Ni4Ti3-precipitation during aging of NiTi shape memory alloys and its influence on martensitic phase transformations
Ni4Ti3-precipitation during aging of NiTi shape memory alloys and its influence on martensitic phase transformations
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DOI：
10.1016/s1359-6454(02)00257-4
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发表时间：
2002-10-09
期刊：
影响因子：
9.4
通讯作者：
Eggeler, G
中科院分区：
文献类型：
--
作者：
Khalil-Allafi, J;Dlouhy, A;Eggeler, G
研究了富镍NiTi形状记忆合金的显微组织及其对马氏体相变热特性的影响。溶液退火的材料状态进行各种等温时效处理，在773 K，这导致在透镜状连贯Ni 4 Ti 3沉淀物，这是定量的特征在于使用透射电子显微镜（TEM）的成核和生长。36 ks的无应力时效导致非均匀微观结构，在晶界附近有沉淀物，在晶粒内部有无沉淀物区域;这种微观结构在差示扫描量热法（DSC）实验中显示出从132制度冷却的三步（“多步”）转变行为，这既不能基于相干应力论证来合理化（Bataillard等人，1997），也不是基于在生长的沉淀物之间变化的Ni浓度（Khalil-Allafi等人，2002年）。提出了一种新的解释演变DSC图的功能，其中考虑到无应力和应力辅助老化过程中的微观结构的演变。最重要的是，它表明，应力小至2 MPa强烈影响沉淀过程。(C)2002 Acta Materialia Inc.由爱思唯尔科技有限公司出版。保留所有权利。
The present work studies the microstructure of a Ni-rich NiTi shape memory alloy and its influence on the thermal characteristics of martensitic transformations. The solution annealed material state is subjected to various isothermal aging treatments at 773 K; this results in the nucleation and growth of lenticular coherent Ni4Ti3-precipitates, which were quantitatively characterized using transmission electron microscopy (TEM). Stress free aging for 36 ks results in a heterogeneous microstructure with precipitates near grain boundaries and precipitate free regions in grain interiors; this microstructure shows a three step ('multiple step') transformation behavior in a differential scanning calorimetry (DSC) experiment on cooling from the 132 regime, which can neither be rationalized on the basis of a coherency stress argument (Bataillard et al., 1997) nor on the basis of varying Ni-concentrations between growing precipitates (Khalil-Allafi et al., 2002). A new interpretation of evolving DSC chart features is proposed which takes the evolution of microstructures during stress free and stress-assisted aging into account. Most importantly it is shown that stresses as small as 2 MPa strongly affect the precipitation process. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.