Reactive Joining Research Articles

Control of Large‐Scale Single‐Phase Ni Silicide Formation from Reactive Multilayers

The Ni/Si reactive multilayer (RML) is full of application potentials including reactive joining, igniters, and power sources. Here, the Ni/Si RMLs with atomic ratios of Ni and Si (2:1, 1:1, and 1:2) are studied, where the bilayer thickness and the total thickness are controlled to be 53 nm and 2 μm, respectively. After laser ignition, a rapid explosive reaction is observed where there are two self‐propagation wavefronts and their velocities reach 7.20 and 11.93 m s−1. The uniform, small grains, and single‐phase Ni silicides are obtained and controlled by tuning growth parameters. From the understanding of the Gibbs free energy diagram, the first wavefront comes from the solid‐state amorphization reaction between the Ni and a‐Si. The formation of the final Ni silicide causes the second wavefront. The entire reaction is described by a transient heat transfer model. It proposes a key parameter called heat loss rate, which explains the importance of RML thickness and the thermal diffusivity of the substrate. It allows to accurately control the reaction rate, which masters the final silicide phase. Thus, the oxidation of samples downgrades the reliability as the self‐propagation velocity of the two wavefronts dropped to 1.34 and 1.91 m s−1 in samples after 200 h of oxidation.

Research Progress of Fusion Welding Techniques for Steel to Other Metals

Welding of dissimilar steel and TiNi shape memory alloys, aluminum alloy, magnesium alloy and other metals is an important issue because of its increasing applications in industries. This review aimed to provide a comprehensive overview of the recent progress in welding and joining of steel and heterogeneous metals and to introduce current research and application. However, the base materials on both sides of the traditional fusion welding must melt and the large melting point difference between the two seriously affects the weld formation. The metal compounds formed by the base materials on both sides also hinder the improvement of the mechanical properties of the joint. The methods available for welding steel and dissimilar metals included fusion welding, brazing, diffusion bonding, friction welding and reactive joining. The current state of the understanding and development of fusion welding method for steel and other metals was addressed. This review focused on the fundamental understanding of the microstructural characteristics, processing and property relationships in the welding and joining of heterogeneous joints.

Characterization of a PCB Based Pressure Sensor and Its Joining Methods for the Metal Membrane.

Essential quality features of pressure sensors are, among other accuracy-related factors, measurement range, operating temperature, and long-term stability. In this work, these features are optimized for a capacitive pressure sensor with a measurement range of 10 bars. The sensor consists of a metal membrane, which is connected to a PCB and a digital capacitive readout. To optimize the performance, different methods for the joining process are studied. Transient liquid phase bonding (TLP bonding), reactive joining, silver sintering, and electric resistance welding are compared by measurements of the characteristic curves and long-term measurements at maximum pressure. A scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX) analysis was used to examine the quality of the joints. The evaluation of the characteristic curves shows the smallest measurement errors for TLP bonding and sintering. For welding and sintering, no statistically significant long-term drift was measured. In terms of equipment costs, reactive joining and sintering are most favorable. With low material costs and short process times, electric resistance welding offers ideal conditions for mass production.

Molecular Dynamics Studies in Nanojoining: Self-Propagating Reaction in Ni/Al Nanocomposites.

Reactive joining with Ni/Al nanocomposites is an innovative technology that provides an alternative to more common bonding techniques. This work focuses on a class of energetic material, produced by high energy ball milling and cold rolling. The initial microstructure is more complex than that of reactive multilayer nanofoils, produced by magnetron sputtering, in which the bilayer thickness is constant. Typical samples are composed of reactive nanocomposite particles that are numerically modelized by randomly distributed layered grains. The self-propagating reaction was studied by means of molecular dynamics simulations. We determined the front characteristics and investigated the elemental mechanics that trigger propagation. Both dissolution of Ni in amorphous Al and sustained crystallization of the B2-NiAl intermetallic compound were found to contribute to the heat delivered during the process.

A review of dissimilar welding for titanium alloys with light alloys

Titanium (Ti) alloys are widely used in industrial manufacturing, medical treatment, vehicles, and other fields. When welded with other alloys, due to great differences in physical and chemical properties of these materials, cracks easily appear in the joint, and obtaining stable welded joints is difficult. Results show that brittle intermetallic compounds (IMCs) formed in the welding process could reduce the plasticity of the joint. This review aimed to provide a comprehensive overview of the recent progress in welding and joining of Ti alloy and light alloys and to introduce current research and application. The methods available for welding Ti alloy and light alloys included fusion welding, brazing, diffusion bonding, friction welding and reactive joining. In this study, control methods of brittle IMCs in the welding process of Ti and other alloys and various improvement measures studied at home and abroad are described.

