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.     

Evaluation of Si3N4 joints: bond strength and microstructure

Joining of pressurelessly sintered silicon nitride ceramics was carried out using adhesive slurries in the system Y-Si-Al-O-N in a nitriding atmosphere. The effects of bonding parameters, such as joining temperature (1450–1650°C), applied pressure (0– MPa) and holding time (10–60 min), on the bond strength of joint were evaluated. A typical microstructure of the joint bonded with the optimum adhesive was investigated. The three point bend testing of joined samples with 3 × 4 × 36 mm³ in dimension was employed to study the bond strength of joints. The results show that an optimum joining process was achieved by holding at 1600°C for 30 min under an external pressure of 5 MPa and the maximum bond strength was 550 MPa, compared to 700 MPa of unbonded Si₃N₄ ceramic, using the adhesive having the Si₃N₄/(Y₂O₃ + SiO₂ + Al₂O₃) ratio of 0.39. The good bond strength is attributed to the similarity in microstructure and chemical composition between joint zone and ceramic substrate. The fracture modes were classified into two types according to the values of bond strength. This revised version was published online in September 2006 with corrections to the Cover Date.     

Low-temperature diffusion brazing of actively metallized Al2O3 ceramic tube and 5A05 aluminum alloy

A low-temperature ceramic–metal joining technique was successfully developed to produce a vacuum-tight Al₂O₃ ceramic and 5A05 aluminum alloy joint, with leak rates of less than 1.0 × 10^− 9 Pa∙m³/s. This involved two steps: active metallization of the Al₂O₃ ceramic surface using Ag–Cu–TiH₂–B composite filler, followed by diffusion brazing of metallized Al₂O₃ ceramic and 5A05 alloy at 530 °C. The microstructure, interfacial reactions and mechanical properties of the actively metallized Al₂O₃ ceramic and diffusion-brazed Al₂O₃/5A05 joint were investigated. The joint properties were determined by the formation of a continuous Ti₃Cu₃O reaction layer adjacent to Al₂O₃ ceramic, in situ synthesized TiB whiskers in the brazing seam, and dissolution thickness of 5A05 alloy. The maximum shear strength of the bonded joints reached 70 MPa, while fracture propagated in the Al₂O₃ substrate, with a bowed crack path. A model for quantitatively evaluating the dissolution thickness of 5A05 aluminum alloy during diffusion brazing process was established.     

Influence of surface modification of alumina on bond strength in Al2O3/Al/Al2O3 joints

The subject of the work was to study the effect of Ti thin film on alumina ceramic on mechanical strength and fracture character of Al₂O₃/Al/Al₂O₃ joints. The joints were formed by liquid state bonding of alumina substrates covered with titanium thin film of 800 nm thickness using Al interlayer of 30μm thickness at temperature of 973 K in a vacuum of 0.2 mPa for 5 min. The bend strength was measured by four–point bending test at room temperature. Scanning and transmission electron microscopy were applied for detailed characterization of interface structure and failure character of fractured joint surfaces. Result analysis has shown that application of the Ti thin film on alumina leads to decrease of bond strength properties of Al₂O₃/Al/Al₂O₃ joints along with the change either of structure and chemistry of interface or of failure character.     

Joint of silicon nitride and molybdenum with vanadium foil,and its high-temperature strength

Joints of silicon nitride and molybdenum with a vanadium interlayer were fabricated using a vacuum hot-pressing facility. The optimum joining conditions for producing a joint with the highest shear strength were found to be as follows: a temperature of 1328 K, a mechanical pressure of 20 MPa and a bonding time of 5.4 ks. The effect of test temperature on shear strength was also examined. The strength level was initially 118 MPa at room temperature and this level gradually decreased as the test temperature rose. At 973 K, the strength level was still 70 MPa. Observations of the interface by scanning electron microscopy (SEM) and electron probe X-ray microanalysis (EPMA) revealed that a layer of reaction product V₃Si formed at the silicon-nitride-vanadium interface.     

