Effect of heat treatment on microstructure and high-temperature wear performance of additive manufactured IN718

The additive manufactured IN718 under Laser Powder Bed Fused (LPBF) was evaluated for its microstructure, microhardness, and wear behavior in both as-printed and precipitation heat-treated condition. The microstructure of as-print IN718 shows slender columnar dendrites oriented directionally along build direction and coarse cellular structure in the remelt zone that formed between the laser-deposited tracks. After solution double aging heat treatment (AMS 5662), reinforcing precipitates (gamma ' and gamma '') were observed in the gamma-matrix and delta-phase precipitation at grain boundaries. Microhardness analysis indicates that the alloy's hardness was improved and stabilized in all direction after the heat treatment. The alloy's tribological behavior was examined at temperatures of 28 degrees C, 400 degrees C, 500 degrees C, and 600 degrees C in a pin on disc setup. SEM and XRD analyses were used to examine the worn-out surface and wear debris. Surface examination of the worn-out sample reveals abrasion wear at 28 degrees C and delamination wear at 400 degrees C, 500 degrees C and 600 degrees C. The topography study highlights that abrasion and delamination wear are considerably reduced after heat-treatment. The friction coefficient and wear loss increase with the test temperature indicates that delamination plays a crucial role in affecting both friction and wear loss. XRD analysis on the worn-out surface detected nickel oxide (NO) formation in all high temperature tested samples and the NiO is ineffective in reducing friction and wear loss. The sectional analysis of worn-out surface shows noticeable variations in delamination intensity as the test temperature rises. A thorough examination of the wear debris reveals delamination marks on the front surface and micro-cracks developing on the back surface. The microstructure examination carried out near the worn-out surface of both as-printed and heat-treated sample tested at 600 degrees C. The analysis confirmed excess delta-phase formation at the grain boundary of as-printed sample aggravates crack propagation and wear loss due to delamination.