Forming quality optimization and microstructure analysis of multilayer coatings with laser powder-fed additive manufacturing.

To clarify the parameters interaction effects and improve the forming quality of Fe-Cr alloy multilayer laser powder-fed additive manufacturing (LPF-AM) on AISI 4340 substrate, experimental research for Fe-Cr alloy multilayer LPF-AM was carried out via the response surface method (RSM). The interaction effects and evolution rules of laser energy density (E), powder feed rate (Q), and Z -axis increment (h) on minimum cladding height, deposition efficiency and surface spheroidization defects were discussed. The multiobjective particle filter resampling particle swarm optimization (MORPSO) algorithm was adopted to optimize the processing parameters. The phase transformation, grain growth, and microhardness of multilayer LPF-AM were analyzed. The results showed that the powder feed rate and Z -axis increment were found to affect the minimum cladding height and deposition efficiency, respectively. Laser energy density played an essential role in spheroidization defects. The forming quality was significantly improved based on the optimal process parameters of E = 33 J/mm², Q = 0.5 g/s, and h = 0.8 mm. The primary and secondary remelting zones are fine equiaxed dendrites and irregular cellular structures, respectively, and the microstructure of the cladding tracks and layers showed a good metallurgical bonding. The microhardness of the cladding layer ranged from 321 ± 18 to 625 ± 24 HV_0.5, and the average microhardness is twice that of the AISI 4340 substrate. [ABSTRACT FROM AUTHOR]