Interfacial structure and reaction mechanism of AlN/Ti joints

Bonding of AlN to Ti was performed at high temperatures in vacuum. The bonding temperature ranged from 1323 to 1473 K, while the bonding time varied from 7.2 up to 72 ks. The reaction products were examined using elemental analysis and X-ray diffraction. TiN, Ti3AlN (τ1), and Ti3Al were observed at the AlN/Ti interface, having various thickness at different bonding conditions. The thickness of TiN and Ti3AlN layers grew slowly with bonding time. On the other hand, growth of the Ti3Al layer followed Fick’s law. The activation energy of its growth was found to be 146 kJ mol-1. When thinner Ti foil (20 μm) was joined to AlN at 1473 K for a long time (39.6 ks), the Ti central layer has completely consumed and another ternary compound Ti2AlN(τ2) started to form. A maximum bond strength was achieved for an AlN/Ti (20 μm) joint made at 1473 K for 28.8 ks, after which the bond strength of the joint deteriorated severely. This revised version was published online in November 2006 with corrections to the Cover Date.     

梯度结构羟基磷灰石生物活性涂层的性能

采用等离子喷涂系统在Ti6Al4V钛合金基体表面制备出真有梯度结构的羟基磷灰石生物活性梯度涂层，利用纳米硬度计等手段分析了生物活性涂层的梯度结构．结果表明：金属基体与陶瓷界面区域的弹性模量和硬度呈梯度变化；生物活性功能涂层的表面具有典型的多孔结构特征，整个涂层沿垂直基体方向从底层致密结构向表面层多孔结构过渡；涂层的成分从生物稳定性的底层至生物活性的表面层呈梯度变化，涂层表面成分为具有生物活性的羟基磷灰石．涂层的这种结构特征保持了涂层的生物活性，提高涂层与基体的结合强度（48．6MPa）。     

Comparative performance of gold wire bonding on rigid and flexible substrates

This paper reports comparative performance of wire bondability of electrolytically plated Au/Ni/Cu bond pads on rigid FR-4 and bismaleimide trazine (BT) PCBs, as well as flexible polyimide (PI) substrate. The metallization surfaces were treated with plasma to study the effect of bond pad surface cleanliness on wire bondability. Process windows were constructed as a function of bonding temperature and bond power for the individual substrate materials. Significant improvements of wire pull strength and process window were noted after plasma treatment with a substantial reduction in minimum bonding temperature from 120°C to 60°C for both the rigid and flexible substrates. The minimum bond power required to produce successful bonds decreased with increasing bonding temperature. At a bonding temperature of 120°C, the process window for the flexible substrate was wider than the rigid substrates. The wire bondability and wire pull strength of rigid substrates decreased with increasing bonding temperature above 120°C due to softening of the substrate which adversely affected the effective bond force and the transmission of ultrasonic energy. In contrast, the wirebonding performance of the flexible substrate remained stable at 120°C or above because the thermo-mechanical properties of flexible PI substrate were rather insensitive to temperature. The process windows of flexible substrates with and without stiffener showed similar bondability.     

Effect of ultrasonic micro-forging treatment on microstructure and mechanical properties of GH3039 superalloy processed by directed energy deposition

In this work,ultrasonic micro-forging treatment(UMFT)was introduced to achieve homogeneous microstructure,reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed energy deposition(DED).The microstructure,defects and mechanical properties of the cladding layers treated by UMFT with different ultrasonic powers(UIPs)were investigated.Results revealed a gradient structure as equiaxed grains distributed at the top,a columnar-to-equiaxed transition(CET)region that mixed of columnar dendrites and equiaxed grains distributed at the middle and colum-nar dendrites at the bottom of the cladding layer was formed.After UMFT,the proportion of equiaxed grains was increased,the average size of equiaxed grains was refined to 10 μm from 16 μm,the orien-tation of grains was more uniform and the phases enriched of Al,Ti,C,Nb and Mo were precipitated.The grain refinement can be attributed to the fracture of columnar dendrites induced by the ultrasonic vibration during solidification.Besides,the porosity of the cladding layer was reduced after UMFT.The microhardness of the cladding layers exhibited a depth-dependent gradient at the top region.The micro-hardness of the top surface was the highest and showed an increasing trend with the increase of UIP.The microhardness of different grain morphologies exhibited no substantial difference.However,due to grain refinement and precipitation of strengthening phase induced by UMFT,the microhadness of some local locations were improved.These results indicated UMFT has a significant effect on improving the microstructure,defects and mechanical properties of the deposited cladding layer.     