Structure and strength of AlN/V bonding interfaces

AlN ceramics are bonded using vanadium metal foils at high temperatures in vacuum. Different bonding temperatures were used in the range 1373–1773 K with bonding times of 0.3–21.6 ks. The AlN/V interfaces of the bonded joints were investigated using SEM, electron probe microanalysis and X-ray diffraction. A bonding temperature of 1573 K was found to be suitable to activate both parts to initiate a phase reaction at the interface, because a thin V(Al) solid solution layer formed adjacent to the ceramic at 1573 K just after 0.9 ks, and a small flake-shaped V₂N reaction product formed inside the vanadium central layer. The formation of V(Al) and V₂N controls the interfacial joining of the AlN/V system at 1573 K up to 5.4 ks bonding time. The pure vanadium layer quickly changed to vanadium-containing V₂N. The diffusion path could be predicted for the AlN/V joints up to 0.9 ks at 1573 K following the sequence AlN/V(Al)/V₂N/V, while after 0.9 ks, the interface structure changed to AlN/V(Al)/V₂N + V by the growth Of V₂N into the vanadium. The AlN/V joints shovyed no ternary compounds at the interface. A maximum bond strength could be obtained for a joint bonded at 1573 K after 5.4 ks having a structure of AlN/V(Al)/V₂N + V. At 7.2 ks, nitrogen, resulting from AlN decomposition, escaped and the remaining aluminium reacted with V(Al) to form V₅Al₈ intermetallic, which is attributable to the decrease in bond strength.     

Bond strength and microstructure investigation of Al2O3/Al/Al2O3 joints with surface modification of alumina by titanium

Joints of Al₂O₃/Al/Al₂O₃ are formed by liquid-state bonding of alumina substrates covered with thin titanium film of 800 nm thickness using an Al interlayer of 30 or 300 μm at 973 K under a vacuum of 0.2 mPa for 5 min and an applied pressure of 0.01 MPa. The bond strength of the joints is examined by a four-point bend testing at room temperature coupled with optical, scanning and transmission electron microscopy. Results show that: (i) bonding occurs due to the formation of a reactive interface on the metal side of the joint with the presence of Al₃Ti precipitates (ii) a decrease in Al layer thickness leads to stronger Al₂O₃/Al/Al₂O₃ bonds accompanied by a change of both the distribution of reaction products (Al₃Ti) in the region of the interface and the failure surface characteristics.     

Interfacial reaction of alumina with Ag-Cu-Ti alloy

The interfacial reaction of Al₂O₃ and Ag-Cu-Ti alloy was investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. It was shown that Al₂O₃ ceramic reacted strongly with Ag-Cu-Ti alloy. With the increasing heating temperature and holding time, the reaction layer thickness increased and its growth was mainly controlled by the diffusion of titanium through the reaction layer. The reaction products were Cu₂Ti₄O and AlTi at or below 1123 K. However, there were two distinct layers at the interface at or above 1173 K, one layer in the vicinity of ceramic consisting mainly of Ti₂O and TiO and the other layer near the alloy was CuTi₂, a layer transition structures with a Al₂O₃/Ti₂O+TiO/Ti₂O +TiO+CuTi₂/CuTi₂/Ag-Cu formed at the interface according to the SEM and XRD analyses results. A lower or a higher joining temperature and a shorter or a longer holding time were disadvantageous for a stable and high reliable joined interface from the point of view of interfacial microstructures and morphologies.     

Interlayer design for joining pressureless sintered sialon ceramic and 40Cr steel brazing with Ag57Cu38Ti5 filler metal

An interlayer design and test was made to enhance the joining strength of the pressureless sintered sialon ceramic and 40Cr steel. Joining was preformed by vacuum brazing using Ag₅₇Cu₃₈Ti₅ filler metal. The joint strength was evaluated by four-point bending. A strong interfacial bond of the Ag₅₇Cu₃₈Ti₅ filler metal on the sialon ceramic with formation of Ti₂AlN, Ti₅Si₄ and TiAg was obtained at brazing temperatures over 1123 K, which could be weakened by a brazed metal such as Kovar or Ni-15Cr-15Co alloy. The joint strength of sialon ceramic with 40Cr steel can be improved by using a layer of soft interlayer such as Cu with a suitable thickness, particularly by the composite interlayer such as Cu/Nb alloy, Cu/Ta, Cu/Mo etc. The maximum strength of the ceramic/steel joint, 280 MPa, was obtained by using Cu/Nb alloy as interlayer and brazing at 1153 K for 5 min. Finally, we discuss how to design an interlayer in ceramic/metal joining.     

Joining of Si3N4 using Ag57Cu38Ti5 brazing filler metal

Hot-pressed Si₃N₄ was joined using Ag₅₇Cu₃₈Ti₅ brazing filler metal at 1103 to 1253 K for 5 min in a vacuum. The interface reactions between Si₃N₄ and the brazing filler metal during brazing are reported. An important event is sufficient interface reaction, characterized by the formation of a layer of TiN with an appropriate thickness at the ceramic-filler interface. The joining strength of the butt joint depends on the interface reaction, and a maximum joining strength of 490 MPa measured by the four-point-bend method is achieved for the Si₃N₄-Si₃N₄ joint brazed at 1153 K for 5 min. It is also discussed how to design the best brazing filler metal for joining ceramic to ceramic or ceramic to metal.     

