Synthesis of CoWSi-WSi2 nanocomposite by mechanical alloying and subsequent heat treatment

In this study, systematic evaluations were performed on the synthesis of CoWSi-WSi2 nanocomposite by mechanical alloying and subsequent heat treatment. In this regard, 25 mol% Co, 35 mol% W, and 40 mol% Si powder mixture was milled for different durations. Then, the mechanically alloyed powders were heat treated at 1000 °C for 1 h. The phase transformations and structural evolutions of the powders after various milling durations and heat treatment were investigated by X-ray diffraction as well as scanning and transmission electron microscopy. The results showed that the phase evolutions during mechanical alloying and subsequent heat treatment were strongly dependent on milling time. After 20 h milling, a Co(ss)-WSi2 nanocomposite was formed. Increasing milling time to 50 h caused the formation of (Co,W,Si) solid solution, WSi2 and CoWSi phases. After heat treatment of 3 h ball milled powders, no new phases were detected. On the other hand, heat treatment of 5 h, 20 h and 30 h mechanically alloyed powders led to the formation of Co(ss)-WSi2-CoWSi-W5Si3. This means that there was a critical milling time (5 h) for the formation of WSi2 and CoWSi phases after heat treatment. Before this milling time, no new phases were formed, but after this time, WSi2 and CoWSi could be formed.