Molecule Dynamics Simulations On Rapid Solidification And Crystal Growth Of Ti And Ti-Al Alloy

As an important alloy, Ti-Al alloy which has a range of unique physical and chemicalproperties, is applied to advanced design. The amorphous alloy has better strength,toughness, wear resistance and corrosion resistance than crystalline alloy, and if the Ti-Alalloy is heat-treated to amorphous alloy, the performance can be greatly improved.Therefore it is necessary to study the formation process and influence conditions of theTi-Al amorphous alloy. In this paper, molecular dynamics simulation method has beenused to study the Transition of microstructure of Ti and Ti-Al alloy melts during rapidsolidification process. The main contents include the effect of cooling rate onmicrostructure, the effect of Al atom content on mechanical properties of Ti-Al amorphousalloy, and the effect of pressure on the solidification process. And the crystal growth of Tihas been observed by using crystal-liquid configuration method.The research shows that, the Ti and Ti-Al alloy melts solidified into amorphous solidat a high cooling rate, and into crystal at a low cooling rate. And Ti-Al alloy is easier tosolidified into amorphous solid than pure Ti. At the same time microstructure and theelastic properties of solidified product are not sensitive to the cooling rate when itsolidified into amorphous solid. The process which Ti-Al alloy melts solidified intoamorphous solid, is influenced by the content of Al atoms, and with the change of Al atomcontent, the variation of elastic modulus of Ti-Al amorphous alloy is similar to thecrystalline alloy.In the study of the effect of pressure on the solidification process, it is found that, thepressure has significant effect on the process of both crystalline and amorphoussolidification. The increase of the pressure increases both crystal forming temperature andglass transition temperature. The pressure will reduce the gap between atoms and the atomvolume, and appropriate pressure is conducive to the process of nucleation. But too muchpressure will inhibit the nucleation.It is very effective to study the crystal growth process by using crystal-liquid configuration method, because the details of the structural changes during the crystalgrowth can be observed. The research shows that, the crystal growth is started from thesolid-liquid interface, which shows that the crystal growth is easily to start from the atomthat is nucleated. It is also found that, the process which Ti atoms crystallize toclose-packed hexagonal structure is longer than face-centered cubic structure, and thestructure is also more stable.