TiNi形状记忆合金断裂机理的研究

【作者】 孙伟；

【导师】 陈剑虹； 王国珍；

【作者基本信息】 兰州理工大学 ， 材料学， 2004， 硕士

【摘要】 形状记忆效应是一种在某一临界温度以下经历的变形当加热时可以恢复的现象。这种恢复现象的微观机制是热弹性马氏体相变。到目前为止，有将近二十种金属间化合物合金具有形状记忆属性。然而，由于价格、强度、可加工性和可恢复应变水平等参数的不同，仅有两个形状记忆合金系列被广泛的用于工程应用中，一种是铜基形状记忆合金，另一种是TiNi基形状记忆合金。在过去的二十年中，人们对TiNi合金中马氏体相变的特征进行了大量的研究。 本文通过对光滑试件机械性能的测定，原位拉伸试件的表面观察、相应的断口观察及计算；缺口弯曲宏观参数的测定、断口观察及计算等对TiNi形状记忆合金试样的断裂过程做了详细研究和分析。对TiNi形状记忆合金断裂情况的研究现状进行了论述。对前人在TiNi形状记忆合金的相组成、相变过程及应力诱发马氏体相变等方面所做的工作进行了分析与比较。在这些实验与计算的基础上，我们初步分析了TiNi形状记忆合金室温断裂机理，得到了以下几个方面的结论：TiNi形状记忆合金的断裂与钢的脆性解理断裂不同。TiNi形状记忆合金的断裂受解理机制和孔洞在第二相颗粒处的形核、长大、连接机制控制。这两种材料失效机制共同作用，其中哪一种占统治地位取决于许多因素。应力诱发马氏体相变对TiNi形状记忆合金的断裂具有重要的影响。更多还原

【Abstract】 Shape-memory effect (SME) is a phenomenon where deformation suffered below a critical temperature can be recovered on heating. The micromechanism of this kind of recovery is the thermal-mechanical martensitic transformations. To date, there are nearly twenty intermetallic alloys which possess shape memory properties. However, due to several variables such as cost, strength, processability, and recoverable strain levels, only two shape memory alloy systems have been extensively used in engineering applications. One is copper based shape memory alloys, the other is TiNi. Over the last two decades, many research efforts have focused on characterizing martensitic transformations in TiNi.This paper sets about studying room-temperature fracture mechanisms of TiNi shape memory alloys through the measurements of mechanical properties, in-situ observations of fracture surfaces and calculations, the measurement of macro-parameters, the observations of fracture surface and calculations on notch specimens (4PB). Fracture mechanisms of titanium nickel shape memory alloys specimens are observed and analyzed carefully through above experiments. The investigation available recently in connection with the fracture of titanium nickel shape memory alloys is analyzed and summarized. The work about phase compositions, process of phase transformation and stress-induced martensite transformation in TiNi shape memory alloys conducted by the predecessors is analyzed and compared. Based on the results of experiments, calculation, the following are found: fracture of TiNi shape memory alloys is different from brittle cleavage fracture of steels. The fracture of TiNi shape memory alloys is controlled by cleavage coupled with void nucleation, growth, and coalescence from the second phase particles. The two mechanisms of material failure act in conjunction with one another and the dominance of one over the other depends on many factors. The reversible stress induced martensitic transformation has a very important effect on the fracture of TiNi shape memory alloys.更多还原