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.     

Interface reactions and bonding strength in aluminium alloy (AA-7075)-alumina diffusion bonds

Diffusion bonds between alumina and high-strength aluminium alloy (AA-7075) have been produced and studied in the present work. Direct diffusion bonding in the solid state was tested as a possible joining method for both materials. The nature of the AA7075-Al₂O₃ interface was investigated paying special attention to the chemical interaction processes between the alloying elements and the ceramic material, as well as their influence on the joint strength. SEM images and energy-dispersive microanalysis were used to determine the formation of reaction layer between both parent materials. Shear strength was used as an optimum method to evaluate the bond strength and the influence of the bonding parameters on it. A maximum shear strength of 60 MPa was achieved using bonding temperatures and pressures of 360 °C and 6 MPa, respectively, during very prolonged bonding times (100h). Fractographic studies of the failure surface gave additional information on those aspects.     

Hot pressing diffusion bonding of a titanium alloy to a stainless steel with an aluminum alloy interlayer

The probability and appropriate processing parameters of hot pressing diffusion bonding (HP–DW) of a titanium alloy (TC4) to a stainless steel (1Cr18Ni9Ti) with an aluminum alloy (LF6) interlayer have been investigated. The microstructure of the bonded joints has been observed by optical microscopy, SEM, XRD and EDX, and the main factors affecting hot pressing and diffusion bonding process were analyzed. The results showed that atom diffused well and no intermetallic compound or other brittle compounds appeared at optimum parameters. The fracture way of joints was ductile fracture. With the increment of bonding temperature, large number of intermetallic compounds such as FeAl₆, Fe₃Al, FeAl₂ which were brittle appeared along the interface between the stainless steel and the aluminum alloy interlayer, as a result, the quality of joints was decreased significantly and the fracture way of joints was brittle fracture.     

Interface microstructure of diffusion bonded Ni3Al intermetallic alloy and austenitic stainless steel

The diffusion bonding of a Ni₃Al intermetallic alloy to an austenitic stainless steel has been carried out at temperatures 950, 1000 and 1050 °C. The influence of bonding temperature on the microstructural development and hardness across the joint region has been determined. The microvoids in the interface have been found to decrease with increasing bonding temperature. The intermetallic phase Al₃Ni has been detected at the Ni₃Al side of the diffusion couple. Diffusion of Cr and Fe from the stainless steel to the Ni₃Al alloy has been observed.     

Diffusion bonding of Ti-6Al-4V alloy at low temperature: metallurgical aspects

The diffusion bonding of the Ti-Al-4V alloy at low temperature (850°C) has been studied. The principal objective of this investigation was the development of a diffusion bonding procedure suitable for Ti-6Al-4V alloy and capable of being used as part of a superplastic forming/diffusion bonding process. It was found that high-quality joints can be obtained by bonding at 850°C, with pressures of 4 MPa and times in the range 90–120 min. Mechanical properties of the joints were determined using cylindrical and plane test pieces. Tensile, shear and peeling tests were used to determine the strength of the joints. On bonding with the above conditions, the parent alloy strength was reached. Little reduction in these values was measured because the heat treatment was applied during bonding. A metallographic study by scanning electron microscopy and energy dispersive spectroscopy was performed to determinate the influence of the previous parameters on the microstructural changes that occur in the joint. Grain growth kinetics and ratio of bonding area were also studied. The results shows that a new method of diffusion bonding for Ti-6Al-4V alloy has been developed. This method can be carried out using lower bonding temperatures than in conventional processes.     

