Development of new Invar-type alloys by controlling stress-induced transformation of thermoelastic martensite and its industrial application

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It has been accepted that it is difficult to control the coefficient of thermal expansion (CTE) because it inversely proportional to the melting point of materials. This study was aimed to develop a new method of controlling the CTE using phase transformation.It is known that plastically deformed alloys undergoing thermoelastic martensitic transformation can exhibit two-way shape memory effect, which is a reversible and spontaneous shape change during heating and cooling. The effect of the pre-deformation on the reversible shape change was quantitatively investigated in this study. It was found that the transformation hysteresis increases by cold-rolling and CTE【approximately equal】0 is obtained in Cu-Zn-Al alloy cold-rolled to 9% reduction. Although the one directional rolling causes anisotropy in CTE, two-dimensional low thermal expansion (LTE) can be obtained by a cross-rolling method. Moreover, the cold-workability is drastically improved in α+β two-phase alloys, which means that C … More u-Zn-Al Invar alloys possessing high electrical conductivity are promising for practical applications.The grain size is one of the important factors to control the thermal expansion property. It was found that higher reduction is required to obtain LTE in a large grain specimen, which was thermodynamically analyzed using the Clausius-Clapeyron relationship, leading to the establishment of a method of controlling the CTE of alloys. Single crystal experiments also clarified the mechanism of the LTE obtained in these new Invar alloys.The stability of Cu-Zn-Al Invar alloys was investigated. 500 thermal cycles between-190℃ and 90℃ hardly changed the thermal expansion property, and good thermal stability up to 80℃ was confirmed. Based on the results in this study, the Cu-based Invar alloys are being examined for applications particularly to a machine part in printers.It should be noted that several interesting results related to this study, including high damping capacity, improvement of fatigue properties and superplasticity, was obtained in the Cu-Zn-Al and Cu-Al-Mn alloys. Less