Liquid Solid Diffusion (LSD) bonding: A novel joining technology

Dissolution and diffusion behavior of solid Mn in Mg melt

Off-eutectic Au–Ge, 10 ± 2 at.% Ge, were formed between Au metallized Si substrates to investigate their high temperature compatibility. High quality joints made with a small bond pressure, 53 kPa, were fabricated. The joints comprised three different types of morphologies; (1) a layered structure of Au / Au–Ge / Au, (2); a layered structure of Au / Au–Ge / Au where some sections of the central Au–Ge band were replaced by a Au section that extended across the joint, and (3); a roughly homogenous Au layer. Joints formed with a higher bond line pressure, 7.6 MPa, were of a reduced quality with voids and cracks at the original bond line. The shear strength of the fabricated joints was found to be at least 50 MPa, and the fracture mode was an adhesive fracture at the adhesion layer. The effective melting point were found to be at least 460 °C, or 100 °C above the eutectic isotherm of the binary Au–Ge system. Electrical resistivity measurements confirmed a melting process at the eutectic isotherm by an abrupt increase in resistivity.

Effect of assisted heating on microstructure, material flow and intermetallic formation during friction stir welding of copper alloy and AA 6063

Anomalous diffusion in liquids and the solid-liquid phase transition (melting) are studied in two-dimensional Yukawa systems. The self-intermediate scattering function (self-ISF), calculated from simulation data, exhibits a temporal decay, or relaxation, with a characteristic relaxation time. This decay is found to be useful for distinguishing normal and anomalous diffusion in a liquid, and for identifying the solid-liquid phase transition. For liquids, a scaling of the relaxation time with length scale is found. For the solid-liquid phase transition, the shape of the self-ISF curve is found to be a sensitive indicator of phase. Friction has a significant effect on the timing of relaxation, but not the melting point.

. Production efficiency as well as the reduction of energy consumption and waste are the main drivers for the improvement of large-scale production in chemical industry. In addition, the demand for new processes – these days especially related to the chemical energy conversion as basis for the Energiewende – are additional triggers for innovation. Catalysis, well recognized by the public e.g. in form of the 3-way automobile catalyst, plays an important role for about 90% of all processes in chemical industry. The development of new and improved catalysts is a challenge for chemists – as is the search for new structural materials for mechanical engineers. Due to the often-necessary noble and thus expensive metals (e.g. palladium) in many catalysts, structural and chemical function have been developed separately in the two communities. Recent progress in catalytically active materials allows replacing expensive noble metals in selected catalytic processes by significant cheaper elements [1]. This offers the new perspective to combine structural and chemical functionality by innovative materials. Within this area, intermetallic compounds with their peculiar combination of crystal and electronic structure [2], represent an interesting class of materials to address this vision as will be shown in the contribution.

New ultrasonic-assisted brazing technology was adopted to weld mini butt joint by SnBi composite solder with 1.5wt% Al 2 O 3 content and 0.5mm, 0.8mm and 1mm three kinds of copper substrate distance.The mechanical properties of the mini butt joint were characterized by means of the micro hardness tester and home-made micro mechanical test system.The microstructure of the samples were observed by scanning electron microscope, and the composition of intermetallic compounds was detected by the energy disperse spectroscopy.The results showed that the ultrasonic-assisted brazing method could promote the expansion of liquid solder on the substrate, improve the wettability, and full of the weld.With the increase of the substrate distance, the alloy microstructure refined, the IMC zone at the interface gradually had a tendency to grow thin, and improved the reliability of the solder joint.Near the composite solder was IMC Cu 6 Sn 5 , and the copper substrate was IMC Cu 3 Sn.Appropriate increase for the substrate distance will contribute to the micro hardness increase.

The microstructure of a bimetallic joint made by explosion welding of orthorhombic titanium aluminide (Ti-30Al-16Nb-1Zr-1Mo) with commercially pure titanium is studied. It is found that the welded joint has a multilayered structure including a severely deformed zone observed in both materials, a recrystallized zone of titanium, and a transition zone near the interface. Typical elements of the transition zone-a wavy interface, macrorotations of the lattice, vortices and tracks of fragments of the initial materials-are determined. It is shown that the observed vortices are formed most probably due to local melting of the material near the contact surface. Evidence for this assumption is deduced from the presence of dipoles, which consist of two vortices of different helicity and an ultrafine duplex structure of the vortex. Also, high mixing of the material near the vortex is only possible by the turbulent transport whose coefficient is several orders of magnitude larger than the coefficient of atomic diffusion in liquids. The role played by fragmentation in both the formation of lattice macrorotations and the passage of coarse particles of one material through the bulk of the other is determined.

