Improved molten-pool boundary stability and residual stress for microstructure control using additive manufacturing utilizing quasi-continuous-wave laser

Abstract

The development of dendrites and solidification textures in laser additive manufacturing is highly influenced by the shape and stability of the molten-pool interface. In this study, we demonstrate that QCW-LAM effectively enhances molten-pool border stability and promotes continuous epitaxial growth of columnar dendrites. We investigate how laser modes impact the stability of the molten pool and the resulting solidification microstructure during laser additive manufacturing of 316L steel. In contrast to CW-LAM, which displays a molten-pool boundary that fluctuates, QCW-LAM is distinguished by in-situ high-frequency reheating and a consistently stable molten-pool border. These features facilitate the directional growth of columnar structures by enabling sustained epitaxial columnar dendrite development. Changing the laser mode from continuous wave (CW) to quasi-continuous wave (QCW) at the same power lowered the greatest residual tensile stress by about 40 %, from 340 MPa to 205 MPa. What’s more, because of the mean ρ^GND of as-received for CW mode, as-received for QCW mode was 0.57 × 10¹⁴ m⁻²,0.94 × 10¹⁴ m⁻², separately, the results indicate an even higher yield strength in the as-receive QCW mode condition. This study provides new insights into controlling dendritic growth and mechanical behavior through improved molten-pool interface stability.