Interferometric detection in picosecond ultrasonics for nondestructive testing of submicrometric opaque multilayered samples: TiN/AlCu/TiN/Ti/Si

An experimental investigation of nanometric thin films by a picosecond ultrasonic technique is presented. A photoelastic model is used with an interferometric device, combined with ultrafast optical pump and probe setup, to measure the thicknesses of submicrometric layers made of TiN, Ti, and AlCu deposited on silicon (Si) wafers. The results are in good agreement with ellipsometry measurements showing that the picosecond ultrasonic technique can give accurate results even when the reflectance signal is very low. Additional important results are first, that the adhesion of the TiN surface film is probed by processing both the frequency and the damping of the oscillation of a resonance acoustic mode; and second, the presence of a thin buried TiN layer under an opaque AlCu film is highlighted by the interferometric setup.     

Fundamentals of thermo-sonic copper wire bonding in microelectronics packaging

Fine copper wire bonding is capable of making reliable electrical interconnections in microelectronic packages. Copper wires of 0.8–6 mil diameter have been successfully bonded to different bond pad metallized and plated substrate materials such as Al, Cu, Ag, Au and Pd. The three metallurgical related factors; solid-solubility and diffusion of dissimilar contact metals, oxide film breakage and plastic deformation of asperities play a critical role in the bonding. Plastic deformation of an asperity is the most significant factor one has to consider to attain good bonding. Soft aluminum metal (30–40 VHN), with a lower % asperity threshold deformation is easier to wire bond than harder metallic surfaces (Ni, W, Mo, Cr, Co, Ta) of 150–500 VHN. Good adhesion of wire bonding is achieved for the surface roughness (Ra) of 0.01–0.15 μm and 0.02–0.6 μm of bare and plated surfaces respectively. It is rationalized that the application of ultrasonic energy principally breaks the oxide film and deform the asperities, while a compressive force increases the proximity of asperities. Hence wire welds to bond pad surface by molecular attraction and inter diffusion. Storage of copper ball bonds at 175 °C for 100–1,000 h forms copper aluminide at the interface. EDAX and Auger analysis reveal 22 at% Al + 78 at% Cu composition of the aluminides and Cu₃Al₂ empirical formula is calculated, which, does not match with any of the reported copper aluminides. Hardness of the copper ball bonds and stitch bonds are higher than wire exhibiting work hardening of the bonds on processing.     

Ti6Al4V合金激光原位制备TiN枝晶增强梯度复合表面层

利用连续波2kW Nd-YAG激光在Ti6Al4V合金表面原位制备TiN枝晶增强梯度金属基复合材料表面层，并研究了该表面层的显微组织和磨损性能。结果表明：该表面层沿激光熔化深度具有明显的梯度结构，表面层与Ti6Al4V基体之间呈现良好的冶金结合，Ti6Al4V的表面硬度及耐磨性得到了显著增强．     

Structure, corrosion, and hardness properties of Ti/Al multilayers coated on NdFeB by magnetron sputtering

Ti/Al multilayers deposited on sintered NdFeB magnets by direct current magnetron sputtering with ion-beam assistance were studied in this report. Ti layers with a hexagonal close packed structure were obtained in the Ti/Al multilayers. The columnar structure growth of Al layers was successfully interrupted by the intercalated Ti layers. The Ti/Al multilayers showed more compact and uniform surfaces than the Al single layer. The corrosion current densities of the sintered NdFeB magnets coated with Ti/Al multilayers were much lower than that of the Al single layer. The Ti/Al multilayers also presented improved hardness.     

Synthesis of C-axis-oriented AlN thin films on high-conducting layers: Al, Mo, Ti, TiN, and Ni

Thin piezoelectric polycrystalline films such as AlN, ZnO, etc., are of great interest for the fabrication of thin film bulk/surface acoustic resonators (TFBARs or TFSARs). It is well-known that the degree of c-axis orientation of the thin films correlates directly with the electromechanical coupling. However, the degree of c-axis orientation of the piezoelectric film is, in turn, influenced by other parameters such as the structure of the substrate material, the matter of whether the c-axis is up or down (polarity), and the growth parameters used. The correlation of these three aspects with the electromechanical coupling of the AlN-thin films, is studied here. Thin AlN films, prepared in a magnetron sputtering system, have been deposited onto thin Al, Mo, Ni, Ti, and TiN films. Such thin high-conducting layers are used to form the bottom electrode of TFBAR devices as well as to define a short-circuiting plane in TFSAR devices. In both cases, they serve as a substrate for the growth of the piezoelectric film. It has been found that the degree of orientation and the surface roughness of the bottom metal layer significantly affects the texture of the AlN films, and hence its electroacoustic properties. For this reason, the surface morphology and texture of the metal layers and their influence on the growth of AlN on them has been systematically studied. Finally, FBARs with both Al and Ti electrodes have been fabricated and evaluated electroacoustically.     

