Intermetallic compounds formed during brazing of titanium with aluminium filler metals

The effect of aluminium filler metal composition on the formation of AI-Ti intermetallic compounds was investigated in brazed aluminium-to-titanium (Al/Ti) joints and titanium-totitanium (Ti/Ti) joints. The clearance filling ability was also studied. In Ti/Ti joints, the thickness of the intermetallic compound layer was strongly dependent on the aluminium filler metal composition, whereas the clearance filling ability was independent of the composition. The maximum intermetallic compound layer thickness was observed in 99.99% highly pure aluminium filler metal; therefore all additional elements reduced the layer thickness. Above all, the addition of 0.8% Si greatly reduced the thickness. After brazing at 680° C for 3 min, the intermetallic compound formed by Al-0 to 0.8% Si filler metal was found to be of type Al₃Ti. Other compounds, of types Ti₉Al₂₃ and Ti₇Al₅Si₁₂, were also found in joints brazed by Al-3 to 10% Si filler metals. AI-0.8% Si filler metals maintained a higher joint strength than pure aluminium filler metal under brazing conditions of high temperature and long heating time. In Al/Ti joints, AI-Cu-Sn and AI-Cu-Ag filler metal mainly formed Al₃Ti, and Al-10Si-Mg filler metal mainly formed Ti₇Al₅Si₁₂ at the brazed interface of the titanium side after brazing at 600 to 620° C.     

Oxidation behaviour of titanium-containing brazing filler metals

Brazements on alumina or partially stabilized zirconia (PSZ) of four silver- or copper-based brazing filler metals that contain titanium to promote wetting of and adherence to structural ceramics, were exposed in a thermogravimetric analyser at temperatures up to 700°C to atmospheres of 100% O₂, Ar-20% O₂ and Ar-3 p.p.m. O₂. The alloys included Cu-41.1Ag-3.6Sn-7.2Ti, Ag-44.4Cu-8.4Sn-0.9Ti, Ag-41.6Cu-9.7Sn-5.0Ti and Ag-37.4Cu-10.8In-1,4Ti, at%. All formed external oxides that were more or less protective under all of the test conditions studied. The growth of the oxides followed a parabolic time law. The gains in weight due to oxidation observed were small, ranging (for 45 h exposure at 400 °C to Ar-20% O₂) from 0.20 mgcm⁻² for the Ag-37.4Cu-10.8In-1.4Ti alloy to 0.46 mgcm⁻² for Cu-41.1Ag-3.6Sn-7.2Ti. As expected, weight gain increased with increasing temperature or . Unexpectedly, the titanium played a minor role in the scale formed on any of the filler metals with a titanium oxide, TiO₂, being found on only one alloy — Ag-41.6Cu-9.7Sn-5.0Ti. The brazements on PSZ gained weight at a higher rate than comparative brazements on alumina. We attribute this behaviour to oxygen transport through the zirconia resulting in the growth of an interfacial layer of titanium oxide.     

Microstructural analysis of germanium modified tin‐copper brazing filler metals for transient liquid phase bonding of aluminium

The present contribution summarises first results that have been achieved with the new brazing material Sn75Cu20Ge5 (wt‐%) for transient liquid phase (TLP) bonding of aluminium cast alloy AlSi7Mg0.3 (wt‐%). The microstructure of the braze ribbons and the obtained joints have been thoroughly investigated on different length‐scales using scanning and transmission electron microscopy as well. Whereas the braze ribbon material is only composed of beta‐tin, η‐phase (Cu₆Sn₅) and some germanium rich precipitates, the transient liquid phase joint displays a much more complex microstructure that consist mainly of beta‐tin and different aluminium‐copper and aluminium‐germanium phases. In addition small silicon oxide rods and a hitherto unreported hexagonal aluminium‐copper‐magnesium‐germanium phase with approximated lattice parameters a = 0.7123 nm, c = 2.40 nm have been found in the seam of the joint.     

