Selective Laser Melting of Ti2AlNb-based intermetallic alloy using elemental powders: Effect of process parameters and post-treatment on microstructure, composition, and properties

Abstract

Additive Manufacturing (AM) of intermetallic titanium components remains a challenging task, but at the same time, it is crucial for their more extensive industrial utilization. The Ti–22Al–25Nb elemental powder mixture was used to successfully elaborate a fully dense Ti2AlNb-based alloy by Selective Laser Melting (SLM) with subsequent Hot Isostatic Pressing (HIP) and heat treatment. The design of experiment allowed the determination of optimized SLM process parameters, which provides bulk samples with 99.5% relative density. Computed tomography and metallographic studies were utilized to investigate the amount and size of pores and unmelted Nb particles in the alloy. It was shown that volume energy density significantly affects the relative density, aluminum content, amount of unmelted Nb, and microstructure of the alloy. The temperatures of the phase transitions of as-is and annealed samples were determined using Differential Scanning Calorimetry (DSC). The samples were subjected to HIP, annealing at 1350 °C, and aging in different phase regions in the range of 700–1100 °C. The effect of heat treatment on phase composition, microstructure, and microhardness was also investigated. The alloy aged at 800 °C demonstrated the highest microhardness due to it having the largest amount of Ti2AlNb-precipitates with the smallest size.