A remarkable property of certain glass-forming liquids is that a fast mode of crystal growth is activated near the glass transition temperature Tg and continues in the glassy state. This growth mode, termed GC (glass-crystal), is so fast that it is not limited by molecular diffusion in the bulk liquid. We have studied the GC mode by growing seven polymorphs from the liquid of ROY, currently the top system for the number of coexisting polymorphs of known structures. Some polymorphs did not show GC growth, while others did, with the latter having higher density and more isotropic molecular packing. The polymorphs not showing GC growth grew as compact spherulites at all temperatures; their growth rates near Tg decreased smoothly with falling temperature. The polymorphs showing GC growth changed growth morphologies with temperature, from faceted single crystals near the melting points, to fiber-like crystals near Tg, and to compact spherulites in the GC mode; in the GC mode, they grew at rates 3-4 orders of magnitude faster with activation energies 2-fold smaller than the polymorphs not showing GC growth. The GC mode had rates and activation energies similar to those of a polymorphic transformation observed near Tg. The GC mode was disrupted by the onset of the liquid's structural relaxation but could persist well above Tg (up to 1.15 Tg) in the form of fast-growing fibers. We consider various explanations for the GC mode and suggest that it is solid-state transformation enabled by local molecular motions native to the glassy state and disrupted by the liquid's structural relaxation (the alpha process).

In-situ ash sintering process analysis during the co-combustion of the coal gasification fine slag and corn straw

<div class="section abstract"><div class="htmlview paragraph">A lightweight multi-material combination of steel and aluminium alloy (Al) is becoming a novel approach towards environmentally sustainable transport systems. Studies show that 10% reduction of vehicle weight results into 3-7% reduction in specific fuel consumption in IC engines and a 13.7% improvement in electric range for electric vehicles. However, dissimilar welding of Al/steel is a key challenge because of incompatible thermo-physical properties (melting point, thermal conductivity, and coefficient of thermal expansion) and low miscibility between Al and steel. The formation of brittle and hard Al-steel intermetallic compound (IMC) at the joint interface is the major concern for dissimilar welding of Al/steel. In this work, efforts are made to check the feasibility of Ni interlayer to control IMC formation at the interface of Al/steel dissimilar welded joint. Resistance spot welding is used to join low carbon steel CR01 and Al AA6061-T6 with pure Ni interlayer. Microstructure and IMC morphology of welded joints are investigated by optical and scanning electron microscope. The mechanical performance of welded joints is evaluated by tensile shear strength (TSS), failure energy and failure mode. Ni-interlayer does not have major effect on physical aspects of weld such as electrode indentation, Al thinning and steel bulging height. Two separate interfaces namely, Ni/Al and Ni/steel are formed with Ni interlayer. Higher amount of expulsion is taken place at the Ni/Al interface, resulting into lower TSS for dissimilar welding with Ni-interlayer compared to without interlayer.</div></div>

The application of electronic assemblies is moving more and more in the “high temperature” range. For instance the automotive industry needs electronic units near the engine with 150°C operating temperature and more. Because these temperatures are to high for common standard solder joints, the development of new materials and technologies is required. For the temperature region up to 150°C the use of special “reacting solders”, a mixture of different alloys, is possible. During the soldering process the powder mixture can react and form a strengthened solder joint, with a higher melting point and improved thermo-mechanical properties. The situation for operating temperatures higher than 200°C is completely different. For these applications normally solder alloys with a high lead content are preferred. Lead-free solder alloys with comparable melting temperatures are not announced today. A new alternative can be the combination of adhesive joints with solder joints, whereas the mechanical function will be realized mainly by the adhesive. In contrast the solder joints can operate even in the liquid state, whereby the mechanical stress in the components hardly disappears. Low melting solder alloys are preferred especially for such “liquid solder joints”. First applications for this new joining technology are under test today.

