Effects of laser melting+remelting on interfacial macrosegregation and resulting microstructure and microhardness of laser additive manufactured H13/IN625 bimetals. (November 2021)

• Record Type: Journal Article
• Authors: Shi, Qimin; Zhong, Gaoyan; Sun, Yi; Politis, Constantinus; Yang, Shoufeng
• Is Part Of: Journal of manufacturing processes. Volume 71(2021)
• Page Start: 345
• Page End: 355
• Publication Date: 2021-11
• Subjects: Selective laser melting -- Multi-material additive manufacturing -- Macrosegregation -- Microstructure -- Microhardness; Production management -- Data processing -- Periodicals; Manufacturing processes -- Periodicals; Procestechnologie; Productietechniek; Production -- Gestion -- Informatique -- Périodiques; Fabrication -- Périodiques; Manufacturing processes; Production management -- Data processing; Periodicals; 670.5
• DOI: 10.1016/j.jmapro.2021.09.036
• Languages: English
• ISSNs: 1526-6125

Abstract

Abstract: Macrosegregation at the interface in Multi-Material (MM) structures fabricated by Selective Laser Melting (SLM) has evidenced deleterious effects on interfacial bonding reliability, but its fundamental understanding is less revealed. Therefore, this work vertically prepared MM parts of H13 tool steel and IN625 superalloy by SLM, as an example, to explore the interfacial macrosegregation mechanism. According to the mechanism, a liquid layer of unmixed H13 can exist at the molten pool bottom due to the no-slip boundary condition in fluid mechanics and solidifies as an H13 macrosegregation beach. Considering the higher liquidus temperature of H13 (1483 °C) than IN625 (1300 °C), a region cooler than the H13 solidification temperature exists within the IN625 molten pool; therefore, when the melted but unmixed H13 liquid is entrained into the cooler region by fluid flows, it can solidify quickly, forming H13 macrosegregation peninsulas/islands. The laser melting+remelting strategy developed to mitigate interfacial macrosegregation reveals its significant contribution to efficient migration of H13 into IN625 molten pools in a layer-by-layer manner, forming a broad interface. As the direct reflection of interfacial macrosegregation, the microstructure experiences a cellular-columnar-cellular transition across the H13/IN625 interface. Even a peninsula with H13 microstructural features is observed in an IN625 molten pool, verifying the rapid solidification of intruded H13 in IN625. Finally, the microhardness values with varying standard deviations across the interface successfully evaluate the interfacial macrosegregation on a macro-scale. These results can provide theoretical support to mitigate interfacial macrosegregation and benefit the development of MM structures with good interfacial bonding reliability by SLM. Graphical abstract: Unlabelled Image Highlights: Explored interfacial macrosegregation in SLM-fabricated H13/IN625 bimetal parts. Proposed mechanisms behind H13 macrosegregation in IN625 molten pools. Laser remelting contributed to the mitigation of interfacial macrosegregation. Developed a broad interfacial region with mitigated macrosegregation. Macrosegregation is associated with microhardness and their standard deviations.