析出相形态对Ni-Ti形状记忆合金力学性能的影响

对室温奥氏体相NiTi形状记忆合金进行热处理,在300和500℃时效温度下,分别获得具有粒状和针状Ni4Ti3析出相的组织特征,对两种组织的合金进行准静态和动态力学性能研究,对比分析析出相形态对奥氏体NiTi形状记忆合金静动态力学行为的影响规律。结果表明,准静态拉伸加载下,随应变率的提高,两种组织的应力诱发马氏体相变过程均呈现明显的应变率效应,对比分析发现,针状组织的NiTi合金发生应力诱发马氏体相变的初始应力值低,材料塑性好,抗拉强度高;准静态压缩加载时,两种组织的力学性能相近;动态压缩加载时,针状组织的动态压缩屈服强度显著高于粒状组织,但是由于粒状组织马氏体塑性变形阶段表现出更强的应变硬化效应,导致二者的动态抗压强度值相近。论文对相关机理进行了讨论和分析。

Effect of Precipitation Phase Morphology on Mechanical Properties of Ni-Ti Shape Memory Alloy

Aging heat treatment was applied to the Austeinitic NiTi shape memory alloy at 300 and 500 °C, and two typical microstructures with grainy precipitation phase and acicular precipitation phase were obtained, respectively. Static and dynamic mechanical property testing were conducted for both the samples with different morphologies of precipitation. Results indicate that under static tension loading, the strain-induced martensite transformation of the both samples has an obvious strain rate effect. The initial stress for strain-induced martensite transformation of samples with grainy precipitation is higher than that of samples with acicular precipitation, while samples with acicular precipitation phase show better?plasticity and higher flow stress of plastic deformation. Under static compression loading, the two kinds of samples exhibit similar mechanical behaviors. Under dynamic loading, the samples with acicular precipitation manifest much higher yielding strength, indicating a better strain rate hardening effect. However, the plastic deformation stage of marstensite transformation for samples with acicular precipitation displays more evident strain rate hardening effect, resulting in close failure strength with that of the other samples. The corresponding mechanism was also discussed