The influence of thermal exposure on the γ′ precipitates characteristics and tensile behavior of superalloy IN-738LC

Abstract

The effects of long term aging on γ′ size and distribution and its influence on tensile behavior of superalloy IN-738LC at room and in elevated temperatures were investigated. Samples were aged isothermally at 850 °C for different times up to 3000 h and tensile tests were performed on samples in both standard heat treatment (SHT) and aged conditions. For samples in SHT condition yield stress ( σ y) was independent of tensile temperature up to 550 °C, after which it decreased slightly and then reached a maximum at 650 °C. Also minimum ductility was observed in this temperature. For aged samples, results showed an initial decrease of σ y up to 550 °C, followed by a subsequent increase in σ y peaked at 750 °C, and decreased again at higher temperatures. Results also showed that the magnitude of the observed peak at 750 °C, increased in aged samples with increasing the aging time. Elongation for material aged for 750 h was similar to that of the material in SHT condition. For samples aged for longer times (1500 and 3000 h) no drop in ductility was observed. The observations were explained based on dislocation–precipitates and dislocation–dislocation interactions.