Interfacial Reaction Products Research Articles

Stability of Proton-Conducting Solid Oxide Electrolyzers for Hydrogen Production and Energy Storage

Proton-conducting solid oxide electrolyzers (H-SOEs) provide promising opportunity to produce pure and dry hydrogen in steam electrolysis at relatively low operating temperatures (550-700˚C) utilizing electricity and heat generated from renewable energy sources. Compared to traditional high temperature (750-1000˚C) oxygen-conducting solid oxide electrolyzers (O-SOEs), lower operating temperature of H-SOE offers ease of thermal management, active stack and BOP materials cost reduction and reduction in chromium evaporation from metallic components. Like O-SOEs, preserving the long-term stability of H-SOEs is one of the technical challenges for large-scale hydrogen production. In this technical contribution, results of experimental evaluation of H-SOEs under real-world operating conditions are presented. As fabricated and posttest cells have been characterized using operando electrochemical impedance spectroscopy, X-ray diffraction, focused ion beam-transmission electron microscopy and other bulk and surface characterization techniques to examine bulk, surface and interface stability of electrochemically active components. Phase and morphological changes, compositional uniformity and interfacial reaction products formation have been examined. Electrolyte/electrode materials stability, cell and gas seal fabrication processes, and gaseous impurities affecting long-term electrochemical performance will be discussed. H-SOE electrochemical performance model based on cell materials and operating conditions has been proposed and validated based on single cell testing data.

Fatigue and Fracture Behavior of Al6061-B4C Aluminium Matrix Composites

In the present day engineering design and development activities many Scientists, Researchers and Engineers are striving hard to develop new and better engineering materials, which accomplishes high strength, low weight and energy efficient materials since the problems of environment and energy are major threshold areas. The development of new materials is growing day by day to replace the conventional materials in aerospace, marine engineering, automobile engineering industries etc., Hence, composite materials are found to be an alternative. A variety of metals and their alloys such as Aluminum, Magnesium and Titanium are comprehensively used as matrix materials. Among these Aluminium alloys have been used extensively, because of their excellent strength, low density, corrosion resistance and toughness. Similarly, many researchers have attempted to develop aluminum based metal matrix composites using different reinforcements such as SiC, Al2O3, B4C, TiC, TiO2, B4C etc., are added to the matrix to get required MMC’s. Among these reinforcements, B4C emerged as an exceptional reinforcement due to its high strength to density ratio, possesses high hardness and avoid the formation of interfacial reaction products with aluminum. Hence, in this paper attempts are made to fabricate Al 6061-3, 6, 9 and 12 wt.% B4C metal matrix composites by stir casting process to study fatigue life and fracture toughness as per ASTM standards. It is evident that fatigue strength and fracture toughness of the composites were enhanced with the addition of the wt.% of the reinforcement.

Designing of a thin Mo diffusion barrier towards strong and reliable Ti/Cu dissimilar brazing

The dissimilar brazing of Ti and Cu has been recognized to be challenging owing to the affinity of forming brittle intermetallic compounds at joint interface. In the current investigation, it was demonstrated that such detrimental interfacial reaction products can be readily circumvented by employing a Mo diffusion barrier deposited on Ti substrate. Combining Mo interlayer and a Ag–Cu–Ti active filler alloy, intermetallic compounds free Ti/Cu brazed joints consisting of Ti–Mo solid solution, Mo interlayer and remnant braze can be obtained. As a result of the eradication of brittle phases, the resultant joints exhibit excellent structural integrity with bonding strength comparable to the parent material properties. Additionally, as a consequence of sluggish solid state diffusion at the Ti/Mo interface and limited dissolution of the Mo interlayer by filler alloy during brazing, the desirable joint microstructure can be reproduced within a wide range of bonding duration. Such results indicate that strong and reliable Ti/Cu dissimilar brazing can be achieved by the combination of a Mo diffusion barrier and Ag–Cu–Ti active filler alloy.

