Simulations of multivariant Si I to Si II phase transformation in polycrystalline silicon with finite-strain scale-free phase-field approach
Simulations of multivariant Si I to Si II phase transformation in polycrystalline silicon with finite-strain scale-free phase-field approach
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DOI：
10.1016/j.actamat.2023.118996
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发表时间：
2023-02
期刊：
影响因子：
9.4
通讯作者：
Hamed Babaei;R. Pratoori;V. Levitas
中科院分区：
文献类型：
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作者：
Hamed Babaei;R. Pratoori;V. Levitas
采用无标度相场方法和有限元方法对多晶集合体中从立方SiI到四方SiII的多元马氏体相变进行了数值模拟。该模型的重要特征是大而各向异性的相变张量ɛt={0。1753；0。1753年；−0.447)和应力张量相关的非热耗散相变阈值，这给计算带来了很大的挑战。具有随机取向的三维多晶在周期性边界条件和零平均侧向应变下承受单轴应变和应力控制载荷。提出并分析了离散马氏体组织、马氏体变异体与SiⅡ的体积分数、应力和相变应变张量以及织构的耦合演化。引入了能有效代表多变量转换行为的宏观变量。55和910晶粒的宏观应力应变和相变行为相近。较大的相变应变和晶界导致了数十Gpa的巨大内应力，影响了组织演变和宏观行为。与单晶相比，由于相变和负的局部切线模数引起的局部力学不稳定性在宏观上是稳定的，它通过晶界阻止/减缓SiII区的生长来实现。这会导致在转变过程中增加压力。该方法可用于研究具有较大相变应变的类似相变，并可通过考虑塑性应变和应变诱发相变而进一步发展。
Scale-free phase-field approach and corresponding finite element method simulations for multivariant martensitic phase transformation from cubic Si I to tetragonal Si II in a polycrystalline aggregate are presented. Important features of the model are large and very anisotropic transformation strain tensor ɛ t={0. 1753; 0. 1753;− 0. 447} and stress-tensor dependent athermal dissipative threshold for transformation, which produce essential challenges for computations. 3D polycrystals with stochastically oriented grains are subjected to uniaxial strain-and stress-controlled loadings under periodic boundary conditions and zero averaged lateral strains. Coupled evolution of discrete martensitic microstructure, volume fractions of martensitic variants and Si II, stress and transformation strain tensors, and texture are presented and analyzed. Macroscopic variables effectively representing multivariant transformational behavior are introduced. Macroscopic stress–strain and transformational behavior for 55 and 910 grains are close. Large transformation strains and grain boundaries lead to huge internal stresses of tens GPa, which affect microstructure evolution and macroscopic behavior. In contrast to a single crystal, the local mechanical instabilities due to phase transformation and negative local tangent modulus are stabilized at the macroscale by arresting/slowing the growth of Si II regions by the grain boundaries. This leads to increasing stress during transformation. The developed methodology can be used for studying similar phase transformations with large transformation strains and for further development by including plastic strain and strain-induced transformations.