Microstructural tailoring of As-Selective Laser Melted Ti6Al4V alloy for high mechanical properties

Abstract

As-Selective Laser Melted (as-SLMed) Ti6Al4V in horizontal direction possess poor ductility because of acicular α’ martensite and columnar β grains in microstructure. However, traditional ductility improvement methods including high-temperature preheating or heat treatment will decrease not only strength but also the efficiency of SLM fabrication to application. For a satisfactory mechanical property of as-SLMed Ti6Al4V alloy, some special temperature evolution conditions brought about from processing parameters such as layer thickness, hatch spacing, energy density and area ratios between support structure and part, were carried out in the paper. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the microstructure. The microstructure of as-SLMed specimens are found to be different extent decomposing of α’ martensite. Also, the formation mechanisms of such microstructural variables are proposed based on temperature evolution vs time during SLM process. Moreover, the tensile test presents high elongation (>8%) is achieved for horizontally as-SLMed Ti6Al4V specimens without lowering their strength (the ultimate tensile strength ∼ 1260 ± 30 MPa and yield strength ∼1160 ± 50 MPa), which markedly exceed ASTM standard for castings. The mechanical properties and fracture mechanisms of specimens are obviously affected by the width of α’/α martensite and the content of β phase. This work marks an important step forward in the understanding of microstructural tailoring in SLM process for a high-performance Ti6Al4V alloy.