A study of reaction processes in SiC fiber reinforced Ni-Fe matrix composite during HIP

ABSTRACT Binary Ni-Fe metal matrix composite containing continuous W-core SiC fibers was fabricated by hot isostatic pressing (HIP) method to study the interface reaction processes. Interfacial reaction products were analyzed via field emission scanning electron microscope, electron probe microanalysis and micro-zone X-ray diffractometer. The results indicate that the reactions are so dramatical that even W core can decompose during the HIP process. The whole reaction processes of W-core SiC fiber can be divided into four stages. In stage 1, SiC starts to react with metal matrix to form Ni silicides with dissolved Fe element, graphite and Kirkendall void zone. In stage 2, SiC decomposes further and W core is exposed, then W core participates in reactions. In stage 3, SiC reacts completely, W core further reacts. In stage 4, W core decomposes completely and transform to be steady WC particles, which means the whole processes terminate. A model to clarify the mechanism of the reaction processes is proposed.

Spark plasma sintering processed α−SiAlON bonded tungsten carbide: Densification, microstructure and tribomechanical properties

Processing, microstructure and tribomechanical performance of spark plasma sintering (SPS) processed α−SiAlON bonded tungsten carbide (WC) have been reported. SPS at 1750 °C under 40 MPa for 25 min resulted in almost theoretically dense composites. Microstructure analysis using scanning and transmission electron microscopy revealed formation of principally micron sized, equiaxed WC grains surrounded by sub-micron to micron sized α−SiAlON having both equiaxed (higher concentration) and elongated (lower concentration) grain morphology. Sharp and clean WC/α−SiAlON interface regions were noticed without any interfacial reaction product. As evidenced from elemental mapping under HAADF-STEM, the α−SiAlON grain boundary region was found to be rich in yttrium and oxygen, whereas, presence of characteristics elements were identified in α−SiAlON and WC grains. Addition of α−SiAlON in WC matrix resulted in progressive improvement in tribomechanical performance of the composites compared to pure WC. The 40 wt% α−SiAlON bonded WC matrix composite offered almost 30–33% higher Vickers hardness and toughness than those obtained for pure WC. Three point flexural strength of the 40 wt% α−SiAlON/WC composite was found to be around 425 MPa. Unlubricated wear tests also indicated significantly higher damage of hard and tough β−Si3N4 ball when sliding against the composites compared to pure WC. Formation of progressively thicker and adherent tribolayer containing broken particles of WC and α−SiAlON having sharp edges was possibly the primary reason that caused severe abrasive wear of the counterbody. Results indicated the efficacy of SPS processed α−SiAlON bonded WC composites having improved tribomechanical performance over conventional monolithic WC.

Effect of hot extrusion temperature on graphene nanoplatelets reinforced Al6061 composite fabricated by pressure infiltration method

In the present work, 0.6 wt% graphene nanoplatelets reinforced 6061Al (GNPs/6061Al) composite was prepared by pressure infiltration process and hot extruded (HE) at 420 °C∼500 °C in order to investigate the evolution of GNPs in different extrusion temperature, which has not been reported yet. The GNPs agglomeration were eliminated by extrusion and were arranged in an orientation. In the sample extruded at 420 °C, the dispersion effect was not significant and agglomeration of large-sized GNPs was still found. However, the agglomeration of the GNPs was eliminated when extruded at 450 °C, and waved structure, exfoliation and bend of GNPs were observed. While in the sample at 500 °C, interlayer sliding of GNPs and interfacial reaction product Al4C3, due to excessively high extrusion temperature, were detected. The composites extruded at 450 °C showed the highest yield strength and ultimate tensile strength of 389 MPa and 500 MPa, respectively, which increased 16.8% and 40.1% comparing with the unreinforced matrix. The present results indicate that the uniform dispersion of graphene is still one of the main challenges in Graphene/Al composites, while the deformation treatment provides the possibility of further dispersion of graphene.