Formation of microlayers of clad residue on aluminium brazing sheet during melting and resolidification in brazing process

Abstract

The present paper is devoted to an analysis of clad residue formation during a controlled atmosphere brazing (CAB) process applied to composite aluminium brazing sheets. Evolution of the microstructure of the clad residue, and in particular the mass of resolidified clad formed, were studied. Observations confirmed that, even under optimal brazing conditions, a residue layer (formed away from the joint zone) always appears after brazing. It was established that the peak brazing temperature plays an important role in the process responsible for formation of the residue mass. However, dwell time at the peak brazing temperature does not have a significant influence on clad residue mass accumulation beyond its known influence on substrate dissolution and core metal erosion in the joint zone.     

Partially alloyed filler sheet for brazing of Ti and its alloys fabricated by spark plasma sintering method

Partially alloyed filler metals in the form of powders and laminated foils were used for the brazing of Ti and Ti alloys to lower the manufacturing cost. In this study, by using a raw elemental powder mixture, a multi-component filler sheet with a nominal composition of 37.5Ti–37.5Zr–15Cu–10Ni was fabricated using a Spark Plasma Sintering (SPS) machine in the temperature range from 650 °C to 785 °C for 1 min. As the sintering temperature was increased from 650 °C to 750 °C, the bending strength of the sheets tended to rise, but the bending strength at 785 °C was drastically reduced. The melting range of the sheets became similar to that of the as-cast alloy. The sheets sintered at 750 °C showed the highest bending strength of 259 MPa, which was much higher than that of the as-cast material, and the melting range of this sheet was from 800 °C to 852 °C. The relatively high strength of the sheet was due to the remaining elemental powders such as Ti or Zr, but the brittle intermetallics, such as Ti₂Cu and (Ti,Zr)₂Ni Laves phases, formed in the sheet during the sintering process deteriorated its mechanical strength. The partially developed eutectic phase between the remaining Ti or Zr powder caused the sheet to exhibit melting behavior similar to that of the as-cast alloy. The brazability of the sheet sintered at 750 °C was examined with commercially pure Ti at 870 °C for 5–60 min. The tensile strength of the Ti joint brazed for 30 min was 431 MPa, which was close to that of the base metal.     

New process for brazing ceramics utilizing squeeze casting

A new joining process for ceramics to ceramics and ceramics to metals, SQ brazing, has been developed. This process utilizes squeeze casting; a brazing material is squeezed into the interface channel to be brazed and is solidified under a high pressure. This new process has several advantages, low cost, mass producibility, high interface strength and high reliability, no severe reaction, etc. Alumina to alumina and silicon nitride to silicon nitride brazing with pure aluminium are shown as examples. Alumina containing silica as a sintering additive brazed by a conventional method severely reacted with aluminium braze so that the joint strength was low. After SQ brazing, reaction was moderate and the strength almost reached that of the parent alumina. Silicon nitride could be brazed by SQ brazing. Although the simple SQ brazing could not make a strong interface, pre-oxidization treatment of silicon nitride increased the joint strength beyond 400 M Pa.     

高熵合金在钎焊和表面工程领域的应用研究进展

随着合金制造水平的提高及性能要求的复杂化,高熵合金逐渐引起极大的关注.目前在材料加工领域内的研究主要集中于钎焊和表面工程两大方向.在钎焊领域,高熵合金可以作为钎焊填充材料应用于高温和低温钎焊,本文归纳了合金高熵化的相关经验参数,阐述了第一性原理计算和相图计算等模拟计算手段在高熵合金填充材料设计领域内的应用;详细介绍了高熵合金钎料在镍基高温合金、陶瓷-金属异种材料、低温封装等连接领域的最新研究进展.同时,分析了工艺参数对高熵合金钎料钎焊接头组织与性能的影响.在表面工程领域,论述了高熵合金薄膜/涂层的应用方向与制备手段,总结了在高温防护涂层、硬质保护层以及其他应用领域的研究进展.同时归纳了高熵合金在钎焊和表面工程领域研究和应用中存在的问题,而未来将在降低钎料熔点、提高焊缝高温力学性能以及发展共晶高熵合金钎料/涂层等领域进一步提高研究水平.     

