Intermetallic Compound Phase Research Articles

Dissimilar fabrication of the TC4/Ni60 bimetallic structure by laser melting deposition using a V/Cu transition bilayer

The bonding of Ti and Ni alloys to manufacture high-quality bimetallic structures represents an optimal integration strategy for fully leveraging their superior performance. However, the metallurgical bonding between TC4 and Ni60 dissimilar metals is extremely challenging due to the formation of TiNi, TiC and TiFe brittle intermetallic compounds and the differences in thermophysical properties. To address this issue, this paper presents a solution based on the compatibility of elemental components. A V/Cu transition bilayer was designed to achieve defect-free bonding between TC4 and Ni60 by laser melting deposition. The microstructure of the TC4/Ni60 bimetallic structure was analyzed by SEM, XRD and EBSD to evaluate its feasibility. The results indicate that the generation of brittle intermetallic compound phases was reduced to a certain extent when a V/Cu transition bilayer was employed, thus preventing cracking and peeling of the TC4 substrate and Ni60 cladding layer. Additionally, the mechanical properties of the bimetallic structure were evaluated through micro-shear tests and tensile tests. The micro-shear test results indicate that the weakest layer of the bimetallic structure is the Cu transition layer with a shear strength of 183.0 ± 108.8 MPa and an indentation rate of 8.25 ± 3.3 %. The room temperature tensile results demonstrate that the developed bimetallic structure fractured at the Cu/Ni60 interface, exhibiting a tensile strength of 286.3 ± 54.1 MPa and an elongation of 6.3 ± 0.5 %. The expected research can provide valuable references for improving the mechanical properties of TiNi dissimilar bimetallic structures produced by laser melting deposition.

Fracture mechanisms of Al-steel resistance spot welds: The role of intermetallic compound phases

This study explores the mechanical and metallographic characteristics of Al-Steel dissimilar resistance spot welds (RSW), with a particular focus on the intermetallic compound (IMC) phases and their impact on fracture mechanisms. Detailed metallographic analyses and novel miniature lap shear tests with in-situ Digital Image Correlation techniques were conducted to observe the crack propagation behavior. The findings revealed that the IMC phases significantly influence the crack path and fracture mechanisms, leading to variations in fracture energy. Specifically, three distinct IMC phases were identified at the weld interface, each exhibiting unique structural and mechanical properties, with corresponding fracture energies of approximately 0.03 kJ/m2, 1.1 kJ/m2, and 7.5 kJ/m2. These variations highlight the critical role of the IMC phase in determining the fracture behavior of the weld. The study further supported the development and validation of a finite element (FE) model, incorporating a Cohesive Zone Model to simulate debonding behavior and the Hosford-Mean fracture criterion to predict ductile fracture in the Al fusion zone, thereby successfully linking local material characteristics to mechanical properties.

Effects of C content on the microstructure and properties of CoCrFeNiTi0.5Mo0.5Cx high-entropy alloy coatings by laser cladding

In order to deeply investigate the influence mechanism of different contents of non-metallic element C on the microstructure, microhardness, wear resistance and corrosion resistance of high-entropy alloy coatings. CoCrFeNiTi0.5Mo0.5Cx high-entropy alloy coating was prepared on the surface of AISI 1045 steel by laser cladding technology. The results show that the microstructure of CoCrFeNiTi0.5Mo0.5 without C addition consists of FCC phase, BCC phase, intermetallic compound phase and σ-phase structure, and the carbide phases (M7C3 and TiC) start to appear after the addition of C element. The microhardness of the coating increases and then decreases with the increase of C content, and the average hardness is the highest when x = 0.03, 495.3HV0.5, which is 27.6% higher than that of C0. The abrasion resistance of the CoCrFeNiTi0.5Mo0.5Cx high-entropy alloy coatings is gradually increased and then decreased with the increase of C content, and the wear amount decreases from 0.0813 mm3 to 0.0514 mm3, and the main frictional wear mechanisms are adhesive wear, abrasive wear and oxidative wear. With the increase of C content, the corrosion resistance of the coating is gradually improved and then reduced, when the C content is 0.03, the highest corrosion potential is −0.818V, the lowest corrosion current is 1.382E-4 A/cm2, at this time, the passivation film on the surface of the coating is the most stable and dense, with the best corrosion resistance. The results of this paper provide a theoretical reference for the effect of adding non-metallic elements on the microstructure and properties of high-entropy alloy coatings.

