Characterization of Al/Ni multilayers and their application in diffusion bonding of TiAl to TiC cermet

The Al/Ni multilayers were characterized and diffusion bonding of TiAl intermetallics to TiC cermets was carried out using the multilayers. The microstructure of Al/Ni multilayers and TiAl/TiC cermet joint was investigated. The layered structures consisting of a Ni₃(AlTi) layer, a Ni₂AlTi layer, a (Ni,Al,Ti) layer and a Ni diffusion layer were observed from the interlayer to the TiAl substrate. Only one AlNi₃ layer formed at the multilayer/TiC cermet interface. The reaction behaviour of Al/Ni multilayers was characterized by means of differential scanning calorimeter (DSC) and X-ray diffraction. The initial exothermic peak of the DSC curve was formed due to the formation of Al₃Ni and Al₃Ni₂ phases. The reaction sequence of the Al/Ni multilayers was Al₃Ni → Al₃Ni₂ → AlNi → AlNi₃ and the final products were AlNi and AlNi₃ phases. The shear strength of the joint was tested and the experimental results suggested that the application of Al/Ni multilayers improved the joining quality.     

Wear-induced microstructure in Ni/Cu nano-multilayers

Sliding wear tests were carried out in order to investigate wear resistance and resultant microstructure of Ni/Cu multilayers. The Ni/Cu multilayers having the component layer thickness h ranging from 5 to 100 nm were fabricated on copper substrates using the elecrodeposition technique. It was found that the wear depths in the multilayers were less than one-fifth of that of a conventional nickel coating at a high load condition. The wear resistance of the multilayer was almost independent of the component layer thickness, except the multilayer of h = 100 nm whose resistance was lower than those of the others. The observation of cross section revealed that the grains were generated locally near the worn surface in the Ni/Cu multilayers. Surface cracks were grown in such grained areas. The multilayer having a large grained area showed relatively low wear resistance. From the TEM observation, there were many equiaxed grains without the laminated structure. It is conceivable that the equiaxed grains without the laminated structure were formed due to dynamic recrystallization occurring after the laminated structure was annihilated by severe deformation. Assuming that the annihilation period is required for the wear of the Ni/Cu multilayer, the high wear resistance can be obtained regardless of the strengths of the multilayers.     

Reaction zone formed during diffusion bonding of TiNi to Ti6Al4V using Ni/Ti nanolayers

This study investigated the interfacial structure of solid state diffusion bonding of TiNi to Ti6Al4V using reactive Ni/Ti multilayer thin films. The TiNi and Ti6Al4V surfaces were modified by sputtering, by deposition of alternated Ni and Ti nanolayers, to increase the diffusivity at the interface. Bonding experiments were performed at 750, 800 and 900 °C at a pressure of 10 MPa with a dwell time of 60 min. The reaction zone was characterized by high-resolution scanning and transmission electron microscopy. Joints free from porosity and cracks were produced with Ni/Ti reactive multilayer thin films. Several phases formed at the interface, ensuring the bonding of these alloys. The reaction zone was constituted by columnar grains of Ti₂Ni and AlNi₂Ti, close to the Ti6Al4V base material, and by alternate layers of Ti₂Ni and TiNi equiaxed grains. The grain size decreased from Ti6Al4V to TiNi base materials. Nanometric grains were observed in the layers closest to the TiNi base material.     

Effect of Ni interlayer on characteristics of diffusion bonded Mg/Al joints

Magnesium and aluminium were joined through diffusing bonding with a Ni interlayer prepared by plasma spraying for the first time. Examination of the microstructure and phase constitution of interfacial regions indicated that Mg–Al reaction was successfully prevented in the presence of the Ni interlayer. With the elevation of temperature, a reaction layer of Mg₂Ni intermetallic was formed at Mg/Ni interface but few Al–Ni intermetallic was generated at Al/Ni interface. The mechanical test results showed that the tensile strength of the Mg/Al joint was substantially improved compared to that of the direct joint of Mg and Al. A maximum value of 5.8?MPa was obtained at 420°C for the joint with Ni interlayer.     

