Fe-based metallic glass particles reinforced Al-7075 matrix composites prepared by spark plasma sintering

Metallic glass (MG) reinforced aluminum matrix composites (AMCs) have attracted the interest of many researchers in the past few years. In this study, Fe₅₀Cr₂₅Mo₉B₁₃C₃ metallic glass (FMG) particles reinforced 7075 aluminum matrix (Al-7075) composites were prepared by spark plasma sintering (SPS) technique. The microstructure of the composites showed good interface bonding between the FMG particles and the matrix. The micro-hardness of the composite with 30 vol% FMG particles reached 160.63 HV, which was increased by 30% compared with that of Al-7075 (119.3 HV). The ultimate compression strength (UCS) of the composite was also improved significantly from 596 MPa for Al-7075 matrix to 749 MPa for the composite reinforced with 30 vol% FMG particles, and the compression strain of the composite reached 22%. These results indicate that the mechanical properties of the composites can be enhanced by adding high volume fraction FMG particles. The enhancement of the strength is resulted from multiple strengthening mechanisms, and the main contributions come from the thermal mismatch and grain refinement.     

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.     

Transient liquid phase (TLP) bonding of Al7075 to Ti–6Al–4V alloy

TLP diffusion bonding of two dissimilar aerospace alloys, Ti–6Al–4V and Al7075, was carried out at 500 °C using 22 μm thick Cu interlayers for various bonding times. Joint formation was attributed to the solid-state diffusion of Cu into the Ti alloy and Al7075 alloy followed by eutectic formation and isothermal solidification along the Cu/Al7075 interface. Examination of the joint region using SEM, EDS and XPS showed the formation of eutectic phases such as, ?(Al₂Cu), T(Al₂Mg₃Zn₃) and Al₁₃Fe along grain boundaries within the Al7075 matrix. At the Cu/Ti alloy bond interface a solid-state bond formed resulting in a Cu₃Ti₂ phase formation along this interface. The joint region homogenized with increasing bonding time and gave the highest bond strength of 19.5 MPa after a bonding time of 30 min.     

Influence of Interfacial Bonding between Metal Droplets on Tensile Properties of 7075 Aluminum Billets by Additive Manufacturing Technique

7075 aluminum billets were fabricated by micro droplet deposition manufacturing technique,and the influence of interfacial bonding between metal droplets on the tensile properties was studied.Three sets of samples were manufactured under different temperature conditions,and their mechanical properties were compared.The results show that the temperature of the metal droplets and substrate signi?cantly affect the tensile strength of the sample.Moreover,with proper temperature setting,the 7075 aluminum billets manufactured by micro metal droplet deposition could achieve very good mechanical properties with a tensile strength of 373 MPa and an elongation of 9.95%,which are very similar to those of an extruded sample.Moreover,a metallurgical bonding diagram based on numerical calculations of interfacial temperature was established to predict the interfacial bonding state.In addition,the fracture morphologies of these specimens were observed.It is indicated that there was a signi?cant transformation of failure mechanism with the improvement of metallurgical bonding,which agreed well with the numerical results.     

Joining Si3N4 to type 405 steel with soft metal interlayers

Abstract

The suitability of four pure metals, Ni, Fe, Ti, and Nb, as interlayers for bonding silicon nitride to type 405 ferritic stainless steel has been examined. Bonding was carried out by hot isostatic pressing at temperatures between 1473 and 1673 K under a pressure of 100 MPa. Of the metals tested, Fe and Nb formed the strongest interfacial bonds with Si₃N₄. To reduce the influence of residual stress in joints, Fe/W and Nb/W laminated interlayers were also examined. The use of W restricted the contraction of Fe or Nb, and the Si₃N₄/steel joints with these interlayers had a tensile strength of more than 50 MN m^?2. A low-pressure (10 MPa) bonding process was also used for the Fe/W interlayer.

MST/470     

Heat-resistant joints of Si3N4 ceramics with intermetallic compounds formed in situ

The possibility of the improvement on the heat resistance of Si₃N₄ ceramic joints with intermetallic compounds formed in situ was investigated. The Si₃N₄ ceramics were joined with Ti/Ni/Ti multi-interlayers between 1000 and 1150°C. The effects of various parameters, which include the thickness of Ti and Ni foils, the pressure imposed during bonding, the bonding temperature and the holding time, on the microstructures and the strength (both at room temperature and at high temperature) of the joints were studied. The results indicated that the sound joints with higher strength both at room temperature and at elevated temperature could be acquired with intermetallic compounds formed in situ under appropriate bonding parameters. The shear strength at 800°C could sustain about 88 MPa.     

