Ceramic/metal joining for structural applications

Abstract

Technological advances are extending the applications for bonded ceramic-metal components and demanding more rigorous performance characteristics. The techniques available for fabricating high–integrity joints for structural applications have been reviewed and attention is drawn to the factors that effect both direct and indirect bonding using liquid– and solid–phase materials. Two processes still largely in the developmental stage – fusion welding and diffusion bonding – have been considered, as well as the more established processes such as brazing. It is suggested that active metal brazing and indirect diffusion bonding will be among the techniques to be further developed and used more extensively in future.

MST/205     

Interfacial structure and strength on Ti(C,N) joint using liquid phase diffusion bonding with Ti/Ni interlayer

Abstract

Partial transient liquid phase diffusion bonding (PTLP-DB) on Ti(C,N) cermet was studied in the present paper using Ti/Ni/Ti foil sandwich structure as the interlayer. The interfacial structure and element distribution at the interface were observed using SEM, electron probe microanalysis and X-ray diffraction. The joint strength was measured using four-point bending test. The results showed that metallurgical bonding between Ti(C,N) cermet was achieved using PTLP-DB. Near Ti(C,N) cermet side, a strong chemical reaction occurred to produce an interfacial multilayer containing Ti–Al and Ti–Ni intermetallics. Different bonding times during PTLP-DB were also studied, and there was an optimum time during bonding. With a shorter bonding time, voids were observed at the interface, while with a prolonged time, the bending strength on the joints also decreased due to the overgrowth on intermetallic layer and the existence of high gradient residual stress at the interface.     

Solid state bonding of superplastic AA 7475

Abstract

Solid state (diffusion) bonds have been developed in AA 7475E sheet material using different regimes of bonding temperature, pressure, and time. The bonds produced have exhibited shear strengths in the range 30–150 MN m^?2 and have been found to be capable of withstanding peel during a slow high-temperature superplastic forming operation. However, the bonds formed under any one set of bonding conditions showed an extremely wide variation in both shear strength and shear fracture mode. The source of this wide variation has not yet been identified.

MST/601     

Fabrication of Al–Cu laminated composites by diffusion rolling procedure

Abstract

A diffusion rolling procedure was employed for the fabrication of Al–Cu laminated composites; the microstructure and mechanical properties of the interface were investigated. With diffusion bonding initially, intermetallic compounds (IMCs) occurred at the Al/Cu interface. After plastic deformation by rolling the laminated composites, the interface strip of IMCs broke and became discontinuous equiaxed particulates. Compared with roll bonding with heat treatment and diffusion bonding, the shear tensile strength of two-stage processed Al/Cu interface reached a maximum value equivalent to 90% of that of Al. Therefore, it is concluded that the diffusion rolling procedure yielded the highest strength of Al–Cu laminated composites.     

Principles of superplastic diffusion bonding

Abstract

Superplastic diffusion bonding is now established as an important technique for solid state bonding. There are two types of superplastic diffusion bonding using either transformation or isothermal superplasticity. In this overview, the principles of these two types are summarised and the applications are discussed, including superplastic forming with concurrent diffusion bonding (the SPF-DB process), pressure welding, and the use of superplastic diffusion bonding in sintering.

MST/835     

Thermodynamic and kinetic analysis of interfacial reaction between CBN and titanium activated Ag–Cu alloy

Abstract

Thermodynamic and kinetic analysis was performed in order to study the interfacial reaction mechanism of cubic boron nitride (CBN) abrasive grains and Ti activated Ag–Cu filler alloy during high temperature brazing. Meanwhile, microstructure of the interfacial layer was experimentally detected using scanning electron microscope (SEM), energy dispersion spectrometer (EDS) and X-ray diffraction (XRD) in the present paper. The results indicate that according to the thermodynamic theory, the interfacial reaction has been proved feasible, and during brazing the special active element Ti concentrated to and reacted with the CBN abrasive to form TiB₂ and TiN, which joined hard the abrasive grain and steel substrate. Furthermore, the diffusion activation energy of the growing process in the interfacial reaction layer has discovered that the layer growth largely depends on the new formed TiN under conditions of 1153–1193 K and 5–30 min.     