Microstructural, mechanical, and wear properties of Sn-based solder alloy modified with graphite nanoparticles

This study investigated the microstructural, mechanical, and wear properties of the Sn-2.5 wt%Ag-0.4 wt%Cu-1.0 wt%In (SAC-1.0In) solder alloy including nano-graphite (0.6–1.2 wt%). The microstructural characteristics of several samples were investigated using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive x-ray spectrometry (EDS), electron probe microanalysis (EPMA), x-ray diffraction (XRD), and x-ray photoelectronic spectroscopy (XPS). The results of this study revealed that the presence of nano-graphite particles stimulated the production of distinct intermetallic compound phases (IMC) identified as Ag3Sn, Cu6Sn5, and γ-InSn4. These IMCs are uniformly dispersed throughout the matrix. The results showed that the addition of nano-graphite particles did not significantly alter the morphology of the microstructure but reduced the particle size of these IMCs. This refining of precipitated IMC particles resulted in considerable improvements in the material’s mechanical properties. The wear properties of both unreinforced matrix and graphite composites were investigated utilizing a pin-on-disc tribometer. The addition of 0.6, 0.9, and 1.2 wt% graphite nanoparticles decreased the sliding wear rate. It is worth noting that the current study is deemed unique and novel in terms of total strain percent behavior as graphite content increases.

A comparative study of structural, elastic, electronic, thermophysical, and optical properties of cubic binary lave-phase intermetallic compounds of HfX2 (X = cr, mo, and W): An ab initio insight

In the present work, we have made a comparative investigation on the structural, elastic, electronic, thermos-physical, and optical properties of cubic binary lave phase intermetallic compound with the common formula HfX2 (X = Cr, Mo and W) based on Density Functional Theory (DFT) using CASTEP. The result of geometrical optimization has been strongly agreed with the experimental results. The HfW2 compound exhibits larger lattice parameters and volumes than HfMo2 and HfCr2 because of the variation of atomic radii of the exhibiting elements in the studied compounds. The elastic properties show that each of the compounds in the ground state is mechanically stable and has a highly ductile nature. Band structures and energy densities of states have been studied to learn more about electronic properties. These compounds display metallic properties in their electrical band structures. They also have high machinability, a low Debye temperature, low bond hardness, and a remarkably high melting point. Our investigation thoroughly examined the reflectivity, absorption coefficient, refractive index, dielectric function, optical conductivity, and loss function of these metals. The optical absorption, reflectivity spectra, and refractive index of HfX2 (X = Cr, Mo, and W) indicate their potential for use as solar reflectors in the IR-Vis region and UV–Vis absorbers.

Understanding crack growth within the γ′ Fe4N layer in a nitrided low carbon steel during monotonic and cyclic tensile testing