Microstructure and strength of diffusion-bonded joints of TiAl base alloy to steel

Diffusion bonding of TiAl-based alloy to steel was carried out at 850–1100 °C for 1–60 min under a pressure of 5–40 MPa in this paper. The relationship of the bond parameters and tensile strength of the joints was discussed, and the optimum bond parameters were obtained. When products are diffusion-bonded, the optimum bond parameters are as follows: bonding temperature is 930–960 °C, bonding pressure is 20–25 MPa, bonding time is 5–6 min. The maximum tensile strength of the joint is 170–185 MPa. The reaction products and the interface structures of the joints were investigated by scanning electron microscopy (SEM), electron probe X-ray microanalysis (EPMA) and X-ray diffraction (XRD). Three kinds of reaction products were observed to have formed during the diffusion bonding of TiAl-based alloy to steel, namely Ti₃Al+FeAl+FeAl₂ intermetallic compounds formed close to the TiAl-based alloy. A decarbonised layer formed close to the steel and a face-centered cubic TiC formed in the middle. The interface structure of diffusion-bonded TiAl/steel joints is TiAl/Ti₃Al+FeAl+FeAl₂/TiC/decarbonised layer/steel, and this structure will not change with bond time once it forms. The formation of the intermetallic compounds results in the embrittlement of the joint and poor joint properties. The thickness of each reaction layer increases with bonding time according to a parabolic law. The activation energy Q and the growth velocity K₀ of the reacting layer Ti₃Al+FeAl+FeAl₂+TiC in the diffusion-bonded joints of TiAl base alloy to steel are 203 kJ/mol and 6.07 mm²/s, respectively. Careful control of the growth of the reacting layer Ti₃Al+FeAl+FeAl₂+TiC can influence the final joint strength.     

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.     

Development of laminated composite materials based on orthorhombic aluminide/titanium alloy and their tensile mechanical properties

Abstract

Laminated composite materials consisting of an orthorhombic Ti₂AlNb based alloy and an (α+β) titanium alloy have been fabricated at a laboratory scale using a two-step process involving diffusion bonding and hot rolling. The feasibility of fabrication of two and three layered materials with high quality bonding between layers was demonstrated. Preliminary assessment of the tensile mechanical properties of the obtained composite materials showed that they were superior to those of the titanium alloy and slightly inferior to the orthorhombic alloy.     

Diffusion bonding of a nickel (chromium) alloy to zirconia: Mechanical properties and interface microstructures

Diffusion bonding of a Ni(Cr) alloy with ZrO₂ has been studied. It was found that the processes were controlled by chemical reactions at the metal/ceramic interface forming compounds within the composition range NiO_1–x Cr₂O_3–y ZrO_2–z (0<x,y,z<1). Reaction products were characterized by examination of the fractured metal/ceramic halves and from cross-sections using optical, scanning and transmission electron microscopy and energy dispersive X-ray microanalysis. These metallographic studies indicate that the interface reactions are accompanied by local melting indicating a possible eutectic reaction following interdiffusion. Pre-oxidizing the metal foil enhances these reactions and lowers the reaction temperatures. Differential thermal analysis found endotherms at 1050 and 1110 °C with sintered NiCr/ZrO₂ powders, and at 980 and 1100 °C when pre-oxidized powders were used. These are shown to be associated with local melting at the metal/ceramic interface. This thus explains the existence of a critical bonding temperature for good-quality diffusion bonding, where a minimum temperature has to be satisfied for the eutectic reaction to occur.     

Diffusion bonding of TiAl based alloy to Ti–6Al–4V alloy using amorphous interlayer

Powder metallurgical TiAl based alloy and Ti–6Al–4V (TC4) alloy were diffusion bonded at 915 °C for 1 h under a pressure of 80 MPa. Single Ti‐based amorphous or Ni‐based amorphous foil was utilized as an interlayer during diffusion bonding process. The tensile mechanical properties of the diffusion bonded joints between TiAl based alloy and TC4 alloy were tested. The fracture surface and microstructure characteristic of these joints were also observed carefully by scanning electron microscope. The TiAl based alloy with a fully lamellar microstructure is more suitable for diffusion bonding to TC4 alloy. Adding a Ti‐based amorphous interlayer is more conducive to the element diffusion, giving rise to the improvement in the mechanical properties of the diffusion bonded joints. Results also show that the diffusion bonded joints form a metallurgical bond and fracture in a brittle manner.     

