Elastic Stiffness Coefficients of Iron from 77° to 673°K

Abstract

The elastic stiffness coefficients of single‐crystal iron have been measured at room (300°K) and liquid‐nitrogen (77°K) temperatures using the ultrasonic pulse‐echo technique. The three coefficients were determined from a total of seven independent modes. The values at 300°K are C₁₁=2.28±0.02, C₁₂=1.32 ±0.04, and C₄₄=1.165±0.01, in units of 10¹² dyn/cm²; the corresponding values at 77°K are 2.36±0.02, 1.34±0.04, and 1.19±0.01. The coefficients C₁₁, (C₁₁+C₁₂+2C₄₄)/2, and (C₁₁+2C₁₂+4C₄₄)/3 of iron have been measured from 77° to about 673°K. C₁₁ and (C₁₁+2C₁₂+4C₄₄)/3, as well as the polycrystalline stiffness λ+2μ, depart from a linear dependence on temperature above about 300°C. It was not possible to say whether the same effect occurred in (C₁₁+C₁₂+2C₄₄)/2 because of significant scatter in the data. The Debye temperature Θ₀ was found from the stiffnesses extrapolated to 0°K, to be 471.5°K.