Effect of heat treatment on the micro-indentation behavior of powder metallurgy nickel based superalloy FGH96

Abstract

The influences of solution treatment temperature on microstructure and micromechanics of P/M nickel-base superalloy FGH96 were investigated by micro-indentation methods. The alloy was heat-treated at the temperatures of 1050°C, 1150°C, 1220°C and 1310°C, respectively. The micro-indentation tests were conducted in the indenter load range from 500mN to 4500mN and the loading rate range from 5.19mN/s to 103.71mN/s at room temperature by using a sharp Berkovich indenter. The influence of solution treatment temperature on microstructure was analyzed based on microstructural observations using both optical and scanning electron microscope. The micro-hardness, Young’s modulus and yield stress were obtained by means of Oliver–Pharr method and reverse analysis algorithms, respectively. The results show that both of micro-hardness and Young’s modulus are significantly affected by indentation depth and solution treatment temperature. Based on microstructure analysis, these effects were attributed to the changes of precipitate properties, e.g., size, distribution and morphology, and the relationship between microstructure and micromechanics was established. Then, the deformation mechanism was explained on the basis of dislocation–dislocation and dislocation–precipitate interactions. In this paper, the descending Young’s modulus was related to localized stress concentration and microcrack propagation. The results reveal that the damage variable is high for P/M nickel-base superalloy FGH96 after high temperature solution treatments.