Characteristics of clad aluminum hollow billet prepared by horizontal continuous casting

The 3003/4045 clad hollow billets are prepared in the present study. Microstructures, solute distribution and bonding strength of the interfacial regions were investigated. The effects of plastic deformation on the evolution of microstructure and microhardness of the interfaces were also studied. The results show that metallurgical bonding between the solid and liquid Al alloys can be obtained with optimal parameters. Si and Mn atoms diffuse across the interface to form a diffusion layer with the thickness about 30 μm on average. The mean tensile-shear strength of as-cast clad hollow billet is 85.3 ± 9.2 MPa, and the strength of the interface is higher than that of 3003 alloy. Incompatible deformation between 3003 and 4045 layers occurs during rolling processes, and the needle-like Si phase transforms to the dispersive particles. The gradient distribution of microhardness across the interface is retained after the deformation.     

Transient liquid phase diffusion bonding of 6061-15 wt% SiCp in argon environment

Extruded 6061-15 wt% SiCp composite was joined by transient liquid phase diffusion (TLPD) bonding process in argon environment using 50-μm thick copper foil interlayer. The bonding was carried out at 560 °C with two different applied pressures (0.1 and 0.2 MPa) and five different holding times (20 min, 1, 2, 3 and 6 h). Kinetics of the bonding process was significantly accelerated in the presence of reinforcement (SiC). This acceleration is attributed to the increased solute diffusivity through defect-rich SiC particle/matrix interface and porosity. Adequate bond strength (90% of the original composite strength) was achieved for bonding at 0.2 MPa pressure with 6 h of holding. This is very close to the reported highest bond strength achieved (92% of the original composite strength) for joining aluminium-based metal matrix composite by TLPD process in vacuum followed by isostatic pressing. The rejection of oxide at periphery on completion of isothermal solidification, and elimination of void at bond interface through solid state diffusion at higher pressure (0.2 MPa) were the main reasons of achieving high bond strength.     

Cu/Al层厚比对波纹辊轧制Cu/Al复合板变形行为和结合性能的影响

本工作通过抗剪切强度测试、剪切断面显微观察和有限元仿真等手段对不同Cu/Al层厚比下波纹辊轧制（CRB）Cu/Al复合板的金属的变形行为和界面结合性能进行了研究。结果发现，CRB过程中界面处形成了局部强正应力和多个“搓轧区”，促进了复合板的塑性变形和界面结合。增大Cu/Al层厚比可提升Cu层的变形率和波谷界面处的正应力，有利于降低Cu/Al复合板的翘曲程度，并增强界面的整体结合性能。当层厚比从2:10增加到2:4时，界面抗剪切强度从40.39MPa上升到47.24 MPa，但界面抗剪切强度的波动逐渐增大。     

Microstructure and bond strength of diffusion-bonded nickel aluminide–titanium joints

Diffusion bonding of Ni₇₅Al₂₅ alloy to commercially pure titanium was carried out at 900 °C for different times under 2 MPa in vacuum. The microstructure of transition joints was revealed by scanning electron microscopy (SEM). Good bonding was observed on all the samples. Chemical compositions of the interface of the bonded samples were identified by energy dispersive spectroscopy. EDS results indicated the formation of the different compositions at the interface of the bonded samples. X-ray diffraction studies showed the presence of TiNi, Ti₂Ni, Ni₃Al, Ni4.22Al0.9 and Ti phases on the fractured surfaces of bonded samples. It was observed that the shear strengths of joints increased with increasing of bonding time. The maximum shear strength was found as 205 MPa for the bonded couple treated for 2 h.     

Titanium to steel joining by spark plasma sintering (SPS) technology

The bonding of Ti–6Al–4V to low alloy steel (AISI4330) using SPS technique in the 850–950 °C temperature range was examined. The formation of a thin (～1 μm) titanium carbide interfacial layer was observed with a thickness only slightly dependent on the joining temperature. This layer separates the joined metals and prevents the formation of Fe–Ti intermetallics in the bonding zone. The maximal tensile strength of the joints (of about 250 MPa) was achieved for bonding at 950 °C for 3.6 ks. The formation of the titanium carbide layer and its evolution are discussed based on the isothermal section of the ternary Fe–Ti–C phase diagram.     

