Search

The micro-segregation in the as-cast AA6082 aluminium alloy were investigated across a range of length scales using a combination of analytical electron microscopes. It is found that the micro-segregation bands form an inter-connected network following grain boundaries and inter-dendritic channels. The micro-segregation can be divided into major micro-segregation and minor micro-segregation; the former is mainly on the grain boundaries consisting of iron-bearing intermetallic; the latter occurs both, along the grain boundaries and inter-dendritic channels, consisting mainly of Mg and Si alloying elements. The atomic-scale imaging reveals that in the minor-segregation bands, the supersaturated solute concertation has formed precipitates that had either nucleated heterogeneously on the dislocation network or homogeneously inside the aluminium matrix. The heterogeneously nucleated precipitates in the dislocation lines are composed of a mixture of phases down the precipitation sequence meanwhile, the homogenously grown ones are discrete phases that appear at the early stages of the precipitation sequence. [ABSTRACT FROM AUTHOR]

Bonding interactions and spin-orbit coupling in the topological insulator SrAg4 Sb2 are investigated using DFT with orbital projection analysis. Ag-Ag delta bonding is a key ingredient in the topological insulating state because the 4dxy+4dx2-y2${4d_{xy} + 4d_{x^2 - y^2 } }$ delta antibonding band forms a band inversion with the 5 s sigma bonding band. Spin-orbit coupling is required to lift d orbital degeneracies and lower the antibonding band enough to create the band inversion. These bonding effects are enabled by a longer-than-covalent Ag-Ag distance in the crystal lattice, which might be a structural characteristic of other transition metal based topological insulators. A simplified model of the topological bands is constructed to capture the essence of the topological insulating state in a way that may be engineered in other materials.

The ternary solid solution Na2Ga7−xInx (x≤0.25) was synthesized by annealing the elements at 300 °C in sealed Ta ampoules. Differential thermal analysis (DTA) indicated incongruent phase formation. The peritectic temperature ranges from 501(2) °C (x=0) to 474(2) °C (x=0.25). In addition, the unit cell parameters increase significantly with In content. At its maximum of x=0.25, the unit cell volume increases by 1 % compared to Na2Ga7. The In positions are deduced from single‐crystal X‐ray diffraction data obtained for the composition Na2Ga6.95In0.05 (space group Pnma; Z=8; a=14.876(3) Å, b=8.688(2) Å, c=11.605(4) Å). In the crystal structure of Na2Ga7, which consists of Ga12 icosahedra and 4‐bonded Ga atoms, the In atoms solely substitute the latter. The Na atoms are located in the channels and cavities of the framework. The phase is electron‐precise and can be considered a Zintl‐Wade compound with the formula unit [Na+]16[(12b)Ga122−]4[(4b)Ga−]7.6[(4b)In−]0.4. [ABSTRACT FROM AUTHOR]

The ternary solid solution Na2Ga7−xInx (x≤0.25) was synthesized by annealing the elements at 300 °C in sealed Ta ampoules. Differential thermal analysis (DTA) indicated incongruent phase formation. The peritectic temperature ranges from 501(2) °C (x=0) to 474(2) °C (x=0.25). In addition, the unit cell parameters increase significantly with In content. At its maximum of x=0.25, the unit cell volume increases by 1 % compared to Na2Ga7. The In positions are deduced from single‐crystal X‐ray diffraction data obtained for the composition Na2Ga6.95In0.05 (space group Pnma; Z=8; a=14.876(3) Å, b=8.688(2) Å, c=11.605(4) Å). In the crystal structure of Na2Ga7, which consists of Ga12 icosahedra and 4‐bonded Ga atoms, the In atoms solely substitute the latter. The Na atoms are located in the channels and cavities of the framework. The phase is electron‐precise and can be considered a Zintl‐Wade compound with the formula unit [Na+]16[(12b)Ga122−]4[(4b)Ga−]7.6[(4b)In−]0.4. [ABSTRACT FROM AUTHOR]

A silver solid amalgam electrode modified with mercury meniscus (m‐AgSAE) was used as a non‐toxic replacement of mercury electrodes in the voltammetric determination of genotoxic environmental pollutant 4‐nitroindane (4‐NI). The m‐AgSAE was used to characterize of the overall electrode process during the 4‐NI conversion using cyclic voltammetry (CV), and it was shown that the electrochemical reduction of 4‐NI is an irreversible process controlled by both diffusion and adsorption. Techniques of direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at the m‐AgSAE were optimized for the development of a method for the sensitive determination of 4‐NI. The application of the more convenient DPV method was proven on authentic drinking and river water samples. Limits of quantification (LQs) obtained under the following optimal conditions were 0.1 μmol L−1 for DCV at the m‐AgSAE (Britton‐Robinson (BR) buffer pH 5.0–methanol (1 : 1); regeneration potentials E1,reg=−200 mV, E2,reg=−1100 mV) and 0.1 μmol L−1 for DPV at the m‐AgSAE (BR buffer pH 9.0–methanol (1 : 1); regeneration potentials E1,reg=−300 mV, E2,reg=−1300 mV). An attempt to decrease the LQ of the 4‐NI determination by differential pulse adsorptive stripping voltammetry at the m‐AgSAE was not successful. The LQs for DPV at the m‐AgSAE in authentic samples of drinking and river water were 1.0 μmol L−1 and 2.0 μmol L−1 (BR buffer pH 9.0–drinking or river water (1 : 9); regeneration potentials E1,reg=−300 mV, E2,reg=−1300 mV), respectively. [ABSTRACT FROM AUTHOR]

