Growth Of Reaction Layer Research Articles

Interfacial structure and formation mechanism of 90 W-7Ni-3Fe/steel using co-sintering method

In this study, we proposed a powder metallurgy method to develop an interlocking interface in tungsten heavy alloy/steel composites, which is achieved by co-sintering technology using tungsten heavy alloy and steel powders with a large difference in particle size. The interfacial microstructure evolution and mechanical properties of the co-sintered joint as a function of co-sintering temperature were investigated systematically. Results showed that a well-bonded interlocking interface was formed along the steel particles as a result of the tungsten heavy alloy particles filling in the gaps between two neighboring steel particles. The co-sintered joint contains four regions: the W alloy matrix, the Fe3W3C layer, the Ni-affected layer, and the steel matrix. Based on the microstructural characterization, the interface formation mechanism and reaction layer growth behavior are discussed in depth. Benefitting from the interlocking structure, the highest tensile strength of the co-sintered specimen is 265 MPa, which is 66% higher than that of the non-interlayer joint obtained by diffusion bonding method. Moreover, its performance is better than that of some W alloy/steel with an interlayer. This technique offers a potential method for the efficient preparation of a W alloy/steel composite structure with outstanding properties.

Effect of Al-Si Coating on the Interfacial Microstructure and Corrosion Resistance of Dissimilar Laser Al Alloy/22MnB5 Steel Joints

This investigation employed different laser powers to conduct the laser welding–brazing process of 5052 aluminum alloy to both Al-Si coated and uncoated 22MnB5 steel. The flux-cored Zn-Al22 filler metal was employed during the procedure. The influence of Al-Si coatings on the microstructure and corrosion resistance of Al/Steel welded joints was investigated using microstructural characterization and electrochemical tests. It was noted that the interfacial microstructure of the laser Al/steel joints was significantly altered by the Al-Si coating. Moreover, the Al-Si coating suppressed the formation and growth of the interfacial reaction layer. Electrochemical corrosion tests showed that the impact of Al-Si coating on the corrosion resistance of laser joints depended on the laser powers and thickness of the interfacial intermetallic compound (IMC) layer. The research suggests that galvanic corrosion occurs due to the differences in corrosion potential between fusion zone (FZ), steel, and Fe-Al-Zn IMCs, which accelerate the corrosion of the joint. The IMC layer acts as a cathode to accelerate the corrosion of the FZ and as an anode to protect the steel from corrosion.

Cu/Al Dissimilar Cold Spot Forge Welding: Effects of Bonding Temperature and Reduction Ratio on Joint Strength and Reaction Layer Growth

Cu/Al Dissimilar Cold Spot Forge Welding: Effects of Bonding Temperature and Reduction Ratio on Joint Strength and Reaction Layer Growth

Linear growth of reaction layer during in-situ TEM annealing of thin film Al/Ni diffusion couples

During reactive layer growth in binary diffusion couples new phases can nucleate and grow. In the present work we perform in- and ex-situ interdiffusion studies in the system Ni-Al using X-ray diffraction (XRD) and analytical transmission electron microscopy (TEM). We investigate the reaction between 270 °C and 500 °C. We show that in the early stages of the solid-state reaction a small polycrystalline aluminide layer forms, while preferential grain growth follows in the later stage. In the reaction layer we detect the presence of Al3Ni by XRD and electron diffraction. Local chemical analysis by EDX in the TEM suggests that a second aluminide phase forms simultaneously. An in-situ TEM study at 380 °C shows layer growth of about 0.042 nm/s with a linear time dependence. We interpret this rate law on the basis of an interface-controlled reaction and discuss our results in the light of what is known about layer growth in thin film diffusion couples (presence/absence of predicted phases, linear/parabolic rate laws) and in view of results from the Ni-Al system published in the literature. Areas in need of further work are identified.

A Joining Process between Beryllium and Reduced-Activation Ferritic-Martensitic Steel by Plasma Sintering.

