Dissimilar metals deposition by directed energy based on powder-fed laser additive manufacturing

摘要

In this research, powder-fed laser additive manufacturing based on directed energy deposition (DED) technology is utilized for 3D printing/fabrication of dissimilar alloy walls. Three-dimensional fabrication of metallic layers (A410-L stainless steel, A316-L stainless steel, and zirconium) with different crystallographic structures such as body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP) are studied. Solidification cracking of the HCP metal structure inhibits the manufacturing of a sound dissimilar wall during direct deposition of zirconium on stainless steel. Different techniques are employed to eliminate cracking during the deposition of such dissimilar walls. First, a functionally graded transition layer is employed to gradually transition from a BCC or FCC layer to a zirconium layer. However, several longitudinal and horizontal cracks are observed in the functionally graded structure, deteriorating the overall integrity of the wall. Subsequently, inter-layers are applied to reduce the metallurgical differences between the BCC, FCC, and HCP metal structures. These inter-layers are designed to suppress the formation of brittle intermetallic compounds and decrease the level of thermal stress leading to cracking. Several metallic powders including nickel, titanium, vanadium, and copper are tested and analyzed as inter-layer materials during layer by layer fabrication of the dissimilar wall. Cross-sectional examinations are performed for each case, in order to study the feasibility of fabricating a sound dissimilar wall without deleterious phases. Embrittlement and presence of nickel-rich intermetallics within the Zr matrix restricts the successful fabrication of a dissimilar alloy wall through the formation of vertical cold cracks. Samples with titanium and vanadium inter-layers demonstrate horizontal hot solidification cracking at the stainless steel interface, which is attributed to the large solidification temperature range. Nonetheless, best results are attained with the copper inter-layer due to its high compatibility with both of the stainless steel and Zr metals.