Papers by Keyword: Intermetallic Phase

Abstract: Aluminum alloys are widely used in automotive industry due to their low density and good corrosion resistance. This category includes alloys based on AlSiMg which are suitable for load bearing parts operating under higher temperatures. This paper deals with analysis of influence of deformation parameters and heat treatment on structure and mechanical properties of EN AW-6082 (AlSi1MgMn) alloy manufactured by horizontal cast module technology. Casted rods were used as a billet, which was formed to defined height by hot open-die forging. Subsequently the precipitation hardening was used as heat treatment. Changes in microstructure were evaluated based on the metallographic analyzes performed by light optical microscopy and scanning electron microscopy using an energy dispersive X-ray spectrometry and electron backscatter diffraction. Mechanical properties were determined by uniaxial tensile test and hardness testing. The results showed, that due to the process parameters, no significant structural changes were observed in the surface layer of forging. However, microstructure is significantly inhomogeneous in the core due to the dynamic softening processes. Mechanical properties are increasing which is significantly influenced by the type and distribution of precipitates emerging during the artificial aging.

Abstract: The results of studies of microstructure and of mechanical properties of the superalloy Udimet 720 in initial and aged states at various temperatures (850 °С, 1000 °С и 1200 °С) are presented in the paper. Mathematical processing methods were used during the analysis of morphological and geometric characteristics of strengthening phases in the alloy. Dependencies of mechanical properties indices on parameters of strengthening phases of the microstructure have been revealed. It has been found that the downtrend of strength and plastic characteristics of the alloy that was aged at high temperatures is due to changes in morphology and content of intermetallic phase.

Abstract: In this work, a ternary system prepared by Ni-Al-Ti mixed powder was synthesized using self-propagation high-temperature synthesis (SHS) process. The weight of the reactant was varied using 3%, 10%, 20% and 30% of the Ti content. The mixtures were compressed in a steel die to form compacted pellets, and subsequently ignited using an external heat source to initiate the combustion process. The synthesized products were characterized using SEM, EDS, and XRD, whereas the mechanical property of the product was measured using a Vickers microhardness test. The identification of the formed phase indicates that Ni-Al, Ti-Al and Ti-Ni systems were formed during the reaction. An increase of Ti content from 3% to 10% improves the density of the synthesized product. Further increase of Ti content to 20% results in the generation of cracks. The addition of Ti with 30% leads to the formation of a porous product. The heat released by the SHS process due to the formation of several intermetallic phases was responsible for the formation of defect products. The highest hardness of the product was achieved in the product prepared by 20% Ti content. However, the higher Ti content than 20% results in hardness reduction. This work shows that the content of 10% of Ti produced a dense and hard product.

Abstract: In the past decade, research into High Entropy alloys (HEAs) have gained significant attention due to their outstanding properties and approach to design alloys for high temperature applications. Strengthening of face centered cubic (FCC) based HEAs, by addition of intermetallic phase or precipitate forming elements is a very captivating direction of alloy designing for high temperature structural applications. However, the knowledge regarding the influence of intermetallic phases on the properties of FCC HEAs is rare. The current study focuses on annealing effects on the microstructure of Cr₂₀Co₂₀Fe₂₅Ni₂₅V₅Mo₅ (at. %) alloy, this alloy was synthesized using induction melting, and was homogenized at 1200 °C for 12h. X-ray diffraction analysis indicated that the principle phase was (FCC) identified. Scanning electron microscopy (SEM) together with Energy Dispersion X-ray Spectroscopy (EDS) showed that there is an additional phases that is Mo-rich. In order to understand the effect of the high temperature annealing on phase stability, the homogenized samples were annealed at 700 °C, 800 °C, 900 °C, 1000 °C each for 6h and quenched. The annealing treatments had considerable effect on the crystal structure and the elemental distribution. The Mo-rich phase is precipitated at the grain boundaries at all temperatures. Additionally, at 1000 °C annealing temperature Mo-rich phase had precipitated inside the grains. The lower annealing temperatures inhibited diffusion of Mo, which restricted the Mo-rich phase formation. Additionally, the hardness is increased to 195 HV at 1000 °C due precipitation hardening. At other annealing temperatures the hardness is reduced to 145 – 158 HV.

Abstract: Aluminum was composited with iron-base shape memory alloy (SMA) fiber. It is important to join between matrix metal and reinforced SMA fiber successfully. Matrix metal can obtain compressive residual stress caused by shape memory effect of SMA fiber without strong interface. In this study, aluminum matrix composite reinforced by iron-base SMA fiber was fabricated by Spark Plasma Sintering (SPS). At this method, sintering of hard-to-sinter materials (Al and Ti), junction of flame bonding materials is easy. The pure aluminum powder with iron-base SMA fiber was joined at 773K. As a result, intermetallic phase was formed at the interface between aluminum and iron-base SMA fiber and it was clarified that the interfacial strength depends on kind and thickness of intermetallic phase. This strong interface gives beneficial residual stress into aluminum from SMA fiber.

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.

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).

Abstract: Ultra-thin Cu/Al clad strip with 0.12 mm thickness was successfully fabricated by accumulative roll bonding and the interfacial structure of Cu/Al clad strip has been characterized by means of optical microscope (OM), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and also X-ray diffraction (XRD). The intermetallic phases and their formation sequence at the interface was experimentally verified. And the growth kinetics of each phase was also modeled considering the diffusion controlled reaction mechanism. The effect of interfacial compounds on tensile fracture of ultra-thin Cu/Al clad strip was also studied. The obtained results indicate that, intermetallic compounds formed in the interface region of ultra-thin Cu/Al clad strip within the experimental condition are confirmed to be Al₂Cu, Al4Cu9 and AlCu in sequence. The calculated activation energies for the growth of Al₄Cu₉, AlCu and Al₂Cu are 101.45、114.30 and 95.15 kJ/mol, respectively. The major cracks propagate through the AlCu intermetallic layer and the Al₂Cu / AlCu interface.

Abstract: The effect of the powder quantity on the effectiveness of the mechanical alloying process using different ductile powder systems was studied. X-ray diffraction, inductively coupled plasma-optical emission spectroscopy and energy dispersive x-ray spectrometry-scanning electron microscopy were the techniques employed to characterize the mechanically alloyed powders. Results showed that a same volume of powders, which represented different powder mass quantities for each system and composition, was used to mechanically alloy in an effective way in horizontal ball mills.

Abstract: Fusion welding of dissimilar metals is in the most cases difficult or even impossible as a result of different melting points and the development of undesirable brittle intermetallic phases. This often leads to joint strengths considerable below the tensile strength of the base materials. By using Friction Stir Welding (FSW) it is possible to reduce the development of the intermetallic phases of Al/Mg-joints significantly but not to avoid them completely. Hence a hybrid welding system at the WKK of the University of Kaiserslautern was developed called “Ultrasound Supported Friction Stir Welding (US-FSW)” with the aim to shatter the brittle interlayer lines and to scatter fragments in the welding area during the FSW process. Pre-investigations have shown that for Al/Mg-US-FSW-joints the strength can be increased up to 30% in comparison to conventional FSW. Moreover for the reliable detection of nonconformities in the weld during a post-process inspection by suitable non-destructive testing (NDT) methods is necessary. Also there is a strong need for better process monitoring and control by in-process NDT methods. Furthermore the corrosion behavior of the basic materials and hybrid-joints was investigated by electrochemical methods indicating an increased corrosion of the Mg alloy in the area of the Al/Mg-butt weld.