Mechanisms of Grain Growth in Ti(C,N)–Ni Sintered Alloys

Abstract

In order to improve the mechanical properties of cemented carbides, Ti(C,N)–Ni–Mo alloys, in which carbon in the titanium carbide is replaced by nitrogen, are of potential interest from the viewpoint of grain size control. Since grain size control by nitrogen was also observed in Ti(C,N)–Ni alloys containing no molybdenum, the effect of nitrogen on grain growth of Ti(C,N)–Ni alloys was investigated by comparing TiC–Ni and TiN–Ni alloys. The grain growth rate of Ti(C,N)–Ni alloys showed a minimum value at the carbon content C/C+N = 0·5. From the results of chemical and grain size analyses, it is considered that the growth rate depends on the solubility of Ti(C,N) in the nickel solid solution and the degree of coalescence because the solubility decreases with decreasing carbon content. With nitride, the amount of liquid increases by denitrification of TiN, owing to the formation of the nickel solid solution or TiNi₃ phases, and growth of TiN grains by Ostwald ripening is observed. The apparent activation energy for the growth of TiC and TiN grains is calculated to be ∼4·4×10⁵ and 1·9 × 10⁵ J mol⁻¹ respectively. PM/0201