Measurement of Structural Parameters Important in Creep of Ni-Mo and Ni-W Solid Solutions

Abstract

To describe effectively the creep behavior of concentrated solid solutions in the diffusion-controlled power law regime in terms of dislocation climb and viscous glide mechanisms, values of key structural and physical properties are needed. The constitutive relations for these mechanisms reveal important contributions from elastic moduli and the appropriate diffusivities to the steady-state creep rate. Empirical modifications of these formulations further suggest the need for structural parameter values, such as the stacking fault energies, short range order coefficients, and atomic size differences, of the alloy systems of interest. The objective of this research is to characterize the Ni-Mo and Ni-W terminal solid solutions in terms of the above parameters and to define and interpret the calculated steady-state creep rates for both climb and viscous glide as a function of solute content. The calculated creep rates for the Ni-W system are lower than those for the Ni-Mo system for both mechanisms due to the higher moduli and atomic size factor, and lower diffusivities of the former. The short range order contribution to the viscous glide parameters of the Ni-Mo system is the largest observed in such analyses to date (up to 12 pct). Reasons for the marked slope differences between the Ni-Mo climb and glide solute dependencies are presented.