Improving the mechanical properties of B4C/Al composites by solid-state interfacial reaction

The effect of solid-state interfacial reaction between B4C and Al was often overlooked in related research. In the present study, B4C/Al composites were successfully produced by hot pressing sintering. Nanoscale interfacial reaction product, aluminum boron carbide (Al3BC), was formed in B4C/Al composites even at a low sintering temperature (570 °C). The distribution and properties of the nanoscale Al3BC were characterized by transmission electron microscopy (TEM). The results indicate that the interfacial product Al3BC can disperse into the Al matrix during hot rolling. The Al3BC nanoparticles located in the Al matrix lead to a significant strength improvement, around 65 MPa through the geometrically necessary dislocations (GNDs) strengthening and Orowan strengthening in B4C/Al composites with 30% weight percent of B4C. The contributions of Al3BC formation on strength and strengthening mechanism are discussed in detail.

Nucleation and growth mechanisms of interfacial carbide in graphene nanosheet/Al composites

The interface reaction is the focus of interface control in the graphene/Al composites, but its evolution processes are still unclear. The present work revealed the nucleation and growth mechanisms of the interfacial reaction product, aluminum carbide (Al4C3), in the graphene nanosheet (GNS)/Al composites. The nucleation of Al4C3 was found to mainly start at the open edge of GNSs due to the high chemical reactivity, and the formed Al4C3 was found to mostly locate either along or at an angle to the Al grain boundary, e.g. (i) ∼25° angle between Al4C3 (003) and Al (-111); (ii) Al4C3 (003)//Al (1-11); (iii) Al4C3 (003)//Al (002); (iv) Al4C3 (003)//Al (2-20). The growth of Al4C3 was controlled by the diffusional growth parallel to (003) plane and the nucleation growth perpendicular to (003) plane. Besides, the possible intermediate states, the C–Al interfacial transition zone, and the interfacial reaction transition phase were also observed. This work provides a theoretical basis for the further tailoring of interface bonding and property improvements of graphene/Al composites.

The effect of testing procedure on DSC measurements of Gd-Ti-Zr alloy using ZrO2 container

Differential Scanning Calorimetry (DSC) was applied to determine the critical temperatures of phase transformations in the Gd40Ti30Zr30 alloy (wt%). The comparative measurements were carried out using three types of measuring devices at a temperature RT- 1650?C in the same flowing gas (Ar, 99.9992%) but applying different testing procedures, which allowed obtaining dissimilar oxygen contents in the surrounding atmosphere. The high temperature interaction and reactivity taking place between molten alloy samples and ZrO2 container during DSC tests were evaluated by structural analysis of the resulting interfaces using alloy samples solidified inside the ZrO2 containers. The conducted research has demonstrated methodological difficulties accompanying measurements of the thermophysical properties of Gd-rich alloys by the container-assisted DSC method, particularly when the tests are performed in flowing argon atmosphere with significantly reduced oxygen content. Under non-oxidizing conditions, the degradation of ZrO2 container can take place during DSC testing because the selected Gd40Ti30Zr30 alloy reacts with the ZrO2 to form a continuous interfacial reaction product layer. Under slightly oxidizing conditions, the gadolinium oxide formed in situ on the alloy surface, plays the role of a barrier for direct contact between molten alloy and container and thus may suppress or even prevent the degradation of the container and its subsequent strong bonding with the holder.

Wetting of h-BN by molten Cu-8.8Zr-xTi ternary alloys at 1373 K

The wetting of hexagonal boron nitride (h-BN) by molten Cu–Zr eutectic alloy with different Ti concentration (0-10 at.%) was studies by a modified sessile drop method at 1373 K under high vacuum. h-BN cannot be wetted by Cu–Zr eutectic alloy (equilibrium contact angle is ~128°), but a small addition of Ti (2.5 at.%) can decrease contact angle significantly. Interfacial reaction products Ti-nitride, Ti-diboride, Zr-nitride and Zr-diboride were observed and identified using SEM and XRD. The reason of contact angle decreasing with Ti concentration in wetting case of Cu-8.8Zr-xTi (x = 2.5, 7.5, 10) system is the reducing of stoichiometry of TiNy, which makes TiNy has a better metallic property. In addition, the adsorption of Ti at liquid/solid interface is not a negligible factor. In non-wetting cases of Cu-8.8Zr and Cu–10Ti, the negative molar exchange energy values between Cu–Zr and Cu–Ti indicate Zr and Ti would be attracted by the bulk of liquid. Thereby, the improvement in the wettability of h-BN by Cu–Zr and Cu–Ti binary alloys is very limited.

