Improving tensile strength and bend ductility of titanium/AlSI 304L stainless steel friction welds

Abstract

The metallurgical and mechanical properties of friction welds between titanium and AISI 304L stainless steel were examined. Joint tensile strength increased when high friction pressure (>196 MN m^?2) and high upsetting pressure (294 MN m^?2) were used during welding. Although the surface roughness of the titanium substrate had no effect on joint strength, decreasing the surface roughness of the AISI 304L material did increase the tensile strength of completed joints. As welded dissimilar joints had poor bend test ductility and failed in the interface region. Detailed microscopy and X-ray diffraction analysis confirmed that the poor bend ductility was caused by a combination of high hardness of the titanium material immediately adjacent to the joint interface, the presence of unrelieved residual strain at the joint interface, and intermetallic phases formed during the welding operation. Detailed transmission electron microscopy and X-ray analysis confirmed that a thin layer rich in intermetallics was present in the as welded joints. (FeNiCr)Ti phases were formed during seizure formation and disruption; this provided the necessary conditions for anomalously high rates of diffusion of titanium in stainless steel, and of iron, chromium, and nickel in titanium. Low temperature post-weld heat treatment (PWHT), involving heating to 500–600°C followed by immediate air cooling, reduced intermetallic precipitation, promoted stress relaxation, and facilitated complete bonding across the whole joint interface. This treatment markedly improved bend ductility and had a negligible effect on joint tensile strength. High PWHT temperatures (≥900°C) and long holding times at temperature markedly reduced joint tensile strength and bend ductility, owing to excessive formation of intermetallic phases at the joint interface.

MST/1521     

Diffusion bonding of titanium alloy to micro-duplex stainless steel using a nickel alloy interlayer: Interface microstructure and strength properties

In the present study, diffusion bonding of titanium alloy and micro-duplex stainless steel with a nickel alloy interlayer was carried out in the temperature range of 800–950 °C for 45 min under the compressive stress of 4 MPa in a vacuum. The bond interfaces were characterised by scanning electron microscopy, electron probe microanalyzer and X-ray diffraction analysis. The layer wise Ni₃Ti, NiTi and NiTi₂ intermetallics were observed at the nickel alloy/titanium alloy interface and irregular shaped particles of Fe₂₂Mo₂₀Ni₄₅Ti₁₃ was observed in the Ni₃Ti intermetallic layer. At 950 °C processing temperature, black island of β-Ti phase has been observed in the NiTi₂ intermetallics. However, the stainless steel/nickel alloy interface indicates the free of intermetallics phase. Fracture surface observed that, failure takes place through the NiTi₂ phase at the NiA–TiA interface when bonding was processed up to 900 °C, however, failure takes place through NiTi₂ and β-Ti phase mixture for the diffusion joints processed at 950 °C. Joint strength was evaluated and maximum tensile strength of ∼560 MPa and shear strength of ∼415 MPa along with ∼8.3% ductility were obtained for the diffusion couple processed at 900 °C for 45 min.     

Solid-state bonding of alumina to austenitic stainless steel

A low temperature and low pressure bonding process for alumina and 316L austenitic stainless steel has been developed using a titanium/molybdenum laminated interlayer. The intermetallic compounds of Ti₃Al (or Ti₂/Al) and TiAl were formed at the alumina/titanium interface on bonding at above 1273 K. The activation energy of the layer growth was about 142 kJ mol^–1. The construction of Al₂O₃/Ti/Mo/steel gave the most stable joints. The highest tensile strength was above 60 MPa with a titanium 0.4 to 0.6mm thick/molybdenum 0.4 to 0.5 mm thick interlayer on bonding at 1273 K for 3 h under pressure of 12 MPa.     

