Sintering of titanium alloys made from blended master alloy powders: J.Bolton, B.S.Becker. (University of Bradford, Bradford, Yorkshire, UK.)

Abstract

Ni-TiC composite powder was synthesized from a NiO/TiO2/C mixture by a joint process of chemical reduction in argon atmosphere, electrochemical reduction of TiO2 and subsequent carbonization of the reduced Ti in molten salt. The reduction was investigated by terminating the electrochemical experiments for various durations, as well as comparing with the results for direct electro-deoxidation of NiTi alloys from a NiO/TiO2 mixture. The results showed that the product consisted of aggregated Ni-TiC composite particles about 1 μm and dissociative TiC particles about 100 nm. The composite particles owned a multicore-rim structure composed of approximately dispersed TiC particles in the Ni matrix. The formation of intermediates, such as CaTiO3, Ni3Ti and NiTi, was evaluated from the viewpoint of thermodynamics. Ni acted as a catalyst via generation and subsequent decomposition of Ni-Ti alloys. Carbon powder undertook a reducing agent for NiO in the sintering process as well as a reactant during carbonization of Ni-Ti alloys in molten salt. The introduction of Ni and C into the precursor accelerated the reduction by the chemical driving force derived from reactions between Ni, Ti and carbon.