Preparation of amorphous powders of Al-based alloy by close-coupled gas atomization

The cooling behavior of liquid droplets and the formation mechanism of amorphous were investigated by close-coupled gas atomization. The results indicate that the critical cooling rate (R-c) is around 10(3) K/s for the formation of amorphous powders of Al-based alloy, inversely proportional to liquid droplets' diameter. When the diameter of droplet is smaller than 25 mu m, it may solidify into amorphous particle, while if larger than 25 mu m it results in crystallization due to the departure to R-c. Furthermore, the amorphous formation of liquid droplet depends on the process of gas atomization. As a result, the final solidify can be amorphous or crystal even for the liquid droplets with the same diameter if the temperature and location of liquid droplets were different due to the different cooling rates.