An Interface-Enriched eXtended Finite Element-Level Set Simulation of Solutal Melting of Additive Powder Particles durin
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TRODUCTION
ADVANCED alloy design and improved solidification processing techniques have resulted in the development of single crystal (SC) precipitation strengthened nickel (Ni)-base superalloys with remarkable elevated temperature properties for producing a new generation of aero-engine components required for higher engine efficiency and lower greenhouse emissions. However, the development that has occurred with SC aerospace superalloys in the past two decades has not been matched by adequate understanding of appropriate techniques for joining these materials without deleterious stray-grains formation. Joining is not only essential for the economical manufacturing of complex shaped engine components, but also vital for the repair and refurbishment of service-degraded aero-engine parts. SC precipitation strengthened Ni-base superalloys are extremely difficult to join by conventional fusion welding processes due to their high susceptibility to cracking during welding and post-weld thermal treatments.[1,2] Transient liquid phase (TLP) bonding, also known as diffusion brazing, has evolved as an attractive alternate technique for joining the difficult-to-weld SC superalloys and other structural alloys.[1–5] In TLP bonding, an interlayer material that contains melting-point depressing (MPD) solute and sandwiched A. GHONEIM, Research Associate, J. HUNEDY, Graduate Student, and O.A. OJO, Associate Professor, are with the Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, MB R3T 5V6, Canada. Contact e-mail: olanrewaju.ojo@ ad.umanitoba.ca Manuscript submitted March 24, 2012. Article published online October 17, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
between two substrates melts at the bonding temperature and rapidly attains equilibrium through liquidphase dissolution of the base-material into the molten interlayer alloy. This is succeeded by isothermal solidification of the liquated insert by solid-state diffusion of the MPD solute away from the liquid into the solid substrates. An approach that has been found effective for reducing the liquid-phase dissolution of the basematerial, which is also known as liquid-metal erosion, during TLP bonding, involves the use of a powder mixture as the interlayer material. The powder mixture consists of regular TLP bonding filler alloy powder that contains the MPD solute and an additive powder alloy that is essentially free of the MPD solute, usually the base-alloy powder. Aside from reduction of substrate liquid-phase erosion, the use of the powder mixture as the interlayer material enables the desirable enrichment of the TLP joint region with the base-material alloying element for enhanced joint properties. Unfortunately, the beneficial powder mixture has been generally considered unsuitable for joining SC superalloys, due to the formation of stray-grains within the joint region, which compromises the properties of bonded SC materials. The stray-grains are formed when additive powder particles (APPs) are partially melted by the liquated filler alloy
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