Solid-state joining of thick section aluminum to steel plate has been achieved using a new process called friction stir dovetailing (FSD). In FSD, a custom designed pin tool is used to flow a lower melting point material (AA6061) into dovetail grooves machined into the surface of an underlying material that has a higher melting point (rolled homogeneous armor [RHA]). Repeating dovetails form a mechanical interlocking structure akin to metallic Velcro. In this study, 38.1 mm (1.5 in.) thick AA6061 was joined to 12.7 mm (0.5 in.) thick RHA plates. The effectiveness of FSD is demonstrated through tensile test data that shows specimens failing in the processed aluminum rather than at the joint interface. Numerical simulations that highlight the importance of optimizing dovetail geometry are presented. The effect of process parameters on joint strength and microstructure also are discussed.

The alloys of magnesium and cadmium are of great interest, since both metals have the same valency, and almost the same atomic volume, but the axial ratios of their close-packed hexagonal structures differ markedly, being 1.885(2) for cadmium, and 1.6237 for magnesium. The equilibrium diagram of the system has always attracted great interest, and very conflicting results have been obtained by different investigators. The earlier investigations led to the conclusion that the liquidus and solidus curveswere very close together, and fell continuously from the melting point of magnesium to that of cadmium, so that, at the higher temperatures, a continuous solid solution was formed, which, at low temperatures, under­went a transformation in the region of 50 atomic % of cadmium, owing to the supposed existence of a compound MgCd. The work of Hume-Rothery and Rowell (1927) confirmed the existence of this transformation, and later work (Grube and Schiedt 1930; Dehlinger 1930; Riederer 1937) showed that this transformation corresponded to the formation of a superlattice based on the composition MgCd, and that at low temperatures two other super­lattices, based on the compositions MgCd 3 and Mg 3 Cd, were also formed. These low temperature transformations were securely established, and all investigations indicated the existence of wide solid solutions in both magnesium and cadmium, but the remainder of the system has been in great dispute. According to Hume-Rothery and Rowell, magnesium could hold approximately 60 atomic % of cadmium in solid solution, and cad­mium could dissolve approximately 24 atomic % of magnesium, whilst, between these two solid solutions, a compound MgCd 2 of fixed composition was formed by a peritectic reaction. Grube and Schiedt (1930) qualita­tively confirmed the limits of the primary solid solutions, but not the existence of the compound MgCd 2 , and, apart from the superlattice trans­formations, their equilibrium diagram showed the two primary solid solutions separated by a two-phase region. Dehlinger (1930) stated that his X-ray investigations confirmed the diagram of Grube and Schiedt, but a careful examination of his powder photographs shows that they are really inconclusive, since, with varying compositions, lines appear and disappear in a way which is consistent with the existence of MgCd 2 . Riederer (1937) concluded that the diagram of Hume-Rothery and Rowell represented stable equilibrium, and that of Grube and Schiedt metastable equilibrium. The present investigation has succeeded in explaining these apparent inconsistencies, and has also shown interesting relations between the two types of crystal structure, which may be interpreted in terms of the Brillouin zone theories.

Phase relations in the Na2MoO4–Cs2MoO4 and Na2MoO4–Cs2MoO4–ZnMoO4 systems, crystal structures of Cs3Na(MoO4)2 and Cs3NaZn2(MoO4)4

Here, the petrological features of numerous primitive achondrites and highly equilibrated chondrites are evaluated to review and expand upon our knowledge of the chondrite–achondrite transition, and primitive achondrites in general. A thermodynamic model for the initial silicate melting temperature and progressive melting for nearly the entire known range of oxidation states is provided, which can be expressed as Tm = 0.035Fa2−3.51Fa + 1109 (in °C, where Fa is the proportion of fayalite in olivine). This model is then used to frame a discussion of textural and mineralogical evolution of stony meteorites with increasing temperature. We suggest that the metamorphic petrology of these meteorites should be based on diffusive equilibration among the silicate minerals, and as such, the chondrite–achondrite transition should be defined by the initial point of silicate melting, not by metal–troilite melting. Evidence of silicate melting is preserved by a distinctive texture of interconnected interstitial plagioclase ± pyroxene networks among rounded olivine and/or pyroxene (depending on ƒO2), which pseudomorph the former silicate melt network. Indirectly, the presence of exsolution lamellae in augite in slowly cooled achondrites also implies that silicate melting occurred because of the high temperatures required, and because silicate melt enhances diffusion. A metamorphic facies series is defined: the Plagioclase Facies is equivalent to petrologic types 5 and 6, the Sub‐calcic Augite Facies is bounded at lower temperatures by the initiation of silicate melting and at higher temperatures by the appearance of pigeonite, which marks the transition to the Pigeonite Facies.