Bonding interactions and spin‐orbit coupling in the topological insulator SrAg4Sb2 are investigated using DFT with orbital projection analysis. Ag−Ag delta bonding is a key ingredient in the topological insulating state because the 4dxy+4dx2-y2 ${4d_{xy} + 4d_{x^2 - y^2 } }$ delta antibonding band forms a band inversion with the 5 s sigma bonding band. Spin‐orbit coupling is required to lift d orbital degeneracies and lower the antibonding band enough to create the band inversion. These bonding effects are enabled by a longer‐than‐covalent Ag−Ag distance in the crystal lattice, which might be a structural characteristic of other transition metal based topological insulators. A simplified model of the topological bands is constructed to capture the essence of the topological insulating state in a way that may be engineered in other materials. [ABSTRACT FROM AUTHOR]

First-principles calculations based on density functional theory (DFT) were employed to investigate the Tb-Ni binary system, and its thermodynamic characterization was reassessed utilizing the CALPHAD (CALculation of PHAse Diagram) methodology. The liquid solution is described by the Redlich-Kister polynomials model, while the binary compounds are treated as stoichiometric phases. The predicted formation enthalpies of all intermediate compounds in the Tb-Ni binary system were used to support the optimization. Leveraging the Thermo-Calc software, a self-consistent set of thermodynamic parameters was obtained. The calculated phase diagram aligns well with experimental phase equilibrium data from the literature, and the resulting thermodynamic properties exhibit greater reasonability. The trend in thermodynamic information across rare earth (RE)-Ni systems is highlighted, showing that with an increase in the RE atomic number, both the enthalpies of mixing of liquid alloys and the enthalpies of formation of intermetallic compounds become more negative. [ABSTRACT FROM AUTHOR]

The further developments of additive manufacturing (AM) provides a possibility for Ti6Al4V and its functionally graded materials (FGMs), but limits further applications due to its low ductility, low microhardness and poor wear resistance. The key lies in the presence of microstructures such as epitaxial columnar β-grain orientation and heterogeneous phase distribution in AM Ti6Al4V, as well as the interfacial bonding problems (intermetallic phases, delamination, cracking) in AM Ti6Al4V FGMs. In order to address these fundamental intra and inter-layer problems, firstly the microstructure and phase evolution process of AM Ti6Al4V columnar-to-equiaxed transformation (CET) promoted by some alloying strategies was summarized in this paper according to alloying elements and reinforcing particle types. Subsequently, controlled changes in the composition and microstructure of AM Ti6Al4V FGMs were achieved by adding interlayers/introducing gradient interfaces, and the metallurgical reactions and phase transformation mechanisms that inhibit the formation of intermetallic compounds and interfacial defects were explored. Finally, the difficulties and future research directions for alloying strategies to achieve high strength and ductility of AM Ti6Al4V were presented. This review aims to improve the reliability of AM Ti6Al4V and its FGMs for applications in critical load-bearing structures through in-situ alloying and multi-material for the microstructure design of AM Ti6Al4V.

Titanium alloys have been gaining importance in various industries due to their advantageous combination of strength, low density, excellent corrosion/oxidation resistance, and superior mechanical properties at elevated temperatures. Recently, eutectoid Ti–Cu alloys have been explored as promising candidates for advanced processes. This work investigates the effects of Fe and Al on a Ti-5.9Cu alloy using multi-scale characterization techniques. While Fe acts as a β-stabilizing element (despite being a sluggish eutectoid former), Al acts as an α-stabilizer. This work focuses on the effects of combined addition of these elements, studied in different heat treatment conditions. The results show that a fine, equiaxed microstructure is obtained in the binary Ti-5.9Cu alloy, whereas the addition of 2 wt% Fe, or 2 wt% Fe combined with 2 wt% Al to the Ti-5.9Cu alloy deteriorates the effect of grain refinement and coarse, columnar grains result and a small amount of β-phase is retained. Further, the microstructure resulting from the eutectoid decomposition is altered dramatically from a lamellar pearlitic in the binary alloy to a lath-like α-phase with diverse decomposition products in the ternary and quaternary alloys accompanied by increasing hardness values. Evaluation of the α misorientation suggests that a substantial amount of non-Burgers α is present in the Ti-Cu alloy in contrast to the results of the ternary and quaternary alloys. The observed Cu-rich intermetallic compound was identified as Ti2Cu phase with off-stoichiometric composition. Results obtained explain how adding either Fe or Fe and Al leads to substantial hardening.

Aluminum‐based glassy alloys and composites exhibit more than two times higher tensile and compressive strength and superior corrosion resistance compared to the conventional Al alloys. However, the low glass‐forming ability (GFA) of Al‐based glass‐forming compositions restricts the synthesis of large dimension Al‐based amorphous alloys. In contrast, powder metallurgy route leads to synthesis of higher‐dimension Al‐based metallic glasses and composites. A detailed review on the efforts made to improve the dimension and mechanical properties of the Al‐based glassy alloys and composites is essential to further develop these materials for industrial applications. Researchers aspiring to develop high‐strength light‐weight materials can be benefited from such a detailed review on Al‐based amorphous alloys and composites. In this review article, a holistic approach is made to understand the GFA, crystallization behavior, corrosion resistance, and mechanical and electronic properties of Al‐based glassy alloys and composites. The effects of various alloying elements on GFA and criteria to optimize Al‐based glass‐forming alloy composition are discussed. The crystallization behavior is discussed with phase‐separation and quenched‐in nuclei models. The effects of various crystalline phases in the amorphous matrix on corrosion resistance and mechanical and electronic properties are discussed in detail. [ABSTRACT FROM AUTHOR]