Transient liquid phase diffusion bonding of continuous SiC fibre reinforced Ti–6AI–4V composite to Ti–6AI–4V alloy

Abstract

A continuous SiC fibre reinforced Ti–6Al–4V composite was diffusion bonded in transient liquid phase to Ti–6Al–4V alloy plate using Ti–Cu–Zr amorphous filler metal. Joint strength increased with bonding time up to 1·8 ks and reached the maximum value of 850 MN m^?2 which corresponded to 90% of the tensile strength of Ti–6Al–4V. The extent of deformation of Ti–6Al–4V in the vicinity of the bonding interface was small compared with that of solid diffusion bonding because of the low bonding pressure. The bonding layer had an acicular microstructure which was composed of Ti₂Cu and α titanium with dissolved zirconium. Brittle products such as (Ti, Zr )₅ Si₃ or (Ti, Zr )₅ Si₄ were formed at the interface between the SiC fibres and the filler metal. These products existed only at the end of fibres, in very small amounts, therefore joint strength was not significantly affected by the products.

MST/1989     

Diffusion bonding of titanium alloy to stainless steel wire mesh

Abstract

The feasibility and appropriate processing parameters of diffusion bonding of titanium alloy to stainless steel wire mesh directly and with a nickel interlayer have been investigated. The microstructures of the diffusion bonded joints were observed by optical microscopy, scanning electron microscopy, X-ray diffraction, and electron probe microanalysis and the main factors affecting diffusion bonding were analysed. The maximum shear strengths of the joints were 72 and 148 MPa for direct bonding and indirect bonding using a nickel interlayer respectively. Atomic diffusion and migration between titanium and iron are effectively prevented by adding pure nickel as the interlayer metal, and a firm joint is obtained.     

Finite element method simulation of residual stresses in Al2O3–AISI 304 steel joints

Abstract

Thermal residual stresses are very detrimental to the mechanical resistance of metal–ceramic joints and thin metallic foils acting as stress relieving interlayers have been used to reduce their effect. The present work presents finite element method simulations of the residual stress field in Al₂O₃–AISI 304 steel joints using interlayers. Different interlayer materials (Ti, Ni, Mo, and Cu) were considered, either separately or in combination. Calculations show that among the different interlayer materials considered, Cu and Ti/Cu are most effective in reducing the thermal stresses and that this role is determined mainly by the ductility of the interlayer material. The calculated results were validated by shear tests performed on real joints obtained by diffusion bonding and it was concluded that residual stresses control the mechanical resistance of the joints.     

Magnetic pulse welding of Al to Mg alloys: structural–mechanical properties of the interfacial layer

Abstract

The magnetic pulse welding of Al-A1050 to Mg alloys was successfully performed, and the structural–mechanical properties of the interfacial bonding layer produced between dissimilar metals were studied. The morphology of the interface layer has a typical wavy pattern with an average thickness of 20 μm. Compositional microanalysis showed that the composition of the interfacial layer is Al–50 at-%Mg and is practically uniform, being a direct outcome of the local melting effect, intensive mixing of the melt and a rapid rate of solidification. The composition of the bonding layer corresponds to the Al supersaturated intermetallic β phase (Mg₁₇Al₁₂). The elastic modulus (and the hardness) of the interfacial layer was measured using the nanoindentation technique, and its value of 60·2±1·4 GPa is in good agreement with the value calculated from first principles in the literature (57·3 GPa) for the Mg₁₇Al₁₂ intermetallic phase.     

Experimental push out testing and analysis of fibre reinforced composites: applicability and test considerations

Abstract

The applicability of the push out technique to fibre composite systems with both excellent and poor interfacial bonding has been considered through experimental push out studies on model polymer matrix and metal matrix composite systems, respectively. Some factors which affect the reliability and reproducibility of data from the push out test have also been established. The findings are applicable to ceramic matrix composites. The interfacial properties of the model steel fibre/epoxy matrix, copper fibre/epoxy matrix, steel fibre/aluminium matrix, and SiC fibre/aluminium matrix composite systems were studied. Factors which influence the reproducibility of interfacial properties such as the interfacial bond strength and the matrix shrinkage pressure as determined from the push out test have been identified. These include the thickness/fibre diameter ratio, the relative diameter of the fibre and the specimen, and the aspect ratio of the fibre in the push out specimen. It was also important to establish the nature offailure at the interface.     

