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Study of pre-martensitic phenomena in shape memory alloys by positron annihilation lifetime spectroscopy

正电子湮没寿命谱研究形状记忆合金中的预马氏体现象

基本信息

批准号：
13650720
负责人：
ARAKI Hideki
金额：
$ 0.51万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

项目摘要

Many anomalous phenomena have been observed above martensite start(Ms) temperature, such as softening of the shear constants and increasing of internal friction. However, little information has been ohtained about the change in the electron system of the parent phase prior to the martensitic transformation, which should be the origin of all pre-martensitic phenomena. In this work, the pre-martensitic phenomena in NiTi alloys have been studied by positron lifetime spectroscopy which is quite sensitive to electronic-structural changes of matter.Near-equiatomic NiTi alloys produced by arcmelting were annealed for 180 ks at 1273 K in argon atmosphere for homogenization and subsequently quenched in iced water. The positron lifetime measurements were made at temperatures between 125 and 320 K using a fast-fast timing coincidence system with a time resolution (FWHM) of 190 ps. In order to determine the Ms temperatures the differential scanning calorimetry (DSC) measurements were also carried out in the temperature range between 150 and 350 K.We have found an anomalous positron lifetime change above martensitic transformation temperature of Ni51Ti49: positron lifetime increases anomalously with decreasing temperature even at temperatures 100 degrees higher than the Ms temperature of the alloy. Almost the same change in positron lifetime also has been observed on the heating run with little hysteresis, which clearly indicates that the observed pre-martensitic change of positron lifetime is due to the intrinsic electronic-structural change of NiTi alloys which causes so-called pre-martensitic phenomena.

在马氏体起始温度（Ms）以上观察到许多反常现象，例如剪切常数软化和内摩擦增加。然而，关于马氏体相变之前母相电子系统变化的信息很少，而马氏体相变应该是所有前马氏体现象的起源。在这项工作中，通过对物质的电子结构变化非常敏感的正电子寿命谱研究了镍钛合金中的前马氏体现象。通过电弧熔炼生产的近等原子镍钛合金在氩气气氛中于1273 K下退火180 ks以进行均匀化，然后在冰水中淬火。正电子寿命测量是在 125 至 320 K 之间的温度下使用时间分辨率 (FWHM) 为 190 ps 的快速定时符合系统进行的。为了确定Ms温度，还在150和350 K之间的温度范围内进行了差示扫描量热法（DSC）测量。我们发现，在Ni51Ti49的马氏体转变温度以上，正电子寿命发生异常变化：即使在比合金Ms温度高100度的温度下，正电子寿命也随着温度的降低而异常增加。在几乎没有滞后的加热运行中也观察到了几乎相同的正电子寿命变化，这清楚地表明观察到的正电子寿命的前马氏体变化是由于镍钛合金的固有电子结构变化引起的所谓的前马氏体现象。