Hot deformation behavior of a novel Ni–W–Co high-density Ni-based alloy with ultra-high W content

Abstract

Ni–W–Co alloy is a recently developed single-phase Ni-based alloy with high density. An ultra-high content of W (35–38 wt%) is essential to ensure the high density but unfavorable to possess outstanding ductility or present large deformation. In this study, the flow stress behavior and hot workability of Ni–W–Co alloy were investigated through simulated compression tests with a temperature range of 1000–1300 °C and strain rate range of 0.01–5 s−1. The Arrhenius-type constitutive equation at peak stress was established. The constitutive equation displays prediction bias due to the lower experimental values at low temperature and high strain rate. The ultra-high solution content of W not only results in the severely inhibited discontinuous dynamic recrystallization (DDRX) and high apparent deformation activation energy (568.5 kJ/mol) but also promotes the generation of subgrain boundaries. Furthermore, continuous dynamic recrystallization (CDRX) occurs during deformation at a low temperature and a high strain rate, which is quite different from the Ni-based alloy with a low W content that only DDRX occurs. The activation of CDRX shortens the stage at which work hardening dominates, and results in lower peak stress values. The prediction bias of the constitutive equation caused by the lower peak stress was eliminated through difference compensation. The hot processing maps at strain values of 0.3, 0.5, 0.7, and 0.9 were constructed. The optimal hot processing parameters of the Ni–W–Co alloy, which aims to obtain full recrystallization microstructure without defects, are strain rate 0.01–0.1 s−1 and temperature 1225–1300 °C in combination with the hot processing maps and microstructure evolution. This study provides a reference for the hot processing and microstructural modification of the novel Ni–W–Co alloy with an ultra-high W content.