An investigation on microstructure and mechanical properties of Al7075 to Ti–6Al–4V Transient Liquid Phase (TLP) bonded joint

Transient Liquid Phase (TLP) bonding of two dissimilar alloys Al7075 and Ti–6Al–4V has been done at 500 °C under 5 × 10⁻⁴ torr. Cu was electrodeposited on Al7075 and Ti–6Al–4V surfaces, 50 μm thick Sn–4Ag–3.5Bi film was used as interlayer and bonding process was carried out at several bonding times. The microstructure of the diffusion bonded joints was evaluated by Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The eutectic and intermetallic compounds formation along Al7075 grain boundaries and Ti/Al interface such as θ(Al₂Cu), TiAl and Ti₃Al were responsible for joint formation at the aluminum and titanium interfaces. Microhardness and shear strength tests were used to investigate the mechanical properties of the bonds. Hardness of the joints increased with increasing bonding time which can be attributed to the intermetallics formation at the interface. The study showed that the highest bond strength was 36 MPa which was obtained for the samples joined for 60 min.     

An investigation on bonding mechanism and mechanical properties of Al/Ti compound materials prepared by insert moulding

Al/Ti metallic composites prepared by insert moulding are attracting more attention now because of their low production costs, low energy consumption, simple production procedure and high interface bonding strength. However, the insert moulding of pure Al and pure Ti has not been reported so far though it can be considered as a fundamental in studying Ti-alloy/Al-alloy interface bonding. Therefore, the insert moulding of pure Al and pure Ti is intended in this paper and the corresponding microstructure, elements distribution and mechanical properties of the interface are also analyzed. As a result, a good metallurgical bonding can be achieved at the interface of Al and Ti, which is mainly comprised of intermetallic compounds TiAl₂ and TiAl₃ formed in the transition zone around Ti insert and Al matrix, respectively, depending on different heat treatment parameters and cooling conditions. It is shown that the hardness of the interface layer varies with the types of interface sublayers. For the compact sublayer, the hardness is higher than those of both base metals (Al and Ti) with the maximum value reaching HV520. However, the hardness of the granular interface sublayer depends on the proportion of the intermetallic compounds and aluminum matrix. The average shear strength of the interface layer could reach about 60 MPa, which is higher than that of the aluminum matrix (43 MPa) tested in this experiment. The result also shows that shear crack initiates at bottom face of the specimen (adjacent to locator) in the aluminum matrix nearby the interface.     

中间层Ni对TC4/2A14异种金属搅拌摩擦焊接头组织和性能的影响

目的 添加0.05 mm厚的Ni箔作为中间层,对3 mm厚的TC4钛合金和2A14铝合金进行搅拌摩擦焊,分析Ni对接头力学性能的影响。方法 采用扫描电镜、EDS能谱及XRD衍射等微观表征分析方法,对焊接接头的断口形貌、成分进行分析,探究Ni箔对焊接接头力学性能的影响。结果 由于钛合金和铝合金存在较大的物理化学性能差异,Ti/Al异种金属焊接性较差,界面容易产生TiAl3、TiAl、Ti3Al等金属间化合物,其中脆性相TiAl3对接头性能的影响最大,会导致综合力学性能下降。当加入中间层材料Ni后,由于Ni与Al晶体结构均属于面心立方,因此Ni与Al的扩散系数大于Ti与Al的扩散系数,Ni和Al之间优先形成金属间化合物且弥散分布于焊缝中,从而缩短了Ti与Al之间的相互扩散时间,减少了TiAl3相的生成。结论 在未添加中间层材料时,接头平均抗拉强度为237.3 MPa,约为2A14铝合金母材抗拉强度的56.7%;当添加中间层Ni后,对焊缝中金属间化合物的种类和数量进行了调控,减少了对性能影响最大的TiAl3相的生成,接头平均抗拉强度达到285.3 MPa,为2A14铝合金母材抗拉强度的68%。     

（Ni,Fe）Al金属间化合物的快速凝固组织与室温塑性

用单辊快速凝固法制备（ＮｉＦｅ）Ａｌ金属间化合物并研究其组织与室温塑性。结果表明，Ａｌ－４５Ｎｉ－５Ｆｅ（原子分散）在快速凝固条件下可形成内部为亚微米级针状亚晶的等轴晶粒，具有高达３．１％的弯曲塑性，Ａｌ－３５Ｎｉ－１５Ｆｅ和Ａｌ－２５Ｎｉ－２５Ｆｅ的快凝组织则为柱状晶，弯曲塑性仅有１．１％１．０％，针状亚晶是一定成分的（Ｎｉ，Ｆｅ）Ａｌ在快速凝固条件下形成的亚稳相，其形成机制和快速凝固过程中原子     

Diffusion bonding of TiAl intermetallic and Ti3AlC2 ceramic: Interfacial microstructure and joining properties

