Composite Powder Production of Intermetallic Compound and Carbide by Mechanical Alloying in Ti-AI-C Ternary Alloy

Composite powder of intermetallic compound (TiAl) and carbide (TiC) was prepared from elemental powders of titanium, aluminum and graphite by means of mechanical alloying, and the formation process of the composite was investigated in relation to the solid state reactions among the elemental powders. Mixed powders with a chemical composition of Ti-25at%Al-25at%C were mechanically milled in vacuum with centrifugel boll mill. After 10.8ks milling, lamellar structure of titanium and aluminum was formed, and graphite seemed to be finely crushed and included into the powder. The solid state reactions forming the composite microstructure occured after about 12ks milling. At first, finely dispersed graphite reacts with titanium to form TiC, and then local temperature rising caused by the exothermic reaction, Ti + Al.N TiC + 180 kJ/mol, activates the diffusion between titanium and aluminum, which enables the elements to form the intermetallic compound (TiAl). The microstructure of TiC/TiAl composite powder prepared by this process is so fine that the components can not be distinguished with EPMA, although they can be identified by means of X-ray diffraction technics.