Evolution of deformation microstructures of cold-rolled Ta–2.5W alloy with coarse grains at low to medium strains

Ta–2.5W alloy with coarse grains was cold-rolled to reductions ranging from 5 to 40%. The evolution of the microstructure was investigated by optical microstructure, electron backscatter diffraction (EBSD). A few microbands appear when the reduction reaches 20%. The density of microbands increases with increasing reduction. When the reduction reaches 40%, grains are composed of one or two groups of microbands except the {001}<110 > orientations. Most of the inclination angle between microbands and RD in this condition is 20–35°. As the strain increases, the inclination angle between microbands and RD gets smaller. The habit plane of microbands can be {110} plane. The microbands and matrix usually share a common < 110 > or < 111 >. The mature body-centered cubic rolling texture, including α and γ fibers, is not developed until the reduction reaches 40%. Meanwhile, shear bands appear. New grains can be seen in shear bands and a model is proposed to explain this process.     

Magnetic pulse cladding of aluminum alloy on mild steel tube

Bi-metal tubes, which combine the advantageous properties of two different metals, are desirable in industries where corrosion resistance is important. A new cladding method named magnetic pulse cladding (MPC) was used to form bi-metal tubes. A cladding of mild steel tube by aluminum alloy (AA3003) was achieved. The effect of the geometry of the field shaper on cladding quality was investigated as well as other main process parameters, such as, feeding size, radial gap and discharge voltage. The mechanical property was evaluated by compression-shear test and a maximum strength of 79.2 MPa and an average of 29.7 MPa were attained to by the following process settings: profiled field shaper, feeding size of 12 mm, radial gap of 2.0 mm and discharge voltage of 15 kV. OM and SEM images show a smooth integral interface and a small wavy one. EDS mapping reveals the interfacial diffusion zone up to 50-μm wide. The results show that the proposed MPC process is able to form sound cladding bonds and could be applicable to a tubular clad component with a high axial length.     

Adhesion properties of tungsten and SiC ceramic-bonded carbon

A newly developed carbon-based composite, SiC ceramic bonded carbon (30 vol% SiC) was directly clad with tungsten (W) at 1700 °C by spark plasma sintering. There were no voids or cracks in the fabricated material. The adhesion strength between W and SiC/CBC is 90 MPa and 33 MPa by the bending and tensile test, respectively. The interface between W and SiC/CBC was analyzed and the cladding mechanism was discussed.     

Sol–gel derived hydroxyapatite coatings on titanium substrates

The oscillatory micromovements at the interface between the implant and the bone induce fretting wear and sometimes, fatigue cracks, causing early failure of the joint prosthesis. Hydroxyapatite films were formed using a sol–gel method from an organic precursor solution. The average film thickness was found to be 1.0 μm. Composite coatings containing HA doped with ZrO₂ were also formed. Hydroxyapatite (HA) and composite films of HA and ZrO₂ formed on commercial titanium substrates using an organic precursor solution by sol–gel route, were tested for fretting wear using a ball-on-flat fretting apparatus. The moderately lower values of the coefficient of friction (0.4–0.5) and morphology of the wear pits for considerably long cycles of fretting indicate strong bonding of the HA coating to the titanium surface. The interface shear strength of a thin hydroxyapatite film on commercial purity titanium has been evaluated using a substrate straining method. The maximum interfacial strength was about 570 and 678 MPa, for the pure HA and composite films, respectively, on the highly polished surface. However, the maximum interfacial strength was found to be about 263 MPa on the oxidized surface.     

Effect of hot pressing temperature on microstructure,mechanical properties and grinding performance of vitrified-metal bond diamond wheels

The self-sharpening vitrified-metal bond diamond wheels added with a 3 wt.% brittle Na₂O-B₂O₃-SiO₂-Al₂O₃-Li₂O vitrified bond were fabricated by hot pressed sintering technique. Using the methods of scan-electroscope, energy spectrum analysis, X-diffraction analysis, XPS analysis, Rockwell hardness test and three-point bending test, the effects of hot pressing temperature on the microstructure, hardness and the transverse rupture strength (TRS) of vitrified-metal bond were investigated. Then the grinding performance of cylinder of the diamond wheels was also studied. The results showed that, when the hot pressing temperature was 850 °C, a thin FeAl₂O₄ transition layer formed, which enhanced the interfacial bending strength between metal and glass phase, and the TRS of vitrified-metal bond reached the maximum value 826.54 MPa. Comparing with metal bond diamond wheel's, the average value of the roundness and straightness of the 50 cylinders ground by the vitrified-metal diamond wheel reduced from 3.1 μm and 2.5 μm to 2.7 μm and 2.1 μm.     

