Comparative study on microstructure and corrosion performance of 316 stainless steel prepared by laser melting deposition with ring-shaped beam and Gaussian beam

Compared with the Gaussian laser beam, the ring-shaped laser beam has the advantages of uniform energy distribution and small temperature gradient. During the laser melting deposition, the ring-shaped beam can produce smaller residual stress in the workpiece, meanwhile avoids excessive sintering and dilution, reduces the heat accumulation, refines the grain size and improves the surface quality of the coating. In this study, hollow-laser beam melting deposition with internal powder feeding (HLB-MD-IPF) and regular Gaussian beam were compared to explore the effect of laser beam shape on the quality of coatings. The microhardness and electrochemical corrosion performance of the 316 stainless steel coatings prepared by different processing parameters were studied. The intrinsic mechanism of the performance difference was analyzed through microstructure and element distribution, and compared with the traditional Gaussian beam. In HLB-MD-IPF, the maximum microhardness was obtained with laser scanning speed of 12 mm/s, powder delivery rate of 1.6 rpm and laser power of 700 W, respectively. The average microhardness of the coatings prepared by different processes was between 270 and 310HV0.2. It was found that the microhardness of the coating decreased with the coarsening of the microstructure. Our results showed that with the same processing parameters, the microstructure prepared by the HLB-MD-IPF was obviously finer than those obtained from the Gaussian beam.