Mechanochemical synthesis of ultrafine Ti(C,N)-Al2O3 composite powders and phase transformation

Titanium carbonitride-alumina (Ti(C,N)-Al2O3) composite powders with ultrafine-sized particles below 0.5 μm were successfully synthesized by mechanochemical method. That is to say, mixed powders of anatase/aluminum/carbon black were mechanically milled for 40 h under N2/Ar atmosphere and were subsequently vacuum heat treated for 1 h at 800-1100 °C. From X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TGA-DSC) results of milled powders, Ti(C,N)-Al2O3 phases were formed during mechanical milling and the remained powders completely reacted at lower heat treatment temperature. However, even if starting powders have been heat treated for 1 h at 1100 °C under N2 atmosphere, one of target products (Ti(C,N)) was not found in heat treatment products. Thus, high-energy mechanical milling has prominent advantages in preparing Ti(C,N)-Al2O3 composite powders through solid-gas reaction between TiO2/Al/C and N2. In addition, phase transformation during mechanochemical synthesis was also analyzed based on experimental results. The processes are as follows: TiO2/Al/C/N2 → TinO2n−1(n > 3)-Al2O3 → Ti3O5-Al2O3 → Ti(N,O)-Al2O3 → TiN-Al2O3 → Ti(C,N)-Al2O3.