To investigate the growth kinetics of the reaction layer and mechanical strength of joined materials, we joined beryllium and reduced-activation ferritic–martensitic steel (F82H) by plasma sintering under various conditions and characterized the joined region. Scanning electron microscopy revealed that the thickness of the reaction layer increased with an increase in the joining time and temperature. Line analyses and elemental mapping using an electron microprobe analyser showed that the reaction layer consists of Be–Fe intermetallic compounds, including Be12Fe, Be5Fe, and Be2Fe, with small amounts of chromium and tungsten. Owing to the time and temperature dependence of the reaction-layer thickness, the layer growth of Be–Fe intermetallic compounds obeys the parabolic law, and the activation energy for the reaction-layer growth was 116.2 kJ/mol. The bonding strengths of the joined materials varied inversely with the thickness of the reaction layer.

Effect of interfacial microstructure evolution on the peeling strength and fracture of AMB Cu‐metalized AlN substrate

AbstractSilver‐titanium (Ag‐Ti) paste was used to prepare copper‐metalized aluminum nitride (AlN) substrate under 2 MPa by brazing. The effects of Ti concentration and brazing temperature on interfacial microstructure were evaluated. The evolution of the interfacial microstructure was examined based on six types of samples. The growth of TiN reaction layer at the AlN/Cu interface is from the island type to the continuous type, and then grows and thickens along the AlN grain boundary until the superficial AlN grains transform into TiN completely. The peeling strength increases as TiN reaction layer tends to be continuous, and reaches the maximum value of 34.6 N/mm. The copper‐metalized AlN substrates crack at the AlN ceramic, accompanied by the local plastic deformation of the copper foil, and then form the typical wave fracture. With further thickening of TiN reaction layer, the porous TiN layer becomes the weak link, and peeling strength decreased.

Vacuum diffusion bonding of Ti2AlNb alloy and TC4 alloy

The Ti2AlNb alloy was joined with TC4 alloy by vacuum diffusion bonding. The relationship between bonding parameters, and joint microstructure and shear strength was investigated. The results indicated that the diffusion of Al, Ti, Nb and V elements across bonding interface led to the formation of three reaction layers: B2/β layer and α2 layer on the TC4 side, and α2+B2/β layer on the Ti2AlNb side. The bonding temperature determined the atomic activity, thus controlling the growth of reaction layers and influencing the shear strength of the joint. When the Ti2AlNb alloy and TC4 alloy were bonded at 950 °C for 30 min under 10 MPa, the shear strength of the joint reached the maximum of 467 MPa. The analysis on the fracture morphology showed that the fracture occurred within the B2/β layer and the fracture model was ductile rupture. Meanwhile, the formation mechanism of the Ti2AlNb/TC4 joint was discussed in depth.

Interface Behavior of Brazing between Zr-Cu Filler Metal and SiC Ceramic

The interface behavior of brazing between Zr-Cu filler metal and SiC ceramic was investigated. Based on the brazing experiment, the formation of brazing interface products was analyzed using OM, SEM, XRD and other methods. The stable chemical potential phase diagram was established to analyze the possible diffusion path of interface elements, and then the growth behavior of the interface reaction layer was studied by establishing relevant models. The results show that the interface reaction between the active element Zr and SiC ceramic is the main reason in the brazing process the interface products are mainly ZrC and Zr2Si and the possible diffusion path of elements in the product formation process is explained. The kinetic equation of interfacial reaction layer growth is established, and the diffusion constant (2.1479 μm·s1/2) and activation energy (42.65 kJ·mol−1) are obtained. The growth kinetics equation of interfacial reaction layer thickness with holding time at different brazing temperatures is obtained.

Growth kinetics of interfacial reaction layer products between cubic boron nitride and Cu-Sn-Ti active filler metal

In the present investigation, the growth kinetics of interfacial reaction layer products between cubic boron nitride (CBN) and Cu-Sn-Ti filler metal has been thoroughly investigated. Detailed morphological and compositional features of respective compounds have been demonstrated for a wide brazing temperature ranging from 1153 K to 1223 K. It is found that within 30 minutes brazing holding time, the reaction layer growth is largely determined by the population of TiN via effective Ti diffusion with an activation energy of 223.51 kJ/mol, leading to parabolic growth patterns. It is further revealed that TiN grows both in axial and length dimensions, which eventually extends to the forefront and covers the reaction layer.

