γ-TiAl中〈110〉倾斜晶界断裂行为的分子动力学模拟

摘要

采用分子动力学(MD)方法研究γ-TiAl合金中〈110〉对称倾斜界面的断裂行为，模拟在不同温度与应变速率下垂直界面方向的拉伸变形。结果表明：晶粒的相对取向及晶界特定的原子结构是影响位错形核临界应力的两个主要因素。取向差角度大于90°的Σ3(111)109.5°、Σ9(221)141.1°和Σ27(552)148.4°界面，位错在晶界处形核和扩展；取向差角度小于90°的Σ27(115)31.6°和Σ11(113)50.5°界面，无位错在晶界处形核，当应力达到峰值后界面直接断裂。γ-TiAl 双晶的断裂机制为微裂纹在界面处的形核及沿界面扩展；不同取向差界面的区别在于裂纹前端有无塑性区增韧。%Molecular dynamics (MD) simulations were carried out to study the fracture behaviors of several symmetric tilt grain boundaries inγ-TiAl bicrystals with〈110〉 misorientation axes. Tensile deformation along direction perpendicular to grain boundary was simulated under various strain rates and temperatures. The results indicate that the relative orientation of the grains and the presence of certain atom units are two critical factors of the interface structure affecting the stress required for dislocation nucleation. Dislocations nucleate and extend at or near the symmetric tilt grain boundaries during the tensile deformation ofΣ3 (111) 109.5°,Σ9 (221) 141.1° andΣ27 (552) 148.4° interfaces. ForΣ27 (115) 31.6° andΣ11 (113) 50.5° interfaces, the interfaces fractured directly in a cleavage manner due to no dislocation emitted from the boundary. The tensile fracture mechanisms of the bicrystals are that micro-cracks nucleate at the grain boundary and propagate along the interface. The variance of crack propagation is whether there is accommodation of plastic region at the crack tips.