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.     

Transient liquid-phase bonding of alumina and metal matrix composite base materials

Transient liquid-phase (TLP) bonding of aluminium-based metal matrix composite (MMC) and Al2O3 ceramic materials has been investigated, particularly the relationship between particle segregation, copper interlayer thickness, holding time and joint shear strength properties. The long completion time and the slow rate of movement of the solid–liquid interface during MMC/Al2O3 bonding markedly increased the likelihood of forming a particle-segregated layer at the dissimilar joint interface. Preferential failure occurred through the particle-segregated layer in dissimilar joints produced using 20 and 30 μm thick copper foils and long holding times (≥20 min). When the particle-segregated layer was very thin (<10 μm), joint failure was determined by the residual stress distribution in the Al2O3/MMC joints, not by preferential fracture through the particle-segregated layer located at the bondline. Satisfactory shear strength properties were obtained when a thin (5 μm thick) copper foil was used during TLP bonding at 853 K. This revised version was published online in November 2006 with corrections to the Cover Date.     

Reaction Phases and Strength of AlN/V Diffusion Couples

Diffusion couples of AlN/V were experimentally examined after annealing in a temperature range of 1373 K1773 K for a bonding time range of 0.9 ks21.6 ks. The interfacial reaction, reaction mechanism, and bond strength of the bonded AlN/V couples have been explained on the basis of phase relations at different bonding conditions, making use of elemental analysis, XRD, and shear testing method. Formation of V(Al) solid solution and V₂N nitride controls the interfacial joining of the AlN/V couples. A complete diffusion path between AlN and V could be predicted at 1573 K before 0.9 ks, following a sequence of AlN/V(Al)/V₂N/V. This sequence can be discussed during the Al-V-N ternary phase diagram. At a high temperature of 1573 K, AlN decomposition at the interface took place. 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.     

Anatase formation on titanium by two-step thermal oxidation

Two-step thermal oxidation of commercially pure Ti was investigated with a focus on the formation of anatase. A first-step treatment was conducted in Ar–(0.1–20)%CO atmosphere at a temperature of 773–1173 K for a holding time of 0 or 86.4 ks, and a subsequent second-step treatment was conducted in air at 473–873 K for 0–86.4 ks. Titanium oxides and titanium oxycarbide were obtained in the first step, with relative amounts depending on heating temperature, holding time, and CO partial pressure. An anatase-rich layer on Ti was obtained after second-step treatment in air at 573–773 K in cases where single-phase titanium oxycarbide formed in the first step. Thus, the formation of single-phase titanium oxycarbide in the first step and temperature control in the second step were required for the formation of an anatase-rich layer. The bonding strength of an anatase-rich layer with a thickness of 0.5 μm was calculated to be around 90 MPa. This study reveals the conditions under which an anatase-rich layer with excellent adherence to Ti can be prepared by thermal oxidation.     

氮化铝陶瓷表面钛金属化的研究

利用熔盐热歧化反应在氮化铝陶瓷表面上成功地进行了钛金属化，成功地在氮化铝陶瓷表面上制备了钛金属化膜。还研究了温度、反应物浓度、反应时间对钛金属化膜厚度的影响。研究了金属膜的组成及界面反应机理和界面层的显微结构。研究发现，在热歧化反应沉积钛金属膜的过程中，沉积到AlN陶瓷表面的钛金属与AlN发生反应生成TiN0.3、TiN和Ti9Al23。     

Counteracting particulate segregation during transient liquid-phase bonding of MMC-MMC and Al2O3-MMC joints

The microstructure and mechanical properties of MMC-MMC and Al2O3-MMC joints (MMC is metal matrix composite) produced at a bonding temperature of 853 K using copper foils ranging in thickness from 10 to 30 μm were examined. The particle segregation tendency during transient liquid-phase (TLP) bonding of aluminium-based MMC material markedly increases when the aluminium-based composite material contains large number of small radius (less than 10 μm) reinforcing particles. Also, the particle segregation tendency is much greater in dissimilar Al2O3-MMC joining since the rate of solid-liquid interface movement is much slower and the time required for completing the isothermal solidification during TLP bonding is much longer. The particle segregation tendency during MMC-MMC and Al2O3-MMC bonding can be counteracted using a combination of a short (1 min) holding time at the bonding temperature (853 K) and subsequent post-weld heat treatment at 773 K for 4 h. This TLP-bonding-heat-treatment cycle removes the retained eutectic phase present at the joint centreline. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis of boride and nitride ceramics in molten aluminium by reactive infiltration

The infiltration of solid powder mixtures with molten aluminium has been investigated as a potential route for the synthesis of ceramic/metal composites. Either titanium or tantalum powder was mixed with boron nitride flakes for the reaction powder mixture. The infiltration occurred spontaneously at 1473K for both [Ti+BN] and [Ta+BN] powder mixtures. Owing to reactions between the starting materials, both boride and nitride ceramics were produced in molten aluminium. TiB2 and AlN were produced from the [Ti+BN] powder mixture, and TaB2 and AlN were produced from the [Ta+BN] powder mixture. When the [Ti+BN] powder mixture was used, a reaction producing Al3Ti took place immediately after the infiltration of the molten aluminium, and a subsequent reaction producing TiB2 and AlN proceeded gradually. The time required to convert BN flakes to TiB2 and AlN particles at 1473K was in the range of 1800–3600 s. On the other hand, when the [Ta+BN] powder mixture was used, there was an initial incubation period to allow the tantalum and molten aluminium to react with each other. The reaction between tantalum, BN and aluminium took place after this incubation period. This revised version was published online in November 2006 with corrections to the Cover Date.     

