Ultrasonic investigation of CMSX-6 superalloy at low and high temperatures

The elastic constants C11, C44 and C' have been measured as a function of temperature in a single crystal of CMSX-6 alloy and from these data the bulk, Young's and shear moduli have been deduced, together with the anisotropy factor A and the elastic constant C12. The temperature coefficient of the elastic constants C11 and C44 becomes gradually more negative on approaching the melting point of the alloy. This softening effect is interpreted in terms of a negative contribution to the elastic stiffness of the material arising from thermal vacancies within the disordered γ phase. The anisotropy factor A is found to fall in the typical range of fcc metals and the Cauchy relationship (C12 = C44) appears to be approximately fulfilled, suggesting that the lattice cohesion is associated with a field of central forces. (orig.)