Investigation of process by-products during the Selective Laser Melting of Ti6AL4V powder

Shane Keaveney,Aleksey Shmeliov,Valeria Nicolosi,Denis P Dowling

doi:10.1016/j.addma.2020.101514

Abstract

This paper investigates the formation of process by-products during the laser processing of titanium alloy powders by Selective Laser Melting (SLM). The study was carried out during the printing of Ti6AL4V parts using a production scale SLM system (Renishaw RenAM500 M). By-product particles were obtained on the surface of powder removed from the area around where the pulsed laser powder treatments had been carried out. The process by-products examined in this study were damaged Ti6AL4V particles along with condensate. The particles were found to exhibit deshelling, fracture, and collision damage. Based on TEM and SEM examination, the condensate particles were found to have sizes in the nanoscale range and exhibited morphologies, similar to those reported in the literature for welding condensates. Energy-dispersive X-ray spectroscopy (EDX) analysis indicated that the condensate formed from processing Ti6AL4V, exhibited a higher level of aluminum than that obtained for the alloy itself, lower levels of titanium with minimal vanadium levels, were also obtained. This may indicate that the alloy partially decomposes, with the emission of the lower melting point alloying element. The use of an in-situ melt pool monitoring system (called Renishaw InfiniAM Spectral), was evaluated for detecting the presence of these by-product particulates, based on photodiode measurements of the melt pool emissions, along with a camera-based imaging of visual per layer conditions. A reduction in the intensity of infrared emissions was detected, in areas where suspected spatter particles had been redeposited. Thus, demonstrating that process monitoring can be used for the in-situ detection of particulate defects formed during printing.

Highlights

Powder consistency is a key consideration for the repeatability and predictability of components manufactured through the Selective Laser Melting (SLM), Additive Manufacturing (AM) process [1,2]
This paper investigates the condensate particles generated during the SLM processing of Ti6AL4V, which due to its material properties is widely used for the printing of medical device and aerospace compo nents [16]
The first step in this investigation is the examination of the Ti6Al4V feedstock powder in order to determine if it was in compliance with ASTM Grade 23 [24]

Summary

Introduction

Powder consistency is a key consideration for the repeatability and predictability of components manufactured through the Selective Laser Melting (SLM), Additive Manufacturing (AM) process [1,2]. In order to facilitate a higher level of SLM process quality control, the use of techniques to monitor the melt pool emissions are clearly important [5]. Spatter is expelled from the melt pool during processing forming as new spherical particles of the alloy, which are noticeably bigger and typically chemically identical to the raw feedstock [6]. Ladewig et al outlined that ejected powder is an SLM phenomenon where particles of feedstock are ejected from the melt pool zone similar to welding plume dynamics [7]. Sutton et al investigated the by-products from the SLM processing of 304 L stainless steel, showing that the condensate was a mixture of all the alloying elements [8]. Wang et al focused on the SLM printing of CoCr, with a number of spatter morphologies observed and reported [6]

Methods

Results

Conclusion