Joining with Reactive Nano-Multilayers: Influence of Thermal Properties of Components on Joint Microstructure and Mechanical Performance

Reactive nano-multilayers (RNMLs), which are able to undergo a self-heating exothermal reaction, can, e.g., be utilised as a local heat source for soldering or brazing. Upon joining with RNMLs, the heat produced by the exothermal reaction must be carefully adjusted to the joining system in order to provide sufficient heat for bond formation while avoiding damaging of the joining components by excessive heat. This heat balance strongly depends on the thermal properties of the joining components: a low thermal conductivity leads to heat concentration within the joining zone adjacent to the RNML, while a high thermal conductivity leads to fast heat dissipation into the components. The quality of the joint is thus co-determined by the thermal properties of the joining components. This work provides a systematic study on the influence of the thermal properties upon reactive joining for a set of substrate materials with thermal conductivities ranging from very low to very high. In particular, the evolution of the microstructure within the joining zone as a function of the specific time-temperature-profile for the given component material is investigated, focusing on the interaction between solder, RNML foil and surface metallisations, and the associated formation of intermetallic phases. Finally, the specific microstructure of the joints is related to their mechanical performance upon shear testing, and suggestions for optimum joint design are provided.

Reactive Joining of Thermally and Mechanically Sensitive Materials

Reactive joining, i.e., utilization of an exothermal reaction to locally generate the heat required for soldering or brazing, represents an emerging technology for flexible and benign joining of heat-sensitive materials, e.g., for microelectromechanical systems (MEMS) applications. However, for successful reactive joining, precise control of heat production and heat distribution is mandatory in order to avoid damaging of the components during the process. For the exemplary case of borosilicate glass, the reactive joining process for a both thermally and mechanically sensitive material is developed. Employing various nondestructive and destructive testing methods, typical problems which can occur upon reactive joining are identified, e.g., exposure of the joining zone to excessive temperatures, experience of thermal shock by the substrate due to sudden temperature increase, and generation of residual stresses in substrate and soldering zone. Utilizing the results of nondestructive and destructive testing, procedures for successful reactive joining of borosilicate glass, silicon and aluminum oxide are provided.

Welding and Joining of Titanium Aluminides

Welding and joining of titanium aluminides is the key to making them more attractive in industrial fields. The purpose of this review is to provide a comprehensive overview of recent progress in welding and joining of titanium aluminides, as well as to introduce current research and application. The possible methods available for titanium aluminides involve brazing, diffusion bonding, fusion welding, friction welding and reactive joining. Of the numerous methods, solid-state diffusion bonding and vacuum brazing have been most heavily investigated for producing reliable joints. The current state of understanding and development of every welding and joining method for titanium aluminides is addressed respectively. The focus is on the fundamental understanding of microstructure characteristics and processing–microstructure–property relationships in the welding and joining of titanium aluminides to themselves and to other materials.

High temperature rapid reactive joining of dissimilar materials: Silicon carbide to an aluminum alloy

Abstract An effective method for bonding of silicon carbide (SiC) ceramic to 5083 Aluminum metal-alloys was developed. This method employed the concept of high-temperature rapid heterogeneous combustion reaction to joint dissimilar materials. Scaled-up welding apparatus, which can accommodate specimens of up to 5″ in diameter and 6″ in height and allow a rapid (∼10 ms) load application (up to 1000 MPa) on the joining stack during reaction, was designed and built. An exothermic mixture of titanium and carbon powders (molar ratio 1:0.4) was utilized as a joining reactive layer. Uniform crack-free bonding of SiC to 5083 Al-alloy was accomplished both without and with application of loads. SEM and focused ion beam (FIB) images revealed that ∼10 μm (without load) and ∼500 nm (with load) transitional joining layers along the interfaces were observed, respectively. Compositional and mechanical properties of joined samples were also characterized by EDS analysis and Vickers microhardness investigations.

