Annular laser metal deposition of Ti-6Al-4V alloy in a semi-open environment: Process optimization, microstructure and mechanical properties

Laser metal deposition (LMD) in open environment is beneficial for the forming of large parts or the online repairing of damaged components. A major challenge in successful deposition of active materials is oxidation. The surface chromatic aberration is adopted to represent the oxidized discoloration. In this paper, response surface methodology (RSM) is used to obtain the process parameters of a single layer of Ti-6Al-4V alloy with low surface chromatic aberration in a semi-open environment, based on annular laser metal deposition (ALMD) process. The results show that low surface chromatic aberration is achieved by appropriately reducing laser power, and increasing powder feeding rate and shielding flow rate. There is good agreement between the predicted and experimental values. The desirability approach is employed for determining the optimal processing window to obtain the deposited layer less than surface chromatic aberration threshold of 5.09 based on oxygen concentration analysis. Furthermore, the microstructure and mechanical properties are investigated. The yield strength of 907 MPa and elongation of 6.5% are achieved at the optimum parameter settings. This study establishes a methodology towards successful deposition of Ti-6Al-4V alloy in a semi-open environment.