Influence of processing parameters on internal porosity and types of defects formed in Ti6Al4V lattice structure fabricated by selective laser melting

Abstract

Ti6Al4V lattice structures were fabricated using selective laser melting with a wide range of processing parameters, namely laser power and scan speed, in order to study their effect on strut diameter and internal porosity morphology. Hence, identifying the optimum processing condition. Scanning electron microscopy (SEM) and optical microscopy (OM) were used to investigate the influence of these parameters on the strut size and internal porosity within the struts. The results show that at low laser power conditions the strut size decreased with increasing the scan speed. At intermediate laser power (200 W) the strut size decreased until it reached 2400 mm/s, beyond which no pattern was observed. Fluctuations in strut size values were found at different scan speeds using high laser power (250 W, 300 W). The micrographs of the sectioned lattice structures showed various morphologies of the internal porosity, from which a process map was developed to pinpoint the various types of defects at the different processing conditions. Five zones were formed which are: gas porosity, keyholing, irregular defects, balling, and lack of fusion defects. SLM processing condition of 100 W–1600 mm/s was selected to be the best condition from the studied samples for producing the lattice structure with strut size closest to the design and with minimum internal porosity. Mechanical and microstructural analysis were performed for this condition.