Papers by Keyword: Intermetallic Phase

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Authors: Grazyna Mrówka-Nowotnik, Jan Sieniawski
Abstract: The main objective of this study was to analyze the evolution of the microstructure (morphology, composition and distribution of intermetallic phases) in the 2024 aluminium alloy cooled with different cooling rates after solidification process. A few techniques: optical light microscopy (LM), scanning (SEM) electron microscopy combined with an energy dispersive X-ray microanalysis (EDS), X-ray diffraction (XRD) were used to identify intermetallics in the examined alloy. The results show that the microstructure of 2024 aluminum alloys in as-cast condition consisted following intermetallic phases: Al2Cu, Al2CuMg, Al7Cu2Fe, Al4Cu2Mg8Si7, AlCuFeMnSi and Mg2Si.
Authors: D.L. Beke, Zoltán Erdélyi, G.L. Katona
Abstract: Two interesting features of formation and growth of intermetallic phases in nanoscale solid state reactions will be discussed:Linear-parabolic “normal” growth: it will be summarized that at the very early stages of the growth of an already existing new phase (i.e. when nucleation problems can be neglected) the linear kinetics can be observed due to the so-called diffusion asymmetry. Indeed, it was shown that if the ratio of the diffusion coefficients differ by orders of magnitude in the parent materials (and so also in the new phase), during the growth of a phase bordered by parallel interfaces from the parent phases (normal growth geometry), the shift of the individual interfaces can be linear at the beginning and a transition to the parabolic regime can take place even after a shift of several tens of nanometres. In addition, an AB compound in contact with the pure A and B phases can be dissolved if the diffusion in B is much faster than in either A and AB. This means that the thickness of this phase should decrease, or even can be fully dissolved, at the beginning and only after some time—when the composition in B will be high enough allowing the re-nucleation of this AB phase—will the AB phase grow further.The common problem of two stages of solid state reactions will be revisited: usually the growth can be divided into two stages: a) the formation (nucleation) and lateral growth of the new phases and b) the “normal” growth of the already continuous phase. It was concluded in different previous reviews that in stage b) in the majority of cases the parabolic growth was observed in accordance with the above i) point: the linear-parabolic transition length was typically below 1 μm, which was the lower limit of detection in many previous investigations. On the other hand recently the application of the linear-parabolic growth law for the analysis of experimental data obtained in nanoscale reactions became very popular, not making a clear distinction between a) and b) stages. It will be emphasized here that care should be taken in all cases when the experimental methods applied provide information only about the increase of the amount of the reaction product and there is no information where and how the new phase (s) grow. We have illustrated in a series of low temperature experiments - where the bulk diffusion processes are frozen - that even in this case a full homogeneous phase can be formed by cold homogenization called Grain Boundary Diffusion Induced Solid State Reaction (GBDIREAC). In this case first the reaction starts by grain-boundary (GB) diffusion and nucleation of the new phase at GBs or their triple junctions, then the growth of the new phase happens by the shift of the new interfaces perpendicular to the original GB. This is a process similar to the diffusion induced grain-boundary motion (DIGM) or diffusion induced recrystallization (DIR) phenomena and in this case the interface shift, at least in the first stage of the reaction until the parent phases have been consumed, can be considered constant. This means that the amount of the phase increases linearly with time, giving a plausible explanation for the linear kinetics frequently observed in stage a).
Authors: Miroslav Jáňa, Milan Turňa, Milan Marônek, Marcel Kuruc, Pavel Bílek
Abstract: Contribution deals with soldering of Mg alloy AZ31B by ternary solder ZnAl6Ag6 with ultrasonic support. Suggested solder has been analyzed from many aspects. Microstructure of solder consistutes of solid solution α-Al (FCC_Al), β-Zn (HCP_Zn) and intermetallic phases AgZn3 and AlAg3. Melting temperature of solder 386.8 °C has been determined by DSC analysis. Metallurgical process of ultrasonic soldering has run at 410 °C for 3 s. Soldered joint has been constituted by eutectic ternary structure β-Mg17(ZnAl)12, solid solution α - Mg, which contains Al and Ag elements. At solder-substrate interface, there has been formed intermetallic phase Mg2Zn11. The highest value of microhardness has been 260 HV. To predict lifetime of soldered joint, calculations in software Thermo-Calc has been performed.
Authors: Joerg Kaspar, M. Zimmermann, A. Ostwaldt, G. Goebel, J. Standfuß, B. Brenner
Abstract: The effective joining of aluminium with copper is one of the central technical goals involved in electro mobility. However, the joining of both metals by conventional fusion welding is challenging because of poor weldability arising from different chemical, mechanical and thermal properties of the materials and especially from the massive formation of hard and brittle intermetallic compounds (IMC) weld interface. In order to accomplish the difficult task of joining aluminium and copper several new joining technologies and strategies such as Laser Beam Welding (LBW) using highly dynamic beam deflection, Friction Stir Welding (FSW), Laser Induction Roll Plating (LIRP) and Electromagnetic Pulse Welding (EMPW) are under development at the Fraunhofer IWS. The current work describes the different technological approaches to the dissimilar joining of aluminium and copper. Thereby, the different joining technologies are compared with respect to weld quality. Special consideration is given to the study of interface morphology and microstructure of the welding zone. It will be shown that, depending on the joining method chosen the kind and extension of intermetallic phase formation differs considerably. Conclusions are drawn with respect to the applicability of the different joining methods.
Authors: Gang Sha, Keyna O'Reilly, Brian Cantor
Abstract: Intermetallic phases formed during directional Bridgman solidification of a 6xxx series Al alloy in the growth velocity range 5-120 mm/min have been characterised using conventional and high-resolution transmission electron microscopy. Cubic αc-AlFeSi and β-AlFeSi were always present in the alloy, but Al13Fe4 was only observed at 5mm/min and monoclinic αT-AlFeSi at 80 mm/min. Cubic αc-AlFeSi was observed to have a variety of morphologies resulting from flexibility in its growth mechanisms. β-AlFeSi with twins and faults showed strongly anisotropic growth by steps, resulting in its platelet morphology. Occasionally blocky β-AlFeSi particles were observed particularly at 30-60 mm/min, suggesting that other mechanisms could influence their morphology. Two types of composite particles, β-AlFeSi/Al13Fe4 and β-AlFeSi/cubic αc-AlFeSi, were observed in this alloy, and likely formed by two quasi-peritectic reactions.
Authors: M. Hofmann, S.J. Campbell, R.I. Smith, S.J. Kennedy, Xiao Li Zhao, A.V.J. Edge
Authors: J.L. Yu, Z.K. Li, Xin Zheng, H. Li, D. H. Wang, J. J. Zhang, H. Wang
Abstract: Mo-9Si-8B-3Hf alloy consisting of a Mo solid solution and intermetallic phases Mo3Si and Mo5SiB2 was fabricated by hot pressing sintering to yield a fine microstructure with all three phases being in the size range of micrometer. The tensile properties of this alloy at elevated temperature were evaluated in vacuum at elevated temperatures. This alloy displayed extensive plasticity or superplasticity at temperatures ranging from 1400 °C to 1560 °C with strain rate of 3×10-4 s-1. The tensile elongation of 410% is measured at 1560 °C. Grain boundary sliding is the main mechanism of plastic deformation for this alloy.
Authors: A. Gude, B. Sepiol, G. Vogl, Helmut Mehrer
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