Temperature dependence of the single-crystal elastic constants of co-rich co-fe alloys

Abstract

The single-crystal elastic moduli, C11, C12, and C44 of three fcc cobalt-iron alloys (Co-6 at. % Fe, Co-8 at.% Fe, Co-10 at.% Fe) were measured in the range 0-315 °c. In addition C11 for the Co-6 at. % Fe alloy, and C' = (1/2)( C11 + C12 + 2 C44) for the three alloys are measured over the temperature range 0-1250 °c. Plots of the elastic moduli vs temperature exhibit a change in slope and deviation from linearity in the neighborhood of the Curie temperature. The temperature variation of the shear anisotropy in the fcc phase A fcc (=2 C44/ C11- C12) differs among the three alloys. A fcc exhibits a highly positive temperature dependence in the Co-10 at. % Fe alloy and a slight negative dependence in the Co-6 at. % Fe and Co-8 at. % Fe alloys. Previous statements in the literature that the hcp → ← fcc transformation in cobalt is preceded by a highly negative temperature dependence of the shear anisotropy ratio A (= C 44/ C 66) in the hcp phase between 523 °K and the transition at about 743 °K is not borne out by the present results. Rather it appears that the hcp → ← fcc transformation involves a change from A >1 in the hcp phase to A < 1 in the fcc phase.