Contact Reactive Joining of TA15 and 304 Stainless Steel Via a Copper Interlayer Heated by Electron Beam with a Beam Deflection

TA15 titanium alloy and 304 stainless steel were joined via a copper interlayer heated by electron beam with a beam deflection towards the stainless steel. Microstructures of the joints were analyzed by optical microscopy, scanning electron microscopy, and X-ray diffraction. The tensile strengths of the joints and the ultramicrohardness of the intermetallic compounds were also measured. The results showed that the joint was formed by three kinds of metallurgical processes. Copper interlayer and TA15 were joined by contact reaction with the reaction products of CuTi, Cu4Ti3, and Cu2Ti. While copper interlayer and 304 stainless steel were joined by fusion and solid state diffusion process. Tensile strength of the joint can reach to 300 MPa, equivalent to 55% of that of 304 stainless steel. Furthermore, the tensile strength was mostly dependent on the volume of the unmelted copper sheet, although the intermetallics layer was the weakest location in the joint.

Localized Parylene-C bonding with reactive multilayer foils

This paper describes a novel bonding technique using reactive multilayer Ni/Al foils as local heat sources to bond Parylene-C layers to another Parylene-C coating on a silicon wafer. Exothermic reactions in Ni/Al reactive multilayer foils were investigated by x-ray diffraction (XRD) and differential scanning calorimetry. XRD measurements showed that the dominant product after exothermic reaction was ordered B2 AlNi compound. The heat of reaction was calculated to be −57.9 kJ mol−1. A numerical model was developed to predict the temperature evolution in the parylene layers and silicon wafers during the bonding process. The simulation results revealed that localized heating occurred during the reactive foil joining process. Our experimental observation showed that the parylene layer was torn when the bond was forcefully broken, indicating a strong bond was achieved. Moreover, leakage test in isopropanol alcohol showed that reactive foil bonds can withstand liquid exposure. This study demonstrated the feasibility of reactive foil joining for broad applications in bio-microelectromechanical systems and microfluidic systems.

Bonding silicon wafers with reactive multilayer foils

In this study, silicon wafers were bonded using Ni/Al reactive multilayer foils as local heat sources for melting solder layers. Exothermic reactions in Ni/Al reactive multilayer foils were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). XRD measurements showed that the dominant product after exothermic reaction was ordered B2 AlNi compound. The heat of reaction was calculated to be −57.9 kJ/mol. A numerical model was developed to predict the temperature evolution in silicon wafers during the bonding process. The simulation results showed both localized heating and rapid cooling during the reactive foil joining process. Our experimental observation showed that the bond strength of the silicon wafer joints was estimated to be larger than the failure strength of bulk silicon. Moreover, leakage test in isopropanol alcohol (IPA) showed that reactive foil bonds possessed good hermeticity.

Combustion joining of refractory materials

This paper overviews heterogeneous exothermic reactive systems as they apply to the joining of materials. Techniques that are investigated fall under two general schemes: so-called Volume Combustion Synthesis (VCS) and Self-Propagating High-Temperature Synthesis (SHS). Within the VCS scheme, applications that are considered include Reactive Joining (RJ), Reactive Resistance Welding (RRW), and Spark Plasma Sintering (SPS). Under the SHS scheme, Combustion Foil Joining (CFJ) and Conventional SHS (CCJ) are discussed. Analysis of the relevant works show significant potential, particularly for the RJ, RRW, and CFJ approaches, in the joining of a variety of materials which are difficult, or impossible, to bond using conventional techniques. More specifically, it is shown that these methods can be successfully applied to the joining of: (i) dissimilar materials such as ceramics and metals and (ii) refractory materials, such as graphite, carbon-carbon composites, W, Ta, Nb, etc.

Effect of reaction heat on reactive joining of TiAl intermetallics using Ti–Al–C interlayers

This study reports on the reactive joining of TiAl intermetallics using Ti–Al–C interlayers. The composition of the interlayer was determined according to the calculation of adiabatic temperature in the reaction system. The effect of the interlayer and joining pressure on reactive joining was studied. The heat generated in the interlayer had a strong influence on the reactive joining.