轧制工艺对工业化试制的真空组坯Q345R/304复合板组织性能的影响

山西太钢不锈钢股份有限公司利用真空组坯复合轧制（真空电子束焊接+轧制复合）技术工业化试制了Q345R/304复合板。本文研究了常规轧制和控轧控冷工艺下轧制复合板的界面结合率、常规力学性能、界面结合强度和界面附近的显微硬度和显微组织变化。结果表明：界面结合不良来自于复合界面处形成的硅铝氧化物和铬锰氧化物,这可能是由于组坯时真空度不足、加热过程中形成的氧化产物。两种工艺下界面附近显微组织差异明显,沿远离界面方向,常规轧制的Q345R钢板组织沿厚度方向为均匀的块状铁素体和珠光体组织,304钢板组织已完全再结晶;控轧控冷工艺轧制的Q345R钢板组织沿厚度方向由多边形铁素体和珠光体组织向针状铁素体和贝氏体组织过渡,304钢板组织仍有变形特征。力学性能检测表明：常规热轧复合板的屈服强度和抗拉强度比控轧控冷复合板分别低115、71 MPa,强度裕量较小;纵向冲击功不小于130 J,外弯、内弯、侧弯后无裂纹,复合板剪切强度在350 MPa以上,高于标准要求(不小于210 MPa),线扫描结果表明界面附近已存在由元素扩散形成的浓度梯度。     

Microstructural evolution during reactive brazing of alumina to Inconel 600 using Ag-based alloy

A metal–ceramic bonding process was developed to produce vacuum tight alumina–Inconel 600 joints using an Ag-based active metal brazing alloy that can withstand continuous operating temperature up to 560 °C. The microstructure and microchemistry of the braze zone was examined using extensive microanalysis of the constituent phases and a mechanism for the interfacial reactions responsible for the bonding is proposed. Prolonged heat treatment at 400 and 560 °C under simulated in-service conditions revealed that the microstructure of braze zone of the joints was stable and maintained leak-tightness and strength. The bond strength of the interface was high enough to cause failure in the alumina side of the joints. Failure of the joints was caused by initiation of crack on the surface of alumina as a result of high tensile residual stress adjacent to the metal–ceramic interface.     

Microstructure,mechanical properties and bonding characteristic of deformed tungsten

We focused on the microstructure, mechanical properties, and bonding characteristic of rolled pure tungsten (PW) and W-1.0 wt.%La₂O₃ (WL10). WL10 exhibited higher microhardness and bending strength despite lower density compared to PW. Charpy tests showed that WL10 displayed higher absorbed energies compared to PW at the same test temperatures, and the delamination fracture appeared at 873 K for WL10 while 1073 K for PW. However, the excellent mechanical properties of WL10 did not lead to high bonding strength when it was bonded with CuCrZr alloys. The shearing and bending strength are 122.26 and 183.91 MPa, lower than 198.69 and 215.27 MPa of PW. The difference of thermal–physical properties between tungsten and La₂O₃ caused the cracks near the interface, resulting in lower bonding strength of WL10.     

Microstructure and mechanical properties of diffusion bonded joints between tungsten and F82H steel using a titanium interlayer

Diffusion bonding between W and ferritic/martensitic steel F82H using a Ti interlayer was carried out in vacuum at temperature range of 850–950 °C for 1 h with 10 MPa. Metallographic analysis with field-emission scanning electron microscopy revealed excellent bonding at both W/Ti and Ti/F82H interfaces. The chemical compositions of the reaction products were analyzed by energy dispersive spectroscopy and their existence were confirmed by X-ray diffraction technique. α–β Ti solid solution was detected at W/Ti interface, while the reaction phases at Ti/F82H interface are dependent on the joining temperature. Joint strength was evaluated and the variations in strength of the joints were significantly related to the microstructural evolution of the diffusion zone. All the joints fractured at Ti/F82H interface during shear testing. The hardness distribution across the joining interfaces was also determined.     

Enhancing room temperature mechanical properties of Mg–9Al–Zn alloy by multi-pass equal channel angular extrusion

Influence of equal channel angular extrusion on room temperature mechanical properties of cast Mg–9Al–Zn alloy was investigated. The results show that room temperature mechanical properties of Mg–9Al–Zn alloy, such as yield strength, ultimate tensile strength and elongation, can be improved heavily by equal channel angular extrusion. Processing routes, processing temperature and extrusion passes have important influence on room temperature mechanical properties of processed Mg–9Al–Zn alloy by equal channel angular extrusion. The optimum room temperature mechanical properties such as yield strength of 209 MPa, ultimate tensile strength of 339 MPa and elongation of 14.1%, can be obtained when Mg–9Al–Zn alloy was processed by equal channel angular extrusion for 6 passes at route B_C at 498 K. Large bulk materials of Mg–9Al–Zn alloy with average grain size of 4 μm and high mechanical properties can be prepared.     