Effect of joint stiffness on peel strength of diffusion bonded joints between Al–Li 8090 alloy sheet

Abstract

The peel behaviour of diffusion bonded joints between Al–Li 8090 alloy sheet depends upon joint geometry, sheet thickness, and the local stiffness of the bonded joint. The local stiffness was increased by bonding 8090 metal matrix composite onto the faces of the joint. At the superplastic forming temperature of 530°C the peel strengths of solid state or liquid phase diffusion bonded joints at peak load were increased from 5–7 N mm^?1 to >8 N mm^?1. This led to superplastic deformation of the sheet without peel fracture at the bonded joint. After air cooling and aging, the corresponding room temperature peel strengths were 174–252 N mm^?1, compared with 30–54 N mm^?1 for an unstiffened joint, an increase by a factor of 3·2–8·4. It was concluded that stiffened bonded joints would enable multiple thin sheet structures to be manufactured in Al–Li 8090 alloy via a diffusion bonding/superplastic forming (DB/SPF) technique. A DB/SPF technique for a three sheet structure is described.

MST/1687     

Spreading kinetics of liquid metals on mild steel

Abstract

The kinetics of the spread of molten copper, Cu–Mn alloy, and aluminium on solid mild steel were investigated at temperatures from 800 to 1100°C under an anhydrous borate flux. The molten copper and Cu–Mn alloy seem to spread largely by surface diffusion and the spread of molten aluminium follows linear kinetics. The spread coefficient, interfacial tension, and work of adhesion are evaluated from the relationship between an observed rate constant and Yin's theoretical formulism. The spread of molten copper on mild steel indicates complete wetting, while the spread of molten aluminium shows the least wetting. In the aluminium–mild steel spread system, the spread tends to increase with temperature: with increasing temperature, the spread coefficient increases and the interfacial tension decreases, while the work of adhesion remains much the same.

MST/743     

Vacuum hot roll bonding of titanium alloy and stainless steel using nickel interlayer

Abstract

Vacuum hot roll bonding of titanium alloy and stainless steel using a nickel interlayer was investigated. No obvious reaction or diffusion layer occurs at the interface between stainless steel and nickel. The interface between titanium alloy and nickel consists of an occludent layer and diffusion layers, and there are the intermetallic compounds (TiNi₃, TiNi, Ti₂Ni and their mixtures) in the layers. The total thickness of intermetallic layers at the interface between titanium alloy and nickel increases with the bonding temperature, and the tensile strength of roll bonded joints decreases with the bonding temperature. The maximum tensile strength of 440·1 MPa was obtained at the bonding temperature of 760°C, the reduction of 20% and the rolling speed of 38 mm s^–1.     

Chromium interaction with TiO2 dispersoids in oxide dispersion strengthened ferritic steel

Abstract

Auger electron spectroscopy and energy filtering TEM were used to study alloying element distributions in the vicinity of matrix–TiO₂ dispersoid interphase boundaries in an Fe–Cr ferritic steel strengthened by dispersed TiO₂ particles. Pronounced interfacial Cr segregation was found to occur in the course of annealing at 700°C. The Cr segregation also leads to Cr diffusion into the dispersoids and to the formation of oxide phases with different Cr/Ti ratios. The observed Cr segregation is described in terms of diffusion into the field of elastic stresses.     