This article presents the results of a study to identify intermetallic phases whose role is to limit austenite grain growth in the low-pressure carburizing process. A drawback of high-temperature low-pressure carburizing is the austenite grain growth during the process. Using low-pressure carburizing with pre-nitriding technology (PreNitLPC®) offers the possibility of reducing austenite grain growth. This technology involves the application of doses of ammonia during the heating stage of the steel, at the carburizing temperature, to introduce nitrogen into the surface layer of the steel and to form nitrides. It is these phases that cause restrictions on austenite grain growth during carburizing. The research carried out in this article was aimed at identifying these phases. The research was carried out on one of the basic steels used for carburizing—16MnCr5 steel. The carburizing of this steel with and without pre-nitriding was performed, followed by an evaluation of the austenite grain size after these processes and the identification of the intermetallic phases present in the surface layer of the steel. [ABSTRACT FROM AUTHOR]

In this study, aluminum–magnesium (Al-Mg) bulk porous materials were fabricated by using uniaxial hot pressing to control the porosity rate of the material over a wide range (up to 50%). The fabricated materials were analyzed by X-ray diffraction and scanning electron microscopy. The results demonstrated the appearance of intermetallic (IM) phase Al3Mg2, and its quantity increased with the applied pressure. In the context of the decline of global fossil fuel reserves, the revalorization of these materials by hydrogen (H2) production was investigated. Hydrolysis of the Al-Mg materials was carried out in a simulated seawater solution (aqueous solution of sodium chloride 35 g/L). The results showed the role of the porosity rate in the H2 production properties of the fabricated materials; the increase of porosity rate from 10% to 50% cuts the reaction time in half. Finally, the role of IM phase Al3Mg2 in H2 production was highlighted through galvanic coupling. [ABSTRACT FROM AUTHOR]

Nickel-based filler metals are frequently used in high temperature vacuum diffusion brazing for austenitic stainless-steel joints when components are subjected to high static or dynamic loads, corrosive environments and elevated temperatures. Due to melting point depressing metalloids such as silicon and boron, hard and brittle intermetallic phases are formed during the brazing process depending on the diffusion mechanisms. These brittle phases significantly affect mechanical and corrosive properties of the compounds. To quantify the influences of their amount, morphology and distribution, deep learning image segmentation was applied to segment these phases of the athermal solidification zone and the diffusion zone. Subsequently, characteristic microstructure parameters were calculated from these. The parameters of six different brazed joint variations were compared with their experimental characterization of mechanical and corrosive properties so that several correlations could be identified. Finally, a layer-by-layer removal of a brazed joint was performed using a focused ion beam, and a 3D model was reconstructed from the generated images to gain a mechanism-based understanding beyond the previous 2D investigations.

The importance of duplex stainless steel in the global steel industries takes from its application because of its utilization in the environment, the paper industries, and pipelines and reactions champers found in the gas, oil, and chemicals industries. This research investigates the effect of various heat treatment cycles on the intermetallic compound precipitation and different constituents' evolution of the AISI 329 steel. Also, this investigation aims at exploring the relationship of the microstructure evolution at various heat treatment cycles and its effect on the tensile properties of selected steel. The phase transformation studies were conducted theoretically utilizing the JMatPro program and experimentally employing differential scanning calorimetry tests and dilatation; the obtained microstructure was inspected by exploiting a light metallographic microscope, a field-emission scanning electron microscope, and x-ray diffraction. The results illustrated that the microstructure includes ferrite, austenite phases, and dispersive particles. The dispersive particles are carbide particles and intermetallic compounds. Furthermore, the sigma phase settled at the boundaries of the ferrite grains. Intermetallic compounds were observed in both cast and heat-treated steel microstructures. Observed intermetallic compounds have no specific engineering geometry with various sizes, and the main alloying elements are Cr, Fe, and Mn. Special heat treatment, including solid solution and aging at high temperatures, leads to thinning of the sigma phase while diminishing the size of the intermetallic compound. Tensile properties were enhanced by controlling the volume fraction of different constituents that are adjusted by heat treatment. The fracture morphology is consistent with the microstructure and tensile properties of the investigated steel. [ABSTRACT FROM AUTHOR]

Black needle‐shaped crystals of the bismuth‐rich mixed halogenide Bi21Rh4Cl6I7 were obtained by slow cooling of a melt of Bi, RhI3 and BiCl3. Single‐crystal X‐ray diffraction revealed an orthorhombic structure that consists of infinite intermetallic rods ∞1[ ${{}_{\infty }{}^{1}[}$ Bi9Rh2]3+ and discrete anionic groups [BiII2Cl2I5]3− and [BiIIICl4I2]3−. The rods consist of Rh‐centered [RhBi8] polyhedra that alternately share triangular and rectangular faces. Using traditional electron counting rules, the rod can be interpreted as a covalent polymer with Rh2 dumbbells bonded to molecular Bi2 and Bi5 units. However, a quantum‐chemical bonding analysis shows that the bonds involving Rh atoms are largely diffuse, while two‐center bonds dominate in the bismuth units. The below 240 K observed semiconducting behavior of Bi21Rh4Cl6I7 is consistent with a complete localization of the valence electrons. Above 240 K, the resistance along the needle axis is largely independent of temperature. [ABSTRACT FROM AUTHOR]