Nitriding is a cost-effective method to realize simultaneous improvements in tensile and fatigue properties and resistance to abrasion and corrosion. Previous studies reported that nitriding pure Fe enhances tensile strength by ~ 70% and fatigue limit by ~ 200%. It is due to the increase in surface hardness caused by the formation of γ′(Fe4N) and ε(Fe2-3N) nitrogen-containing intermetallic compound phases. However, the intermetallic compound layer is prone to brittle-like cracking. To better design nitrided steels, it is crucial to identify the crack growth mechanisms via analysis of the microstructural crack growth paths within the ~ 4–6 µm thick nitride layer. In the current work, we statistically evaluate the crack propagation behavior in the γ′ Fe4N layer during monotonic and cyclic tensile deformation in nitrided low-carbon steel (0.1 wt% C). Since nitriding typically results in the formation of columnar grains, the effect of morphology needs to be clarified. To this end, the steel was shot-peened and subsequently nitrided to promote equiaxed nitride grains morphology (~ 16% increase). Crack growth paths were comparatively evaluated for multiple cracks, and no significant effect of nitride morphology was observed. {100}γ′ is the predominant transgranular crack path in the monotonic tensile tested specimen, followed by {111}γ′. It is despite the elastic modulus of {111}γ′ < {100}γ′. This contrary behavior is explained by {100}γ′ plane having the lowest surface energy (density functional theory calculations). In the cyclic tensile loaded specimen, experiments revealed that transgranular cracking along {100}γ′ (cracking via symmetric dislocation emission) or {111}γ′ (slip plane cracking) is equally likely.Graphical abstract

Microstructure modification and mechanical reinforcement in sub-10 μm scale Cu/Sn–Ag/Cu microbump joints via Co-addition of Zn and Ni in Cu substrates

The trend towards miniaturization of solder joints addresses the need for high-density interconnections in microelectronics. Excessive intermetallic compounds (IMC) and phase transformations cause internal stresses, leading to voiding and cracking in conventional microbumps. Therefore, advanced microbump design must focus on IMC suppression and phase stabilization. This study explores Cu–26Zn–18Ni/Sn-3.5Ag/Cu–26Zn–18Ni microbumps, comparing them to conventional Cu/Sn-3.5Ag/Cu under various reflow times. High-field emission electron probe micro-analysis and transmission electron microscopy reveal improved microstructures. Electron backscatter diffraction confirms the (Cu,Ni)6(Sn,Zn)5 grain size of several hundreds of nanometers. Fracture modes were established based on the correlation between shear testing and fracture surfaces. Cu–26Zn–18Ni/Sn-3.5Ag/Cu–26Zn–18Ni microbumps enhanced shear strength (19.6 %–97.8 %) and failure toughness (10.6 %–132.1 %) compared to Cu/Sn-3.5Ag/Cu. The solid solution strengthened and refined (Cu,Ni)6(Sn,Zn)5 combined with tough bulk (Cu,Ag)5(Sn,Zn)8 in Cu–26Zn–18Ni/Sn-3.5Ag/Cu–26Zn–18Ni microbumps, demonstrate a tough microstructure. These findings provide insights into the design of microbumps with a bonding height in sub-10micron scales.

Phase engineering and surface reconstruction of FeNiMo alloys as high efficient electrode for oxygen evolution reaction

In the field of electrocatalysis, most of the electrodes have the problem of poor mechanical properties, which leads to the electrode can not be used on a large scale. At present, most bulk electrodes are used to study their mechanical properties due to their unique phase composition distribution and facile fabricate methods. But their novel properties in the field of electrocatalysts have not been fully developed. Multi-element bulk electrodes not only diversified the electronic states, but also build complex surface morphology by different dissolution rate between multi-phase distribution. In this paper, we synthesized the FeNiMo bulk electrode for oxygen evolution reaction (OER) with two-phase coexistence of Mo-doped face center cubic phase (FCC) and Mo-rich intermetallic compound (IMC) phase. During cyclic voltammetry activation, the surface reconstruction of Mo-rich IMC phases generated by ion leaching leaves Fe–Ni pore structures with more active area, which enhances OER performance. Meanwhile, the electron states get more diverse on the surface of remaining FCC phases due to Mo doping, which provides more suitable sites for four-step OER process. The FeNiMo electrode shows an ultra-low overpotential of 212 mV and 293.4 mV at a current density of 10 mA cm−2 and 100 mA cm−2, respectively. Moreover, it can maintain stability at 100 mA cm−2 for up to 72 h. This work provides a strategy for studying the relationship between phase composition and electrochemical performance of alloy bulk electrodes.

