Nano-clusters Structure And Mechanical Property In Ti₃Al Alloy

In recent years,as a promising new generation of high-temperature structural materials,Ti-Al intermetallic compounds have been widely used in aerospace and automotive fields.Ti₃Al alloy has attracted much attention because of its excellent high temperature mechanical properties,low density and good oxidation resistance.The macroscopic properties of the material are determined by its microstructures.However,under the existing experimental conditions,it is difficult to observe and analyze the microstructure of Ti₃Al alloy during the rapid solidification.In this paper,the formation and evolution of microstructures and the deformation behavior of Ti₃Al alloy under tensile load were simulated by molecular dynamics simulation method at different cooling rates.The embedded atomic potential function was used to characterize the microstructure in this system by radial distribution function and cluster type index method,the evolution of specific cluster structure could be visualized by visual analysis technology.Microstructures such as average atomic energy,radial distribution function analysis and cluster type index method were used to rapidly solidify Ti₃Al alloy at four different cooling rates of 10¹⁰ K/s?10¹¹ K/s?10¹² K/s and 10¹³ K/s.It was found that the lamellar and flake twinning structures of system consist of hexagonal close-packed crystal clusters?12 0 0 0 6 6?and face-centered cubic crystal clusters?12 0 0 0 12 0?at 10¹⁰ K/s?10¹¹ K/s and 10¹² K/s cold rates,the two clusters played an important role in the evolution of cluster structure of the Ti₃Al alloy during solidification,and their number increased with the decrease of temperature.At the cooling rate of 10¹³ K/s,the system formed an amorphous structure consisting of a large of icosahedral clusters?12 0 12 0 0 0?and part of body-centered cubic crystal clusters?14 6 0 8 0 0?.These icosahedral clusters will be evenly distributed in the system to maintain the stability of the amorphous structure.At the cooling rate of 10¹⁰ K/s,a large number of?12 0 0 0 12 0?clusters in Ti₃Al alloy were interconnected with themselves,and a small number of?12 0 0 0 6 6?clusters also tended to be connected to themselves.Meanwhile,founding that?12 0 00 12 0?and?12 0 0 0 6 6?clusters??12 0 0 0 12 0?and?12 0 0 0 12 0?clusters were connected by the coherent twin boundaries to form the coherent twin structures.At the cooling rate of 10¹³ K/s,?12 0 12 0 0 0?clusters in Ti₃Al alloy were connected to each other by forming the modes of chain and triangular;?14 6 0 8 0 0?clusters were formed by forming the modes of triangular?tetrahedron?quadrangular?double triangular?hexagonal and quadrangle-bipyramid.In order to research the influence of different microstructures on mechanical properties,the deformation behavior of the initial structure of Ti₃Al alloy containing different clusters under tensile load was simulated.By analyzing the simulation results of mechanical properties of different initial structures,the results showed that the number of crystal clusters?12 0 0 0 12 0?decreased with the increase of strain during the stretching process at the cooling rate of 10¹⁰ K/s?10¹¹ K/s and 10¹² K/s,while the number of crystal clusters?12 0 0 0 6 6?increased.After the crack forming,?12 0 0 0 12 0?clusters increased and?12 0 0 0 6 6?clusters decreased.At 10¹³ K/s cold speed,the number of?12 0 12 0 0 0?and?14 6 0 8 0 0?clusters first decreased and then increased,and then the number fluctuated constantly,but the overall trend remained basically unchanged.The results of visual analysis showed that during the stretching process,the fine cracks were first generated inside the system,and the cracks would connect to each other to form holes.Finally,the material would fracture with the increase of strain.