Characterization of transition joints of commercially pure titanium to 304 stainless steel

Solid-state direct bonding between commercially pure titanium and type 304 austenitic stainless steel has been carried out in the temperature range of 850–950 °C, under a uniaxial pressure of 3 MPa for 1 h. The diffusion bonds have been evaluated using light microscopy, electron probe microanalysis (EPMA), X-ray diffraction (XRD) technique and tensile testing. Light microscopy shows that different intermediate layers are formed in the reaction zone, and the width of these layers increases with an increase in bonding temperature. EPMA revealed that, at any particular bonding temperature, Ti traverses a minimum distance in the 304 stainless steel side, whereas Fe, Cr and Ni travel comparatively larger distances in the Ti side. This microanalysis also indicated different step formations in the concentration profile of Ti, Fe and Cr over different composition ranges in the diffusion zone indicating formation of intermetallic phases that were detected by XRD. Brittle intermetallic phases lower the strength and ductility of the diffusion bonded couples significantly. Best room temperature tensile strength, 217 MPa, has been obtained at 850 °C processing temperature due to minimal deleterious effects.     

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.     

钛－镍－不锈钢接头中元素的扩散及其对性能的影响

采用纯镍作中间过渡金属，对钛合金ＴＣ４与不锈钢１Ｃｒ１８Ｎｉ９Ｔｉ扩散焊接头的结合性能进行了试验研究，利用电子探针测定了扩散层中元素的分布。结果表明，采用镍作中间过渡金属，可以获得钛合金与不锈钢的牢固连接，但在镍与钛之间还是形成了金属间化合物薄层，对接头的性能有较大的影响。     

Effects of temperature on interface microstructure and strength properties of titanium–niobium stainless steel diffusion bonded joints

Abstract

The effects of temperature on interface microstructure and strength properties of Ti/stainless diffusion bonded joint using Nb interlayer, processed in the temperature range 800–950°C for 1·5 h in vacuum were investigated. The stainless steel/Nb interface is free from intermetallic phase up to 900°C; however, Fe₂Nb+Fe₇Nb₆ phase mixture has been observed at 950°C processing temperature. The Nb/Ti interface is free from intermetallic for all processing temperatures. The maximum tensile strength of ～287 MPa (～90% of Ti) and shear strength ～222 MPa (～75% of Ti) along with 6·9% ductility have been achieved in the diffusion bonded joints, when processed at 900°C. The bonded samples failure takes place through the stainless steel/Nb interface for all processing temperatures during the loading.     

Investigations on the mechanical properties and microstructure of dissimilar cp-titanium and AISI 316L austenitic stainless steel continuous friction welds

Friction welding process is a solid state joining process that produces a weld under the compressive force contact of one rotating and one stationary work piece. In this study, the friction welding of dissimilar joints of AISI 316L stainless steel and cp-titanium is considered. The optical, scanning electron microscopy studies of the weld were carried out. Moreover, the X-ray diffraction analysis was performed. The integrity of welds was achieved by the micro hardness and tensile tests. The fracture surface was examined by the scanning electron microscopy. The study showed that the magnitude of tensile strength of the dissimilar welded specimen was below that of the titanium base material if preheating was not applied at the interface. The high weld tensile strength was achieved by preheating the 316L stainless steel material to 700 °C, smoothing and cleaning of the contact surfaces. Results illustrated that in dissimilar joints, different phases and intermetallic compounds such as FeTi, Fe₂Ti, Fe₂Ti₄O, Cr₂Ti and sigma titanium phase were produced at the interface. The presence of brittle intermetallic compounds at the interface resulted in degradation of mechanical strength which in turn led to premature failure of joint interface in the service condition. Preheating caused to produce oxide layer at the interface which was harmful for bonding. The oxide layer could be eliminated by applying pressure and smoothing the surface. Results of hardness tests illustrated that the high hardness was occurred in the titanium side adjacent to the joint interface. Moreover, the optimum operational parameters were obtained in order to achieve the weld tensile strength greater than the weak titanium material.     

Effects of reaction products on the bond strength of the transition joint formed between titanium and stainless steel

Abstract

Solid state diffusion bonding was carried out between commercially pure titanium and 304 stainless steel in the temperature range 800 - 950°C for 120 min in vacuum under uniaxial load. The transition joints were characterised using optical and scanning electron microscopy. The study shows the presence of different reaction layers in the diffusion zone and their chemical compositions were determined by energy dispersive spectroscopy. The occurrence of different intermetallic phases such as FeTi, λ, χ, and σ has been predicted from the ternary phase diagram of Fe - Cr - Ti and they were confirmed by the X-ray diffraction technique. A maximum bond strength 76% of that of titanium was obtained for the diffusion couple processed at 800 ° C owing to finer size intermetallic compounds and the increment in joining temperature, which results in growth of brittle intermetallics leading to a sharp fall in the strength of the transition joints.     