Revisiting porous foam Cu host based Li metal anode: The roles of lithiophilicity and hierarchical structure of three-dimensional framework

Lithium (Li) metal anode (LMA) is one of the most promising anodes for high energy density batteries. However, its practical application is impeded by notorious dendrite growth and huge volume expansion. Although the three-dimensional (3D) host can enhance the cycling stability of LMA, further improvements are still necessary to address the key factors limiting Li plating/stripping behavior. Herein, porous copper (Cu) foam (CF) is thermally infiltrated with molten Li-rich Li-zinc (Li-Zn) binary alloy (CFLZ) with variable Li/Zn atomic ratio. In this process, the LiZn intermetallic compound phase self-assembles into a network of mixed electron/ion conductors that are distributed within the metallic Li phase matrix and this network acts as a sublevel skeleton architecture in the pores of CF, providing a more efficient and structured framework for the material. The as-prepared CFLZ composite anodes are systematically investigated to emphasize the roles of the tunable lithiophilicity and hierarchical structure of the frameworks. Meanwhile, a thin layer of Cu-Zn alloy with strong lithiophilicity covers the CF scaffold itself. The CFLZ with high Zn content facilitates uniform Li nucleation and deposition, thereby effectively suppressing Li dendrite growth and volume fluctuation. Consequently, the hierarchical and lithiophilic framework shows low Li nucleation overpotential and highly stable Coulombic efficiency (CE) for 200 cycles in conventional carbonate based electrolyte. The full cell coupled with LiFePO4 (LFP) cathode demonstrates high cycle stability and rate performance. This work provides valuable insights into the design of advanced dendrite-free 3D LMA toward practical application.

The influence of building parameters on residual stress, interfacial structure, and cracking control of laser powder bed fusion processed Ti6Al4V/AlMgScZr multi-material parts

With the growing demand for lightweight and high-performance components applied in extreme aerospace environments, there is a prospective interest in producing the integrated multi-material components consisting of titanium alloy and aluminum alloy. Laser powder bed fusion (LPBF), as a laser powder bed based additive manufacturing process with a high production flexibility, shows a promising potential in creating multi-material components. However, due to the possibility of the generation of various intermetallic compounds (IMCs) at the interface, it has been a significant challenge to fabricate reliable Ti/Al alloy multi-material components without any crack formation by LPBF. In this study, the Ti6Al4V/AlMgScZr multi-material parts were fabricated by LPBF and the effects of building parameters of AlMgScZr on the residual stress and crack control of Ti6Al4V/AlMgScZr multi-material parts were investigated. The evolution mechanisms of IMC phases at the interface under laser interaction were further revealed. Due to the change of elemental compositions and difference in Gibbs free energies of IMCs, a gradient ordered transition zone with a width of about 450 μm consisting of Al3Ti, TiAl, and Ti3Al was formed from AlMgScZr to Ti6Al4V. A finite element model was established to explain the effects of process parameters on residual stress evolution, cracking formation and its control. As the scan speed increased from 500 to 1100 mm/s and the attendant building height of AlMgScZr increased to 60 layers, the residual stress of laser processed Ti6Al4V decreased from 439 to 364 MPa, but the residual stress of AlMgScZr increased from 195 to 303 MPa. As the applied scan speed was enhanced to process AlMgScZr, the element diffusion was mitigated, thereby reducing the formation of IMCs and stress concentration. This study shows the possibility of in-situ control of IMCs and residual stress by process optimization during LPBF preparation of titanium alloy/aluminum multi-material parts without crack formation.