Diffusion bonding SiC or Si3N4 to Nimonic 80A

A method of diffusion bonding SiC or Si₃N₄ to Nimonic 80A was developed to establish the fundamental technology for the application of ceramics to machinery components used at elevated temperature. An analysis of the thermal stress that occurs in ceramic/Nimonic 80A bonded composites was done using the finite element method, and a bonding experiment based on the analytical results was conducted. The composites were produced by the insert metal bonding method, using varying thickness of Ni, W, Kovar, Cu and so on. It was found that the residual thermal stress in the ceramic part of the composite was extremely low and that the composite had a tensile strength of more than 98 MPa at room temprature. Furthermore, the paper describes the feasibility of the application ofthis bonding method to components for marine diesel engines.     

Interfacial microstructure, bonding strength and fracture of magnesium-aluminum laminated composite plates fabricated by direct hot pressing

A direct hot pressing method is developed to fabricate duplex metal plates of magnesium alloy base plate and aluminum cover plate. A metallurgical bonding between the base plate and the cover plate is achieved with formation of three distinct bonding subzones, two single-phase layers Al₃Mg₂ and Mg₁₇Al₁₂, and one two-phase layer Mg₁₇Al₁₂ and α-Mg. The tensile strength across the bonding interface is as high as 24 MPa, and the Al₃Mg₂ layer is the weak link of the bonding where fracture occurs.     

HAp/Ti<Subscript>2</Subscript>Ni coatings of high bonding strength on Ti–6Al–4V prepared by the eutectic melting bonding method

Eutectic melting bonding (EMB) method is a useful technique for fabricating bioactive coatings with relatively high crystallinity and bonding strength with substrate on titanium substrates. Using the EMB method, hydroxyapatite/Ti₂Ni coatings were prepared on the surface of Ti–6Al–4V at a relatively low temperature (1,050 °C) in a vacuum furnace. The coatings were then characterized in terms of phase components, microstructure, bonding strength and cytotoxicity. The results showed that the coatings were mainly composed of HAp and Ti₂Ni, and the thickness of the coatings was approximately 300 μm. X-ray diffraction analysis showed that the coatings exhibited relatively high crystallinity. The tensile bonding strength between the coatings and the substrates was 69.68 ± 5.15 MPa. The coatings had a porous and rough surface which is suitable for cell attachment and filopodia growth. The cell culture study showed that the number of MG-63 cells increased, and the cell morphology changed with the incubation time. This study showed that the EMB method can be utilized as a potentially powerful method to obtain high quality hydroxyapatite coatings with desired mechanical and biocompatibility properties on Ti-alloy substrates.     

Physico‐mechanical characterization of garnet and fly ash reinforced Al7075 hybrid composite

The aim of present work was to study the effect of adding garnet and fly ash on the physical and mechanical performance of Al7075 hybrid composites. Al7075 hybrid composites reinforced with varying weight percentage (0 wt.%–15 wt.%) of each of garnet and fly ash were fabricated and characterized for the comparative assessment of their physical and mechanical properties. The physical and mechanical tests such as void content test, hardness test, tensile strength test, impact strength tests, flexural and fracture toughness test were performed for both garnet and fly ash reinforced composites. The finding of results indicated that the addition of 0 wt.%–15 wt.% of garnet increased the void content, hardness, flexural strength, tensile strength, impact strength and fracture toughness in the range of 1.01 %–2.69 %, 33 HRB–88 HRB, 165 MPa–275 MPa, 205 MPa–263 MPa, 12 J–22 J and 0.11 MPa ? m^1/2–0.58 MPa ? m^1/2 at crack length 0.1 respectively whereas addition of 0 wt.%–15 wt.% of fly ash increased the void content, hardness test, flexural strength, tensile strength, impact strength and fracture toughness in the range of 1.010 %–1.351 %, 33 HRB‐80 HRB, 165 MPa–225 MPa, 205 MPa–236 MPa, 12 J–20 J, 0.11 MPa ? m^1/2–0.48 MPa ? m^1/2 at crack length 0.1 respectively. Apart from the economic concern and void issue, Garnet indicated better choice of reinforcement as compared to fly ash in terms of mechanical properties.     

