Study On The Characteristic Temperatures Of Metal Melt By Molecular Dynamic Simulation Method

The influence of super-heated temperature and cooling rate on homogeneous nucleation undercooling and microstructure evolution of fcc-Al and bcc-Fe metals is investigated in detail during the solidification processing by using the method of molecular dynamics simulation. The main conclusions are drawn as follows:When the Al melt solidifies at the cooling rate of 1×1011.0K/s, homogeneous nucleation undercooling increases gradually with increasing super-heated temperature and it tends to be a constant value as the initial temperature is higher than a certain value. The maximum homogeneous nucleation undercooling for Al melt reaches 388 K. As the Fe melt solidifies at the cooling rate of 1×1011.0 K/s, homogeneous nucleation undercooling increases firstly and then turns to be steady with the increase of the initial temperature increasing. The simulated results indicate that the maximum homogeneous nucleation undercooling is found to be 847 K for Fe melt.The Al melt is solidified from 1437 K to 50 K under different cooling rates and is relaxed at 50 K. When the cooling rate is less than 1012.5 K/s, a mixed crystalline structure composed of fcc and hcp structure can be found in the as-solidified microstructure. As the cooling rate is larger than 1015.0K/s, amorphous structure is formed. Additionally, a mixture structure consisting of crystalline and amorphous structure is found to coexist for the Al melt solidified at a cooling speed ranging from 1012.5 K/s to 1015.0 K/s. The critical cooling rate to form ideal amorphous of Al melt is estimated to be 1014.5 K/s, which is in accordance with that calculated from theoretical approach.Fe melt is solidified from 2169.6 K to 50 K under the condition of different cooling rates, and relaxed at 50K. When the cooling speed is not larger than 1011.97K/s, the pure bcc crystalline structure is formed after solidification, when the cooling speed is larger than 1014.8 K/s, the amorphous structure is formed completely for Fe melt after solidification, when the cooling rate is between 10120 K and 10148 K/s, a mixture structure composed of crystalline and amorphous is obtained. The critical cooling rate to form ideal amorphous of Fe melt is 1014.8K/s, which is in accordance with that calculated from theoretical approach.