The effect of nitrogen on the tensile strength of Ti-22Al-25Nb alloy using laser beam powder bed fusion

Titanium-aluminum (TiAl) based alloys have a wide application prospect in aerospace and auto-industry fields due to low density, good physical and mechanical performances. However, the mechanical strength of TiAl-based alloys is also put forward more stringent requirements with the complexity of the application conditions. In this work, an argon-nitrogen (Ar-N-2) reactive atmosphere was designed to achieve nitrogen interstitial solid-solution strengthening of Ti-22Al-25Nb alloy during the laser beam powder bed fusion (PBF-LB) process. An in-depth microstructure and mechanical performance analysis for the as-printed sample under various atmosphere conditions were performed via scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The nitrogen atoms can be dissolved in the octahedral gap of the beta phase through the PBF-LB in the Ar-N-2 atmosphere, and a small amount of nitride was detected when the volume ratio of Ar to N-2 was 95:5. Compared with 100 vol% Ar atmosphere condition, finer grains of the beta phase can be obtained after using the mixed gas atmosphere, and the ratio of the O phase was significantly reduced. The yield strength and ultimate tensile strength can be increased from 932 MPa to 947 MPa-1080 MPa and 1099 MPa at room temperature, respectively. At the same time, the elongation reaches similar to 11 % while obtaining higher tensile strength. The strength of as-printed Ti-22Al-25Nb alloy was improved by adopting a practical methodology without sacrificing plasticity.