Fabrication of porous low crystalline calcite block by carbonation of calcium hydroxide compact

Calcium carbonate (CaCO₃) has been widely used as a bone substitute material because of its excellent tissue response and good resorbability. In this experimental study, we propose a new method obtaining porous CaCO₃ monolith for an artificial bone substitute. In the method, calcium hydroxide compacts were exposed to carbon dioxide saturated with water vapor at room temperature. Carbonation completed within 3 days and calcite was the only product. The mechanical strength of CaCO₃ monolith increased with carbonation period and molding pressure. Development of mechanical strength proceeded through two steps; the first rapid increase by bonding with calcite layer formed at the surface of calcium hydroxide particles and the latter increase by the full conversion of calcium hydroxide to calcite. The latter process was thought to be controlled by the diffusion of CO₂ through micropores in the surface calcite layer. Porosity of calcite blocks thus prepared had 36.8–48.1% depending on molding pressure between 1 MPa and 5 MPa. We concluded that the present method may be useful for the preparation of bone substitutes or the preparation of source material for bone substitutes since this method succeeded in fabricating a low-crystalline, and thus a highly reactive, porous calcite block.     

Diffusion bonding of alumina to steel using soft copper interlayer

The diffusion bonding of a low steel to alumina has been studied in the present work. Thin foils of a soft metal (copper) were used to reduce the effects of the residual stresses produced in the joint by thermal expansion mismatch. The strength of the joint was found to be influenced by the bonding parameters, but principally by the oxygen content both on the surface and in the copper matrix. The diffusion bonds have been mechanically tested using a three-point bending test. Maximum bending strengths of 100 MPa were achieved by using a 0.1 mm copper foil, and bonding in a oxidizing atmosphere (P _{O 2}=10₄Pa). SEM and EDS investigations have shown the presence of reaction products in the copper-alumina interface which controls the mechanical properties of the joint.     

Refinement of microstructure and improvement of mechanical properties of Al/Al2O3 cast composite by accumulative roll bonding process

Some important problems associated with cast metal matrix composites (MMCs) include non-uniformity of the reinforcement particles, high porosity content, and weak bonding between reinforcement and matrix, which collectively result in low mechanical properties. Accumulative roll bonding (ARB) process was used in this study as a very effective method for refinement of microstructure and improvement of mechanical properties of the cast Al/10 vol.% Al₂O₃ composite. The average particle size of the Al₂O₃ was 3 μm. The results revealed that the microstructure of the composite after eleven cycles of the ARB had an excellent distribution of alumina particles in the aluminum matrix without any noticeable porosity. The results also indicated that the tensile strength and elongation of the composites increased as the number of ARB cycles increased. After eleven ARB cycles tensile strength and elongation values reached 158.1 MPa and 7.8%, which were 2.54 and 2.36 times greater than those of the as-cast MMC, respectively.     

Evaluation of the acceptance of glass in bone

Six glasses in the SiO₂-Na₂O-CaO-P₂O₅-Al₂O₃-B₂O₃-system were implanted in rabbit tibia. The bone-implant interfaces were studied by scanning electron microscopy (SEM) and in a push-out test. In SEM it seems possible to distinguish between physical contact and chemical bonding between glass and bone. The measured push-out strength is about 0.5 MPa if no bone contact exists. If physical contact exists the push-out strength is 2–3 MPa. The push-out strength of titanium falls within these limits. Glasses, which on basis of the SEM study are concluded to chemically bond to bone, show push-out strengths of 16–23 MPa. Two non-bonding glasses are compared. One possesses only a silica-rich surface, whereas the other possesses a calcium phosphate-rich surface. Both develop a close contact with bone, but neither bonds chemically. There is no significant difference in their push-out strengths, which are comparable to that of titanium. Even if a calcium phosphate-rich layer forms at the glass surface, bonding may be reduced if Al₂O₃ is included in the glass composition. Further, a phosphate-free bioactive glass is compared with two phosphate-containing bioactive glasses. The phosphate-free glass bonds by incorporating phosphate from the body fluid into its surface. Push-out data indicate that this glass is not as firmly attached to bone as the phosphate-containing ones. The calcium phosphate layer formed is non-uniform, which might explain the lower bonding strength.     

The influence of brazing conditions on joint strength in Al2O3/Al2O3 bonding

The brazing of alumina ceramic to itself was performed using Ag₅₇Cu₃₈Ti₅ filler alloy. The bonding was carried out in a vacuum of 7 × 10^?3 Pa, and the joining conditions were at 1073, 1123, 1173, 1223, 1273 and 1323 K for 1.8ks under a pressure of 0.01 MPa, at 1123 K with a pressure of 0.01 MPa for 0, 0.3, 0.9, 1.8, 2.7 and 3.6 ks, and at 1123 K for 1.8 ks with pressures of 0, 0.01, 0.05, 0.10, 0.15, 0.20 and 0.30 MPa, to determine the effects of joining temperature, pressure and holding time on the joint strength. The joint strength was measured by shear tests. The interface microstructures and fractured surfaces after testing were observed by scanning electron microscopy (SEM). It was shown that the shear strength of Al₂O₃/Al₂O₃ joints was largely affected by the joining conditions; it first increased and then decreased with increasing joining temperature, pressure and holding time and depended mainly on the strength of interfacial reaction layer itself and the interface bonding strength between the reaction layer and the ceramic. The maximum joint strength was obtained when the reaction occurred under a suitable temperature, pressure and time, and the reaction layer thickness was about 2 μm. SEM observations revealed that there were four types of fracture and each kind corresponded to a different strength.     

