In-situ control of residual stress and its distribution in a titanium alloy additively manufactured by laser powder bed fusion

Remarkable residual stress is commonly present in metal components produced by laser additive manufacturing due to the inherent rapid heating/cooling rate and high temperature gradient. This is especially true in the laser powder bed fusion (LPBF) process, whereas solid-state phase transformation further adds to its complexities. This work presents the strategies for in-situ controlling the magnitude and distribution of residual stress by regulating layer thickness, preheating temperature, and scanning strategies in LPBF of Ti-6Al-4V alloy. A combination of characterization techniques was used for revealing the residual stress from mesoscale to microscale, measured in millimeters and micrometers, respectively. By manipulating the thermal gradient and heat accumulation in the LPBF process, the residual stress was altered from an inhomogeneous distribution with a local value of up to 600 MPa, to a relatively flat distribution below 100 MPa. This in-situ control method significantly reduced the stress concentration to a level equivalent to the effect of stress-relieving treatment. The findings from this work provide an effective approach for in-situ stress reduction during LPBF, which is critical for the fabrication of large-scale or complicated-shape metal components.