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首页> 外文期刊>Science and Technology of Advanced Materials >Pre-martensitic phenomena of thermoelastic martensitic transformation of NiTiCu alloys studied with positron annihilation lifetime spectroscopy
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Pre-martensitic phenomena of thermoelastic martensitic transformation of NiTiCu alloys studied with positron annihilation lifetime spectroscopy

机译：正电子an没寿命谱研究NiTiCu合金的热弹性马氏体转变前马氏体现象

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摘要

Many anomalous phenomena have been observed in NiTi alloys above martensite start temperature, such as softening of the shear constants, increase of internal friction and diffuse scattering of TEM. However, little information has been obtained 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 temperature change of positron annihilation lifetime, which is quite sensitive to electronic-structural changes of matter, were carried out for NiTiCu alloys. The alloys show martensitic transformation from a B2 (cubic) phase to a B19′ (monoclinic) phase via a B19 (orthorhombic) phase as the temperature is lowered. We have found anomalous positron lifetime changes in Ni_(10)Ti_(50)Cu_(40)) and Ni_(15)Ti_(50)Cu_(35) alloys which show a B2-B19-B19′ phase transformation. Positron lifetime increases anomalously with decreasing temperature at temperatures higher than the transformation temperature into a B19' phase. On the other hand, positron lifetime does not show any anomaly in the B2 phase of Ni_(30)Ti_(50)Cu_(20) alloy which shows B2-B19 phase transformation. The positron lifetime of the parent B2 phase shows good agreement with the theoretically-calculated value. Those of the martensite phases of B19 and B19′, although, are about 30 ps longer than calculated ones. This big difference between experimental and calculated positron lifetimes cannot be explained by any existing theory.
机译：在马氏体起始温度以上的NiTi合金中已观察到许多异常现象，例如剪切常数的软化，内摩擦的增加和TEM的散射。但是，关于马氏体相变之前母相电子系统变化的信息很少，这应该是所有马氏体前现象的起源。在这项工作中，对NiTiCu合金进行了正电子an灭寿命的温度变化，该温度变化对物质的电子结构变化非常敏感。随着温度降低，合金显示出从B2（立方）相到B19（单斜晶）相到B19'（单斜晶）相的马氏体转变。我们发现Ni_（10）Ti_（50）Cu_（40））和Ni_（15）Ti_（50）Cu_（35）合金中的正电子寿命异常变化，显示出B2-B19-B19'相变。在高于转变成B19'相的温度的温度下，正温度的降低会导致正电子寿命异常增加。另一方面，在Ni_（30）Ti_（50）Cu_（20）合金的B2相中，显示B2-B19相变的正电子寿命没有异常。母体B2相的正电子寿命与理论计算值显示出良好的一致性。但是，B19和B19'的马氏体相的长度比计算的相长约30 ps。实验和计算出的正电子寿命之间的巨大差异无法用任何现有理论来解释。

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