Interfacial Characterization and Mechanical Properties of 6511SS/GH3536 Multi-material Based on Selective Laser Melting
Multi-material parts are promising for aerospace,biomedical and automotive applications due to their multi-functionality and environmental adaptability.Selective laser melting(SLM)technology is an effective way to fabricate multi-material parts.Since the material is deposited layer-by-layer in SLM,the interface characterization of the multi-materials directly determines the performance of the part.Therefore,the work aims to study the interfacial characterization and mechanical properties of multi-materials prepared by SLM.GH3536 alloy,as a solid solution strengthening nickel-based superalloy with the main strengthening elements of Cr and Mo,has the advantage of elevated-temperature strength.Stainless steel(SS)6511 has an excellent corrosion resistance.As a result,the multi-material part with 6511SS and GH3536 has a promising application in light water reactors,power and chemical plants and gas turbines.In the SLM of multi-materials,the material deposition sequences lead to the varied interface characterization,due to the effects of gravity and process parameters on melt pool formation and material diffusion at the interface.Therefore,in this study,multi-material samples of 6511SS/GH3536/6511SS sandwich structure were prepared by SLM to investigate the effect of material deposition sequence on the interfacial properties.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD)were used to study the interfacial microstructure and elemental distribution at 6511SS/GH3536 interface and GH3536/6511SS interface.The phase migration and grain morphologies at the interface were observed and analyzed.It was found that no obvious defects existed at both interfaces,indicating that 6511SS and GH3536 had a good metallurgical bonding.The optimal laser energy for 6511SS was 87.5 J/mm3,and for GH3536 was 57.1 J/mm3,respectively.Therefore,when 6511 SS was deposited on the GH3536,the melt pool depth was larger,leading to a larger interfacial diffusion zone,compared to the condition in which GH3536 was deposited on 6511SS.Marangoni convection were observed at both the 6511SS/GH3536 and GH3536/6511SS interfaces,which facilitated the mixing of different elements at the interface.Microhardness and tensile tests were used to characterize the mechanical properties of the interface.The hardness at the 6511SS/GH3536 diffusion zone was lower than that of 6511SS and higher than that of GH3536,while the hardness of the GH35636/6511SS diffusion zone was lower than that of 6511 SS and GH3536.The XRD results showed that no new phases were generated at the interfaces of 6511SS/GH3536 and GH3536/6511SS,and thus no brittle intermetallic compounds were formed.The decrease in hardness at the GH3536/6511SS interface was due to the intrinsic heat treatment generated by the high energy density of 6511SS.The tensile test results showed that the multi-material samples were fractured at GH3536 section.Even though the GH3536/6511SS interface had the lowest hardness,the strain-hardening behavior at this interface led to a high strength.Since the proportion of major deformed materials within the multi-material directly affected the elongation of the multi-material samples,the ultimate tensile strength was comparable to that of GH3536,and the elongation at fracture was lower than that of GH3536.This study demonstrates the feasibility of SLM preparation method for multi-material parts of stainless steels and superalloys,which provides guidance for multi-material parts fabrication by SLM.
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