Fabrication and evaluation of Ti6Al4V /NiCrBSi bimetallic structure with Nb/Cu bilayer by laser melting deposition

The fabrication of high-quality bimetallic structures using titanium and nickel alloys is a desirable integration for fully leveraging their remarkable properties. This study is dedicated to the surface modification of titanium brake discs, using laser melting deposition to produce the Ti6Al4V/NiCrBSi bimetallic structure and inhibition of brittle phase formation by Nb/Cu bilayer. The results showed the generation of brittle intermetallic compound phases was effectively resisted using Nb/Cu bilayer, thus preventing cracking and peeling of the Ti6Al4V substrate and NiCrBSi coatings. Moreover, the bimetallic structure fractured at the weakest position, i.e. at the Nb/Cu interface, with a maximum strength of 243.20 ± 55.16 MPa during the tensile testing, exhibiting brittle-like failure behaviour. Additionally, the friction and wear properties of the Ti6Al4V substrate and NiCrBSi coatings were evaluated at both room temperature and elevated temperature (600 °C). The results reveal that the NiCrBSi coatings effectively improved the friction and wear properties of the Ti6Al4V.

Optimization of TLPS Bonding Process and Joint Property using Ni-Sn Paste for High Temperature Power Module Applications

Recently, as interest in eco-friendly vehicles such as electric and hybrid vehicles increases, the demand for power semiconductors, a key component, is also increasing. Power semiconductors convert, distribute, and control power and operate in harsh environments such as high temperature and high pressure. In order to ensure stable reliability in such harsh environments, research on a technology that can stably form joints even at high temperatures is essential. Transitional liquid phase (TLP) bonding was proposed as a high-temperature power semiconductor chip bonding technology, which has the advantage of forming an intermetallic compound (IMC) phase with a high melting point at the joint. However, it takes a long time to convert the joint into full IMC phase. Therefore, in this study, in order to shorten the process time, a paste was manufactured by mixing high-melting point Ni metal powder and low-melting point Sn metal power, and a joint was formed through a TLPS (Transition liquid phase sintering) bonding using the paste. Pastes of different compositions were prepared by adjusting the ratio of Ni and Sn powders. The chip and substrate were bonded through a thermocompression (TC) bonding process, and the highest shear strength was obtained at a bonding temperature of 250 ℃ for 10 min. Heat treatment was performed at 200 ℃ for up to 500 h to evaluate the high temperature long-term reliability of the joints. The Ni-Sn TLPS bonded joints remained reliable joints after a long-term aging test at a high temperature of 200 ℃.

Calculation and Experimental Verification of Zn–Al–Mg Phase Diagram

The liquid phase projection diagram, three-dimensional phase diagram, and vertical section diagram of the Zn–x%Al–x%Mg alloy system was calculated using the phase diagram calculation software Pandat. Simultaneously making full use of the self-developed hot-dip galvanizing process simulation machine by China Steel Research produced a 75%Zn–19%Al–6%Mg coating. A method combining phase diagram calculations and experimental verification was used to investigate the equilibrium phases and solidification process of the alloy. The microstructure of the 75%Zn–19%Al–6%Mg coating was studied using scanning electron microscopy and energy dispersive spectrometry. The results indicate that the coating structure consists of primary Al dendrite phase, MgZn2 inter-metallic compound and Zn-rich phase. There is no ternary eutectic structure in the coating structure. Al dendrites grow on the surface of the coating, while there are no Al dendrites on the cross-section. The experimental results strongly concur with the calculated results from the Pandat phase diagram. The solidification sequence of the 75%Zn–19%Al–6%Mg coating is L→L + Al→L + Al + MgZn2→Al + MgZn2 + Zn. The phase diagram guides industrial production significantly, avoiding the waste of transitional materials and zinc caused by small scale trial and error experiments, thus reducing unnecessary production costs. The factory can select a reasonable coating composition designing scheme in the phase diagram, based on the performance requirements of customers for the coating.