The Zintl–Klemm idea is a remarkable formalism that can guide us through the crystal structure–electronic structure relationships of solids showing a particular correlation between charge transfers, (8–N) rule and the corresponding structural fragments. Accordingly, this approach has been applied to interpret the relationships between the crystal and electronic structures for numerous intermetallics; yet, are all of these applications of the Zintl–Klemm idea indeed helpful? To answer this question, quantumchemical means were used to explore the electronic structures of three prototypical intermetallics, i.e. LiY2Si2, Sc2Si2Al, and Y2Pd2In. These compounds crystallize with the Mo2FeB2 type of structure whose structure model may be derived from that of the widely encountered U3Si2‐type. The explorations of the electronic structures included examinations of the Mulliken charges, the projected crystal orbital Hamilton populations (pCOHP), the recently introduced crystal orbital bond indices (COBI) and the respective integrated pCOHP as well as COBI values (IpCOHP and ICOBI). The outcome of these investigations indicates that widely diverse types of bonding are evident for the inspected intermetallics so that the predictive power of the Zintl–Klemm idea is limited. [ABSTRACT FROM AUTHOR]

Like many complex intermetallic phases, the crystal structures of REZn5+x compounds (RE = lanthanide or Group 3 element) based on the EuMg5 type have gradually unfolded. The original reports described a complex hexagonal structure with an unusual combination of tetrahedrally close‐packed regions and open spaces, as well as observations of superstructure reflections. More recently, we reinvestigated the structure of YZn5, reclassifying it as the EuMg5+x‐type compound YZn5+x (x≃0.2), in which disordered channels run along c through the spaces formerly considered open. In addition, DFT‐chemical pressure (DFT‐CP) analysis of ordered models of YZn5+x highlighted paths for communication between neighboring channels setting the stage for superstructure formation. Herein, the experimental elucidation of this effect is presented with the synthesis and structure determination of a modulated form of YZn5+x. By slow‐cooling samples of YZn5+x from the annealing temperature, crystals were obtained that exhibit satellite reflections with the modulation wavevector q = a* + b* + 0.3041c*. Structure solution and refinement using a (3+1)D model in superspace group P31c(σ3)00s reveals incommensurate order in the structure's channels. Here, two Zn sites associated with the channels are present, each with discontinuous atomic domains that are slanted in the x3x4 plane. Their slanting corresponds to adjustments along the c axis for the presence or absence of close neighbors along that axis, while the occupation patterns of neighboring channels are shifted by of the modulation period. These features follow earlier predictions from CP analysis, highlighting how this approach can be used predictively in search of new phenomena. [ABSTRACT FROM AUTHOR]

The object of this study is the formation of intermetallic phases (IMPhs) in the heat-affected zone (HAZ) of joints of steel–titanium bimetal plates produced by arc welding. A titanium layer (2 mm) was welded by the plasma method (PAW), a barrier layer of Cusi3Mn1 bronze was deposited on it by the TIG method, the first steel layer was deposited by CMT, and Puls-MAG was used for filling the groove. Here, heating in the solid phase takes place in the HAZ, which may lead to undesirable formation of brittle IMPhs and further welded joint failure. Mathematical modeling was performed and metallurgical features formed during the processes of heating of the HAZ in bimetal steel–titanium plates were studied to identify the risk of IMPh formation. It was found that at a temperature increase from 900 to 1450 °C, a continuous intermetallic layer formed on the steel–titanium interface, which contained FeTi IMPh, and the width of which increased from 1 to 10 μm. In the temperature range 1300...1430 °C, an intermetallic TiFe2-type phase additionally formed from the titanium side. In the temperature range 1430...1450 °C, the TiFe2 phase was replaced by the TiXFe phase, which formed both from the steel side and from the titanium side. This phase consists of intermetallics (73–75% Ti + 27–25% Fe) and (80–85% Ti + 20–15% Fe), and it is close to the Ti2Fe-type phase. The interlayer of intermetallics, formed at temperatures of 900...1300 °C, has a continuous morphology (HV0.01–650...690). At temperatures rising above 1300 °C, the IMPh interlayer became more ramified (HV0.01–590...610) because of the formation of a larger number of pores and microcracks within it. In the temperature range 900...1450 °C, solid-phase diffusion proceeded in the steel–titanium bimetal near the interface of the two metals. A zone of iron diffusion, 5–10 μm to 40–60 μm in width, formed in titanium. In steel, a zone of titanium diffusion 15–20 μm to 120–150 μm in width formed, starting from 1300 °C and higher. It is recommended to perform industrial welding of steel–titanium bimetal in modes, for which the heat input is equal to 200...400 J/mm. Here, during the period 10–12 s, the heating temperature of the HAZ 1.5–3.5 mm in width is equal to 900–1150 °C. It promotes formation of an intermetallic FeTi-type interlayer of up to 1–2 μm width. [ABSTRACT FROM AUTHOR]