Microstructure evolution and reaction mechanism during reactive joining of TiAl intermetallic to TiC cermet using Ti–Al–C–Ni interlayer

This study reports on a new approach for joining of TiAl intermetallic to TiC cermets by self-propagating high-temperature synthesis. The adiabatic combustion temperature in the Ti–Al–C–Ni system was calculated and the composition of the reactants was determined by the calculated result. For a typical microstructure of the joint, two continuous grey reaction layers were found near the TiAl substrate and massive Ni-rich zones were observed adjacent to the TiC cermet. It was noted that the voids were inevitable in the reaction products. The crack was always formed at the interface between the interlayer and TiC cermet due to the residual stress. The interfacial joining between TiC cermet and the interlayer depended on the formation of Ni-rich layer. The joining between the TiAl and the interlayer was simplified as the reaction between liquid Al and solid TiAl. The SHS reaction in Ti–Al–C–Ni system was ignited at the melting point of Al. The first reaction took place between liquid Al and solid Ti to form TiAl 3. With the increase of the temperature, Ti reacted with C to form TiC phase.

Thermal and microstructural effects of welding metallic glasses by self-propagating reactions in multilayer foils

We have previously demonstrated that Zr-based metallic glass components can be welded using the heat produced by self-propagating exothermic reactions in multilayer metallic foils. Here, we examine the evolution of the temperature field during reactive joining of bulk amorphous Zr 57Ti 5Cu 20Ni 8Al 10, as well as the microstructure of the resulting joints. Numerical simulations predict that the metallic glass near the glass/foil interface heats very rapidly (∼10 7 K s −1) to temperatures of ∼1350 K, well above the liquidus temperature of the amorphous alloy (∼1115 K), followed by rapid cooling (∼10 5 K s −1) once the reaction front has passed. The maximum temperature, heating rate, and cooling rate of the glass all decrease with increasing distance from the interface. Infrared measurements of the temperature of the metallic glass components during joining show that the cooling rate exceeds the critical cooling rate of the alloy. Optical and scanning electron microscopy reveal no evidence of crystallization of the glass components due to the joining process.

Effects of physical properties of components on reactive nanolayer joining

We studied the effects of the physical properties of components on a reactive joining process that uses freestanding nanostructured Al∕Ni multilayer foils as local heat sources to melt AuSn solder layers and thereby bond the components. Stainless-steel reactive joints were compared with Al reactive joints. The strengths of both the stainless-steel and the Al joints increase as the foil thickness and thus the total heat of reaction increases until the foil thickness reaches a critical value. For foils thicker than the critical value, the shear strengths are constant at approximately 48 and 32MPa for the stainless-steel joints and Al joints, respectively. The critical foil thickness for stainless-steel joining is 40μm, compared with 80μm for the joining of Al. Numerical studies of heat transfer during reactive joining and the experimental results suggest that the duration of melting of the AuSn solder is shorter when Al specimens are joined. Thus, a thicker foil is required to enable a sufficient duration (0.5ms) of melting of the AuSn solder and full wetting of the metallic samples in order to form a strong joint. In general, when components with higher thermal conductivity, higher heat capacity, and higher density are joined, the duration of melting of the solder or braze layer is shorter and therefore a thicker foil is required to ensure the formation of a strong joint.

アルミナイド系金属間化合物の反応接合

アルミナイド系金属間化合物の反応接合

Investigating the effect of applied pressure on reactive multilayer foil joining

This paper describes the effect of applied pressure on reactive joining of stainless steel specimens and Al alloy specimens using nanostructured Al/Ni foils and AuSn and AgSn solder layers. For a given material system, higher applied joining pressure enhances the flow of the molten solder and thus improves wetting and bonding. Shear strengths of the reactive joints are shown to increase as the pressure that is applied during joining rises to a critical value. At higher applied pressures joint shear strengths remain relatively constant. The critical applied joining pressure is shown to be dependent on the foil thickness (or total heat of reaction), and the properties of the solder material and components, which determine the duration of melting of the solder and the maximum temperature at the solder/component interface. Longer durations of melting and higher interface temperatures enhance the flow of solder, improve wetting conditions and result in lower critical applied pressures.

Reactive nanostructured foil used as a heat source for joining titanium

We have joined titanium alloy (Ti-6Al-4V) specimens at room temperature and in air by using free-standing nanostructured Al∕Ni multilayer foils to melt a silver-based braze. The foils are capable of undergoing self-sustaining exothermic reactions and thus act as controllable local heat sources. By systematically controlling the properties of the foils and by numerically modeling the reactive joining process, we are able to conclude that the temperatures reached by the foils during reaction are critical in determining the success of joining when using higher melting temperature braze layers.