Superelastic Behavior of Ti-Nb Alloys Obtained by the Laser Engineered Net Shaping (LENS) Technique

The effect of Nb content on microstructure, mechanical properties and superelasticity was investigated for a series of Ti-xNb alloys, fabricated by the laser engineered net shaping method, using elemental Ti and Nb powders. The microstructure of as-deposited materials consisted of columnar beta-phase grains, elongated in the built direction. However, due to the presence of undissolved Nb particles during the deposition process, an additional heat treatment was necessary. The observed changes in mechanical properties were explained in relation to the phase constituents and deformation mechanisms. Due to the elevated oxygen content in the investigated materials (2 at.%), the specific deformation mechanisms were observed at lower Nb content in comparison to the conventionally fabricated materials. This made it possible to conclude that oxygen increases the stability of the beta phase in beta-Ti alloys. For the first time, superelasticity was observed in Ti-Nb-based alloys fabricated by the additive manufacturing method. The highest recoverable strain of 3% was observed in Ti-19Nb alloy as a result of high elasticity and reverse martensitic transformation stress-induced during the loading.