Bonding strength of Al/Mg/Al alloy tri-metallic laminates fabricated by hot rolling

One of major drawbacks of magnesium alloy is its low corrosion resistance, which can be improved by using an aluminized coating. In this paper, 7075 Al/Mg-12Gd-3Y-0·5Zr/7075 Al laminated composites were produced by a hot roll bonding method. The rolling temperature was determined based on the flow stresses of Mg-12Gd-3Y-0·5Zr magnesium alloy and 7075 Al alloy at elevated temperature. The bonding strength of the laminate composites and their mechanism were studied. The effects of the reduction ratio (single pass), the rolling temperature, and the subsequent annealing on the bonding strength were also investigated. It was observed that the bonding strength increased rapidly with the reduction ratio and slightly with the rolling temperature. The bonding strength increases with the annealing time until the annealing time reaches 2 h and then decreases. The mechanical bond plays a major role in the bonding strength.     

Vacuum diffusion bonding of TiB2 cermet to TiAl based alloys

Abstract

Vacuum diffusion bonding of TiB₂ cermet to TiAl based alloys was carried out at 1123 – 1323 K for 0.6 – 3.6 ks under 80 MPa. The microstructural analyses indicate that a compound Ti(Cu, Al)₂ is formed in the interface of the TiB₂ /TiAl joints, and the width and quantity of the Ti(Cu, Al)₂ compound increase with the increase of the bonding temperature and bonding time. The experimental results show that the shear strength of the diffusion bonded TiB₂ /TiAl joint is 103 MPa, when TiB₂ cermet is bonded to TiAl based alloy at 1223 K for 1.8 ks under 80 MPa.     

Plasma-sprayed zirconia bond coat as an intermediate layer for hydroxyapatite coating on titanium alloy substrate

This study aims to strengthen the bonding at HA coating/Ti–6Al–4V interface by adding an intermediate ZrO₂ bond coat between them. The bonding strength of the HA/ZrO₂ coating was evaluated with the separately prepared HA coating as control. The phase, microstructure and chemistry, and surface roughness of the plasma-sprayed two-layer HA/ZrO₂ coating on Ti–6A1–4V substrate were investigated by X-ray diffractometry, scanning electron microscopy, and surfcorder, respectively. Experimental results indicate that the bonding strength increases from 28.6±3.22 MPa for HA coating to 36.2±3.02 MPa for HA/ZrO₂ composite coating. Elemental analysis employed on the surface of ZrO₂ bond coat, on which the HA top coat was first dissolved completely in HCl acid, reveals the sign of diffusion of calcium ions from HA to ZrO₂ bond coat. In addition, rougher surface morphology provided by ZrO₂ bond coat is also considered to aid in the bonding at HA/ZrO₂ interface. Similar coating system done by other researchers is compared and discussed.     

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.     

Effects of Al-Ni powder addition on dissimilar friction stir welding between AA7075-T6 and 304 L

Friction stir welding between AA7075-T6 aluminum alloy and 304 L stainless steel sheet metal was performed with the addition of Al−Ni powder between the joining interfaces to increase the joining performance. The welding tool was rotated at 200 min⁻¹ to 800 min⁻¹ with the constant traverse speed of 25 mm/min. The resulting joint interfaces were analyzed using a field emission-scanning electron microscope and energy-dispersive x-ray spectroscopy analysis. The tensile strength was greater for the Al−Ni powder added specimens at the lower tool rotational speeds. The tensile strength of 360 MPa was obtained for the ‘with-powder’ specimen as compared to 220 MPa for the ‘without-powder’ specimen at the 200 min⁻¹ tool speed. Electron microscope images of the stir zone showed a significant mixing of the Al−Ni powder with the base materials, increased contact at the interface, which resulted in increased joining strength at the lower tool rotational speeds. However, based on the images, intermetallic compound that may contribute to the joining strength in the vicinity of the interfacial region was not detected.