A comprehensive study of the anisotropic tensile properties of laser additive manufactured Ni-based superalloy after heat treatment

In this work, the anisotropic tensile properties of laser additive manufactured (LAMed) GH4169 in as deposited and different heat-treated conditions are presented and the underlying mechanisms are analyzed in detail. Vertical and horizontal specimens for tensile tests were taken from as deposited (AD) and heat-treated blocks. Two heat treatment conditions with solution temperature of 980 degrees C and 1050 degrees C were considered. The tensile test results indicate different tensile properties of the vertical and horizontal samples, and such anisotropy is related to heat treatment conditions. The vertical AD sample has higher tensile strength than its horizontal counterpart, while after heat treatment, the horizontal direction shows higher tensile strength. Microstructure characterization, texture and grain morphology analyses were conducted through SEM with EBSD, XRD and TEM observations in order to figure out the main influential factors of the anisotropic tensile properties. Besides, fracture surfaces of the tensile specimens were observed to study the role of precipitates. In addition, the residual stresses in the LAMed samples in AD and heat-treated conditions were measured, and their effects on the anisotropic tensile strength were clarified by correlating the residual stress levels with the recrystallization fractions extracted from EBSD data. The obtained results show that a large number of brittle Laves phases growing along the vertical direction are distributed in the AD samples, which leads to different separation manners of Laves phase/gamma matrix interfaces under different loading directions. Besides, the residuals stress level is high direction dependent in the AD samples. After heat treatment, most of the Laves phases are dissolved, and the residual stress experiences a significant variation. On the whole, the anisotropic tensile strength is mainly influenced by the residual stress level before and after heat treatment, and slightly influenced by the dissolution of the Laves phase. The present study provides a deeper understanding of the anisotropic tensile properties of LAMed GH4169, which may contribute to future engineering applications of Ni-based superalloys.