Understanding interface stability in solid-state batteries

Solid-state batteries (SSBs) using a solid electrolyte show potential for providing improved safety as well as higher energy and power density compared with conventional Li-ion batteries. However, two critical bottlenecks remain: the development of solid electrolytes with ionic conductivities comparable to or higher than those of conventional liquid electrolytes and the creation of stable interfaces between SSB components, including the active material, solid electrolyte and conductive additives. Although the first goal has been achieved in several solid ionic conductors, the high impedance at various solid/solid interfaces remains a challenge. Recently, computational models based on ab initio calculations have successfully predicted the stability of solid electrolytes in various systems. In addition, a large amount of experimental data has been accumulated for different interfaces in SSBs. In this Review, we summarize the experimental findings for various classes of solid electrolytes and relate them to computational predictions, with the aim of providing a deeper understanding of the interfacial reactions and insight for the future design and engineering of interfaces in SSBs. We find that, in general, the electrochemical stability and interfacial reaction products can be captured with a small set of chemical and physical principles. The reliable operation of solid-state batteries requires stable or passivating interfaces between solid components. In this Review, we discuss models for interfacial reactions and relate the predictions to experimental findings, aiming to provide a deeper understanding of interface stability.

The influence of columnar microstructure on diffusion reaction between Ti thin films and aluminum nitride ceramics

In this paper, Ti films with certain thickness were deposited on a polished AlN ceramic substrates by direct current magnetron sputtering at room temperature (RT) and 400 °C, respectively. After deposition, the samples were annealed at 600 °C for 1 h in the mixture gases of argon and hydrogen atmosphere. The microstructure of the Ti films and interface reaction products between Ti/AlN were investigated using X-ray diffraction, and transmission electron microscopy. The effects of deposition temperature on the microstructure and grain orientation of Ti films were studied. It is found that the decomposition of AlN would mainly take place at the AlN/Ti interface during the heat-treated process. After annealing, Al and N react with Ti to produce AlTi3N in the film deposited at 400 °C, while TiN0.3 be formed if deposited at RT. The subsequent rolling-contact-fatigue test proved that after annealing at 600 °C for 1 h, the adhesion strength of Ti/AlN interface deposited at 400 °C is superior to that deposited at RT.

Joining of high thermal-expansion mismatched C-SiC composite and stainless steel by an Ag + Ti + Mo mixed powder filler

Abstract High thermal-expansion mismatched C-SiC composite and 304 stainless steel have been bonded by a 72Ag + 18Ti + 10Mo (at%) mixed powder filler. At the bonding temperature (1020 °C), the filler was in semi-solid state, i.e. solid-liquid mixed state of Mo particles, TiAg grains and Ag(Ti) liquid. Microstructural analysis indicated that the high activity and viscosity of the semi-solid filler help to obtain a large-thickness homogeneous joining layer (∼416 mm), in which Mo particles were clad by (Ti,Mo) solid solution and uniformly dispersed in Ag matrix together with the TiAg grains. The large thickness joining layer mainly composed of low coefficient of thermal expansion (CTE) Mo particles and ductile Ag matrix can effectively reduce the high residual stresses of the joint caused by the thermal-expansion mismatch between the dissimilar materials. Additionally, interfaces between the base materials and the joining layer were well bonded without continuous layered brittle compounds. The interfacial reaction products at C-SiC side were TiC, Ti5Si3 and Ti3SiC2 grains in Ag matrix. At 304 interface, Ti2Ni + Ti(Fe,Ni) compounds grew in columnar and gathered nearby. The characteristics of the joining layer and the bonding interfaces contribute to the high joint strength. The average shear strength of the joint at room temperature was 156 MPa.