TiAl intermetallics and Ti₃AlC₂ ceramics were jointed through diffusion bonding using Ti/Ni interlayer. The effect of bonding temperature and holding time on interfacial microstructure and mechanical properties of the bonded joints were investigated. The typical interfacial microstructure of the joint from TiAl to Ti₃AlC₂ side could be divided into τ₃-Al₃NiTi₂, α₂-Ti₃Al, α-Ti + δ-Ti₂Ni, δ-Ti₂Ni, β₂-TiNi, η-TiNi₃, γ-(Ni)_ss, γ′-Ni₃(Al, Ti), γ′-Ni₃(Al, Ti) + Ti₃AlC₂, respectively. The value of the microhardness in the reactive zones increased due to the formation of intermetallcs. Lower or higher bonding temperature and longer or shorter holding time both resulted in low strength owing to the insufficient diffusion of atoms or excessive formation of intermetallics. A high bonding strength can be obtained when bonding at 920 °C for 60 min. Fracture occurred through the intermetallic layer adjacent to the Ti₃AlC₂ substrate during shear test, showing brittle intergranular and transgranular characteristic.     

Diffusion bonding between Ti‐6Al‐4V alloy and interstitial free steel

This work deals with diffusion bonded joints between Ti–6Al–4V alloy and interstitial free (IF) steel at different temperatures under a pressure of 5 MPa for 30 min. The effect of bonding temperature on the microstructure and mechanical properties of the joint interface was investigated using optic microscopy, a scanning electron microscope (SEM) equipped with X‐ray energy dispersive spectrometer (EDS) and shear strength measurements. The intermetallic phases such as FeTi and Fe₂Ti occurred at the interface of bonded specimens. In addition, it was seen that shear strength of bonded specimens decreased with increasing temperature due to growing intermetallics.     

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.     

Effect of Nb?+?Ti coating on the wetting behavior, interfacial microstructure, and mechanical properties of Al/Al2O3 joints

The subject of the work was to study the effect of Nb + Ti thin film deposited by PVD method on alumina substrates on the wetting behavior, bond strength properties, and structure of interface in the Al/Al₂O₃ joints. Applying the sessile drop method, the wetting behavior of molten Al (99,999%) on coated alumina substrates was studied in the temperature range between 953 and 1373 K under a vacuum of 0.2 mPa for 30 min of contact. The sessile drop samples were used to examine the interface structure, shear strength, and interfacial fracture toughness under the concentrated load. The introduction of the thin Nb + Ti film layer of 900 nm thickness: (1) greatly improves the wettability of alumina by molten Al at above 1223 K and the shear strength of Al/Al₂O₃ joints produced at 1223 K, (2) has positive effect on structure transformation in the interface and leads to fabrication of reliable metal–ceramic joints. Microstructural investigations of the interface indicated that the precipitates of Nb and Ti-rich intermetallic phases were formed at the Al/Al₂O₃ interface, which influenced strengthening of these joints. Hence a conclusion can be drawn that the interface structure influences the durability increase in Al/Al₂O₃ joints.     

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.     

Improvement of Joint Strength of SiCp/Al Metal Matrix Composite in Transient Liquid Phase Bonding Using Cu/Ni/Cu Film Interlayer

The compact oxide on the surface of SiCp/Al metal matrix composite （SiCp/Al MMC） greatly depends on the property of the joint. Inlaid sputtering target was applied to etch the oxide completely on the bonding surface of SiCp/Al MMC by plasma erosion. Cu/Ni/Cu film of 5μm in thickness was prepared by magnetron sputtering method on the clean bonding surface in the same vacuum chamber, which was acted as an interlayer in transient liquid phase （TLP） bonding process. Compared with the same thickness of single Cu foil and Ni foil interlayer, the shear strength of 200 MPa was obtained using Cu/Ni/Cu film interlayer during TLP bonding, which was 89.7% that of base metal. In addition, homogenization of the bonding region and no particle segregation in interfacial region were found by analysis of the joint microstructure. Scanning electron microscopy （SEM） was used to observe the micrograph of the joint interface. The result shows that a homogenous microstructure of joint was achieved, which is similar with that of based metal.     

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

Diffusion bonding between W and steel using V/Ni composite interlayer was carried out in vacuum at 1050 °C and 10 MPa for 1 h. The microstructural examination and mechanical property evaluation of the joints show that the bonding of W to steel was successful. No intermetallic compound was observed at the steel/Ni and V/W interfaces for the joints bonded. The electron probe microanalysis and X-ray diffraction analysis revealed that Ni₃V, Ni₂V, Ni₂V₃ and NiV₃ were formed at the Ni/V interface. The tensile strength of about 362 MPa was obtained for as-bonded W/steel joint and the failure occurred at W near the V/W interface. The nano-indentation test across the joining interfaces demonstrated the effect of solid solution strengthening and intermetallic compound formation in the diffusion zone.     