Preparation and mechanical properties of high-purity Al2O3 fibre/Al2O3 matrix composite

Al₂O₃ matrix composites with unidirectionally oriented high-purity Al₂O₃ fibre with and without carbon coating, were fabricated by the filament-winding method, followed by hot-pressing at 1573–1773 K. The composite with non-coated Al₂O₃ fibre exhibited a bending strength (594 MPa) comparable to that of monolithic Al₂O₃ (589 MPa). While the composite with a carbon-coated fibre had lower strength (477 MPa), it showed improved fracture toughness (6.5 MPa m^1/2) compared to the composite with an uncoated fibre (4.5 MPa m^1/2) and monolithic Al₂O₃ (5.5 MPa m^1/2). This toughness enhancement was explained based on the increased crack extension resistance caused by the fibre pull-out observed by SEM at the notch tip. This revised version was published online in November 2006 with corrections to the Cover Date.     

A new method for preparation of direct bonding copper substrate on Al2O3

The oxygen content is usually difficult to control in direct bonding copper process. In this study a new method for preparation of direct bonding copper on alumina ceramic substrates was realized. 96% Al₂O₃ ceramic substrates were first oxidized by pasting a thin layer of Cu₂O and firing at 1150 °C in air. Then copper foil was bonded to the substrate by heating to 1070 °C in pure N₂ atmosphere. Microstructure and composition of the interface between the copper and Al₂O₃ ceramic were analyzed. The XRD and EDS results show that an interphase of CuAlO₂ was formed and a eutectic transformation between oxygen and copper took place at the interface of the copper and the ceramic substrate. The interface was much thicker than the traditionally bonded substrates, which resulted in a better bonding strength. The directly bonded copper alumina substrate samples showed no evidence of de-bonding after 50 thermal cycles comprising quenching from 220 °C to room temperature.     

Liquid-phase bonding of silicon nitride ceramics using Y2O3–Al2O3–SiO2–TiO2 mixtures

Hot-pressure sintered β-Si₃N₄ ceramic was bonded to itself using Y₂O₃–Al₂O₃–SiO₂–TiO₂ mixtures. Reactive behavior at interface between Si₃N₄ and Y₂O₃–Al₂O₃–SiO₂–TiO₂ mixtures during silicon nitride ceramic joining was studied by means of scanning electron microscopy (SEM), electron probe microanalyses (EPMA), X-ray diffraction (XRD) and auger electron spectroscopy (AES). The joint strength under different bonding conditions was measured by four-point bending tests. The results of EPMA, AES and XRD analyses show that the liquid glass solder reacts with silicon nitride at interface, forming the Si₃N₄/Y–Si–Al–Ti–O–N glass/TiN/Y–Si–Al–O glass gradient interface. From the results of four-point bending tests, it is known that with increase of bonding temperature and holding time, the joint strength increased reaching a peak, and then decreased. The maximum joint strength of 200 MPa measured by the four-point bending tests is obtained for silicon nitride bonded at 1823 K for 30 min.     

5A06/TA2 diffusion bonding with Nb diffusion-retarding layers

The structure and performance of 5A06/TA2 diffusion bonding joints with or without Nb diffusion-retarding layers were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and shear strength measurement. The results showed that a diffusion reaction occurred and Al₁₈Ti₂Mg₃ was formed, which markedly decreased the joint strength, and the highest shear strength of 5A06/TA2 joint in direct bonding was 83 MPa. The Nb interlayer impeded the diffusion of Mg atoms from the Al side to the Ti side and also retarded the diffusion of Ti atoms from the Ti side to the Al side, which was acting as a diffusion-retarding layer. The joint strengths were increased by the Nb diffusion-retarding layers, and the highest shear strength reached 105 MPa. When Ti diffused across the Nb layer and achieved saturation nearby the interface with Al alloy, the diffusion reaction of Ti, Al and Mg occurred and Al₁₈Ti₂Mg₃ appeared which decreased the joint strength.     