Phase transformation study during diffusion brazing of γ-TiAl intermetallic using amorphous Ni-based filler metals

The paper aims at understanding the microstructure evolution of the diffusion brazing of γ-TiAl intermetallic compound using two Ni-based filler metals, a ternary Ni-Si-B, and a quinary Ni-Cr-Fe-Si-B. It was found that the joint region comprised of two distinct zones: analogous reaction layers adjacent to the TiAl substrates and a solidified zone at the middle of the joint region. The reaction layers consisted of separate intermetallic phases regions including ternary and binary Ti-Ni-Al intermetallic compounds. The solidified zone mainly composed of the Al_1-xNi₃Si_x isostructural solid solution and athermally Ni-boride or Ni-Cr rich borides containing eutectic microstructures at the joint centerline. The maximum shear strength was 240?MPa, and obtained by using Ni-Cr-Fe-Si-B filler metal. Fracture of the joint with Ni-Cr-Fe-Si-B filler occurred in the reaction layer/solidified zone interface, but joint with Ni-Si-B filler was fractured at solidified zone.     

Development of low‐melting‐point filler materials for laser beam brazing of aluminum alloys

In order to develop low‐melting‐point filler materials for laser beam brazing of aluminum alloys, Al–Si–Cu based alloys and Al–Si–Zn based alloys were produced via spray forming and associated deformation processes. The selected alloys were spray formed in the form of billet with a diameter around 160 mm and hot extruded into wire rods with a diameter of 8 mm. The extrusions were further cold worked into thin wires with a diameter of 1.2 mm via rotary swaging. Finally, the filler wires were applied in the laser beam brazing of AA6082 structures. It showed that the newly developed filler materials could meet the requirements of the laser beam brazing of aluminum alloys. Particularly, the laser beam brazing process using the spray‐formed filler materials required a significantly lower energy input and allowed for higher brazing speed as compared to the conventional AlSi12 filler material.     

Development of a copper-based filler alloy for brazing stainless steels

The filler alloy of nominal composition Cu–40Mn–10Ni (all in wt%) was prepared in the form of ribbon of 40 μm thick by melt spinning technique. The ribbon exhibits narrow melting zone and comprise single phase of Cu–Mn–Ni solid solution. The melt spun ribbon successfully brazed 304 stainless steel butt joints. The formation of solid solution in the joining area without any intermetallics is observed. The bonding strength of filler alloy is achieved around 456 MPa.     

Bending of square aluminium extrusions with aluminium foam filler

Summary An experimental programme consisting of 24 tests was carried out to study the three-point-bending behavior of square AA6060 aluminium extrusions filled with aluminium foam under quasi-static loading conditions. The outer cross section width and span of the beams were kept constant at 80 mm and 800 mm, respectively. The main parameters investigated were the foam density, the extrusion wall strength and the extrusion wall thickness. The experiments showed that the foam filler significantly altered the local deformation pattern of the beams. Simple design formulae were developed in order to predict the load bearing capacity of the foam filled beams.Notation d load cell displacement - total beam rotation - ₀₂ total beam rotation at extrusion flange yielding (non-filled beam) - ₁, ₂ beam end rotations - b outer component cross section width - h component wall thickness - L total beam span length - s central load section of beam - A _e extrusion cross sectional area - A _f foam cross sectional area - P load cell force - M total cross section moment - M _e extrusion moment - M ₀₂ maximum elastic moment capacity of extrusion - M _pl perfect plastic moment capacity of extrusion - M _f foam core moment - M _sf maximum foam core moment - M _s total initial peak moment - M _sa total moment capacity after foam failure - M _u ultimate extrusion moment capacity - M _se calculated moment resistance of extrusion at foam failure - stress, engineering - ₀₂ extrusion wall stress at 0.2% plastic strain - _U extrusion wall ultimate stress - ₀ extrusion wall characteristic stress, 0.5(₀₂+ _U ) - _f foam plateau stress - _s foam tensile failure stress - strain, engineering - ₀₂ extrusion strain corresponding to yield stress ₀₂ - _u extrusion strain corresponding to ultimate stress _U - _s foam tensile failure strain - beam curvature - ₀₂ beam curvature at extrusion flange yielding - _u beam curvature at extrusion ultimate stress - _s beam curvature at foam tensile failure strain - f extrusion section shape factor - k elastic bending stiffness ratio between foam core and extrusion - E extrusion Young's modulus - E _t extrusion tangential modulus - n extrusion material hardening constant - _f foam density - _i foam batch density,i=1, 2, 3 - x, y, z coordinate reference system (x-beam axis) - x _c distance from beam end (change in formula for curvature)     

