CHARACTERISATION OF THE MICROSTRUCTURE AND DEFECTS DURING THE DIRECT ENERGY DEPOSITION OF HYBRID Ti6Al4V IN A LOW-QUALITY ATMOSPHERE

Abstract

Additive manufacturing is a complicated process, including powder preparation and post-processing. The atmosphere during the processing of sensitive alloys like Ti6Al4V is among the most important factors. The N content influences the mechanical properties in a significant way. Therefore, it is essential to understand, recognise, and identify the problems in case of machine malfunction or human error. The influence of a low-quality atmosphere on the microstructure evolution and mechanical properties was investigated during the direct energy deposition of hybrid additive-manufactured Ti6Al4V. The properties of the built parts were characterised by chemical analyses, light and electron microscopy, and mechanical testing. High concentrations of N, which absorbed and dissolved with every deposition layer of the direct-energy-deposition process, promoted the formation of a layer of α-scale on the part’s surface. The presence of α-scale was confirmed by observing the sample surfaces and the lack of fusion pores where a layer of α-scale remained. The α-scale partially or entirely dissolved during the next deposition layer. The morphology of the partially melted, α-scale depended on the size of the deposition and, thus, on the temperature evolution during the direct energy deposition.