Like many complex intermetallic phases, the crystal structures of REZn5+x compounds (RE = lanthanide or Group 3 element) based on the EuMg5 type have gradually unfolded. The original reports described a complex hexagonal structure with an unusual combination of tetrahedrally close‐packed regions and open spaces, as well as observations of superstructure reflections. More recently, we reinvestigated the structure of YZn5, reclassifying it as the EuMg5+x‐type compound YZn5+x (x≃0.2), in which disordered channels run along c through the spaces formerly considered open. In addition, DFT‐chemical pressure (DFT‐CP) analysis of ordered models of YZn5+x highlighted paths for communication between neighboring channels setting the stage for superstructure formation. Herein, the experimental elucidation of this effect is presented with the synthesis and structure determination of a modulated form of YZn5+x. By slow‐cooling samples of YZn5+x from the annealing temperature, crystals were obtained that exhibit satellite reflections with the modulation wavevector q = a* + b* + 0.3041c*. Structure solution and refinement using a (3+1)D model in superspace group P31c(σ3)00s reveals incommensurate order in the structure's channels. Here, two Zn sites associated with the channels are present, each with discontinuous atomic domains that are slanted in the x3x4 plane. Their slanting corresponds to adjustments along the c axis for the presence or absence of close neighbors along that axis, while the occupation patterns of neighboring channels are shifted by of the modulation period. These features follow earlier predictions from CP analysis, highlighting how this approach can be used predictively in search of new phenomena. [ABSTRACT FROM AUTHOR]

The effects of Ca addition on the microstructure and oxidation properties of a new Mg alloy were studied. The oxidation behavior of the alloys was analyzed by thermal analysis and material characterization of the alloys exposed in flame environment; and both electrical and induction furnaces. Moreover, the surface layers were characterized using field emission scanning electron microscopy, and X-ray diffraction technique. It was found that increasing the Ca addition reduces the grain size and increases the fraction of the secondary phases, and enhances the mechanical properties. Moreover, increasing the Ca contents resulted in the formation of a dense CaO/MgO layer on the surface prohibited the oxygen diffusion and assisted in protection of the substrate against further oxidation. Therefore, ignition temperature was increased from 680 °C to 890 °C after addition of the Ca element. The mechanical properties and ignition behavior of the current materials was compared with the literature which it showed an excellent combination of the properties in the developed alloys.

We compare microstructure formation during laser powder bed fusion (LPBF) of a Ti-22Al-25Nb alloy applying low and high pre-heating build plate temperatures. Fast cooling rates during low-temperature LPBF lead to metastable weakly ordered β phase, i.e., bcc–(Ti,Al,Nb) with pronounced 〈100〉 texture in build direction and nanosized segregations within grains elongated in the build direction. For high-temperature LPBF a Widmanstätten microstructure was observed with lenticular O phase precipitates within the β matrix. Microscopical and in situ high-energy synchrotron diffraction investigations demonstrate that the microstructure formation can be widely explained by the precipitation of O phase from supersaturated β rather than by a sequence of solid-state phase transformations, as it would be expected under thermodynamic equilibrium conditions. A detailed analysis of the microstructural gradient in the subsurface region, however, demonstrates that precipitation from metastable β cannot fully explain the observed microstructures, and that the process energy density, i.e., the intensity of the intrinsic heat treatment of LPBF, plays a relevant role. The investigation of the graded area near the surface of the LPBF materials produced with high pre-heating temperature is particularly interesting as it reveals preferred nucleation of the O phase at subgrain boundaries and dislocations.

Novel aluminum-copper compound castings devoid of oxide layers at the interface between the joining partners were developed in order to increase the thermal conductivity of the hybrid component. Due to the natural oxide layers of both aluminum and copper, metallurgical bonds between such bi-metal castings cannot be easily achieved in conventional processes. However, in an atmosphere comparable to extreme high vacuum created by using silane-doped inert gas, metallurgical bonds between the active surfaces of both aluminum and copper can be realized without additional coatings or fluxes. An intermetallic was created between aluminum and copper. Thus, very high thermal conductivities could be obtained for these hybrid castings, exceeding those of conventionally joined samples considerably. The intermetallic phase seams emerging between the joining partners were investigated using scanning electron microscopy and X-ray diffraction. The reduction of casting temperatures resulted in narrower intermetallic phase seams and these in turn in a much lower contact resistance between the two joining partners. This effect can be utilized for increasing the heat transfer capabilities of compound casting components employed for cooling heat sources such as high-power light-emitting diodes. [ABSTRACT FROM AUTHOR]

Mechanical alloying of dissimilar metals employing the severe plastic deformation techniques established itself to be a perspective method of obtaining in situ metal matrix composites with advanced properties. Recent investigations in this field discovered that besides severe mixing of elements, intensive formation of non-equilibrium intermetallic phases takes place. The presence of intermetallic particles in the composite affects both its physical and mechanical properties. In this work, we have realized the consolidation of Al–Cu composites by means of high-pressure torsion (HPT) technique. A non-trivial phenomenon of annealing-induced growth of microhardness was revealed. It was explained by the precipitation of intermetallic phases in the vicinity of Al–Cu interphases. The microstructural observations and X-ray diffraction analysis identified the set of the intermetallic phases present in the deformed composite. Formation of Al 2 Cu and Al 4 Cu 9 phases was observed. It is a well-known fact that the phase composition of the material has a strong impact on both electronic and mechanical properties being dependent on both the interatomic bonding nature and strength. In this work, using the density functional theory approach, we have calculated the work function (WF) values of intermetallic phases and compared them to the experimentally measured WF values of the metal matrix composite. Comparison of results allowed us to conclude that they demonstrate a fair coincidence. Due to the fact that the quantitative and qualitative composition of the intermetallic phases in the composite can be controlled using thermomechanical treatment modes, this approach can be considered as a way to control the WF value of the material. And after establishing the correlation of electronic and mechanical properties, a definite metal-matrix composites (MMC) can be treated as an approach for creation the composite with tailorable complex of physical and mechanical properties. [ABSTRACT FROM AUTHOR]

