Enhancing geometric integrity and surface hardness of SLM-printed Ti-6Al-4V components with support structures and laser nitriding
Weijie Xie, C S Kirk, Amal Rejee, H.C. Man, Chi-Wai Chan
Abstract
This study investigated the effect of support structure and post-processing surface nitriding on high aspect ratio Ti-6Al-4V components fabricated using Selective Laser Melting (SLM). It examined changes in geometric integrity, porosity, and mechanical properties. Samples were printed without support structures (S1) and with support structures (S2). After SLM printing, both samples underwent open-air laser nitriding at duty cycles (DC) ranging from 50 % to 100 %, aiming to create crack-free nitride layers to increase surface hardness. The results indicated that support structures effectively mitigate thermal-induced deformation, with S2 exhibiting minimal warping and closer adherence to design specifications than S1. Although S2 showed increased porosity as revealed by X-ray Computed Tomography (XCT), its refined microstructure contributed to increased hardness. Optical Microscope and Scanning Electron Microscope (SEM) analyses demonstrated that laser nitriding at a 50 % duty cycle produced uniform, crack-free titanium nitride (TiN) layers. Vickers hardness tests revealed a significant enhancement in the surface hardness of both laser-nitrided samples, with S2 displaying finer TiN dendrites that further improved its surface hardness. The use of support structures was found to be effective in achieving a more uniform microstructure and enhanced hardness in the nitride layer. • High aspect ratio Ti6Al4V samples are printed using selective laser melting (SLM), with and without support structures. • Support structures reduce part deformation, ensuring geometric integrity. • Post-SLM laser nitriding produces crack-free TiN layer, increasing surface hardness. • Support structures result in finer TiN dendrites, further improving surface hardness.