Strengthening mechanisms of aluminum matrix composite containing Cu-coated SiC particles produced by friction stir processing

ABSTRACT

A friction stir processing (FSP) method has been developed to fabricate a locally reinforced aluminum matrix composite (AMC) by stirring electroless-copper-coated SiC particles into AA6061 matrix. The interfacial bonding between particulate reinforcement and the matrix was enhanced by the copper coating. Effective improvement in hardness and in tensile strengths has been proved. Microstructural investigation and analyses were conducted to correlate the microstructural evidences with the possible strengthening mechanisms. The effect of copper coating on the bonding between SiC particles and Al-matrix; the role of the dispersed Cu debris and the increased Cu content in solid solution on the strengthening; and the effect of friction stir on dislocation density and on the recrystallization behavior were analyzed. Multiple strengthening mechanisms due to diffusion between copper film and matrix; dispersion of fine copper debris and Al-Cu intermetallic compounds (IMCs) in the matrix; solid solution due to increased copper content and dislocation punching were four major mechanisms in interpreting the strengthening phenomena in AMC containing copper coated SiC reinforcements.     

Characterisation of interfacial imperfections of TiAl and 40Cr diffusion bonding by ultrasonic amplitude and phase

Abstract

A characteristics extraction algorithm is proposed to characterise the interfacial imperfections in TiAl and 40Cr diffusion bonding. The algorithm is based on analysing the variation of the ultrasonic amplitude and phase after interacting with the bonding interface. Ultrasonic measurements were performed by an ultrasonic imaging testing system, and broadband transducers with central frequency of the 10 and 20 MHz were employed. Metallographic analyses and shear tests were also performed on the joints. It was found that the amplitude of the reflection coefficient is almost a constant, and the phase of the reflection coefficient is the same for the perfectly bonded interface; for the kissing bond interface, the amplitude increases with the ultrasonic frequency, and the phase is the same at the low frequencies and opposite at the high frequencies; the amplitude does not vary with the frequency, and the phase is opposite for the unbonded interface.     

A new cladding technology to bond aluminium on magnesium

ABSTRACT

An in situ hot press bonding technology has been developed to clad aluminium on magnesium. Followed by regular hot rolling, magnesium sheets, covered by ductile and corrosion-resistant aluminium without detectable oxides in the interface, are produced. The new technology requires no welding, vacuum, protective atmosphere or barrier layer, and it makes good interfacial strength and rollability. Aluminium–magnesium intermetallic phases are formed along the clad–core interface at elevated temperatures. They are not detrimental under compression but may cause clad-core delamination in tensile strain. However, the tensile failure is more dependent on the formability of magnesium core than on the strength of interface.     

Microstructure and mechanical properties of low alloy steel T11–austenitic stainless steel 347H bimetallic tubes

Abstract

A low alloy steel (T11) has been bonded to an austenitic stainless steel 347H by hot coextrusion under industrial conditions. The final product was a seamless bimetallic tube with 347H cladding the exterior for corrosion resistance in severely corrosive environments at high temperatures. The microstructures of the coextruded bonding have been compared to those obtained in the laboratory, after diffusion bonding experiments, using hot isostatic pressing (hipping). In all cases both the interdiffusion of the different elements across the interface and the microstructure have been analysed by optical microscopy, SEM, and TEM. On the 347H side a profuse precipitation, mainly of NbC, was found in a region near the interface. Only in the hipped specimens, as result of nickel and chromium diffusion from the stainless steel to the T11 steel, a martensite band was observed parallel to the interface. The heat treatment performed on the bimetallic tubes, to obtain the optimum combination of mechanical properties and corrosion resistance, consisted of austenitisation between 1050–1100°C, water quenching, and a stabilisation treat ment at 850–900°C, followed by slow cooling.     

Modelling wide gap TLP bonding of Ti–48 at.-%Al–2 at.-%Cr–2 at.-%Nb alloys

Abstract

Modelling of the wide gap transient liquid phase (TLP) bonding of a Ti–48 at.-%Al–2 at.-%Cr–2 at.-%Nb (48–2–2) alloy with 48–2–2+Cu composite interlayers is examined. The role of the 48–2–2 powder particles in the composite interlayers during the isothermal solidification process was studied. This work was based on a high apparent diffusion coefficient of Cu in the multiphase γTiAl/α ₂ Ti₃Al 48–2–2 alloy, combined with a low Cu solubility in 48–2–2. The redistribution, during bonding and post-bond heat treatment, of the Cu placed into the original composite interlayer is discussed. The model is used to account for the observed behaviour of 48–2– 2+Cu composite interlayer bonds.