Abstract
In this paper, 316 L stainless steel were fabricated by direct laser deposition (DED) using both continuous-wave (CW) and pulsed-wave (PW) laser modes. Effects of laser modes on residual stress, geometric dislocation density (GND) and solid phase transformation with a given heat energy input were investigated. Results showed that PW mode tends to generate less concentrated, lower residual stress than that CW mode does, which the decline range was reached about 42% at the joint of the deposition and the substrate and approximately 75% on the deposition respectively. This is determined by the process characteristics of PW mode. Firstly, the relatively small temperature gradient in PW mode directly causes small thermal stress. Secondly, the characteristic of periodic temperature history and an improved cooling rate of molten pool in PW mode leads to more thermal stress relaxation. The released thermal stress can be used as a driving force for the formation of dislocations at grain boundaries. In addition, solid phase transformation does not occur with PW mode, which has little contribution to the reduction of residual stress.
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