Synthesis of Mo5SiB2 based nanocomposites by mechanical alloying and subsequent heat treatment

Abstract

In this study, systematic investigations were conducted on the synthesis of Mo5SiB2-based alloy by mechanical alloying and subsequent heat treatment. In this regard, Mo–12.5mol% Si–25mol% B powder mixture was milled for different times. Then, the mechanically alloyed powders were heat treated at 1373K for 1h. The phase transitions and microstructural evolutions of powder particles during mechanical alloying and heat treatment were studied by X-ray diffractometry and scanning electron microscopy. The results showed that the phase evolutions during mechanical alloying and subsequent heat treatment are strongly dependent on milling time. After 10h of milling, a Mo solid solution was formed, but, no intermetallic phases were detected at this stage. However, an α-Mo–Mo5SiB2 nanocomposite was formed after 20h of milling. After heat treatment of 5h mechanically alloyed powders, small amounts of MoB and Mo2B were detected and α-Mo–MoB–Mo2B composite was produced. On the other hand, heat treatment of 10h and 20h mechanically alloyed powders led to the formation of an α-Mo–Mo5SiB2–MoSi2–Mo3Si composite. At this point, there is a critical milling time (10h) for the formation of Mo5SiB2 phase after heat treatment wherein below that time, boride phase and after that time, Mo5SiB2 phase are formed. In the case of 20h mechanically alloyed powders, by increasing heat treatment time, not only the quantity of α-Mo was reduced and the quantity of Mo5SiB2 was increased, but also new boride phases were formed. Finally, after 5h heat treatment, the Mo phase completely disappeared and a Mo5SiB2-based composite was completely formed.