Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear
Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear
复制标题
高压大剪切下塑性应变诱发相变的相场模拟
DOI：
10.1103/physrevb.94.214104
复制
发表时间：
2016
影响因子：
3.7
通讯作者：
Levitas, Valery I.
中科院分区：
文献类型：
--
作者：
Javanbakht, Mahdi;Levitas, Valery I.
利用相场方法研究了纳米晶双晶中位错堆积时的压应变和剪应变诱导相变。耦合马氏体PT，位错演化和力学在大应变的PFA方程的完整系统，并使用有限元法（FEM）求解。高压相（HPP）在流体静力学条件下的单个位错附近的成核压力被确定为15.9 GPa。在剪切作用下，出现在左侧晶粒中的位错堆积在其尖端附近产生强烈的应力集中，并显着增加了PT的局部热力学驱动力，这导致即使在零压力下HPP也成核。在1.59和5 GPa的压力和剪切，一个晶粒的主要部分转化为HPP。当在转变晶粒中也考虑位错时，它们松弛应力并导致比没有位错时稍小的稳定HPP区域。然而，它们强烈抑制HPP的成核，并且需要更大的剪切。出乎意料的是，固定HPP形态是由最简单的热力学平衡条件，其中不包含从塑性和表面能的贡献。这些平衡条件满足大多数点的相界面或（近似）在HPP区域或整个晶粒的平均应力，尽管应力场的强异质性。在稳态下，PT的驱动力主要来自偏应力而不是压力。虽然最少数量的位错在堆积形核HPP线性增加所施加的压力，最少相应的剪切应变依赖于压力非单调。令人惊讶的是，PT和位错的动力学系数的比率影响固定溶液和纳米结构。因此，有多个固定的解决方案，在相同的施加载荷和PT，变形过程是路径依赖的。随着样品尺寸增加两倍，尽管堆积中的位错数量不同，但未发现对平均压力和剪切应力以及HPP纳米结构的影响。所获得的结果代表了纳米尺度的基础上的压缩和剪切下的旋转金刚石压砧单元和高压扭转的PT的理解和描述。
Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using the finite element method (FEM). The nucleation pressure for the high-pressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force for PT, which causes nucleation of HPP even at zero pressure. At pressures of 1.59 and 5 GPa and shear, a major part of a grain transforms to HPP. When dislocations are considered in the transforming grain as well, they relax stresses and lead to a slightly smaller stationary HPP region than without dislocations. However, they strongly suppress nucleation of HPP and require larger shear. Unexpectedly, the stationary HPP morphology is governed by the simplest thermodynamic equilibrium conditions, which do not contain contributions from plasticity and surface energy. These equilibrium conditions are fulfilled either for the majority of points of phase interfaces or (approximately) in terms of stresses averaged over the HPP region or for the entire grain, despite the strong heterogeneity of stress fields. The major part of the driving force for PT in the stationary state is due to deviatoric stresses rather than pressure. While the least number of dislocations in a pile-up to nucleate HPP linearly decreases with increasing applied pressure, the least corresponding shear strain depends on pressure nonmonotonously. Surprisingly, the ratio of kinetic coefficients for PT and dislocations affect the stationary solution and the nanostructure. Consequently, there are multiple stationary solutions under the same applied load and PT, and deformation processes are path dependent. With an increase in the size of the sample by a factor of two, no effect was found on the average pressure and shear stress and HPP nanostructure, despite the different number of dislocations in a pile-up. The obtained results represent a nanoscale basis for understanding and description of PTs under compression and shear in a rotational diamond anvil cell and high-pressure torsion.