Study On The Preparation And Phase Stability Of Non-Stoichiometric TiN_x

In this paper, the structure, property and preparation method of non-stoichiometric TiNx(x<1) were investigated. First principle calculation has been used to study the structure and property of TiNx. The TiNx powders were synthesized by mechanical alloying (MA) of titanium powders and urea. The mechanical properties of TiNx bulks sintered by hot pressing were studied.The TiNx phases were constructed by using NaCl unit cell, and the properties of TiNx were calculated and forecasted. Effects of different ratio of titanium and urea and effects of different milling time on the synthesis of TiNx powders were studied. Additionally, the formation mechanism of TiNx powders was studied. The results indicated that the formation rate of TiNx increased with the increase of the proportion of tatinum in starting materials. The TiNx milled powders treated by MA were sintered; the phases and ratio of N to Ti of the sintered bodies were analyzed. The density, hardness, bending strength and fracture morphology of sintered bodies were measured. The influences of MA treatment and nitrogen content on the properties of TiNx sintered samples were also studied.The results of first principle calculation indicated that the TiNx phases retained a TiN structure with the changing of nitrogen contents in a certain range. The density of Ti-N bonds increased and metal bonds reduced with increasing nitrogen contents. The lattice parameter, crystal volum, bulk modulus and shear modulus C44 also increased with increasing nitrogen contents.The results showed that non-stoichiometric TiNx powders were synthesized by MA of titanium and urea. The structure and phase analysis of the sintered bodies indicated that the nitrogen contents and the lattice parameter, density, hardness and bending strength of sintered bodies increased with the milling time increasing. The results were consistent with that of first principle calculation. Compared with pure TiN sintered body without ball milling treatment, the sintered body that milled for 50h has best mechanical properties. Its density, hardness and bending strength were 5.16 g/cm3, 21.86 GPa and 307.6 MPa, respectively. The sinterd body had fine grains. Few pores can be found in the microstructure.These results showed that MA treatment of the starting materials and non-stoichiometric reduced the sintering temperature of TiNx powders.