Microstructure and mechanical properties of hot rolled ODS copper

Abstract

• The previous thermal treatment of the powder affects to the alloy densification. • Higher hot rolling passes are necessary in order to close the voids. • The as HIP material exhibits the higher mechanical strength. • The hot rolling process increases the thermal conductivity. Dispersion strengthened copper alloys have been produced by following a powder metallurgy route that have consisted of milling copper and yttrium acetate powders in a planetary ball milling and subsequently sintering by hot isostatic pressing (HIP). In order to increase the degree of densification of the materials, they were subjected to a thermal treatment in vacuum and to a hot rolling process at 1173 K. The decomposition of the yttrium acetate during the thermal treatments resulted in the formation of voids, with a loss of densification that could not be satisfactorily improved with the hot rolling processing. The microstructure and the mechanical and thermal properties of the alloys were analyzed by scanning electron microscopy, electron backscattering diffraction, micro and nanohardness measurements, and compression tests and thermal conductivity measurements, both in the range 300–780 K. The best mechanical properties were obtained for the as-HIP material, with a mean grain size of 0.3 ± 0.3 μm and a yield strength value at room temperature of 520 MPa. In contrast, the material with the highest thermal conductivity for the entire range of temperature was found to be the alloy thermal treated in vacuum at 1273 K and later subjected to the hot rolling processing. The different microstructural characteristics of the alloys such as grain size, defects present in the grains and size of voids seems to be responsible of the differences on their thermal conductivity values.