Phase prediction of high-entropy alloys based on machine learning and an improved information fusion approach

The phase design of high entropy alloys (HEAs) is an important issue since the phase structure affects the comprehensive properties of HEAs. Accurate prediction of phase classification can accelerate material design. In this paper, a new phase prediction framework is proposed using machine learning (ML) and an improved information fusion approach based on the Dempster-Shafer (DS) evidence theory. Considering that the classification results of different ML algorithms may conflict, and the traditional DS evidence theory cannot solve the problem of high conflict, we propose an improved information fusion approach based on the DS evidence theory. The basic probability assignment function is constructed using the ML algorithms. 761 HEAs samples are collected consisting of amorphous phase (AM), solid solution (SS), intermetallic compound (IM), and a mixture of SS and IM (SS + IM). For the small dataset of HEAs, we use a conditional generative adversarial network (CGAN) for data augmentation. Based on the enhanced dataset, the ML model is optimized by sparrow search algorithm (SSA), which can accelerate searching speed of model hyperparameters and improve the performance of the model. The results show that the proposed information fusion method performs better than several other existing techniques on the test set, and the prediction accuracy reaches 94.78 %. Meanwhile, the prediction accuracy of the proposed method is higher than that of the existing technology (93.17 %). It is proved that the proposed method can solve the high conflict problem effectively. Moreover, we present the interpretability analysis of the features by the Shapley additive explanations (SHAP) and the sensitivity matrix. A smaller atomic size difference δ (<6.6 %) is conducive to the formation of SS phase, while a larger δ (>6.6 %) is conducive to the formation of AM phase. A smaller enthalpy of mixing ΔHmix tends to form AM phase. In binary and ternary alloy systems, IM phase can be extracted by the mixing enthalpy ΔSmix < 10. In addition, we find that mean bulk modulus (K) and standard deviation of melting temperature (σT) are critical features to distinguish between SS and SS + IM.

A review of emerging trends in Laves phase research: Bibliometric analysis and visualization

Abstract The rapid development of modern aerospace and energy industries requires increasingly high service performance of metallic materials. Laves phase intermetallic compounds with the chemical formula AB2-type have attracted much attention due to their high melting point, excellent high-temperature strength, and oxidation resistance, and are regarded as one of the promising candidates for a new generation of high-temperature structural applications. Although it can be identified that Laves phase alloy research has been an active research field in the last 20 years in terms of the trend of literature volume growth, there is still a lack of systematic descriptions and comprehensive overviews of the latest frontiers and hotspots in the field. In this article, a quantitative and visual knowledge mapping of the articles published in the field of Laves phase research in the last 20 years has been carried out based on the bibliometric analysis methodology of Cite Space software. Quantitative analysis of high-frequency keywords to understand the basic development of Laves phase and the evolution of the main research hotspots in each period of time identified the hotspots of common concern seven themes: Laves phase, electronic structure, precipitation, Inconel 718 alloy, phase diagram, high-entropy alloys, and TiAl-based alloys. The analysis of the emergent keywords shows that electronic structure, high-entropy alloys, total energy calculations, and laser cladding can represent the research frontiers of Laves phases. This study provides systematic and valuable reference information to gain insight into the current state of Laves phase research and the evolution of the theme, which will be useful for further research.

Microstructural evolution and mechanical properties of FeCrNiCuTix high entropy alloys

