Thermodynamic and Kinetic Aspects of the Phosphorus Effect on the Stability of the Structure and Properties of Single-Crystal Refractory Nickel Alloys

Abstract

The nature and mechanisms of the negative effect of phosphorus on the structural stability and service properties of single-crystal refractory nickel alloys are considered. It is demonstrated that the phosphorus admixture induces the appearance of low-melting phosphides. The segregation of phosphorus on phase interfaces decreases their cohesive strength and increases their diffusion permeability. Moreover, the phosphorus admixture increases the porosity, promotes the coagulation of the hardening γ' phase, and decreases the long-term and cyclic strength and the yield of suitable single crystals. The data on the physicochemical parameters (the enthalpy and Gibbs free energy of formation of phosphides and their melting and boiling temperatures and density), which simplify the selection of additives neutralizing an adverse effect of phosphorus, are systematized and generalized.