Comparative Quantitative Analysis of the Evolution of Precipitates in Inconel 625 Superalloy Manufactured by Laser Powder Bed Fusion Subjected to High-Temperature Creep and Annealing

Abstract The aim of the study is to contribute to understanding how prolonged exposure to high temperature and stress affects the morphology, size, and distribution of secondary phase precipitates in Inconel 625 manufactured by laser powder bed fusion. Creep tests were performed under a constant stress of 100 MPa at temperatures of 600 °C, 700 °C, and 800 °C. Samples creep tested at 600 °C and 700 °C were terminated after 2000 hours, while at 800 °C, the creep test was carried out until rupture. Isothermal annealing was carried out at temperatures of 700 °C and 800 °C for the same duration as creep tests. Microstructural analysis of creep-deformed and annealed samples was performed with the use of light microscopy, scanning, and transmission electron microscopy. The first-ever comparison of the evolution of precipitates in Inconel 625 LPBF after creep tests and annealing at 700 °C and 800 °C was shown. The qualitative and quantitative analysis revealed that the stress applied during creep tests leads to more pronounced nucleation of δ phase precipitates, although the growth of δ particles occurs more slowly compared to annealing. Furthermore, in creep-tested samples, the growth and coalescence of carbides and Laves phase particles were more intensive, compared to stress-free annealing, particularly at a temperature of 800 °C. Moreover, we show that the evolution of carbides and Laves phase particles along grain boundaries contributes to cavity and microcrack formation during high-temperature creep of Inconel 625 LPBF.