In this study, the microstructural evolution and mechanical properties of a series of FeCrNiCuTix (x = 0, 0.2, 0.4, 0.6, 0.8, and 1, in mole ratio) high entropy alloys (HEAs) were analyzed in detail to study the influence of Ti content on the HEAs. The microstructures of the alloys transformed from single-phase face-centered cubic (FCC) phase structure to FCC and body-centered cubic (BCC) diphase, finally to FCC, BCC and intermetallic compound (Fe2Ti) phase with the increase of Ti content. The addition of Ti element significantly refined the grain of the alloys. The hardness, strength and tribology tests of the alloys were also carried out. The results indicated that the Vickers hardness, yield strength, and fracture strength increased first and then decreased, the average friction coefficient variation law was just the opposite, and the plastic strain reduced monotonically, with the increase of x values for the alloys. At x = 0.4, the maximum yield strength and fracture strength of the alloy were 1646.89 MPa and 1947.09 MPa, respectively, and the average friction coefficient was a minimum of 0.47, with a hardness value of HV 489.68 and a plastic strain of 13.98%. The maximum hardness value of the alloy was HV 656.19 at x = 0.8. The fracture mechanism of the alloys was from ductile fracture to brittle fracture and the wear mechanism was form of abrasive wear. Accordingly, the FeCrNiCuTi0.4 alloy obtained the optimal mechanical properties overall. This research is of great significance for the development of engineering and structural materials with excellent mechanical properties.

Novel design of Mo-Si-B + La2O3 powder with multi-shell structure for ideal microstructure and enhanced mechanical property

In this study, the multi-shell structured Mo-Si-B powder with La2O3 particles (MSB + L powder) was designed to obtain the ideal microstructure of sintered body, and the effects of the La2O3 addition on the microstructural and mechanical characteristics were investigated. Mo-Si-B powder (MSB powder) was prepared via mechano-chemical powder metallurgy methods, and MSB + L multi-shell powder was fabricated via chemical methods such as mixing and calcination processes. Using this powder, MSB + L alloys were prepared under cold isostatic pressing followed by pressureless sintering. Our unique powder's architecture allows us to fabricate the ideal microstructure of MSB + L alloys which consist of isolated intermetallic compound phases and uniformly dispersed La2O3 particles in continuous α-Mo matrix. This ideal microstructure contributes to the enhancement of fracture toughness of MSB + L alloys by changing fracture behavior, compared to MSB alloys without La2O3 particles. For example, intergranular fracture mode in MSB alloys changed to intragranular fracture mode in MSB + L alloys. In addition, the fracture toughness was enhanced around 26% in MSB with 0.3 wt% La2O3 particle at room temperature (17.0 MPa·m1/2) while MSB alloys have around 13.50 MPa·m1/2. The addition of La2O3 particles in MSB alloys highly affect the fracture behavior at room temperature through the grain refinement and oxide particle strengthening.

Transient Liquid-Phase Sinter-Bonding Characteristics of a 5 um Cu@Sn Particle-Based Preform for High-Speed Die Bonding of Power Devices

To ensure the high-temperature stability of a bondline under next-generation power devices such as SiC semiconductors, a die bonding test was performed by transient liquid-phase (TLP) sinter-bonding using a Sn-coated Cu (Cu@Sn) particle-based preform. Compared to the existing 20 min-bonding result using a 30 μm Cu@Sn particle-based preform, a 5 μm Cu@Sn particle-based preform was used to significantly reduce the bonding time to 5 min, and the optimal levels of the amount of Sn in the Cu@Sn particles, the thicknesses of Sn surface finish layers on the chip and substrate, and compression pressure during the bonding were investigated. The Sn content in the Cu@Sn particles significantly changed the microstructure, including the porosity of the prepared preform. The preform porosity of 0.01% was confirmed after the formation of sufficient Sn shells with an average thickness of about 602 nm at Sn 30 wt%. In addition, in the preform with Sn 30 wt% content, the Sn phase was almost depleted after 3 min after annealing at 250 °C. The Sn finish layer was evaluated in the thickness range of 0.63−4.12 µm, and it was observed that the shear strength of the formed bondline tended to increase with increasing pressure for all Sn layer thicknesses. In particular, when the bonding was carried out at a pressure of 2 MPa using a dummy Cu chip and substrate coated with a 1.53 μm thick Sn layer, the best shear strength value of 36.89 MPa was achieved. In this case, all the Sn phases transformed into intermetallic compound phases of Cu&lt;sub&gt;6&lt;/sub&gt;Sn&lt;sub&gt;5&lt;/sub&gt; and Cu&lt;sub&gt;3&lt;/sub&gt;Sn, and all the phases formed within the bondline, including Cu, exhibited high melting-point characteristics. Therefore, it was determined that there would be no remelting of the bondline or a drastic decrease in mechanical properties in a high-temperature environment below 300 &lt;sup&gt;o&lt;/sup&gt;C, as initially intended. By increasing the content of the Sn shell up to 30 wt%, it was possible to achieve a nearly full density (porosity: 0.3%) bondline structure, due to the rearrangement behavior of particles, by maintaining liquid Sn for a long time during the bonding process. In conclusion, the optimal Sn finish thickness was determined to be at the level of 1.5 µm, and the optimal pressure was at the level of 2 MPa. The short bonding time of 5 min represents a significant advance in TLP bonding processes, and it is expected to contribute to a substantial improvement in the die bonding of future SiC power devices.

