Effect of laser scannings speed on microstructure, tribological and corrosion behavior of Ti-23Nb alloys produced by laser metal deposition

The effect of different laser scanning speeds on the microstructural evolution and associated tribological and corrosion behavior of Ti-23Nb alloys produced by laser metal deposition (LMD) was systematically investigated. The microstructures of all specimens were composed of equiaxed β grains, acicular α″ phases, and unmelted Nb particles. With the increase of scanning speed, the volume fractions of the α″ phase and unmelted Nb particle increased, while the volume fraction and grain size of the β phase decreased. This results in a high hardness (∼ 304 HV) for the specimen with a high scanning speed (2.6 mm/s). Although the hardness of the specimen produced at 2.0 mm/s is slightly lower (∼ 296 HV), it possesses less unmelted Nb particles (soft phases, low hardness of ∼ 107 HV), resulting in a lower wear rate (∼ 4.9 × 10⁻⁴ mm³N⁻¹ m⁻¹). Compared to fully alloyed areas, unmelted Nb particles corrode preferentially. The specimen produced at 2.6 mm/s possesses a lower corrosion potential (E_corr) value owing to the presence of more α″ phase and unmelted Nb particles. Grain size is a critical factor in determining the corrosion current density (i_corr). The high scanning speed specimen (2.6 mm/s) with small grain sizes has high resistance and low i_corr.