O相对Ti2AlNb合金B2基体相拉伸性能影响的分子动力学模拟

Molecular Dynamics Simulation of Effect of O Phase on Tensile Properties of B2 Matrix Phase in Ti2AlNb Alloy

本研究基于分子动力学研究了Ti2AlNb合金中不同数密度的O相对基体B2相力学性能的影响。结果表明:B2相中含有O相时材料的屈服强度和塑性均得到了提升。这是因为在拉伸变形过程中析出相阻碍了基体中滑移系的开动,从而提高了基体B2相的塑性变形抗力。研究发现材料塑性的提升主要与内应力的释放有关,其中B2相通过马氏体相变释放内应力占主导作用,位错释放内应力为次要作用。当基体B2相中含有O相时,O相对位错阻碍作用会导致应力集中,从而诱导大量bcc结构发生马氏体相变,在此过程中应力集中的程度降低,延缓了孔洞形核长大;另一方面由于O相为韧性相,因此孔洞在O相和B2相边界生长受到抑制,从而使Ti2AlNb合金的塑性和韧性大大提高。并且随着析出相数密度的增加,材料的屈服强度和屈服应变下降,但其强度和塑性相比不含O相时仍有提升。这是因为随着O相数密度的增加,导致变形过程中基体原子发生马氏体相变的比例降低,因此相变对应力集中的释放程度降低,孔洞的产生与扩大速度提高,从而使材料更容易发生断裂失效。

The effect of different number densities of O phase on the mechanical properties of the matrix B2 phase in Ti2AlNb alloy was investigated based on molecular dynamics.The results show that the yield strength and plasticity of the B2 phase are improved when the O phase is contained.This is because the precipitated phase hinders the start of the slip system in the matrix during the tensile deformation process,thereby improving the plastic deformation resistance of the B2 phase of the matrix.It is found that the improvement of material plasticity is mainly related to the release of internal stress,in which the release of internal stress by the B2 phase through martensitic phase transition is dominant,and the release of internal stress by play a less prominent role.When the matrix B2 phase contains the O phase,the hindering effect of O phase on dislocation will lead to stress concentration,thereby inducing martensitic phase transition of a large number of bcc structures,and the degree of stress concentration in this process decreases,delaying the growth of pore nuclei.In addition,since the O phase is a ductile phase,the growth of holes at the boundary between the O phase and the B2 phase is inhibited,so that the plasticity and toughness of Ti2AlNb alloy are greatly improved.And with the increase in the number density of precipitated phases,the yield strength and yield strain of the material decrease,but its strength and plasticity are still improved compared with those without the O phase.This is because with the increase in O phase number density,the proportion of martensitic phase transition of the matrix atoms decreases during the deformation process,so the release degree of the stress concentration by the phase transition decreases,and the generation and expansion rate of the holes increase,with makes it more prone for the material to fracture failure.