Microstructure and heat transfer characteristics of active brazed Ceramic–Metal joints

This work reports on the bonding of Al2O3–Cu, AlN–Cu, and AlN–Ni by active brazing for the thermoelectric module support plate. Ag63Cu35.25Ti1.75 braze alloy in the form of paste and sheet was used for this purpose. Investigation of the microstructure using scanning electron microscope (SEM) attached with energy dispersive spectroscopy (EDS) showed that Al2O3–Cu brazed joint alone had an interface with a continuous reaction layer. On the other hand, AlN when brazed to Cu and Ni showed a relatively weak bonding due to the poorly developed reaction layer at the interface. The growth of reaction layer while brazing of AlN–Cu and AlN–Ni was impeded by the dissolution of the respective metals into the molten braze alloy. In AlN–Ni, the decrease in Ti activity due to such dissolution is so low that the interface reaction layer was absent. The temperature difference (ΔT) measured across the ceramic–metal joints showed little resistance to heat transfer in Al2O3–Cu. On the other hand, other joints have shown a significant ΔT, mainly due to the poorly developed and less thermally conductive (TiAl)1+xN interface reaction layer. Thus, this study demonstrates that a stable ceramic–metal joint with high thermal conductivity could be made with Al2O3 using Cu by active brazing.

Formation of intermetallic compounds in reaction between Cu–Ni alloys and solid Sn – a new look at the prominent effect of Ni

Diffusion-controlled interaction of pure Cu with Sn at 488 K results in the formation of ε-Cu3Sn and η-Cu6Sn5 intermetallic compounds, and small additives of Ni in the Cu-substrate (up to 1 at. %), do not influence phase composition of the diffusion zone. It was found that in the η-phase, Sn diffuses somewhat faster than Cu (and Ni) does, and diffusion porosity is developed in the vicinity of the substrate/reaction product interface.When a Cu–Ni alloy containing (5–25) at. % of Ni is involved in the interaction at 488 K, no ε-phase is formed and no pores can be found in the vicinity of the reaction interface. In these couples, ThO2-particles introduced as fiducial markers at the contact surface, end up after the interaction inside the (Cu,Ni)6Sn5 product layer close to the interface with Sn. The reaction layer growth follows a parabolic kinetics, and the growth rate of the (Cu,Ni)6Sn5 product in the Cu1-xNix/Sn (x = 0.05–0.25) couples is much higher than that of η-phase in binary Cu/Sn and ternary couples with lower Ni-content.TEM investigation revealed that reaction product in the Cu25Ni/Sn couple consists of domains of differently oriented unit cells of long-period superlattice formed in the (Cu,Ni)6Sn5 phase. In each domain, there is a periodic array of antiphase boundaries which provide a high density of short-circuit paths for diffusional transport resulting in the fast growth kinetics of the product intermetallic layer.

Visible Observation and Formation Mechanism of Porous TiAl3 Intermetallics During the Continuous Sintering Process

The formation mechanism of porous TiAl3 intermetallics from Ti-75 at.% Al powder compact was explored through a continuous sintering process. The exothermic behavior, temperature changes and open porosity were investigated by ranging the sintering temperature from 600°C to 700°C. Results show that a thermal explosion (TE) occurs once the sample temperature reaches to 675°C, upon which it rapidly climbs to 1148°C within 10 s. Visual observation was achieved and revealed the exothermic state at every step, showing the overall heating and instantaneous reaction of TE. The open porosity increased significantly from 24.8% to 58.7% by increasing the sintering temperature from 670°C to 675°C. The reaction mechanism of porous TiAl3 materials in the Ti-75 at.% Al system indicates that sintering at 600°C, 650°C, and 670°C was controlled by atomic diffusion, diffusion-induced TE, and liquid-induced TE reaction, respectively. The diffusion reaction activation energy was 161.5 kJ mol−1 for diffusion-controlled growth of the TiAl3 reaction layer.

