Mechanical and microstructural characterization of Nimonic 263 superalloy after constrained groove pressing at elevated temperatures

Abstract

Nimonic 263 superalloy is primarily being used in gas turbines, high-pressure pipelines, steam heaters, etc. due to its capability to withstand high temperatures and pressure for a longer duration. In this work, an experimental investigation on Nimonic 263 alloy has been carried out to improve its mechanical and microstructural properties using constrained groove pressing (CGP) at various temperatures. CGPed specimens have been characterized through mechanical tests (tensile test and hardness test) and microstructural studies (XRD, SEM fractography, and optical microscope). The results demonstrated that the CGP process had a significant impact on the alloy's properties. Compared to the as-received material, the CGPed specimens exhibited substantial improvements in yield strength (YS), ultimate tensile strength (UTS), and micro hardness, with average values of 234.58%, 43.79%, and 110.31%, respectively. The average grain size gets reduced due to CGP from 220.70 μm for the as-received material to 106.02 μm, 117.09 μm and 94.01 μm for CGP at room temperature, 250o C, and 450o C, respectively. An increase in the peak intensity is observed in the XRD after the CGP process due to a decrease in crystal size and an improvement in dislocation density with an average value of 31.68%. Fractography studies have revealed a mixed-mode (ductile and brittle) failure for the CGPed specimens compared to the ductile failure mode in the as-received material. Using Abaqus 6.14 software, the finite element analysis of the CGP process has been performed and the results have been found in good agreement with the analytical results. Thus, the CGP process can effectively improve the mechanical and microstructural properties of Nimonic 263 alloy for high-temperature applications.