Mechanochemical synthesis of ultrafine Ti(C,N)–Al 2O 3 composite powders and phase transformation

Abstract

Titanium carbonitride–alumina (Ti(C,N)–Al 2O 3) 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 N 2/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)–Al 2O 3 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 N 2 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)–Al 2O 3 composite powders through solid–gas reaction between TiO 2/Al/C and N 2. In addition, phase transformation during mechanochemical synthesis was also analyzed based on experimental results. The processes are as follows: TiO 2/Al/C/N 2 → Ti n O 2 n−1 ( n > 3)–Al 2O 3 → Ti 3O 5–Al 2O 3 → Ti(N,O)–Al 2O 3 → TiN–Al 2O 3 → Ti(C,N)–Al 2O 3.