Electrode interface optimization advances conversion efficiency and stability of thermoelectric devices

Although the CoSb3-based skutterudite thermoelectric devices have been highly expected for wide uses such as waste heat recovery and space power supply, the limited long-term service stability majorly determined by the degradation of electrode interface obstructs its applications. Here, we built up an effective criterion for screening barrier layer based on the combination of negative interfacial reaction energy and high activation energy barrier of Sb migration through the formed interfacial reaction layer. Accordingly, we predicted niobium as a promising barrier layer. The experimental results show the skutterudite/Nb joint has the slowest interfacial reaction layer growth rate and smallest interfacial electrical resistivity. The fabricated 8-pair skutterudite module using Nb as barrier layer achieves a recorded conversion efficiency of 10.2% at hot-side temperature of 872 K and shows excellent stability during long-time aging. This simple criterion provides an effective guidance on screening barrier layer with bonding-blocking-conducting synergetic functions for thermoelectric device integration.

Interfacial behaviors of p-type CeyFexCo4–xSb12/Nb thermoelectric joints

Interfacial diffusions and/or chemical reactions are one of the key issues for the reliability of CoSb3-based skutterudite thermoelectric (TE) joint, especially for the [Formula: see text]-type joint, which limits the applications of TE devices. We investigate the interfacial evolution for [Formula: see text]-type CeyFexCo[Formula: see text]Sb[Formula: see text]/Nb joints ([Formula: see text]–1, [Formula: see text], 3, 4) and combine the previous study on [Formula: see text]-type Yb[Formula: see text]Co4Sb[Formula: see text]/Nb joint to demonstrate the effect of TE materials on the interfacial microstructure and interfacial resistivity. The reaction–diffusion kinetic analysis shows that the TE materials has little effect on chemical reactions but strongly influence the Sb diffusions. The low energy barrier of Sb diffusion leads to the absent phase decomposition of skutterudites in CeyFexCo[Formula: see text]Sb[Formula: see text]/Nb joints. The interfacial resistivity of CeyFexCo[Formula: see text]Sb[Formula: see text]/Nb joints is related with Fe content and the interfacial reaction layer (IRL) growth. In addition, since the interfacial reaction layer growth rate and interfacial resistivity of CeyFexCo[Formula: see text]Sb[Formula: see text]/Nb joints are both low, Nb is an adequate barrier layer candidate material.

Formation sequence of intermetallics and kinetics of reaction layer growth during solid state reaction between titanium and aluminum

Understanding on the reaction kinetics associated with the formation of intermetallic compounds and the mechanisms involved in evolution of the reaction product at different temperatures due to solid state reaction in Friction Stir Welding (FSW) of dissimilar materials is very important in selecting optimum operating condition to control intermetallic compounds for safety-critical applications. In this study, the evolution sequence of intermetallic compounds and reaction kinetics during the solid state reaction between Ti and Al has been investigated. It was found that the mechanical mixing of Al and Ti affects evolution of reaction layers (RL) and intermetallic compounds. The thickness of the RL increases with reaction temperature and titanium trialuminide (Al3Ti) was found to be the only ordered phase that is formed at a higher temperature (650 °C). The activation energy for the growth of the reaction layer was found to be significantly lower when compared to conventional welding. The sequence of formation of these intermetallic compounds is proposed based on kinetics and thermodynamic principles such as inter-diffusion and free energy of formation. The variation in stoichiometry at the Al/Ti interfaces due to mechanical mixing as occurred during FSW and difference in diffusivity of Al and Ti through reaction layers are considered responsible for the phase evolution and growth of these layers. The mechanism of the reaction with the reduced activation energy was attributed to fragmentation, mechanical mixing, development of dislocation and twinning in materials, activation of atoms due to severe deformation and grain boundary diffusion.

Formation Sequence of Intermetallics and Kinetics of Reaction Layer Growth During Solid State Reaction between Titanium and Aluminum

Understanding on the reaction kinetics associated with the formation of intermetallic compounds and the mechanisms involved in evolution of the reaction product at different temperatures after Friction Stir Welding (FSW) of dissimilar materials is very important in selecting optimum operating condition to control intermetallic compounds for safety-critical applications. In this study, the evolution sequence of intermetallic compounds and reaction kinetics during the solid state reaction between Ti and Al following FSW has been investigated. It was found that the mechanical mixing of Al and Ti that occurs in FSW affects evolution of reaction layers (RL) and intermetallic compounds. The thickness of the RL increases with reaction temperature and titanium trialuminide (Al3Ti) was found to be the only ordered phase that is formed at a higher temperature (650 °C). The activation energy for the growth of the reaction layer was found to be significantly lower when compared to conventional welding. The sequence of formation of these intermetallic compounds is proposed based on kinetics and thermodynamic principles such as inter-diffusion and free energy of formation. The variation in stoichiometry at the Al/Ti interfaces due to mechanical mixing as occurred during FSW and difference in diffusivity of Al and Ti through reaction layers are considered responsible for the phase evolution and growth of these layers. The mechanism of the reaction with the reduced activation energy was attributed to fragmentation, mechanical mixing, development of dislocation and twinning in materials, activation of atoms due to severe deformation and grain boundary diffusion.

