Microstructural morphology and evolution of austenite stainless steel deposited using pulsed laser and wire

A deposition process based on pulsed laser processing and wire feeding was employed in this study to fabricate high-performance components. The microstructural morphology and evolution of SUS304 austenite stainless steel were examined in detail. The thin wall and ladder block samples, considered as two representative structures of metal additive manufacturing, were deposited. It was found that the microstructure is homogeneous in all the deposited samples. For the thin wall, columnar grains, which are normal to the substrate with a growth tendency to the surface and scanning direction, dominate the deposition. Columnar grains along the cooling gradient and equiaxed grains are both observed in the surface. These different grain morphologies result in different microhardness values, and the microhardness in pulsed laser deposition is universally higher than that in a 304 cold rolling metal substrate. For the ladder block, columnar grains are observed along various directions. Further, it is found that the variation in the shape of the molten pools is an essential reason for the evolution of the microstructures with the addition of the deposited layers. It not only change the nucleation condition and cooling directions near the boundaries in the molten pools, but also leads to a recrystallization along the new cooling directions in the heat-affected zone.