An experimental investigation of phase transformation superplastic diffusion bonding of titanium alloy to stainless steel

The solid-state direct diffusion bonding of a near α-phase titanium alloy to an austenitic stainless steel by means of the phase transformation superplasticity (PTSP) caused by the cycles of heating and cooling has been carried out. The test results showed that, under the conditions of T_max = 890°C, T_min = 800°C, cyclic number of heating and cooling N = 10 cycles, specific pressure P = 5 MPa, heating rate V_h = 30°C/s and cooling rate V_c = 10°C/s, the ultimate tensile strength of the joint reached its maximum value (307 MPa), and the bonding time was only 120 s. In the phase transformation superplastic state, the deformation of titanium alloy has a character of ratcheting effect and it accumulates with the cycles of heating and cooling. The observations of tensile fracture interface showed that both the brittle intermetallic compound (FeTi) and the solid solution based on β-Ti were formed on the interface, and the more in quantity and the smaller in size the solid solutions are, the higher the ultimate tensile strength is.     

Structure and properties of diffusion bonded transition joints between commercially pure titanium and type 304 stainless steel using a nickel interlayer

The solid-state diffusion bonding was carried out between commercially pure titanium and Type 304 stainless steel using nickel as an interlayer in the temperature range of 800–900 °C for 9 ks under 3 MPa load in vacuum. The transition joints thus formed were characterized in the optical and scanning electron microscopes. The inter-diffusion of the chemical species across the diffusion interfaces were evaluated by electron probe microanalysis. TiNi₃, TiNi and Ti₂Ni are formed at the nickel–titanium (Ni–Ti) interface; however, the stainless steel–nickel (SS–Ni) diffusion interface is free from intermetallic compounds up to 850 °C temperature. At 900 °C, the Ni–Ti interface exhibits the presence of α-β Ti discrete islands in the matrix of Ti₂Ni and λ + χ + α-Fe, λ + FeTi and λ + FeTi + β-Ti phase mixtures occur at the SS–Ni interface. The occurrence of different intermetallics are confirmed by the x-ray diffraction technique. The maximum tensile strength of ∼276 MPa and shear strength of ∼209 MPa along with 7.3% elongation were obtained for the diffusion couple processed at 850 °C. At the 900 °C joining temperature, the formation of Fe–Ti base intermetallics reduces the bond strength. Evaluation of the fracture surfaces using scanning electron microscopy and energy dispersive spectroscopy demonstrates that failure takes place through Ni–Ti interface up to 850 °C and through the SS–Ni interface of the joint when processed at 900 °C.     

Microstructure and mechanical properties of diffusion bonded SiC/steel joint using W/Ni interlayer

This paper describes the design and examination of W/Ni double interlayer to produce a joint between SiC and ferritic stainless steel. Diffusion bonding was performed by a two steps solid state diffusion bonding process. Microstructural examination and mechanical properties evaluation of the joints show that bonding of SiC to steel was successful. EDS and XRD analysis revealed that W₅Si₃ and WC were formed at SiC/W interface. The diffusion products at W/Ni interface, Ni-rich solid solution Ni(W) or intermetallic compound Ni₄W, was found to be dependent on the second step joining temperature. Neither intermediate phases nor reaction products was observed at Ni/steel interface for the joints bonded at the temperature studied. The average tensile strength of 55 MPa which is insensitive to the second step process was measured for as-bonded SiC/steel joint and the failure occurred at SiC/W interface. The hardness near the various bonded interfaces was also evaluated.     

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.     