Interfacial Reaction Between Mg-40Al and Mg-20Ce Using Liquid-Solid Diffusion Couples

Interfacial reactions and growth kinetics between molten Mg-40Al and solid Mg-20Ce were investigated. Reaction temperatures were 475, 500 and 525 °C, with reaction time ranging from 5 to 30 min. The results show that Al11Ce3, Al3Ce and Al2Ce are formed via the reaction of Al and Ce in the diffusion reaction layers. The volume fraction of the intermetallic compounds in the diffusion reaction layers increases with temperature increasing. The growth kinetics of the diffusion reaction layers well conform to the parabolic law. The activation energy for the growth of the diffusion reaction layers is (42±3.7) kJ/mol. Liquid-solid diffusion experiment helps to better understand the formation of compounds in the smelting process. Kinetics data are provided for the formation of the compound during the smelting process.

Investigation of the interfacial reactions between steel and aluminum coatings for hybrid casting

Coating of AA7075 was applied by means of cold gas spraying on steel substrates of 22MnB5 and DC04 as an interlayer for high pressure die casting of aluminum/steel hybrid components. The morphology and growth kinetics of intermetallic compounds formed at the interface between coating and steel has been investigated. Furthermore, the effect of alloying elements on the formation of the intermetallic phases was analyzed. The coated samples were heat treated by means of induction heating at the temperature T = 550 °C with different dwell times in the range of 10 s < t < 5 min. The reaction layer growth was examined by means of scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). Additionally, the intermetallic compounds were characterized by means of nanoindentation. Intermetallic compounds of AlFe phases occurred as the major constituent in the reaction zone for different combinations of coating and substrates.

Thermochemical calculations of the oxidation behavior of Nb2AlC MAX phase in ZrO2–matrix composites

The oxidation behavior of Y-TZP/Nb2AlC composite was explored by thermo-chemical phase equilibrium calculations and experimental oxidation studies at 1200 °C. Growth of a compact surface reaction layer requires migration of oxygen from the surface to the reaction front and a gradient of oxygen content is likely to develop. The results of phase equilibria calculations show that at low oxygen concentration preferential oxidation of Al favors thermal degradation of Nb2AlC which yields Al2O3 and Nb-carbides. With increasing oxygen content various Nb-oxides are formed and finally a mixture of NbAlO4 and Nb2O5 is present after full oxidation of a Nb2AlC particle. Experimental measurements confirmed the formation of a compact oxidation reaction layer at 1200 °C composed mainly of NbAlO4 and a co-doped (Nb,Y)-TZP matrix.

Effect of Alloying Elements on Growth Behavior of Intermetallic Compounds at the Cold-Sprayed Coating/Steel Interface During Immersion in Aluminum Melt

The formation of the intermetallic compounds at the interface between cold-sprayed coatings and steel as well as interaction between coatings and aluminum melt was investigated. Coatings of AA7075 (AlZn5.5MgCu) and AA4145 (AlSi10Cu4) were deposited on the sheets of the deep drawing steel DC04. The coated samples were then immersed in the aluminum melt AlSi9Mn at the temperature of T = 610 °C for different durations in the range 30 s < t < 10 min. The reaction layer growth was examined metallographically and by means of scanning electron microscope with energy-dispersive spectroscopy. Furthermore, the intermetallic phases were identified by X-ray diffraction analysis and characterized by microhardness measurements. For both coatings, β-AlFeSi phases were shown to be the major constituent in the reaction zone. The growth kinetics of the intermetallic phases appeared to be similar for AA4145 and AA7075 coatings, while their morphology was completely different.