This paper presents the results of laboratory tests related to high-alloy silicon cast iron (HSCI). These materials are corrosion-resistant and commonly used in cathodic protection systems as protective electrodes. Due to their high fragility, alloys with increased Si content are not suitable for producing elements exposed to dynamic loads. This paper analyzes the crystallization process of silicon alloys (with Si content between 23% and 25%) using thermal and derivation analysis methods. The tests also included an extended analysis of chemical composition. The metallographic tests included scanning electron microscopy with an EDS system, and the phase composition was determined using X-ray diffraction. As a result of the tests, the warp components were identified, the primary share of which are intermetallic phases of the Fe5Si3 type. Moreover, single silicon crystals were found. The test results allowed for clarification of the temperature range of the transition of the Fe2Si phase into the Fe5Si3 phase and the determination of characteristic points of the crystallization process (TSolidus i TLiquidus). Furthermore, bifilm-type inclusions were identified in the alloys. We also managed to present the silicon crystals and Fe5Si3 phases in a spatial layout via observation of the surfaces of contraction cavities using scanning electron microscopy. [ABSTRACT FROM AUTHOR]

In this study, an Al–Zn–B alloy was developed to investigate AlB2 intermetallic phase effect on electrochemical performance in Al–air battery anodes. Self-corrosion, galvanostatic dissolution tests, electrochemical measurements, and surface characterization methods were conducted to observe the effect of 1–5 wt% B doping to the Al-5 wt% Zn (Al5Zn). In 3 wt% B doped alloy (Al5Zn3B), 20% higher corrosion rate was achieved than Al5Zn alloy. The corrosion potential of the alloy samples was changed from − 1.841 V vs Ag/AgCl to − 1.870 V vs Ag/AgCl values, by adding 3 wt% B elements to Al5Zn alloy. [ABSTRACT FROM AUTHOR]

The formation of iron (Fe)‐containing intermetallics during solidification is challenging due to the influences of cooling rate and chemical composition. Differential scanning calorimetry (DSC) is an accurate analysis method but merely replicates adjustable cooling conditions. Thereby, the solidification range is traversed several times before DSC measurement. For this purpose, thermal analysis cooling curves with double thermocouple are conducted to investigate the formation temperature of Fe‐rich intermetallics in different AlSi casting alloys. In addition, the influence of chemical composition is examined by increasing the initial contents of iron, manganese, and chromium to 0.8 wt% each. The double thermocouple setup allows determining feeding points and solid fractions of the alloy compounds. To evaluate the data sets, the statistical program R is used to improve data processing and smoothing. The signature of Fe‐rich intermetallics in the temperature–time plots corresponds to the detected phases in optical micrographs. In addition, scanning electron microscopy with energy‐dispersive spectroscopy and electron backscattering diffraction are used to measure the local chemical composition and identify the iron‐rich intermetallics. Real‐time evaluation (differential calculation, first derivative, incl. smoothing) for an applicable filtration process can be performed using thermocouples with analog‐to‐digital converter and Python programs with an interactive graphical interface. [ABSTRACT FROM AUTHOR]

Ternary mixture of choline chloride, ethylene glycol and urea (molar ratio 1 : 1 : 1) has been proposed as non‐aqueous media for the electrochemical plating in galvanostatic mode of tin‐silver alloy coatings. The conditions for the deposition of an alloy with a composition and melting temperature close to the eutectic, which is in demand for microassembly in the electronic industry, have been determined. The significant features on the simultaneous tin(II) and silver(I) reduction and the alloy formation are revealed. It has been determined that silver(I) is reduced from the solution both electrochemically and by the galvanic displacement with freshly deposited tin. The presence of silver on the surface of the coatings initiates underpotential tin(II) reduction. The interactions of components in the non‐aqueous electrolyte have been studied for the first time by IR spectroscopy, and the formation of coordination compounds between tin(II) and silver(I) ions and solvent molecules has been revealed. [ABSTRACT FROM AUTHOR]

The phases, microstructure, and magnetic properties in a severely deformed Cr-Ni–Al alloy have been studied. The eutectic microstructure observed in localized regions of the alloy can be interpreted as a result from the super-Arrhenius relaxation of the alloy. According to X-ray diffraction and magnetometry, the nanosized nickel inclusions in the matrix of the chromium-nickel γ-solid solution are formed. It is shown that, after severe (superplastic) deformation, a unidirectional magnetic anisotropy is induced, which may be associated with the antiferromagnetic coupling between the CrNi2 matrix and the nickel inclusions. [ABSTRACT FROM AUTHOR]

The effects of Ca addition on the microstructure and oxidation properties of a new Mg alloy were studied. The oxidation behavior of the alloys was analyzed by thermal analysis and material characterization of the alloys exposed in flame environment; and both electrical and induction furnaces. Moreover, the surface layers were characterized using field emission scanning electron microscopy, and X-ray diffraction technique. It was found that increasing the Ca addition reduces the grain size and increases the fraction of the secondary phases, and enhances the mechanical properties. Moreover, increasing the Ca contents resulted in the formation of a dense CaO/MgO layer on the surface prohibited the oxygen diffusion and assisted in protection of the substrate against further oxidation. Therefore, ignition temperature was increased from 680 °C to 890 °C after addition of the Ca element. The mechanical properties and ignition behavior of the current materials was compared with the literature which it showed an excellent combination of the properties in the developed alloys. [ABSTRACT FROM AUTHOR]

