Physical and thermodynamic simulations of gamma-prime precipitation in Haynes® 282® using arc heat treatment

Abstract

Abstract Haynes 282 is a Ni-based gamma prime (γ′) strengthening alloy with a balanced combination of high temperature properties and fabricability. This paper aims to study the evolution of the microstructure and hardness using a novel physical simulation method called arc heat treatment, followed by thermodynamic modeling of γ′ precipitation. For the arc heat treatment, a steady state temperature gradient was generated using a stationary tungsten inert gas arc on a sample mounted onto a water-cooled chamber. The steady state condition ranged from room temperature to the liquidus and was achieved within the first few seconds. Aged and solutionized samples were arc heat treated for 1.5\u202fmin, 30\u202fmin, and 4\u202fh. The experiments were complemented with temperature modeling, equilibrium calculations, and γ′ precipitation simulations. A unique graded microstructure formed in the arc heat-treated samples. It consisted of a fusion zone with a dendritic microstructure; a region with the dissolution of all secondary phases (MC carbides, grain boundary carbides, and γ′); a region with MC and grain boundary carbides; a γ′ precipitation zone; and the base metal. The temperature range of the dissolution area extended to lower temperatures with increasing arc heat treatment dwell time. The γ′ precipitation zone showed a distinct etching response coupled with high hardness. The hardness and the temperature range of the γ′ precipitation zone increased with increasing arc heat treatment time. The γ′ radii increased with increasing time and temperature. The γ′ precipitation model, simulated with TC Prisma, showed very good agreement with the experimental results. Finally, the results were used to develop time-temperature precipitation and hardness diagrams.