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基于位错理论和Olson等人提出的层错能模型,考虑到外加应力场的作用,建立了fcc(γ)→hcp(ε)马氏体相变在小角度晶界处形核时,胚核尺寸与能量之间的关系模型,用此应用模型讨论了温度、切应力以及晶界位错密度对FeMnSi基合金中fcc(γ)→hcp(ε)马氏体相变形核的影响,结果表明,fcc(γ)→hcp(ε)相变形核过程中存在着一些特征尺寸的胚核:亚临界胚核和临界胚核,它们之间的能量差构成了马氏体相变的能垒,这些特征胚核的尺寸将随着外部条件(应力和温度)的改变而变化,随着温度降低,切应力增加将使临界胚核尺寸变小,直至最终能垒消失,基于上述讨论,从动力学的角度讨论了Ms点及临界切应力τ_c诱发fcc(γ)→hcp(ε)相变的能量条件,解释了在Ms点处合金的层错能不为零的实验结果,另外,小角度晶界处位错密度的增加,也有利于hcp相形核。
Based on the theory of dislocation and the model of layer-fault energy proposed by Olson et al., Considering the effect of applied stress field, the fcc (γ) → hcp (ε) martensitic transformation is established at the small angle of grain boundaries. The relationship between nucleus size and energy is discussed. The effects of temperature, shear stress and dislocation density on fcc (γ) → hcp (ε) martensitic transformation in FeMnSi-based alloys are discussed. The results show that The results show that there are some characteristic sizes of embryo nuclei in the process of fcc (γ) → hcp (ε) transformation nucleation: the subcritical nuclei and the critical nuclei, the energy difference between them forms the energy barrier of martensitic transformation , The size of these characteristic nuclei will change with the change of external conditions (stress and temperature). As the temperature decreases, the increase of shear stress will make the size of the critical nucleus become smaller until the final barrier disappears. Based on the above discussion, from Kinetic point of view of Ms point and the critical shear stress τ_c induced fcc (γ) → hcp (ε) phase transition energy conditions, explained the Ms point at the alloy layer fault energy is not zero experimental results, in addition, the small The increase of dislocation density at the angle grain boundary also helps the hcp phase nucleation.