Selective Laser Melting of the Intermetallic Titanium Alloy

Abstract

The in situ synthesis of the Ti₂AlNb-based intermetallic alloy was studied using selective laser melting of powder materials. The object of research was the Ti–22Al–25Nb (at %) alloy, the main phase of which is the Ti₂AlNb intermetallic compound with an ordered orthorhombic lattice (O phase). The Ti–22Al–25Nb alloy has high mechanical properties both at room temperature and at elevated temperatures, as well as a low specific weight, and is considered a promising material for use in the aerospace industry. To perform the experiments, a mechanical mixture of pure powders of titanium, aluminum, and niobium in a ratio necessary to synthesize the Ti–22Al–25Nb alloy was used. Selective laser melting relating to additive technologies is most promising to fabricate parts by the layer-by-layer addition of materials. The use of this technology makes it possible to fabricate complexly shaped parts based on the CAD model data. Compact samples for the investigation are performed by selective laser melting. The microstructure, density, phase composition, and microhardness of these samples are investigated. The influence of the thermal treatment in the form of homogenization at 1250°C for 2.5 h and subsequent aging at 900°C for 24 h on the microstructure, phase composition, and chemical homogeneity of the samples is also investigated. It is shown that the compact material formed by selective laser melting contains unmolten niobium particles. Homogenizing annealing makes it possible to attain the complete dissolution these particles in the material; due to this, the material microstructure consists of B2 phase grains of various sizes and needlelike precipitates of the orthorhombic phase.