Research on the energy properties and the storage stability of Al–Si–Li ternary alloy powders

To solve the problems of storage stability and compatibility of the Al–Li alloy powders, a series of Al–Si–Li alloy powders containing two-phase structure were prepared based on Al–Si–Li ternary phase diagram. The energy release, attenuation and compatibility of the Al–Si–Li alloy powders were studied by oxygen bomb calorimeter, XRD, SEM, TG-DSC and SIMS. As the content of the AlSiLi intermetallic compound phase increased, the measured mass combustion enthalpies increase before decreasing. When the proportion of the AlSiLi intermetallic compound phase is 20 wt.% (denoted as 20%-ASL), it has the maximum mass combustion enthalpy (31729 J⋅g−1) which is higher than the theoretical mass enthalpy of the pure aluminum powder (31000 J⋅g−1). The aging test of the 20%-ASL alloy powder show that its measured mass combustion enthalpy only decreased by 5.5 % (from 31739 J⋅g−1 to 29921 J⋅g−1), along with the thermal oxidation weight gain decreasing from 95.82 % to 80.04 %, while mass combustion enthalpy of the Al–Li alloy powder with the same Li content decreased by 17.5 % (from 30325 J⋅g−1 to 25031 J⋅g−1), and the weight gain decreased from 96.68 % to 41.05 %. This indicates that the AlSiLi phase effectively improves the oxidation resistance and storage stability of the Al–Li alloy powders. To explain this, surface Li distribution of the 20%-ASL alloy powder was analyzed by SIMS. The results show that the AlSiLi phase can immobilize Li inside the particles to reduce surface Li content from 2.920 × 106 to 1.439 × 106 and improve its oxidation resistance, thereby improving its storage stability and compatibility.

Modulating the exposed facets of Pd-Pb intermetallic compounds via morphology engineering for efficient multifunctional electrocatalysts

To develop Pd-based intermetallic compounds (IMCs) nanomaterials with specific morphologies for exposing specific facets is essential yet full of challenges for highly efficient electrocatalysts. Herein, we utilized morphology engineering to successfully acquire Pd-Pb concave nanocubes (Pd-Pb CNCs) with Pd3Pb IMC phase and exposing (200) facet mainly. The Pd-Pb CNCs catalyst displays the ultrahigh activity of 4.01 A mgPd-1 for ethanol oxidation reaction (EOR), surpassing than that of Pd-Pb nanoparticles with Pd3Pb IMC phase but exposing (111) facet mainly, and far exceeding than commercial Pd/C. Density functional theory simulation manifests that the excellent EOR activity for Pd-Pb CNCs is attributed to the weakened reaction intermediates adsorption on catalyst surface. Importantly, the Pd-Pb CNCs are also with excellent reactivities for methanol oxidation reaction and glycerol oxidation reaction, indicating potentials as outstanding multifunctional electrocatalysts. This work may not only furnish a simple strategy for fabricating Pd-based IMCs exposing specific facets, but also promote their high-efficient applications in alcohol oxidation reactions and beyond.