Control of thermal strain and residual stress in pulsed-wave direct laser deposition

•The temperature gradient and thermal strain show different characteristics in continuous-wave (CW) mode and pulsed-wave (PW) mode during laser additive manufacturing.•In the direct laser deposition process, residual stress was reduced by about 61% using PW laser mode.•The reduction of temperature gradient and stress release contributing to the reduction and homogenization of the residual stress in PW laser mode. Components manufactured by direct laser deposition (DED) are prone to produce excessive residual stress due to its rapid heating by laser and cooling. Excessive residual tensile stress leads to cracking of deposited sample, even cause failure to serve. Understanding thermodynamic behavior during processing is critical for controlling residual stress. In this study, in-situ transient strain and temperature gradient evolution of each layer on deposited sample 316L stainless steel thin wall during DED using both continuous-wave (CW) and pulsed-wave (PW) laser modes were emerged by digital image correlation (DIC) method and thermal imager. The longitudinal residual stress of deposited sample was evaluated using two laser modes. The results demonstrated that the PW mode creates a smaller temperature gradient and hence a lesser thermal strain than the CW mode. Furthermore, the cyclic thermal stress characteristics of PW mode was observed. All these factors contribute to the reduction of residual stress.