The suitability of the direct energy deposition process of exothermic powders Fe-Ti in joining dissimilar metals to produce small parts of a complete shape for various applications is considered. The procedure of the direct energy deposition of commercial pure iron and titanium in various proportions and the modes of the process are described. Optical microscopy and SEM with EDX analysis, X-ray analysis, and microhardness measurements of laser-fabricated intermetallics are applied. Intermetallic compounds of FeTi, Fe2Ti, eutectoids, complex titanium oxides and nitrides, and iron carbides are found. Interlayer and trans-layer cracks and pores are observed. A microhardness growth from 150 HV to 900 HV was obtained for all samples due to the precipitation of brittle intermetallic phases in the gradient Fe-Ti system during the DED. The dispersion of microhardness values becomes significant in Ti-rich areas; there, pores and cracks are found. The revealed structure features are considered in relation to published results and explained. Increased concentrations of Ti to Ti + Fe = 3:1 on the Fe- and Fe + Ti -substrate with concentrations of Ti + Fe = 1:1 and Ti + Fe = 1:3 lead to increasing hardness and its distribution, but also increases in residual microstress. Recommendations are given to reduce the power during the direct energy deposition of titanium layers and to apply Fe-substrate, which can reduce residual stress, pores, and cracks. [ABSTRACT FROM AUTHOR]

Abstract—The structure, the phase composition, the physicomechanical properties, and the corrosion resistance of a precipitation-hardened composite material fabricated by hot pressing (1050°C, 30 MPa, 30 min) of powders of high-alloy ferritic steel (Fe base alloy, 30% Cr, 0.2% C) and molybdenum in an amount of 1, 5, and 10% are studied. The maximum compressive strength (1815 ± 3 MPa) is characteristic of the composite material with 10% Mo. After quenching from 1050°C, the composite material (Fe–Cr–Mo) has no χ phase, its strength decreases to 1656 ± 21 MPa, and the residual deformation (shortening) increases by 2.5–3 times. [ABSTRACT FROM AUTHOR]

Laser beam welding of metals has progressed dramatically over the last years mainly arising from joining applications in the field of electromobility. Allowing the flexible, automated manufacturing of mechanically, electrically, and thermally stressed components, the process is more frequently applied for joining highly reflective materials, for example for battery tab and busbar connections. The local, non-contact energy input favors this welding technology; however, joining of copper and aluminum sheets still poses a challenge due to the physical properties of the joining partners and intermetallic phases from dissimilar metal interaction, which reduce seam performance. The use of green laser radiation compared to infrared laser radiation offers the advantage of a significantly increased absorptivity for copper materials. A changed incoupling behavior is observed, and a lower deep penetration threshold has been already proven for 515 nm wavelength. When copper and aluminum are welded with the former as top sheet, this welding mode is essential to overcome limited aspect ratios from heat conduction welding. However, the opportunities of applying these beam sources in combination with spatial power modulation to influence the interconnection area of copper-aluminum joints have not yet been studied. The aim of this work is therefore to investigate the seam properties and process stability of different overlap welding strategies using green laser radiation for dissimilar metal welding. A microstructural analysis of the different fusion zones and mechanical strength of the joints are presented. In addition, the experimental parameter sets were analyzed regarding their application in battery module busbars by examining the electrical resistance and temperature distribution after welding. A parameter window was identified for all investigated welding strategies, with the stitched seam achieving the most stable results. [ABSTRACT FROM AUTHOR]

In welding of aluminium (Al) alloys to steels, a major challenge is excessive growth of brittle intermetallic phases along the bonded Al-steel interfaces. The formation and growth of these phases are influenced by the heat input and the alloying elements present. This work focuses on the phases formed between a low alloyed steel and an Al-Si-Mn alloy that was used as the filler wire in a cold metal transfer joint. During lap shear testing of the joint, fracture ran through the melted Al, and the joint reached a strength of 174 ± 21 MPa. Scanning and transmission electron microscopy showed that the formed ∼2.5 µm thick intermetallic phase layer consisted of polyhedral αc-Al-(Fe,Mn)-Si, elongated or rounded θ-Fe4Al13 and near equiaxed η-Fe2Al5 grains. Electron backscatter diffraction was used to study the crystal orientations of the formed phases. Altogether this work aims to contribute to better understanding of the formation and growth of intermetallic phases in Al-steel welds where the Al alloy contains Si and Mn. [ABSTRACT FROM AUTHOR]

This article presents the results of a study to identify intermetallic phases whose role is to limit austenite grain growth in the low-pressure carburizing process. A drawback of high-temperature low-pressure carburizing is the austenite grain growth during the process. Using low-pressure carburizing with pre-nitriding technology (PreNitLPC®) offers the possibility of reducing austenite grain growth. This technology involves the application of doses of ammonia during the heating stage of the steel, at the carburizing temperature, to introduce nitrogen into the surface layer of the steel and to form nitrides. It is these phases that cause restrictions on austenite grain growth during carburizing. The research carried out in this article was aimed at identifying these phases. The research was carried out on one of the basic steels used for carburizing—16MnCr5 steel. The carburizing of this steel with and without pre-nitriding was performed, followed by an evaluation of the austenite grain size after these processes and the identification of the intermetallic phases present in the surface layer of the steel.