Reinitiation of substrate oxide undermining by Ni-P filler metals during wetting of nickel-base alloys

The process of wetting of nickel and nickel-chromium substrates by nickel-phosphorus high-temperature brazing filler metals has been examined. The filler was found to wet the substrate by undermining the oxide layer on the substrate. Evidence was found that the undermining process is halted temporarily at discontinuities in the substrate oxide which typically occur above substrate grain boundaries. It is suggested that it is initially more favourable energetically for the filler to spread along the oxide defects than to continue undermining. Mechanisms for the reinitiation of undermining have been considered. It is proposed that undermining recommences after the onset of isothermal solidification of the filler spreading along oxide defects.     

Vacuum brazing of NiTi alloy by AgCu eutectic filler

Abstract

Joining of NiTi alloy to itself has been realised by vacuum brazing process using AgCu28 eutectic as filler metal. Microstructures, mechanical and shape memory behaviour have been investigated. The shearing strength of the brazed joint exceeds 100 MPa, and rupture occurs at the diffusion layer of parent metal beside brazing metal. The brazed joint will be stronger than parent metal on condition of the specimen with a joint of lap length 10 times of plate thickness. The brazed specimen shows a good shape memory behaviour. From the point of view of practice, the brazing joint design principle and brazing quality improvement have been discussed.     

High-performance joining technology for aluminium matrix composites using ultrasonic-assisted brazing

High-performance aluminium matrix composite joints were fabricated using a new joining technology assisted by ultrasonic vibration. The performance of the joints was close to that of the parent materials. The microstructure and the mechanical performance were found to be systematically dependent on the volume fraction and the distribution of reinforcement particles in the bond region. The authors believe that this study can be generalised to the bonding of other ceramic-reinforced metal matrix composites.     

The wetting of carbon by aluminium and aluminium alloys

The contact angle made by molten aluminium with vitreous carbon was measured by the sessile drop method in vacuum at temperatures up to 1100° C. The effect on wetting behaviour of the oxide layer on the molten metal was highlighted by using two samples of aluminium in different states of oxidation. The investigation involved the variation of certain parameters affecting the stability of the oxide film, e.g. the temperature, additions of Ti, Si, Cr, Be, Ca and Li to aluminium and the time held at a certain temperature. The state of the molten aluminium surface under various experimental conditions was determined indirectly by surface tension measurements.     

Corrosion behavior of Al–Si–Cu–(Sn, Zn) brazing filler metals

The corrosion behavior of Al–Si–Cu–(Sn, Zn) filler metals in a 3.5% NaCl aqueous solution were studied using electrochemical tests. The results showed that the addition of Sn or Zn to the Al–Si–Cu filler metal raised its corrosion current density sharply and caused its corrosion potential to become more active. Sn or Zn elements exert harmful effects on such low-melting-point brazing filler metals in that the corrosion resistance is degenerated, and damage is accelerated with an increase in the Sn or Zn content. Scanning electron microscopy (SEM) micrographs of the corroded surfaces of these Al–Si–Cu–(Sn, Zn) filler metals indicate that the Al-rich phase (i.e., Al–Si, Al–Si–Cu, and Al–Si–Cu–Sn eutectic phases) dissolves preferentially, while the Si particles and CuAl₂(θ) intermetallic compounds remain intact.