Maßgeschneiderte Schicht-Interfacesysteme mittels ionenstrahlgestützter Beschichtung

Custom-Tailored Coating-Interface Systems by Means of lon Beam Assisted Deposition A coated sample represents in its most simple form a threefold junction consisting of substrate interface and top layer. In many cases the top layer consists again of several sublayers or the interface contains a modified substrate surface and an interconnection between top layer and interface. An ideal coating technique is evaporation under simultaneous ion bombardment with an ion source it is possible because of several free parameters to come close to an ideal system. For the coating Al/Al₂O₃ on steel it is shown that the width of a composition gradient between the sublayers Al and Al₂O₃ can be optimized with respect to excellent corrosion resistance. The example Cr_xN coating on steel or corrosion and wear resistence demonstrate the ability to optimize the corrosion and wear resistence by modifying the microstructure via variation of the parameters ion energy, ion impact angle, ion to atom ratio and process temperature. Finally, TiN layers on steel were chosen to show that the ion beam parameters influence the porosity and the crystal structure of the coatings. This fact can be used to optimize the corrosion protection or wear reduction obtained by the coating. Especially the multilayer Ti/TiO₂/TiN exhibits very interesting properties.     

Irregular Characteristics of Bond Interface Formation in Ultrasonic Wire Wedge Bonding

The mechanism of ultrasonic wire wedge bonding, one of the die/chip interconnection methods, was investigated based on the characteristics of the ultrasonic wire bonding joints. The Al-1%Si wire of 25 μm in diameter was bonded on Au/Ni/Cu pad and the joint cross-section was analyzed by scanning electron microscopy （SEM） and energy-dispersive X-ray spectroscopy （EDX）. The results indicated that it is irregular for the ultrasonic bond formation, non-welded at the centre but joining well at the periphery, especially at the heel and toe of the joint. Furthermore, the diffusion and/or reaction at the cross-section interface are not clear at C-zone, while there exists a strip layer microstructure at P-zone, and the composition is 78.96 at. pct Al and 14.88 at. pct Ni, close to the Al3Ni intermetallic compound. All these observations are tentatively ascribed to the plastic flow enhanced by ultrasonic vibration and repeated cold deformation driving interdiffusion between AI and Ni at bond interface.     

Texture and sheet resistance of Al alloy thin films on Ti and TiN thin films

Ti films prepared by ionized physical vapor deposition (I-PVD) and TiN films prepared by metalorganic chemical vapor deposition (MOCVD) were examined as the underlayers of the Al interconnect films. The crystallographic texture of the Al films and the sheet resistance of the thin-film stacks were investigated at various thicknesses of the Ti or TiN thin film. The sheet resistance of the thin-film stacks was also measured after annealing at 400 °C in an N₂ ambient. For the I-PVD Ti underlayer, the excellent texture of the Al (1 1 1) was obtained even on a 5-nm thick Ti film. However, the sheet resistance of the multilayer structure increased after the annealing due to the reaction between Al and Ti. MOCVD TiN layers between the Ti film and the Al film could suppress the Al–Ti reaction without severe degradation of the Al (1 1 1) texture. Excellent texture of the Al film was obtained with thin MOCVD TiN films below 5 nm.     

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.

     

A general strategy for the reliable joining of Al/Ti dissimilar alloys via ultrasonic assisted friction stir welding

Ultrasonic assisted friction stir welding (UaFSW) was used to join 6061-T6 aluminum and Ti6Al4V alloys. A small plunge depth endowed with the low heat input was used and the sound joints without obvious thickness reduction were achieved. A diffusion-type bonding without the intermetallic compounds layer was observed at the joint interface. The ultrasonic improved the diffusion thickness and decreased the average size of grains and titanium alloy fragments. A hook-like structure was formed at the bottom interface of the UaFSW joint, which improved the bonding length and the mechanical interlocking. The microhardness of the stir zone was increased because of the further grain refinement induced by ultrasonic. The maximum tensile strength of the UaFSW joint was 236 MPa, which reached 85% of the base 6061-T6 alloy.     

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.     