Effect of a silicon sintering additive on solid state bonding of SiC to Nb

Pressureless-sintered (PLS) SiC was joined to Nb by solid state bonding in a vacuum. The joining strength of the PLS SiC/Nb joint increases to the saturated value of 108 MPa with increasing joining pressure at a joining condition of 1673 K and 7.2 ks. This saturated value of PLS SiC/Nb joint is higher than that of the reaction sintered (RS) SiC/Nb joint. The strength of SiC itself affects the strength of the SiC/Nb joint. The high stability of the intermediate phase Nb₅Si₃ in the interface at elevated temperature leads to the high heat resistance of the joint. The thickness of the intermediate phase Nb₅Si₃ in the PLS SiC/Nb system is lower than that of the RS SiC/Nb system at a constant joining time, although the activation energy, 452 kJ mol^–1, of growth for the phase in the PLS SiC/Nb system is almost the same as the RS SiC/Nb system, 456 kJ mol^–1. The rate constant of the growth for the phase in the PLS SiC/Nb system is lower than that in the RS SiC/Nb system. The excess silicon in RS SiC promotes the formation of the Nb₅Si₃ phase at the interface between SiC and Nb.     

Fabrication and interaction mechanism of Ni-encapsulated ZrO2-toughened Al2O3 powders reinforced high manganese steel composites

In order to solve the cast-infiltration difficulty and low interface bonding strength of ZrO₂-toughened Al₂O₃ (ZTA) powders reinforced high manganese steel (HMS) matrix composite, uniform and continuous Ni-encapsulated ZTA powders (ZTA_p@Ni) as reinforced phase are fabricated by electroless deposition assisted with ionic liquid additive. The effects of Ethaline concentration, temperature, ZTA concentration and deposition times on the morphology of ZTA_p@Ni have been investigated. Experimental results show that the thickness of Ni coating is about 7–10 μm, and there is no casting crack or shrink on the composite, so compact bonding between ceramic and matrix is obtained. In addition, the impact abrasive wear resistance testing demonstrates that the performance of ZTA_p@Ni reinforced HMS composite is superior to that of matrix. On the basis of experimental analysis, a schematic illustration of the cast-infiltration process is put forward. It implies that Ni-encapsulated ZTA can be wetted with molten HMS matrix to form a ZTA/Al₂NiO₄-Al₂MnO₄/Fe interface layer through Ni diffusion and reactive wetting. The interdiffusion of Ni and other elements at ZTA interface layer can reinforce the interfacial bonding strength to form an interface layer between metal and hard phases.     

化学镀锡层对镁铝异种金属超声波焊接的影响

为提高镁铝异种金属超声波焊接接头强度,预先在铝合金表面镀锡后进行镁铝异种金属超声波点焊,并对接头的微观组织和力学性能进行分析.研究表明:无镀锡层的镁铝超声波焊接接头界面出现了大量的Mg_3Al_2和Mg_(12)Al_(17)相,其接头的最大拉伸剪切强度为27.5 MPa;含镀锡层的铝镁超声波焊接结合区由镁锡反应扩散层、残余锡层和铝锡反应扩散层组成,其中,铝锡反应层是固溶体层,镁锡反应层主要是过饱和的固溶体基体及弥散析出的中间相Mg_2Sn,其接头的最大拉伸剪切强度为32.9 MPa.镀锡层的加入有效阻止了镁铝的相互扩散,抑制了硬脆的Mg-Al系金属间化合物的生成,提高了镁铝超声波焊接接头强度,与镁铝超声波焊接相比最大拉伸剪切强度提高了19.6%.     

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.     

Effect of holding time on microstructure and mechanical properties of Si3N4/Si3N4 joints brazed with Au58.7Ni36.5V4.8 filler alloy

Si₃N₄ ceramics were brazed using Au–Ni–V metal foils at 1423 K for different holding times. Effect of holding time on microstructure and mechanical properties of the joints was investigated. The results indicate that a reaction layer of VN exists at the interface between Si₃N₄ ceramic and filler alloy. With increasing holding time from 0 to 90 min, thickness of the VN reaction layer increases from 0.4 to 2.8 μm, obeying a linear relation. Mechanism of the interfacial reaction was discussed by calculating the formation of free energy of VN. No specific orientation relationship exists between VN reaction layer and Si₃N₄ ceramic. In addition, Ni₃Si intermetallic compound appears in the joint when the holding time increases to 90 min, resulting in the deterioration of the joint strength.     

Microstructure and Strength of the TiB2 Cermet/TiAl Joint Diffusion Bonded with Ni Interlayer

Vacuum diffusion bonding of TiB2 cermet to TiAl -based alloys using Ni interlayer has been carried out at 1123～1323 K for0.6～3.6 ks under 80 MPa. The effects of joining parameters on the microstructure of the joints and mechanical propertieswas investig