Effect of Heat Treatment on Decreasing of Thermal Expansion Coefficient of Cr-Cu Materials

W-Cu and Mo-Cu materials have been applied for heat sink application. Low thermal expansion coefficient is required as well as high thermal conductivity for heat sink. Chromium is the same 6A group element as W and Mo, but its thermal properties, namely thermal expansion coefficient and thermal conductivity are a little inferior to these of W and Mo. Furthermore the Chromium is dissolved slightly in Cu during solution treatment and precipitated by aging treatment. In this paper, to improve the thermal expansion coefficient of Cr-Cu close to that of Mo Cu and W Cu, the effect of Cr precipitation treatment on thermal expansion coefficient of Cr-Cu was investigated. A commercial alloy 1.1 mass% Cr-Cu and 50 mass%Cr-Cu produced by powder infiltration process were prepared for the investigation. They were solution treated without quenching and aged at various temperatures to make relatively large Cr precipitates, and then their thermal expansion coefficient were measured. As the result, the drastic decrease of thermal expansion coefficient was discovered in the bottom at 823 K. The phenomenon was estimated to relate to larger warp contrast by coherent Cr precipitate at 823 K. In the rolled plates of both Cr-Cu materials, anisotropic behavior of the phenomenon was observed in the rolling and transverse directions.