镍基单晶高温合金定向粗化行为的取向依赖性 Ⅰγ’形态的SEM观察

利用ＳＥＭ对镍基单晶高温合金中γ’颗粒定向粗化及其取向依赖性进行了观察，结果显示， γ’颗粒形态依赖于应力轴取向，而粗化方向均为〈１００〉．

B2结构Fe_3Al单晶室温拉伸变形切应力切应变曲线的取向依赖性

研究了18个取向B2结构Fe3Al单晶室温真空条件下的拉伸塑性变形,发现随晶体取向不同,切应力切应变曲线出现不同数目的线性硬化及抛物线软化阶段.曲线上不同硬化率各阶段的形成与塑性变形中滑移系的数量、次滑移作用的强弱及二分超位错的运动和分解状态有关.第Ⅰ阶段为单系滑移的易滑移段;第Ⅱ阶段对应共轭滑移的出现,硬化率较高;第Ⅲ阶段表现为比较弱的次滑移作用,硬化率较低;第Ⅳ阶段除了多系滑移之外还伴随二分超位错的扩展及拖着反相畴(APB)的不全超位错运动,硬化率最高;第Ⅴ阶段与分解了的单个超分位错的交滑移相关,表现为软化.随拉伸轴取向所处区域不同,切应力切应变曲线硬化段的数目及同一阶段硬化率的大小也不同.

高锰钢高速压缩时γ→ε-M和ε-M→α′-M的相变特征

利用XRD技术对静态压缩和高速压缩高锰相变诱发塑性(TRIP)钢中γ(奥氏体)、ε-M(六方马氏体)和α′-M(体心马氏体)的体积分数进行计算,以确定应变速率对γ→ε-M和ε-M→α′-M相变动力学特征的影响。利用EBSD技术和相变晶体学计算对高速压缩样品中的γ→ε-M和ε-M→α′-M相变取向依赖性进行分析。结果表明:应变速率对γ→ε-M和ε-M→α′-M相变具有不同的影响。与静态压缩相比,高速压缩使得γ→ε-M相变被抑制、ε-M→α′-M相变被促进,这是由于两阶段相变分别受层错能和应力的影响较大。高应变速率使得变形初期的马氏体相变速率显著提高。高速压缩变形样品仍具有马氏体相变取向依赖性,这取决于不同取向γ晶粒内相变机械功的大小。γ→ε-M相变难易与ε-M的相变机械功有关;ε-M→α′-M相变难易则同时取决于ε-M和α′-M的相变机械功。

Strain-induced α-to-β phase transformation during hot compression in Ti-5Al-5Mo-5V-1Cr-1Fe alloy

The dynamic phase transformation of Ti-5Al-5Mo-5V-1Cr-1Fe alloy during hot compression below theβtransus temperature was investigated.Strain-inducedα-to-βtransformation is observed in the samples compressed at 0-100 K below theβtransus temperature.The deformation stored energy by compression provides a significant driving force for theα-to-βphase transformation.The re-distribution of the solute elements induced by defects during deformation promotes the occurrence of dynamic transformation.Orientation dependence for theα-to-βphase transformation promotion is observed between{100}-orientated grains and{111}-orientated grains.Incomplete recovery in{111}-orientated grains would create a large amount of diffusion channels,which is in favor of theα-to-βtransformation.The effects of reduction ratio and strain rate on the dynamic phase transformation were also investigated.