In this work, brazed diamond wheels were fabricated using NiCr alloy either in a 0.05-Pa vacuum or in H₂/CH₄ plasmas at a temperature of 1,020°C for 5 min. The surface of the diamond grits brazed in H₂/CH₄ plasmas and protruding out of the filler alloy is not graphitized. The layer of carbide formed on the interface between the filler alloy and diamond brazed in H₂/CH₄ plasmas allows the liquid filler alloy to soak the diamond grits better. This is good for the filler alloy gaining a firm hold on the diamond grits. Diamond grits brazed in H₂/CH₄ plasmas undergo compressing stress due to the penetration of carbon into the filler alloy. There is a white band, which denotes firm metallurgical bond, between the filler alloy and the substrate of a brazed diamond wheel fabricated in H₂/CH₄ plasmas or in the 0.05-Pa vacuum, but the bandwidth in the brazed diamond wheel fabricated in H₂/CH₄ plasmas is almost twice that in the brazed diamond wheel fabricated in the 0.05-Pa vacuum. Grinding tests showed that the percentages of both whole grain fractures and pullouts from the matrix of diamond grits brazed in H₂/CH₄ plasmas are lower than those of diamond grits brazed in the 0.05-Pa vacuum.