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.     

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.     

Behavior of magnesium and silicon in the formation of MgO/AlN composite

MgO/AlN composites have been fabricated by directed metal nitridation of Al–Si alloy in flowing N₂ at 1473 K. A mixture of magnesia particles and chemically pure magnesium powder was placed on the surface of Al–Si alloy block as reinforcement materials. Mg powder initiates the infiltration and nitridation of Al alloy melt by eliminating protective Al₂O₃ film at the reaction frontier. New Mg vapor from the interface reaction between Al and MgO particles, keeps as continuous deoxidization agent as the added Mg powder. The spinel layer thickness due to the reaction of Al melt with MgO particles is controlled by Mg content. Si not only reduces the surface tension and viscosity of Al alloy melt, but also leads to increase in N₂ content.     

三元层状化合物Ti2 AlN在800℃,900℃和1000℃空气中的循环氧化行为

Ti、Al和TiN粉按化学计量比1:1:1配料,采用热压工艺在1300℃保温2h,30MPa压力下制备了Ti2AlN块体材料.研究了该材料在800℃,900℃和1000℃空气中的循环氧化行为.利用X射线衍射仪和扫描电镜对氧化层的相组成,厚度以及元素含量进行了测量和分析.结果表明:Ti2AlN在空气中的循环氧化行为基本上是符合抛物线规律,氧化层的主要成分是由TiO2和α-Al2O3组成.在温度高于800℃时,氧化膜由于氧化区域的热应力过大容易脱落.Ti2AlN材料在空气中的氧化性能明显低于Ti3AlC2和Ti3SiC2材料.     

The effect of silicon on the wettability and interfacial reaction in AlN/Cu alloy systems

Wetting behavior of AlN by Cu alloys has been studied in vacuum through sessile drop technique. The contact angle was determined by high temperature photography and shape analysis software. Pure copper does not wet AlN. The contact angle of the AlN/Cu system at 1200 °C is 138°. Adding 20 at% Si leads to the decrease of the contact angle from 138° to 96°, and a reaction layer forms in the interfacial area. The addition of Si can also improve the wettability of AlN/Cu10Ti (the atomic ratio of Cu:Ti is 90:10) system. The contact angle of the system decreases to the values less than 20° at 1200 °C by adding 20 at% or 27 at% Si. During the wetting experiment, Ti diffuses to and reacts with AlN, leading to the formation of TiN. Addition of Si can retard the reaction between Ti and AlN by forming a Si-rich layer, mainly composed of Ti-Si compound, between the reaction layer, mainly composed of TiN, and the CuSiTi alloy. The Si-rich layer also contributes to the improvement of the wettability of the system. In the meantime, the addition of Si contributes to the decrease of the stress in the interfacial area and to the bonding at the interfaces.     

Studying diffusion in multilayer thin-film structures on silicon by the contact melting technique

Features of the contact melting in thin-film structures comprising an aluminum layer with a thickness of h ₁ = 5 μm and a metal (Ti, Ni, Mo) or semiconductor (Si, Ge) sublayer (h ₂ = 0.1 μm) on a single crystal silicon plate (h ₃ = 500 μm) have been studied. The contact melting was caused by single rectangular electric pulses with a current density of j < 9 × 10¹⁰ A/m² and a duration of τ = 100–1000 μs passing through the Al layer. The duration and rate of melting in the samples were determined using voltage waveforms measured by an oscillograph. A method has been developed based on an analysis of the mechanisms of contact interaction in the Al film—sublayer system (with allowance for experimental data on the time of sublayer dissolution in the Al film) for estimating the coefficients of mutiphase diffusion of the system components during the passage of a current pulse.     

Growth mechanism of TiN reaction layers produced on AlN via active metal bonding

Interfacial reactions related to the TiN layer growth process between nanocrystalline epitaxial layers of AlN deposited on c-plane sapphire and a Ti-containing metal brazing or sintering layer using Ag–Cu–TiH₂, Ag–TiH₂ and Cu–TiH₂ pastes have been investigated. The brazed/sintered samples were heated in vacuum at 850 °C for 30 min. The TiN layer produced at the metal/AlN interfaces consists of TiN particles?<?50 nm in size and grain boundary phases including Al-containing Ag and Al-containing Cu. The Al concentration within the TiN layer decreases as the distance increases from the AlN epitaxial layer. These experimental observations all suggest that when AlN is used as a starting material in the active metal bonding method, interfacial reaction processes take place with the generation of a local Al-based eutectic liquid phase and elemental transport through this eutectic liquid phase.

