Synthesis of AlN–TiN nanostructured composite powder by reactive ball milling and subsequent thermal treatment

Abstract

In the present article, synthesis of AlN–TiN nanostructured composite by high-energy ball milling process (HEM) of Ti and AlN by 1:1 molar ratio and subsequent heat treatment was investigated. The microstructural evolution of samples was studied by scan electron microscopy (SEM) and energy dispersive X-ray analysis (EDS), composition map analysis by electron probe micro-analyzer (EPMA) and phase determination using X-ray diffraction (XRD) patterns. It was found that a Ti(Al,N) solid solution was formed at the early stages of milling and while Al causes the Ti lattice to contract, N has the opposite effect. The nonlinear variation of interplanar distance and c/ a ratio of Ti is considered due to the competition between these two processes during MA and finally led to complete dissolution of Al and only 1 at.% of N in Ti lattice. On further milling, mechanochemical reaction between Ti solid solution and AlN took place in the gradual mode which led to the formation of TiN with an average crystallite size of 10 nm. It is generally acknowledged that the reactions between Ti and AlN includes three stages: (i) reduction of AlN under the effect of Ti; (ii) diffusion of dissolved Al and N atoms into the Ti lattice and (iii) reaction between Al,Ti and N. XRD results revealed that annealing of the milled powders resulted in greater formation of “in situ” TiN particles from supersaturated solid solution and increases the crystallite size of TiN from 10 nm to 14.62 nm.