Interface microstructures in diffusion bonding of titanium alloys to stainless and low alloy steels

Abstract

Commercial purity Ti and a Ti 6242 alloy have been diffusion bonded to an AISI 316L stainless steel and an AISI 4130 low alloy steel. The microstructures of the as processed products have been analysed using optical metallography, scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) techniques. The interdiffusion of the different elements through the interface has been determined using energy dispersive spectroscopy microanalysis in both a SEM and a STEM. For the combinations AISI 316L–commercially pure Ti and AISI 316L–Ti 6242 several regions surrounding the original interface have been observed. Starting from the 316L side, first a α phase is observed, followed by an Fe₂ Ti intermetallic, an FeTi intermetallic, and finally an Fe₂Ti₄O oxide just before the Ti and Ti 6242. Because the diffusion ofTi in Fe is faster than the diffusion of Fe in Ti, a Kirkendall effect is produced. In the AISI 4130–Ti 6242 combination a thin layer of TiC is observed at the interface, limiting the interdiffusion of elements.

MST/1746     

Explosive cladding of a thin Ni-film to an aluminium alloy

A thin Ni-film has been cladded to an aluminium alloy by the use of an explosive. Two film thicknesses (50 and 100 μm) and four explosive compositions have been used. The cladding has been characterised by surface topography, microhardness measurements, optical and scanning electron microscopy, and energy dispersive spectroscopy; residual stresses through the film and the bonding have been determined by X-ray diffraction. In all cases, a good quality bonding is obtained, with a low roughness on the film surface. Compressive residual stresses have been measured from the surface to the bonding.     

Transient liquid phase diffusion bonding of oxide dispersion strengthened nickel alloy MA758

Abstract

Transient liquid phase diffusion bonding has been used to join an oxide dispersion strengthened (ODS) nickel alloy (MA758) using an amorphous metal interlayer with a Ni–Cr–B–Si composition. A microstructural study was undertaken to investigate the effect of parent metal grain size on the joint microstructure after isothermal solidification. The ODS alloy was bonded both in fine grain and recrystallised conditions at 1100°C for various hold times. The work shows that the final joint grain size is independent of the parent alloy grain structure and the bonding time. However, when the alloy is bonded in the recrystallised condition and given a post-bond heat treatment at 1360°C, the joint grain size increases and a continuous parent alloy microstructure across the joint region is achieved. If MA758 is bonded in the fine grain condition and then subjected to a recrystallising heat treatment at 1360°C, the grains at the joint appear to increase in size with increasing bonding time. The joint grains are generally larger than those produced when the alloy is bonded in the recrystallised condition. The differences in microstructural developments across the joint are discussed in terms of stored strain energy of the parent metal grains.     

Das Diffusionsschweißen von Titanlegierungen

Diffusion Bonding of Titanium Alloys. Diffusion bonding is a 4 stage process involving surface deformation atomic bonding interface diffusion and grain growth. These processes can proceed in the above order or more or less simultaneously. The effect of production parameters and material properties on the basic mechanisms is investigated. Several diffusion bonding techniques for industrial applications have been developed and are discussed in detail. Experience with the diffusion bonding of titanium alloys has shown that base material properties may be obtained in the weld zone. Actual parts fabricated by diffusion bonding sometimes show higher strength than made without welding. Some of the difficulties associated with diffusion bonding are presented. The economical and technical advantages of the diffusion bonding process are shown by reference to typical applications where this technique can be successfully applied.     

Diffusion Bonding Technology of a Titanium Alloy to a Stainless Steel Web With an Ni Interlayer

The probability and appropriate processing parameters for diffusion bonding of a titanium alloy to a stainless steel web with an Ni interlayer have been investigated. The microstructure of the diffusion bonding joint has been observed by microscopy, SEM, and EPMA, and the main factors affecting diffusion bonding have been analyzed. The results show that atom diffusion and migration between Ti and Fe or C are effectively prevented by adding pure Ni as the interlayer metal, and a firm joint is obtained. When products were diffusion bonded, the relationship of exerting pressure and deformation is analyzed. A method of controlling deformation and attaining nondeformation bonding has been proposed. The optimum parameters are as follows: bond temperature is 850°C, bond-specific stress is 10MPa bond time is 10–15 min, and difference between ring-shaped bonding area radii D-d is 1–1.5mm.     