In this study, aluminum–magnesium (Al-Mg) bulk porous materials were fabricated by using uniaxial hot pressing to control the porosity rate of the material over a wide range (up to 50%). The fabricated materials were analyzed by X-ray diffraction and scanning electron microscopy. The results demonstrated the appearance of intermetallic (IM) phase Al3Mg2, and its quantity increased with the applied pressure. In the context of the decline of global fossil fuel reserves, the revalorization of these materials by hydrogen (H2) production was investigated. Hydrolysis of the Al-Mg materials was carried out in a simulated seawater solution (aqueous solution of sodium chloride 35 g/L). The results showed the role of the porosity rate in the H2 production properties of the fabricated materials; the increase of porosity rate from 10% to 50% cuts the reaction time in half. Finally, the role of IM phase Al3Mg2 in H2 production was highlighted through galvanic coupling.

The 5083Al/1060Al/TA1/Ni/SUS304 five-layer composite plate was fabricated successfully by explosive welding to improve the bond strength. The four interfaces exhibited wave structures that exhibited significantly different wavelengths and amplitudes. The microstructure of the interfaces underwent a certain degree of dynamic recovery and recrystallization which displayed refined grain with different preferred orientations. Intermetallic phases such as Al3Ti, Al2Ti, AlTi, and Ti3 Al were observed at the 1060Al/TA1 interface. The TiNi3, Ti2Ni, and TiNi phases were found at the TA1/Ni interface. The α′ martensite, Cr7C3, Fe3C, and Ni3Fe phases were found at the Ni/SUS304 interface. Microhardness at each interface was the highest and gradually decreased away from the interface. The tensile-shear strength of each interface prominently exceeded the corresponding acceptable standard value. In addition, the average pull-off strength was 173 MPa, and the sample fractured at the 5083Al/1060Al interface. The excellent bonding strength was mainly attributed to the ideal periodical wave structure and the refined grain at each interface.

Changes in the microstructure and selected mechanical properties of two-phase ferritic-austenitic cast steel containing 24% Cr-5% Ni-2.5% Mo-2.5% Cu after isothermal holding at 750 °C and 900 °C are presented. The choice of the two temperatures of isothermal holding was dictated by the precipitation of brittle phases within a range of 600 °C–950 °C, while the holding time depended on the casting cooling time in the mould. Changes in the microstructure were studied by the SEM-EDS and XRD techniques. As a result of the decomposition of the eutectoid ferrite, a σ phase that was rich in Cr, Mo, and Ni and a secondary γ2 austenite with Widmannstätten morphology were formed. Compared to the austenite, the chemical composition of the secondary γ2 austenite showed depletion of Cr and Mo. In the ferrite, the presence of Cr2N nitrides was also detected. After a holding time of 3 h at 900 °C, these phases increased the hardness of the tested cast steel to approximately 275 HV10. At the same time, the UTS value was recorded to decrease with the increasing temperature based on the tensile test results. At 750 °C, the value of UTS was 250 MPa for 1 h of holding and 345 MPa for 3 h of holding. These values decreased after increasing the temperature to 900 °C and amounted to 139 for 1 h holding and 127 MPa for 3 h holding. It was also found that the elongation values at 750 °C ranged from 7–10%, while they amounted to 35–37% at 900 °C. A fracture analysis of the tested cast steel showed that in the prevailing part, the fractures were made of ductile nature with an arrangement of dimples that is typical for this type of fracture. Non-metallic inclusions that are typical for cast steel (i.e., oxides and nitrides) were also found in the area of the fractures. [ABSTRACT FROM AUTHOR]

Hot dip galvanizing is among the cheapest methods for protecting ferrous alloys against corrosion. The success is due to both the low cost of the process and the high degree of protection in many corrosive environments, where the coatings serve as sacrificial protection. The purpose of this analysis is to study the mechanical characteristics of steel plates, that have been hot dip coated with five different zinc alloy molten bath for different time periods. The mechanical tests performed is a non-standardized four-point bending test considering three distinct bending angles. Results are examined in terms of both mechanical behaviour and coating phase damage. The development of intermetallic phases and their damage are both influenced by the chemical compositions of the zinc bath, demonstrating that fractures arise mostly at the substrate-coating interface. All the coatings showed the arising of micro-cracks except for the Aluminium, which demonstrated its ductility. In addition, Zn-Ti coatings showed the arising of a new compact phase rich in iron, characterized by a great hardness. More research is needed to explore the aluminium impact on the zinc bath, the lack of tiny fractures in the phase, and the lesser thickness compared to the other coatings tested. [ABSTRACT FROM AUTHOR]

Combustion-assisted flame spraying (CAFSY) is a novel method that allows in-flight synthesis of alloys during flame spraying. The in-flight synthesis of alloys by the CAFSY method during flame spraying combines two different methods: the self-propagating high-temperature synthesis (SHS) and flame spraying (FS). The present work studies the corrosion performance (by cyclic polarization and chronoamperometry in aerated 3.5 wt.% NaCl) of NiAl coatings fabricated by the CAFSY technique in relation to main process parameters (composition of the initial feedstock, spraying distance, substrate temperature, postdeposition heat treatment) and their effect on the microstructure and porosity of the coatings. Most of the coatings exhibited limited susceptibility to localized corrosion. In all cases, the steel substrate remained intact despite corrosion. Interconnected porosity was the main parameter accelerating uniform corrosion. Localized corrosion had the form of pitting and/or crevice corrosion in the coating that propagated dissolving Al and Al-rich nickel aluminides along coating defects. Substrate preheating and postdeposition heat treatment negatively affected the corrosion resistance. A short spraying distance (1.5 inch) increased the corrosion resistance of the coatings. [ABSTRACT FROM AUTHOR]