Microstructure Simulation Of TiAl Alloy In Rapid Solidification

In this paper, molecular dynamics simulations are applied to explain the glass formation processes of Ti-Al alloys in structural perspective and to reveal the microstructural evolution of Ti-Al alloys during rapid solidifications. First, we investigate the influence of cooling rate on short and medium-range order of TiAl alloy. Amorphous TiAl alloy has relatively full growth of icosahedral short and medium-range order structures under the cooling rate of 1011 K/s.Moreover, the connections between different clusters and the network connectivity of icosahedral clusters are investigated from medium-range order perspective. In order to understand the icosahedral medium-range order structures in Ti-Al alloys, the microstructural evolutions of several special formations which link via intercross-sharing icosahedral clusters are investigated in this study. At the same time, we define a parameter which is a more precise and sensitive characterization method compared with previous parameters to describe the network connectivity of icosahedral clusters in a higher level of structural organization. The first 50 ns isothermal process at glass transition temperature significantly enhances the numbers of the FK polyhedral clusters in TiAl3 alloy, especially for Z16 FK polyhedral cluster. The connections between FK polyhedral clusters and icosahedral cluster and themselves in TiAl3 alloy are notably enhanced after the isothermal processes.Based on the investigations of medium-range order structures in Ti-Al alloys, we further study the growth of nano-clusters during rapid cooling processes in these systems. The dendritic icosahedral clusters based on hexagonal icosahedral formation as the potential growth of nano-clusters have good configural continuity. Meanwhile, the hexagonal icosahedral formation as the foundation structure of nano-clusters has good structural stability during the rapid solidification. Furthermore, the second 50 ns isothermal running time during the isothermal process at glass transition temperature has an influence on improving the growth of the pentagonal connected clusters of Z16 FK polyhedral clusters in the amorphous structure.Furthermore, the microstructural evolutions of different compositions of Ti-Al alloys are investigated during rapid solidifications. Among the amorphous Ti-Al alloys in this study, TiAl3 alloy contains more icosahedral clusters than other Ti-Al alloys at the end of the solidification. And the coherent twins are found in the nanocrystalline Ti3 Al alloy.