Modeling of Intermetallic Compounds Growth Between Dissimilar Metals

Abstract

A model has been developed to predict growth kinetics of the intermetallic phases (IMCs) formed in a reactive diffusion couple between two metals for the case where multiple IMC phases are observed. The model explicitly accounts for the effect of grain boundary diffusion through the IMC layer, and can thus be used to explore the effect of IMC grain size on the thickening of the reaction layer. The model has been applied to the industrially important case of aluminum to magnesium alloy diffusion couples in which several different IMC phases are possible. It is demonstrated that there is a transition from grain boundary-dominated diffusion to lattice-dominated diffusion at a critical grain size, which is different for each IMC phase. The varying contribution of grain boundary diffusion to the overall thickening kinetics with changing grain size helps explain the large scatter in thickening kinetics reported for diffusion couples produced under different conditions.

The Influence of Grain Structure on Intermetallic Compound Layer Growth Rates in Fe-Al Dissimilar Welds

“…A more physically realistic model for intermetallic layer growth in a reactive couple has been previously developed by Wang et al [8] and applied to the case of Al to Mg dissimilar joints, with good agreement to experimental results from annealing experiments. The Al-Mg couple also leads to the formation of a two-phase intermetallic layer structure, similar to the Al-Fe case.…”

“…The model properly accounts for the effect of the interfacial compositions on the layer growth, and the boundary conditions that are enforced at the interface between the phases involved. [8] Both grain boundary and lattice diffusion are also accounted for. This was shown to be essential in correctly capturing the growth kinetics in the Al-Mg system, since for the grain sizes typically encountered in the IMC layer, grain boundary diffusion generally makes a significant contribution to the overall solute flux.…”

“…The model used here has been previously applied to predict IMC formation in Al to Mg joints, [8] where an IMC bi-layer consisting of two phases with different thickening constants also forms. In this work, an identical approach was used, but the model parameters were recalibrated for the g and h phases that form in the present system, rather than the Grain boundary diffusion and the dynamic effect of grain growth in the IMC layer during thickening are included in the model.…”

Intermetallics formed at interface of ultrafine grained Al/Mg bi-layered disks processed by high pressure torsion at room temperature

“…Refs 6, 9, 10 and 16). Moreover, -Al 3 Mg 2 has been reported to grow faster and is thicker than -Mg 17 Al 12 [9,16]. The present unusual formation of intermetallic at the Al/Mg interface (a thin layer of only -Mg 17 Al 12 ) is attributed to the unique conditions created during HPT, e.g.…”

“…Amongst the Mg/Al composites fabricated through these techniques, a substantial variation in bonding quality and intermetallics formed at the interface is found. The intermetallics formed at the interface include -Mg 17 Al 12 , -Al 3 Mg 2 or both -Mg 17 Al 12 and -Al 3 Mg 2 , with thickness depending on bonding temperature and time [9,10]. The intermetallic type and its thickness may strongly influence the bonding quality as well as the properties of the composite.…”