The effect of thermomechanical pretreatment on the allotropic transformation in cobalt

Abstract

The effect of prior thermomechanical treatment on the allotropic transformation in cobalt was investigated utilizing continuous resistivity measurement, X-ray diffraction, and pole figure determinations. Initially, a significant amount of metastable cubic phase was always present at room temperature, the existence of which was independent of the prior thermomechanical treatment employed. For material fully recrystallized, a pronounced reduction in the amount of metastable cubic phase is observed in cycling through the transformation. A much less pronounced effect was observed on cycling material recovered prior to the recrystallization treatment; however, interpretation of data is less clear due to the presence of texture which was always evident. The anomalously low Residual Resistance Ratios always found in high-purity cobalt is interpreted to be due to the presence of this metastable cubic phase, since cycling resulted in significant improvements in the ratios observed. The results of this investigation are in strong disagreement with those of Bibring and Sebilleau21–23 on the effects of prior thermomechanical treatment on the allotropic transformation in cobalt.