δ→γ相变诱发缺陷对FeMnSi基合金记忆效应的影响及其调控

Processed FeMnSi-based shape memory alloys suffer from a poor shape memory effect. A special treatment, i.e. training, has to be performed to attain good shape memory effect. The recent developed training-free cast FeMnSi-based alloys exhibit good shape memory effect, but their mechanical properties are worse as well as their recovery stress is lower as compared with processed FeMnSi-based alloys. Through summarizing and analyzing domestic and foreign researches as well as our previous studies, we proposed that the defect-configuration consisting of high density stacking faults and few annealing-twin boundaries, which is beneficial to the excellent shape memory effect, could be induced based on δ→γ phase transformation. We succeeded in fabricating the training-free processed FeMnSi-based alloy by realizing nearly the above proposition. For the purpose of clarifying the key factor that influences the types and quantities of δ→γ phase transformation induced defects as well as mastering the methods adjusting and controlling these defects, we will investigate following contents: (1) building the predictive model to predict the δ phase region of processed FeMnSi-based alloys; (2) effects of the migration velocity of δ/γ interface and the stacking fault energy as well as the volume fraction of δ phase on the types and quantities of δ→γ phase transformation induced defects, and their resulting effects on shape memory effect; (3) the effect of annealing on the types and quantities of δ→γ phase transformation induced defects, and its resulting effect on shape memory effect. This research will provide a simple method to fabricate the training-free FeMnSi-based alloys.

针对目前变形加工制备的FeMnSi基记忆合金必须训练才能具有优良记忆效应，而免训练铸造FeMnSi基合金的力学性能和恢复应力显著低于变形加工合金的问题，在总结分析国内外及前期研究的基础上，本项目提出基于δ→γ相变直接获得有利于优良记忆效应的由高密度堆垛层错和低退火孪晶界面分数组成的缺陷组态的构想，并通过初步实现该构想制备了免训练变形加工FeMnSi基合金。为了认识控制δ→γ相变诱发缺陷的类型和数量的关键因素及其作用机制，实现δ→γ相变诱发缺陷的调控，本项目拟建立预测变形加工FeMnSi基合金δ相区的模型；研究δ/γ界面迁移速度、合金的层错能和δ相的体积分数对δ→γ相变诱发缺陷的类型和数量的影响及机制，及其对合金记忆效应的作用机制；研究退火对δ→γ相变诱发缺陷的类型和数量的影响规律，及其对合金记忆效应的影响。本项目的研究结果将为制备免训练FeMnSi基合金提供一种简单的技术。

针对目前变形加工制备的FeMnSi基合金必须训练才能拥有优良形状记忆效应，而免训练铸造FeMnSi基合金的力学性能和恢复应力显著低于变形加工合金的问题，本项目在总结分析国内外研究结果的基础上提出基于δ→γ相变直接制备免训练变形加工FeMnSi基合金。为了认识控制δ→γ相变诱发缺陷的类型和数量的关键因素及其作用机制，实现δ→γ相变的调控，本项目首先研究了合金成分对FeMnSi基合金γ+δ双相区的影响规律，建立了预测FeMnSi基合金γ+δ双相区的模型。该预测模型为指导基于δ→γ相变制备免训练变形加工FeMnSi基合金提供了成分设计的依据。在此基础上，本项目研究了冷却速度对δ→γ相变诱发缺陷类型和数量的影响规律，及其对合金记忆效应的影响。研究结果明确了冷却速度是控制δ→γ相变制备免训练变形加工FeMnSi基合金的关键因素。研究了层错能对经历δ→γ相变的FeMnSi基合金形状记忆效应的影响，发现不同层错能的合金在各自适当的冷却速度下均能获得相当的形状记忆效应。所以，合金的层错能不是影响基于δ→γ相变制备免训练变形加工FeMnSi基形状记忆合金的关键。研究了δ铁素体体积分数对δ→γ相变诱发缺陷的类型和数量的影响及其对形状记忆效应的影响，明确了利用δ→γ相变制备免训练变形加工FeMnSi基形状记忆合金时热处理温度应该在δ铁素体单相区。研究了退火对δ→γ相变诱发缺陷的类型和数量的影响及其对形状记忆效应的影响，结果表明经历δ→γ相变的合金经600℃退火30min处理后形状记忆效应进一步提高，而经1100℃退火30min后形状记忆效应反而降低。因此，适当温度的退火处理能进一步提高经历δ→γ相变的变形加工FeMnSi基合金的形状记忆效应。综上，本项目为利用δ→γ相变制备形状记忆性能优良的免训练变形加工FeMnSi基合金提供了成分设计依据和制备技术，对促进FeMnSi基形状记忆合金的大规模应用具有重要的工程价值和科学意义。