Si(100)衬底上PLD法制备高取向度AlN薄膜

采用脉冲激光沉积法(PLD),以KrF准分子为脉冲激光源,Si(100)为衬底,同时引 入缓冲层TiN和Ti_0.8Al_0.2N,制备了结晶质量优异的A1N薄膜,X射线衍射(XRD)及反射 式高能电子衍射(RHEED)分析表明A1N薄膜呈(001)取向、二维层状生长.研究发现,薄膜 的生长模式依赖于缓冲层种类,直接在Si衬底上或MgO／Si衬底上的A1N薄膜呈三维岛状生 长;而同时引入缓冲层TiN和Ti_0.8Al_0.2N时,A1N薄膜呈二维层状生长.此外,激光能量密 度大小对A1N薄膜的结晶性有显著的影响,激光能量密度过大,薄膜表面粗糙,有颗粒状沉积 物生成.在氮气气氛中沉积,能使薄膜的取向由(001)改变为(100).     

镍基合金基体上离子镀TiN薄膜的制备及性能

在镍基合金Inconel 740H基底上通过多弧离子镀制备Ti N薄膜.控制温度、气体流量、过渡层成分等重要参数,研究其对Ti N薄膜的表面形貌、力学性能以及耐腐蚀性的影响.多弧离子镀沉积过程中,沉积温度分别为200、250、300℃;过渡层成分分别为Al、Cr、Ti;气体流量分别为Ar 5 Sccm∶N240 Sccm,Ar 6 Sccm∶N248 Sccm,Ar 8 Sccm∶N264 Sccm.实验结果表明:在本实验的温度范围内,Ti N薄膜的致密度、结合力以及表面硬度均随着沉积温度的提高而提高;Cr作为过渡层的效果优于Al和Ti,薄膜成分均匀、表面致密,硬度更高,且耐腐蚀性能优异;在Ar、N2流量比一定的情况下,气体流量对Ti N薄膜的表面形貌和力学性能影响不大.本实验的最佳参数是:沉积温度300℃,过渡层成分为Cr,气体流量为Ar 6 Sccm、N248 Sccm.     

The effect of different methods to add nitrogen to titanium alloys on the properties of titanium nitride clad layers

In this investigation, titanium nitride (TiN) reinforcements are synthesized in situ on the surface of Ti–6Al–4V substrates with gas tungsten arc welding (GTAW) process by different methods to add nitrogen, nitrogen gas or TiN powder, to titanium alloys. The results showed that if nitrogen gas was added to titanium alloys, the TiN phase would be formed. But if TiN powder was added to titanium alloys, TiN + TiN_x dual phases would be presented. The results of the dry sliding wear test revealed that the wear performance of the Ti–6Al–4V alloy specimen coated with TiN or TiN + TiN_x clad layers were much better than that of the pure Ti–6Al–4V alloy specimen. Furthermore, the evolution of the microstructure during cooling was elucidated and the relationship among the wear behavior of the clad layer, microstructures, and microhardness was determined.     

铝合金等离子体基离子注入形成AlN/TiN层结构研究

用X射线光电子能谱和小掠射角X射线衍射研究了铝合金LY12等离子体基离子注入形成的AlN/TiN改性层的结构。结果表明 ,N和Ti能注入铝合金表面 ,N在注入层呈类高斯分布 ,而Ti沿注入方向呈梯度递减。后注入的Ti和N对先注入的N的含量和分布有重要影响。同时注入Ti和N ,能在试样表面形成一层稳定的Ti,N层。所形成的AlN/TiN改性层主要由TiO2 ,TiN ,TiAl3 ,Al2 O3 ,AlN相组成     

Interfacial structures and mechanical properties of steel–Ni and steel–Ti diffusion bonds

Static and fatigue shear tests of steel–Ni bonds and steel–Ti bonds were carried out to obtain the relations between the strengths and the bonding conditions. Ultrasonic measurements were also made to examine the relations between the strengths and the size of the bonded region (the estimated diameter). At the bonding interface of the steel–Ni bonds, no intermediate phase was observed. At the bonding interface of the steel–Ti bonds, a thin layer of intermetallic compound was formed at lower bonding temperatures but, at higher bonding temperatures, the interlayer melted and the bonding interface became rough. The intensity of the ultrasonic wave reflected from the bonding interface changed, depending on the state of the bonding interface. In shear tests of the steel–Ni and steel–Ti bonds, cracks propagated along the bonding interface, and the strength was proportional to the square of the estimated diameter. In fatigue tests, cracks propagated in the thickness direction of the plate and no relation was obtained between the fatigue life and the estimated diameter. Fatigue life distributions were represented by two- and three-parameter Weibull distributions. This revised version was published online in November 2006 with corrections to the Cover Date.