     

Microstructure and Strength of Brazed Joints of Ti3Al Base Alloy with Cu-P Filler Metal

Brazing of Ti3AI alloys with the filler metal Cu-P was carried out at 1173-1273 K for 60-1800 s. When products are brazed, the optimum brazing parameters are as follows: brazing temperature is 1215-1225 K; brazing time is 250-300 s. Four kinds of reaction products were observed during the brazing of Ti3AI alloys with the filler metal Cu-P, i.e., Ti3AI phase with a small quantity of Cu (Ti3AI(Cu)) formed close to the Ti3AI alloy; the TiCu intermetallic compounds layer and the Cu3P intermetallic compounds layer formed between Ti3AI(Cu) and the filler metal, and a Cu-base solid solution formed with the dispersed Cu3P in the middle of the joint. The interfacial structure of brazed Ti3AI alloys joints with the filler metal Cu-P is Ti3AI/Ti3AI(Cu)/TiCu/Cu3P/Cu solid solution (Cu3P)/Cu3P/TiCu/Ti3AI(Cu)/Ti3AI, and this structure will not change with brazing time once it forms. The thickness of TiCu+Cu3P intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K0 of reaction layer TiCu+Cu3P in the brazed joints of Ti3AI alloys with the filler metal Cu-P are 286 kJ/mol and 0.0821 m2/s, respectively, and growth formula was y2=0.0821exp(-34421.59/T)t. Careful control of the growth for the reaction layer TiCu+Cu3P can influence the final joint strength. The formation of the intermetallic compounds TiCu+Cu3P results in embrittlement of the joint and poor joint properties. The Cu-P filler metal is not fit for obtaining a high-quality joint of Ti3AI brazed.     

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     

AlN与Mo-Ni-Cu活性封接的微观结构和性能分析

AlN陶瓷是一种性能优良的电子封装材料,但不容易与金属直接连接在一起.实验采用98（Ag28Cu）2Ti活性焊料, 在真空条件下实现了AlN陶瓷与Mo Ni Cu合金的活性封接.利用EBSD、EDS、XRD方法研究了焊接区域以及剪切试样断裂表面的微观结构和相组成,测定了焊区的力学性能和气密性.研究结果显示：在AlN陶瓷界面上有TiN生成,说明陶瓷与焊料之间是一种化学键合,而在Mo Ni Cu合金的界面上有少量的Ni Ti金属间化合物存在.剪切后试样的断裂面上有TiN和AlN,说明断裂发生在靠近陶瓷的焊层区域.焊接试样性能优良：气密性达到1.0×10^-11Pa·m³/s,平均抗弯强度σ_ｂ=78.55MPa,剪切强度σ_τ=189.58MPa.     

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.     

Diffusion bonding of Fe-28Al(Cr) alloy with low-carbon steel in vacuum

Fe-28Al(Cr) alloy and low-carbon steel were diffusion bonded in a vacuum of 10⁻⁴-10⁻⁵ Pa. The relationship of the bond parameters and shear strength at the interface was discussed. Microstructure characteristics and the reaction products at the interface were investigated by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The thickness of the diffusion reaction layer was measured with electron probe microanalysis (EPMA). The results indicated that controlling bonding temperature 1333 K for 3.6 ks, shear strength at the interface can be up to 112 MPa. Three kinds of reaction products were observed to have formed during the vacuum diffusion bonding, namely FeAl, Fe₃Al and α-Fe (Al) solid solution. The thickness (X) of the diffusion reaction layer increases with bonding time (t) according to a parabolic law X²=6.4×10³ exp(−104.1/RT)(t-t₀) (μm²).     

Interfacial microstructure and strength of partial transient liquid-phase bonding of silicon nitride with Ti/Ni multi-interlayer

Partial transient liquid-phase bonding (PTLP bonding) of silicon nitride (Si₃N₄) ceramic has been performed using Ti/Ni multi-interlayer in vacuum at 1273–1423 K. Interfacial microstructures were examined by scanning electron microscope, electron probe micro-analysis, and X-ray diffraction. The joint strength has been measured by four-point bending tests from room temperature up to 1000 °C. Interfacial structure of Si₃N₄/TiN/Ti₅Si₃ + Ti₅Si₄ + Ni₃Si/(NiTi)/Ni₃Ti/Ni is formed after bonding process. The NiTi layer is gradually consumed with simultaneous growth of the reaction layer and the Ni₃Ti layer. The room temperature joint strength is significantly affected by the reaction layer thickness, whereas the elevated temperature joint strength significantly depends on whether the low melting point NiTi layer exists in the joint. The joint strength of more than 100 MPa is retained up to 800 °C as the NiTi layer is completely consumed. A model is proposed to optimize the PTLP bonding parameters for optimizing joint strength at both room temperature and elevated temperature.