高Nb-TiAl合金的高温变形行为及其板材的性能

对高Nb-TiAl合金进行多步热压缩,研究其高温变形行为及其板材的性能。结果表明,热压缩变形后高Nb-TiAl合金的组织中等轴γ晶粒和α晶粒的增多、层片晶团的体积分数和尺寸降低,使其变形能力提高。根据这些结果确定了最优轧制工艺为应变速率低于0.5 s-1、道次变形量前期应不高于25%、变形温度高于1150℃。选用上述工艺对其其进行5道次大变形量轧制,制备出表面质量良好、无缺陷的高Nb-TiAl合金板材,其尺寸为600 mm×85 mm×3 mm。这种板材具有双态组织,平均晶粒尺寸小于5μm,其室温屈服强度、抗拉强度和塑性分别为948 MPa、1084 MPa和0.94%,800℃下抗拉强度为758 MPa。     

Transient liquid phase bonding of AA 6082 aluminium alloy

Transient liquid phase bonding (TLP) on AA 6082 samples were performed under ambient non‐vacuum conditions, which was possible by a suitable pre‐treatment. This treatment involves a zincate treatment followed by copper plating, which is a common industrial process and can be performed in large batches. This treatment allows to remove the natural aluminium oxide layer and to protect the aluminium surface from excessive oxidation. Different bonding conditions were investigated and showed the feasibility of the transient liquid phase bonding process for AA 6082. Energy dispersive X‐ray spectroscopy (EDX) investigations showed that the isothermal solidification is already terminated after 5 min. The microstructure of the bonding zone showed no metallurgical discontinuity such as eutectic microstructure or intermetallic Al–Cu phases. However the microstructure shows numerous voids with a size of approximately 30 µm in the bonding zone. It is assumed that these voids were formed during the bonding process due to solidification shrinkage and the presence of interfacial oxide layers. The transient liquid phase bonded samples that were mechanically tested under tensile load showed an average strength of approximately 270 MPa, the minimum yield strength required for the base material according to EN 754‐2 is 255 MPa. Due to the notch effect of the voids, the tensile sample failed under forced fracture and showed no plastic deformation.     

Fe/Al异质金属接头界面组织演变、生长动力学及力学性能

采用真空扩散连接方法研究Fe/Al异质金属接头界面组织演变规律、金属间化合物(intermetallic compound,IMC)生长动力学及力学性能。结果表明：焊接温度为550 ℃时,接头界面无IMC生成,当焊接温度超过575 ℃时,界面由Fe₂Al₅及少量FeAl₃ IMC构成,且随焊接温度升高IMC层迅速长大。在120 min保温时间条件下,接头剪切强度随焊接温度的升高先增加后降低,当焊接温度为575 ℃时,接头剪切强度达到最大值37 MPa。在550~625 ℃范围内,基于热力学分析得出Fe₂Al₅的吉布斯自由能ΔG_Fe-Al最低,而FeAl₃的ΔG_Fe-Al次之,在接头界面处IMC生成顺序为Fe₂Al₅→FeAl₃。Fe/Al接头界面IMC的生长随焊接温度呈抛物线规律,其生长激活能为282.6 kJ·mol^-1。在575,600,625 ℃条件下,界面IMC的生长速率分别为1.13×10^-14,3.59×10^-14,1.21×10^-13 m²·s^-1。     

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.     

Effect of phase transformation and intermetallic compounds on the microstructure and tensile strength properties of diffusion-bonded joints between Ti–6Al–4V and AISI 304L

The occurrence of a phase transformation and the effect of intermetallic compounds on the microstructure and tensile strength properties of diffusion-bonded (DB) joints between Ti–6Al–4V and AISI 304L were studied in the temperature range of 875–950 °C with an interval of 25 °C, a bonding time of 60 min and pressures of 4 MPa and 8 MPa. A maximum tensile strength of 242.6 MPa, was observed for diffusion-bonded joints that were processed at a temperature of 900 °C, bonded for 60 min at a pressure of 4 MPa and annealed for 2 h at 750 °C. Optical microscopy and scanning electron microscopy (SEM) were used to examine the grain growth and the fine details of the interface structure. Energy dispersive X-ray analysis (EDAX) and X-ray diffraction analysis (XRD) revealed the existence of intermetallic compounds and corroborated the phase transformation.