A Study on Microstructure Evolution, High Temperature Deformation, and Fracture Characteristics of Wire Arc Additively Manufactured Inconel 625 Alloy

The present research focuses on the hot deformation behavior, microstructure, texture evolution, and fracture mechanisms of wire arc additively manufactured Inconel 625 alloy. The deposited material exhibits columnar, cellular, and dendritic grain structures, with grain widths ranging between 10 to 40 μm and lengths extending up to 150 μm. Deformation characteristics were studied across a temperature range of 700 to 900°C. At medium temperatures, distinct serrations were observed, transitioning from B-type to C-type as the temperature increased. At elevated temperatures, B-type serrations reappeared, attributed to interactions between C14-Ni2Nb Laves phases and mobile dislocations, as revealed by TEM analysis. Conversely, C-type serrations were associated with the nucleation and growth of deformation twins. Grain size and boundaries under varying deformation temperatures were examined using EBSD and TEM, which revealed occurrence of dynamic recrystallization (DRX). It was observed that preferred orientation for DRX nucleation in the Inconel 625 alloy is along the <001> direction. At 900°C, recrystallized grains were prominent, with EBSD results confirming both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), where CDRX acted as a secondary nucleation mechanism. Below 900°C, cracks primarily nucleate due to stress concentrations near Nb-rich phases. At 900°C, crack initiation was influenced by slip band impingement at grain boundaries combined with stress concentrations around Nb-rich phases. The high-temperature deformation behavior of WAAM-deposited Inconel 625 is strongly influenced by the interplay of DDRX and CDRX mechanisms.