【作者】 李岩；

【导师】 杨大智；

【作者基本信息】 大连理工大学 ， 材料学， 2001， 博士

【摘要】 智能材料的概念产生与二十世纪八十年代后期。形状记忆合金机敏复合材料一直是智能材料中的研究热点与重点之一，而形状记忆合金在基体材料约束态下相变行为的研究是应用与发展这类机敏材料的关键基础性问题。但是，这方面的研究仍然缺乏。 本论文基于形状记忆合金机敏复合材料的应用特点，以近等原子比TiNi形状记忆合金为研究对象，采用电阻法，DSC，电阻应变仪，SEM和TEM等手段，对TiNi记忆合金在恒应变约束下的相变和力学行为及TiNi合金丝在水泥基体约束下的相变进行了系统研究，主要结论如下： 采用DSC方法和回复应变的测量，对小预应变(＜10％)TiNi形状记忆合金的相变及不完全相变行为进行了研究。结果表明，逆相变开始温度随预应变增加而增大，其原因是预应变造成马氏体再取向使弹性能降低，引起的塑性变形和晶粒间的约束提高了耗散能。晶粒的塑性变形及位错的引入是第二次逆相变开始温度低于未预应变时逆相变开始温度的主要原因。经不完全相变的样品由自适应马氏体和取向马氏体组成，第二次逆相变过程中，两者先后发生相变，其中自适应马氏体逆相变温度降低，取向马氏体逆相变需要过热。 研究了预应变TiNi形状记忆合金的回复力及驱动特性。发现经973K(再结晶温度以上)退火以后的TiNi合金丝，回复力与温度变化成正比，即加热时上升，冷却时下降。回复力与预应变有关，当预应变为8％左右时可以得到最大回复力，预应变再增大，最大回复力反而减小：材料参数(do／dT)也随预应变增加而增大。在第二次加热时的回复力与第一次的变化路径明显不同。在约束态加热温度，第二次加热时的回复力比第一次的低。经723K热处理的TiNi合金丝在加热时的回复力，出现下降现象，可能与拔丝过程中形成的特殊取向马氏体有关。 采用电阻法，DSC和TEM等手段研究了恒应变约束下预应变TiNi记忆合金的相变行为。实验结果表明，回复力的作用及其导致的取向马氏体再变形的发生，是约束态逆相变温度区间比自由态相变区间显著拓宽的两个原因；在约束态正相变过程中，由于回复力的诱导而生成应力诱发马氏体：正相变过程中的R相变与取向马氏体再变形过程中引入的位错有关。经不完全相变后的第二次逆相变中，应力诱发马氏体和剩余取向马氏体先后发生相变，并可以输出两 QZ段回复力（约束态）或两段回复应变（自由态人 制备了界面结合状况良好的TWi合金丝／水泥复合材料，研究了Tei合金在水泥基体约柬下的相变行为。实验结果表明，当记忆合金丝的预应变较大时，由于较大的回复力而导致复合材料的破坏。小预应变TINi记忆合金在水泥基体约束下的逆相变是取向马氏体再变形过程。在复合材料DSC加热曲线上吸热峰所在的逆相变温度区间内，马氏体逆相变的平均速率较大；在复合材料DSC加热曲线吸热峰的结束温度以上，取向马氏体的逆相变仍在进行，但平均相变速率较小。更多还原

【Abstract】 The concept of intelligent materials came into being in the late 1980’s. Shape memory alloy smart composites have been one of the most absorbable things hi the diversity of intelligent materials. Phase transformation behaviors of shape memory alloy under constraint of matrix materials has been a crucial issue for application of the shape memory alloy smart composites. However, systemic research is absent in this field.Based on the practical feature of shape memory alloy smart composites, phase transformations and associated thermomechanical behaviors of prestrained near-equiatomic TiNi shape memory alloy under a constant strain constraint and TiNi/cement composite were explored using electric resistance measurement, DSC, resistance strain gauge, SEM, TEM etc., in this dissertation. And the major conclusions are listed as follows.Phase transformation and incomplete phase transformation behaviors of TiNi shape memory alloy within small prestrain level (<10%) were studied by DSC and recovery strain measurements. The results show that the reverse martensitic transformation start temperature increases with the increase of prestrain, which may be due to the elastic energy released by prestrain, and the energy dissipated increased by plastic deformation and the constrain effects of grains. The main reason that the start temperature of the second reverse transformation is lower than that of the first one is due to the plastic deformation of the grains and induced dislocations. After an incomplete reverse transformation, the prestrained TiNi alloy sample is composed of the self-accommodation martensite and the remained oriented martensite. In the following reverse transformation, the start temperature of the former is lowered and the start temperature of the latter is raised.The recovery stress and actuating characteristic were studied. To the TiNi alloy heat-treated at 973K, the recovery stress is a monotonous rise function of temperature and reaches its maximum at prestrain 8%. The parameter da/dT increases with increasing prestrain level. The route of the recovery stress upon the second heating is obviously different from that upon the first heating, but the amounts of the recovery stress is similar to each other at the first stop heating temperature. To the TiNi alloy heat-treated at 723 K, a decrease stage appears in the recovery-temperature curve, whichmay due to the particular oriented martensites formed during the wire drawing process.Phase transformation behaviors of TiNi shape memory alloy under constraint of a constant strain were explored by use of resistance measurements, DSC and TEM. The results indicated that the expansion of the temperature span of the reverse martensite transformation under constraint comparing with that in free state is due to two contributions, the effect of recovery stress and the oriented martensite re-deformation process induced by recovery stress. In the forward transformation, the stress-induced martensite is induced by the recovery stress and the appeared R phase transformation is associated with induced dislocations hi the oriented martensite re-deformation process. After an incomplete constrained transformation cycle, a two-stage recovery stress in constrained state or a two-stage recovery strain hi free state will emerge in the subsequent heating as the result of the reverse transformation of the stress-induced martensite and the remained oriented martensite to parent, respectively.A TiNi fiber/ cement composite with a perfect interfacial bonding was fabricated and its phase transformation behaviors were explored. The results show that if the prestrain level exceeds a certain amount, the composite will rupture due to the large recovery stress upon heating. The reverse transformation of the TiNi alloy fiber under the constraint of cement matrix is the oriented martensite re-deformation process. In the temperature span of the endothermic peak of the DSC heating curve, the average transformation rate is relatively large. The reverse transformation of oriented marte更多还原