An Overview of Quasicrystal Reinforced Magnesium Metal Matrix Composites

The strength of metals and their alloys are enhanced by adding secondary reinforcement particles like Conventional crystalline and non-crystalline particles such as SiC, glass and Al2O3. These particles provide weak interfacial bonding due to the crystallographic structure mismatch or undesirable interface reaction products. Quasicrystals provide strong interfaces with the matrix due to their low interfacial energy. Their low strength and stiffness make them useful in non-critical stress applications such as instrument panels, seat frames and gear box housings. Reinforcing quasicrystals to Mg alloys greatly enhances their strength or stiffness. The literature on quasicrystal (in-situ and ex-situ) reinforced Mg alloy composites are critically reviewed to show the importance of quasicrystal reinforcement in Mg alloys and the effect of different manufacturing process technologies such as casting process, powder metallurgy, hot extrusion on mechanical properties.

Butt Laser Welding–Brazing of AZ31 Mg to Nickel-Coated Ti-6Al-4V

Mg and Ti alloy are hard to be bonded due to their huge discrepancy in physical and metallurgical characteristics. As an intermediate element, Ni is feasible for joining of Mg and Ti. The interfacial microstructure and mechanical properties of laser-welded–brazed AZ31 Mg/Ti-6Al-4V joints in butt configuration were investigated with different thicknesses of electrodeposited Ni interlayer. The interfacial reaction products evolved from an ultra-thin Ti3Al layer to Ti2Ni layer mingled with Ti3Al, and more Mg3AlNi2 compounds were produced in the fusion zone (FZ) as Ni coating thickness increased. Slag inclusions and cracks were observed in interfacial layer when coating thickness exceeded 2.5 μm. The quantity of Mg3AlNi2 and the thickness of interfacial layer decreased from the top to bottom of groove of the same joint owing to high thermal gradient during laser welding. The chemical potential of Al and Ni indicated that Al-Ti reaction product was produced more easily than Ni-Ti in 0.001Mg-(Ni-Al-Ti) system. The thermodynamic calculation results of Gibbs free energy suggested the preferential formation Ti-Al phase and Ti-Ni phase along the interface while the Mg-Al-Ni ternary phase in the FZ. Fracture loads of joints increased first followed by a decline with the increase in coating thickness. The joint fractured at the Mg base metal, reaching a maximum value of 3900 N with the Ni coating thickness of 1.5 μm. In the case of using thinner or thicker Ni coating, crack propagated along the interface due to the insufficient metallurgical bonding or defects existed in the interfacial layer. The characteristic of fracture surface changed from the tear ridges and terraces to river pattern when interfacial failure occurred.

Microstructure Evolution and Mechanical Properties of Titanium/Alumina Brazed Joints for Medical Implants

Medical titanium and alumina (Al2O3) bioceramic are widely utilized as biomaterials. A reliable brazed joint of titanium and alumina was successfully obtained using biocompatible Au foil for implantable devices in the present study. The interfacial microstructure and reaction products of titanium/Au/Al2O3 joints brazed under different conditions were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). In this study, the typical interfacial microstructure of the titanium/Au/Al2O3 joint was titanium/Ti3Au layer/TiAu layer/TiAu2 layer/TiAu4 layer/Au + granular TiAu4 layer/TiOx phase/Al2O3 ceramic. With increasing brazing temperature or holding time, the thicknesses of Ti3Au + TiAu + TiAu2 layers adjacent to the titanium substrate increased gradually. Shear tests indicated that the joint brazed at 1115 °C for 3 min exhibited the highest shear strength of 39.2 MPa. Typical fracture analysis displayed that the crack started at the Al2O3 ceramic and propagated along the interface of TiAu2 and TiAu4 reaction layers.

