Ni4Ti3-precipitation during aging of NiTi shape memory alloys and its influence on martensitic phase transformations

被引:636
作者
Khalil-Allafi, J
Dlouhy, A
Eggeler, G
机构
[1] Ruhr Univ Bochum, Inst Werkstoffe, D-44780 Bochum, Germany
[2] AS CR, Inst Phys Mat, CZ-61662 Brno, Czech Republic
关键词
Ni-rich NiTi shape memory alloys; aging; Ni4Ti3; precipitation; martensitic transformation; transmission electron microscopy (TEM); differential scanning calorimetry (DSC);
D O I
10.1016/S1359-6454(02)00257-4
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
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.
引用
收藏
页码:4255 / 4274
页数:20
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