Evolution of interface microstructure and strength properties in titanium – stainless steel diffusion bonded transition joints

Abstract

Diffusion bonding was carried out to produce transition joints between commercially pure titanium and 304 stainless steel at a temperature of 800°C for different times ranging from 30 to 180 min. in steps of 30 min under load in vacuum. The diffusion couples thus produced were studied using optical microscopy, scanning electron microscopy, and electron probe microanalysis to characterise the reaction layers formed in the diffusion zone. The chemical compositions of these layers indicate that intermetallics like σ phase, Fe₂ Ti, Cr₂ Ti, χ phase, FeTi, β-Ti, and Fe₂ Ti₄ O are formed in the reaction zone. The presence of these intermetallic compounds was also confirmed by the X-ray diffraction technique. Maximum bond strength of ~242 MPa was obtained for diffusion welded joints processed for 120 min. At this joining time, the plastic collapse of the surface asperities reaches near completion, favouring the interdiffusion of chemical species. Reduction in the bond strength of the transition joint processed for 180 min is due to the formation of a large volume fraction of voids in the reaction zone. Under tensile loading, failure takes place through α-Fe + χ phase mixture for transition joints processed in the time range of 30 – 90 min and through β titanium for joining times greater than 120 min.     

Friction welding process of 5052 aluminium alloy to 304 stainless steel

Abstract

Type 5052 aluminium alloy was joined to type 304 austenitic stainless steel via a continuous drive friction welding process. The joint strength increased, and then decreased after reaching a maximum value, with increasing friction time. Joint strength depended on the size and shape of the tensile testpiece. Friction weldability could be estimated by electrical resistmetry. The process of friction welding between the aluminium alloy and the stainless steel is proposed to evolve as follows: welding progresses from the outer to the inner region; an unbonded region is retained at the centre of the weld interface with shorter friction time; longer friction time causes the formation of an intermetallic reaction layer at the weld interface; and the reaction layer grows as the friction time increases. When the thickness of the reaction layer increased above a critical value, the joint was brittle and fractured at the weld interface. The joint was sound when there was no unbonded region and a thin reaction layer formed along the entire weld interface.     

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 between Ti -6Al -4V alloy and microduplex stainless steel with copper interlayer

Abstract

In the present study, diffusion bonding was used to join Ti -6Al- 4V alloy to a microduplex stainless steel using a pure copper interlayer. The effects of heating rate and holding time on microstructural developments across the joint region were investigated. After bonding, microstructural analysis including metallographic examination and energy dispersive spectroscopy (EDS), microhardness measurements, and shear strength tests were carried out. From the results, it was seen that heating rate and holding time directly affect microstructural development at the joint, especially with respect to the formation of TiFe intermetallic compounds, and this in turn affects the shear strength of the bonds. A sound bond was obtained with a heating rate of 100 K min ^-1 and holding time of 5 min, and this was related to the small amount of TiFe intermetallics formed close to the duplex stainless steel side at this bonding condition. Although Ti₂Cu and TiFe intermetallics were formed in all specimens, it was seen that the most deleterious intermetallic was TiFe. As the heating rate was decreased and holding time increased the amount of TiFe intermetallics increased, and consequently shear strength decreased. As a result, from the microstructural observations, EDS analysis, microhardness measurements, and shear strength tests, it was concluded that a high heating rate and a short holding time must be used in the diffusion bonding of Ti-6Al- 4V to a microduplex stainless steel when pure copper interlayers are used.     

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.     

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.     

Research on explosive welding of aluminum alloy to steel with dovetail grooves

In order to explore a new method for the explosive welding of aluminum alloy to steel, a 5083 aluminum alloy plate and a Q345 steel plate with dovetail grooves were respectively employed as the flyer and base plates. The parameters adopted in the explosive welding experiment were close to the lower limit of weldable window of 5083 aluminum alloy to Q345 steel. The bonding properties of 5083/Q345 clad plate were studied through mechanical performance tests and microstructure observations. The results showed that the aluminum alloy and steel plates were welded under the actions of metallurgical bonding and meshing of dovetail grooves. The tensile shear strength of 5083/Q345 clad plate met the requirements of the bonding strength of Al/Fe clad plate. The interfaces between aluminum alloy and the upper and lower surfaces of dovetail grooves were mainly welded through direct bonding, and discontinuous molten zone emerged in the local region; while the interface between aluminum alloy and the inclined surface of dovetail grooves was bonded by continuous molten layer. The brittle intermetallic compounds FeAl₂ and Al₅Fe₂ were generated at the bonding interfaces of 5083/Q345 clad plate. The fracture surface of the tensile specimen exhibited ductile and quasi-cleavage fractures.