A new laser remelting strategy for direct energy deposition of 316L stainless steel

Abstract

At present, components produced by Direct energy deposition (DED) still have many shortcomings, such as rough surfaces, many internal pores, and the formation of long columnar grains that will lead to anisotropy due to large temperature gradients. Laser remelting (LR) is an effective method to improve the top surface quality and densification of samples. In the present work, in the process of manufacturing 316L stainless steel samples with DED, an additional LR process without powder conveying is added after each deposition layer of the samples is deposited. The smoothness of the sample surface has been greatly improved, and the density of the samples has been increased to nearly fully dense. The number and size of pores inside the samples are significantly decreased. By changing laser power and spot size, the effect of the LR process with different energy densities on microstructure and mechanical properties was studied. After the LR process, the coarse and long columnar grains in samples are transformed into fine equiaxed grains and fine columnar grains. Experimental results show that the LR process with appropriate energy density can reduce the residual stress of the samples made by DED and significantly improve the tensile strength and elongation of the samples. LR with the same processing parameters as the deposition has the most obvious effect on refining the microstructure and improving tensile properties. However, the LR process with low energy density will increase the residual stress of the sample, resulting in poor mechanical properties.