Effect of Si on the Growth Behavior of the Fe 2 Al 5 Phase at Al- x Si (liquid) /Fe (solid) Interface During Holding by
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The Al(liquid)/ Fe(solid) interface is commonly observed in the fabrication of bimetallic Al-Fe and hot-dip aluminizing.[1–3] When Fe is in contact with liquid Al, various hard and brittle intermetallic phases form at the interface due to the chemical reaction between the solid Fe substrate and the molten Al. After solidification, the Al/Fe joint presents a multilayer structure, consisting of an Al topcoat, a layer of intermetallic phases, and a partly consumed Fe substrate, among which the intermetallic layer plays a key role on the interfacial toughness and mechanical strength of the joint. Fe2Al5 and FeAl3 are the most commonly observed intermetallic phases at the Al (or its alloys)/Fe
NAIFANG ZHANG, QIAODAN HU, WENQUAN LU, ZONGYE DING, LIAO YU, XUAN GE, and JIANGUO LI are with the Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: [email protected] FAN YANG is with the School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: [email protected] SHENG CAO is with the School of Materials, The University of Manchester, Oxford Road, Manchester M13 9PL, UK. Manuscript submitted December 21, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
interface.[4–6] The Fe2Al5 layer is much thicker than the FeAl3 layer, indicating that the former is the dominant phase of the intermetallic compound (IMC) layer. The Fe2Al5 phase has a tongue-like morphology due to a large number of vacancies (about 30 pct) along the c-axis of its orthorhombic structure, as well as the stress field caused by the Fe fi Fe2Al5 transformation.[7] The tongue-like IMC leads to a reduced interfacial toughness of the joint, which is prone to crack during subsequent processing.[8] Furthermore, the irregular interface between the intermetallic layer and the Fe substrate induces a stress gradient, which impairs the thermal stability of the joint at high temperatures.[9] Previous studies suggest that a thin intermetallic layer with a flat interface is beneficial to an enhanced thermal stability and a high interfacial strength.[10,11] Microalloying is widely used to inhibit excessive growth of the IMCs.[12–15] For example, addition of Si to pure Al has been reported to reduce the thickness of the intermetallic layer at the Al/Fe interface significantly.[16,17] One explanation is that Si atoms can partly occupy the vacancies along the c-axis of the orthorhombic Fe2Al5 phase, which hinders the diffusion of Al and consequently inhibits the growth of the IMCs.[6,18] An alternative explanation is that addition of Si leads to the formation of a new ternary phase FexAlySiz,[18,19] which has a much lower growth rate than the Fe2Al5 phase and thus results in a thinner IMCs layer.[19] Komatsu et al.[20,21] propose that Si accelerates the dissolution of Fe rather than slows down the growth of Fe2Al5, which is opposed by Eggeler et al.[22] Solid conclusion on the role of Si on the g
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