铬青铜与不锈钢瞬间液相扩散焊接界面行为

为了掌握铜合金与不锈钢的连接机理,为工程应用提供技术指导,对铬青铜和不锈钢异种材料扩散焊接进行了研究,对不同厚度的银、铜镀层在不同焊接条件(焊接温度和时间)下的试验进行了分析,利用金相显微镜、扫描电镜以及能谱分析仪分别研究了宏观爆破压力和微观组织结构对焊接质量的影响,对焊接过程发生的冶金结合机理和元素的扩散形式进行了探讨.结果表明,将银、铜镀层的厚度控制在一定范围内,选取950～970℃保温15～60min,焊缝强度可以达到150MPa以上,界面没有脆性相产生.焊缝界面主要表现为铜的扩散、银的反应扩散及TLP过程、银的熔态扩散、铬的聚集析出、镍的网状析出以及柯肯达尔(Kirken-dall)效应等微观特征.     

Mechanical and corrosion properties of Al/Ti film on magnesium alloy AZ31B

Preparation of titanium film on magnesium substrate faces a challenge due to non-Fickian inter-diffusion between titanium and magnesium. Aluminum can build a bridge between titanium and magnesium. Al/Ti duplex coatings were deposited on magnesium alloy AZ31B using magnetron sputtering (MS). The low temperature diffusion bonding behavior of the Mg/Al/Ti coating was investigated through SEM and its affiliated EDS. The phase structure and critical load of the coatings were examined by means of XRD and scratch tests, respectively. The results demonstrated that the bonding strength was significantly improved after a post heat treatment (HT) at a temperature of 210°C. The diffusion mechanism of the interfaces of Mg/Al and Al/Ti in the coating was discussed based on the analysis of formation energy of vacancies and diffusion rates. The Al/Ti dual layer enhanced the corrosion resistance of the alloy. And the HT process further increased the corrosion resistance of the coated alloy. This result implies that a post HT at a lower temperature after MS is an effective approach to enhance the bonding strength and corrosion resistance of the Al/Ti film on Mg alloys.     

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.     

Diffusion bonding of electroless Ni plated WC composite to Cu and AISI 316 stainless steel

In this study, a composite containing WC (Tungsten Carbide) and Ni was produced by two different processing routes. Electroless Ni coated WC powders were consolidated and sintered at 1200 °C. Diffusion bonding couples of WC(Ni)-electrolytic Cu, WC(Ni)-AISI 316 stainless steel and WC(Ni)-WC(Ni) were manufactured by using a preloaded compression system under Ar atmosphere. Diffusion bonding was carried out at varying bonding temperatures; 750 °C for (WC)Ni-Cu diffusion couple and 1200 °C for (WC)Ni-(WC)Ni and (WC)Ni-AISI 316 stainless steel diffusion couples. Standard metallographic techniques, Scanning Electron Microscopy and a shear test were employed to characterize the microstructure of bondline and mechanical properties of each diffusion couple, respectively.     

Joining of tungsten carbide to nickel by direct diffusion bonding and using a Cu–Zn alloy

The objective of this work was to study various aspects of liquid and solid state diffusion bonding of cylindrical samples of WC (with 6% Co) and commercially pure nickel (99.5%) produced by direct bonding and brazing using a 25 μm thick 70Cu 30Zn (wt%) alloy as joining element. Joining experiments were carried out on WC/Ni and WC/Cu Zn/Ni combinations at temperature of 980 °C using 1, 15, 25 and 35 min holding times in argon (Ar). The results show that it is possible to create a successful joint at temperature and times used. Joining occurred by the formation of a diffusion zone. The joining interface is feasible because it presents a homogeneous interface with no several interfacial cracking and porosity. In both combinations, it can be observed a diffusion of cobalt decreasing in the direction of the metal, as well as, the diffusion of nickel decreasing in the direction of the ceramic.