Shear strength of CMT brazed lap joints between aluminum and zinc-coated steel

Higher shear strength and fusion line failure were measured in CMT brazed lap joint of aluminum alloy 6061 and zinc coated steels with high strength (DP600) or thick plate (1.2 mm). Lower shear strength and interface failure were observed only if aluminum was brazed with low strength (270 MPa) and thin steel sheet (0.7 mm). A numerical model was developed for the prediction of shear strength and failure modes of the CMT lap joints. The maximum principle stress and deformation energy at the interface layer of the CMT joints were adopted as failure criteria for interface failure prediction. The equivalent plastic strain in the weld metal, HAZ and base metal of aluminum side of the CMT brazed joints was used as a criterion for failure prediction occurred on the fusion line. The shear strength of CMT joints and the two failure modes can be accurately estimated by the developed numerical model.     

Mechanical properties and rolling behaviors of nano-grained copper with embedded nano-twin bundles

By means of dynamic plastic deformation (DPD) at liquid nitrogen temperature (LNT), bulk nano-grained copper samples with embedded nano-twin bundles were prepared. Subsequent cold rolling (CR) of the LNT-DPD Cu led to a reduction in quantity of nano-twin bundles and a slight grain coarsening, accompanied by a decrease in grain boundary (GB) energy from 0.34 to 0.22 J m⁻². An increasing CR strain leads to a saturation grain size of ∼110 nm, which is less than half of that in the severely deformed Cu from the coarse-grained form. Decreased strength and enhanced ductility were induced by CR in the LNT-DPD sample. The saturation yield strength in the LNT-DPD Cu during CR was ∼105 MPa higher than that in conventional severely deformed Cu, which originates from the finer grains as well as the nano-scale twins in the LNT-DPD sample. The enhanced ductility is primarily attributed to CR induced GB relaxation.     

Nanostructured Al–Al2O3 composite formed in situ during consolidation of ultrafine Al particles by back pressure equal channel angular pressing

Ultrafine pure Al particles were consolidated into fully dense bulk material using back pressure equal channel angular pressing (BP-ECAP). The consolidation was carried out at 400 °C with a back pressure of 200 MPa. A fully dense Al–Al₂O₃ composite consisting of mostly nanocrystalline Al and γ-Al₂O₃, a small fraction of ultrafine Al grains and amorphous alumina was produced after four passes from the freshly formed particles. In contrast, no consolidation was achieved from the aged particles which had been kept for between 18 and 24 months. The formation of the nanostructure was attributed to the interaction between severe shear deformation and in situ oxidation during ECAP. The ultimate strength of the nanostructured material reached ～740 MPa in compression with a plastic strain to fracture of the order of ～1%. It is demonstrated that ultrafine particles can be well consolidated by ECAP when they are sheared to change shape rather than to slide over each other.     

Diffusion bonding of SU 263

Using a specially constructed apparatus, diffusion bonding of SU 263 alloy was studied in the temperature range of 1123–1323 K and compressive stress of 90% of its yield strength at the corresponding temperatures to determine the relative importance of the process parameters, the mechanism(s) responsible for bonding and the joint characteristics. Bond quality was assessed by optical metallography and lap shear testing. The mechanism of bonding was evaluated by grain growth equation. The experimental results were compared with a model developed by Pilling [Pilling, J., 1988. The kinetics of isostatic diffusion bonding in superplastic materials. Mater. Sci. Eng. 100, 137–144] in which the void closure by creep flow and diffusion are considered. Quantified EPMA line scan analysis was carried out to confirm the bonding mechanism and to determine the composition at the interface.     

Deformation mechanisms in a Ru–Ni–Al ternary B2 intermetallic alloy

Deformation mechanisms in a B2 Al50Ni5Ru45 alloy have been studied in compression over the temperature range 298–1323 K. The alloy exhibited a low temperature sensitivity of the flow stress over the temperature range 298–973 K. The strain rate sensitivity below 973 K was relatively low, similar to binary RuAl-based alloys. Dislocation analyses after room temperature compression indicate the presence of 〈1 0 0〉 and 〈1 1 0〉 dislocations on {1 1 0} planes, with the 〈1 0 0〉 dislocations present with slightly higher densities. Compression creep tests at stress levels between 300 MPa and 500 MPa revealed exceptional creep strength in the temperature range investigated. The predominant dislocation substructure after creep deformation consisted of uniformly distributed, cusped 〈1 0 0〉-type screw dislocations on {1 1 0} planes. The deformation behavior and creep mechanisms are discussed in comparison with other high melting temperature B2 intermetallics.