Microstructure-based modeling on structure-mechanical property relationships in carbon nanotube/aluminum composites

The present work investigates structure-mechanical property correlations of carbon nanotube/aluminum (CNT/Al) composites through characterization and microstructure-based modeling. The nanoscale architecture of these composites, produced by flake powder metallurgy, was established using a transmission electron microscope equipped with an automated crystal orientation mapping system. The architecture mainly consists of elongated Al grains with submicron widths and micron lengths, intergranular CNTs and an interfacial reaction product, namely Al4C3 particles. The stress-strain behavior found with our dislocation-boundary/reinforcement interaction mechanical model, matched our experimental tensile curves. This model was also used to predict several key factors, namely grain dimensions, CNTs volume fraction, intergranular or intragranular distribution and aspect ratio, interfacial reaction rate, impacting tensile strength and ductility. It was found that intergranular CNTs induced strengthening will not result in lower uniform elongations, while intragranular distribution of low aspect ratio CNTs and Al4C3 nanoparticles can increase both strength and uniform elongations by the Orowan mechanism. It is expected that the model in the present work can assist in microstructure design of metal matrix nanocomposites.

Wetting of amorphous and partial crystalline Co73Si10B17 by Sn and Sn-based lead-free solders

Using wetting balance method, the wetting of Co73Si10B17 in amorphous and partial crystalline states by Sn and Sn-based lead-free solders (Sn-0.7Cu and Sn-0.3Ag-0.7Cu) were studied at 290–310 °C. The surface energy of the Co-based alloys was calculated by three methods (Zisman method, Fowkes and Owen theory). Although the calculated surface energy shows the presence of oxide film on the surface of all Co-based alloy, the amorphous Co73Si10B17 has a relatively higher surface energy. The wetting mechanism is the oxide film removal, which was caused by a series of complex multiple reactions. The final wettability of Co73Si10B17 was affected by the interfacial reaction products and surface oxide film, but was determined by the degree of the oxide film removal. In addition, RMA flux is not very effective for soldering of Co-based alloy whether in amorphous or partial crystalline state owing to its weak activity, especially it is not suitable for soldering of partial crystalline Co73Si10B17.

Probing Solid-Solid Interfacial Reactions in All-Solid-State Batteries

We have developed a hierarchy of DFT-based approaches to understand and design electrode/buffer/SE interfaces in all-solid-state batteries. Even with relatively efficient thermodynamics approximations, we reveal that S-O exchange reactions between oxides (O2-) and thiophosphates (PS4 3-) resulting in the formation of phosphates (PO4 3-) are responsible for large reaction driving force between the common NaMO2 (M = Co, Ni, Fe, Mn) cathodes and Na3PS4 SE. Such reactions, with their associated large volume changes, can be mitigated by careful selection of the cathode/SE combination, or the use of buffer layers with good stability between both materials. We have also identified several promising binary oxides with similar or better chemical compatibility with most electrodes and SEs than the commonly-used Al2O3. Despite the success of thermodynamics-based approximations, we further demonstrate that explicit modelling of the electrode/SE interface via ab initio molecular dynamics (AIMD) simulations sometimes yield different and more realistic predictions of interfacial reaction products. For example, AIMD predicts that formation of SO4 2– are kinetically favored over the formation of PO4 3– at the NaCoO2/Na3PS4 interface model, in contrast to the predictions of the thermodynamic models. These observations have been validated experimentally. We have also extended such studies to the LiNi0.85Co0.1Al0.05O2/Li6PS5Cl interface, with and without buffer layers, and the predicted interfacial reactions are in good agreement with experimental characterizations.

Interfacial characterization with wettability, microstructure and interfacial thermodynamics for Ti–Al/VN system

Interfacial characterization, which includes wettability, interfacial microstructure and interfacial thermodynamics between VN substrate and Ti–Al molten alloy with different Al concentrations, was studied by the sessile drop method at 1758 K. The wettability between molten Ti–Al alloy and VN depends on alloy composition. The initial apparent contact angle increases from 95 to 120° with increasing Al content from 40 to 80 wt.% in the Ti–Al alloys. The Ti–Al/VN system is a typical dissolution system. The effect of dissolution on the apparent contact angle is reflected in the initial stage and progresses synchronously with movement of the triple-phase line. The wettability of Ti–Al/VN system shows no remarkable improvement with the dissolution of V. AlN and TiN should be formed as the interfacial reaction products during dissolution reaction of VN substrate.