Evolution of microstructure and tensile properties during solution treatment of nickel-based UNS N10276 alloy

Abstract

Influence of solution treatment (ST) on microstructure evolution and mechanical behavior of nickel-based UNS N10276 alloy were investigated by a variety of techniques such as optical metallography, scanning electron microscopy, transmission electron microscopy and tensile testing. The average grain size remained almost unaffected by hold time at 1050°C, resulting from the pinning effect of secondary phase on the grain boundary. A sharp increase in grain size and grain growth rate was observed with increasing solutionizing temperature up to 1150°C irrespective of hold time, which was mainly related to the complete dissolution of precipitated particles as well as to the enhanced diffusion of solute atoms. The rate of grain growth reduced with extending solutionizing time and decreasing temperature. Flow curve parameters based on Ludwigson equation for the alloy after heat treatment were determined. The dissolution of secondary phase particles, combined with the grain growth, increased the work hardening exponent (n) and dramatically improved the tensile ductilities (TD), but reduced the tensile strengths (TS) to large extent. Both TD and n monotonically increased with increasing solutionizing temperature and prolonging hold time as the alloy was solutionized beyond 1100°C, while the TS and strain hardening rate (SHR) showed a reverse varying trend to that of TD and n. As the heat treatment was performed at 1050°C, tensile properties were not monotonically changing with hold time, which is associated with the increase in amount of precipitates and with the Ostwald ripening of precipitated particles. On the basis of Hall–Petch relation and experimental data, the mathematical relationships between tensile properties and grain size of the alloy solutionized at temperatures higher than 1150°C, were obtained by linear regression analysis. The Hall–Petch strengthening coefficient for yield strength of the UNS N10276 alloy was estimated to be 18.35MPamm1/2.