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.     

Morphology and growth of e-beam deposited YSZ thin films

Yttria-stabilized zirconium (YSZ) thin films were grown from the tetragonal phase of ZrO₂ stabilized by 8 wt% of Y₂O₃ (8% of YSZ) ceramic powders using e-beam deposition technique (EB-PVD). The influence of the type of substrate on the microstructure of deposited YSZ thin films was analysed. YSZ thin films (2-3 μm of thickness) were deposited on three different types of substrates: optical quartz (SiO₂), porous Ni-YSZ substrates and Alloy 600 (Fe-Ni-Cr). The dependence of the substrate temperature (from 20 to 600 °C) on the thin film structure and the surface morphology were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that (i) the substrate temperature has an influence on the crystallite size, which varied between 12 and 50 nm, (ii) the substrate type has an influence on the growth mechanism of YSZ thin films, and (iii) a bias voltage applied to the substrate during the deposition of thin films has an influence on the densification of YSZ layers.     

Intermittent bonding for high toughness/ high strength composites

High strength and high toughness are usually mutually exclusive in brittle filament/brittle matrix composites. The high tensile strength characteristic of strong interfacial filament/matrix bonding can, however, be combined with the high fracture toughness of weak interfacial bonding, when the filaments are arranged to have alternate sections of high and low shear stress (and low and high toughness). Such weak and strong areas can be achieved by appropriate intermittent coating of the fibres. The strong regions ensure that the filament strength is picked up; weak areas randomly in the path of running cracks serve to blunt them by the Cook/Gordon mechanism which, in turn, produces long pull-out lengths with an associated large contribution to toughness. Boron-epoxy composites of volume fraction 0.20 to 0.25 have been made in this way which have fracture toughnesses of over 200 kJ m^?2, whilst retaining rule of mixtures tensile strengths (～ 650 MN m^?2). At the volume fractions used, this apparently representsK _IC values greater than 100 MN m^?3/2. An analysis is presented for toughness and strength which demonstrates, in broad terms, the effects of varying the coating parameters of concern. Results show that the “toughness” of interfaces is an important parameter, differences in which may not be shown up in terms of interfacial “strength”. The choice of coating material is crucial in getting the desired effect. Some observations are made upon methods of measuring the components of toughness in composites.     

基于YSZ液料的液流/雾化等离子熔射射流形态及微观组织研究

采用8％(摩尔分数)YSZ粉末(d50=700 nm)配置熔射悬浮液料,比较了送料气压、熔射功率对液流和雾化等离子射流形态特征的影响.利用SEM对制备涂层的微观组织进行表征,结果表明:雾化较液流液料输送方式制备涂层组织结构更致密,两种液料输送方式下熔射距离的增加均导致部分熔融粒子增多,其有助于形成孔隙结构.基于雾化送料制备了厚度为30μm,孔隙率为1.5％的精细结构YSZ涂层,可用于固体氧化物燃料电池的电解质层.     

Hydroxyapatite coating by dipping method,and bone bonding strength

Hydroxyapatite (HA) was coated onto titanium rods by a dip coating method using HA sol. The HA sols were prepared by dispersing HA crystals less than 100 nm length in distilled water or physiological salt solution using an ultrasonic homogenizer. The surface of the HA coating was homogeneous as determined by scanning electron microscopy (SEM). After implantation of uncoated and HA dip coated titanium rods in dog femurs, new bone formation was observed only around the coated material. The bone bonding strength to HA coated rods was 1.0, 1.5, 2.0 and 2.5 Mpa after 1,2,3 and 4 weeks implantation, respectively, as determined by pull-out testing. These values were over twice that of the uncoated titanium rods at 1–4 weeks after implantation. The dip coated titanium exhibited superior biocompatibility to the uncoated implant and may be of great value for bone repacement applications.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Joint strength and interfacial microstructure in silicon nitride/nickel-based Inconel 718 alloy bonding

Joining of Inconel 718 alloys to silicon nitrides using Ag–27Cu–3Ti alloys was performed to investigate the microstructural features of interfacial phases and their effect on joint strength. The Si3N4/Inconel 718 alloy joints had a low shear strength in the range 70.4–46.1 MPa on average, depending on joining temperature and time. When the joining time was held for 1.26 ks at 1063 K, shear, tension, and four-point bending strength were 70.4, 129.7, and 326.5 MPa on average. The microstructures of the joints typically consisted of six types of phases. They were TiN and Ti5Si4 between silicon nitride and filler metal, a copper- and silver-rich phase, island-shaped Ti–Cu phase, a Ti–Cu–Ni alloy layer between filler and base metal, and diffusion of titanium into the Inconel 718 alloys. With increasing joining temperature, the thickness increase of the Ti–Cu–Ni alloy layer was much greater than that of the reaction layer. Thus the diffusion rate of titanium into the base metal was much greater than the reaction rate with silicon nitride. This behaviour of titanium results in the formation of a Ti–Cu–Ni alloy layer in all the joints. The formation of these layers was the cause of the strength degradation of the Si3N4/Inconel 718 alloy joints. This fact was supported by the analyses of fracture path after four-point bending strength tests.     

Interfacial reaction product and its effect on the strength of copper to alumina eutectic bonding

Cu-Cu₂O eutectic bonding of copper to alumina has been studied at 1075°C in nitrogen gas. In order to elucidate the reaction at the Cu/Al₂O₃ interface, the bonding time was prolonged up to 24 h at 1075°C in nitrogen gas. CuAlO₂ was found at the Cu/Al₂O₃ interface, and it seems that CuAlO₂ was formed even with a short bonding time. CuAlO₂ enhanced the bonding strength. There seem to be two kinds of bonding mechanism working at the Cu/Al₂O₃ interface.     

First principles study of effect of lattice misfit on the bonding strength of Ni/Ni3Al interface

By using a discrete variational X (DV-X) method, the electronic structures and bonding strengths of Ni/Ni₃Al (or /) interface with different lattice misfits () were calculated in the framework of the nonrelativistic first-principles theory. In order to describe the effect of on the interfacial binding strength and the structural stability of coherent / interface, we calculated the interfacial binding covalent bond density (CBD) and the local environmental total bond overlap population (LTBOP). Very obvious effects of lattice misfits on the electronic structures of coherent / interface were found. On one hand, less than –0.6% negative lattice misfit can increase the binding strength of the /' interface. On the other hand, the local environmental total bonding strength of the /' interface decreases with increasing magnitude of . Therefore, the magnitude and sign of lattice misfit must be carefully controlled to balance the high-temperature creep strength of Ni-base single crystal superalloy and the structural stability of the /' interface when one designs new alloys.     

Interface chemistry and bonding strength for diffusion-bonded Fe/Fe-FeO/Al2O3 systems

The samples for this study were made by oxidizing the interface region of an Fe/Al₂O₃ system containing either wüstite or Fe-FeO composite (I) as interlayer. The bonded materials of Fe/FeO/Al₂O₃ and Fe/I/Al₂O₃ were prepared by hot-pressing. For analysis of the boundary region electron probe microanalysis (EPMA), transmission electron microscopy and X-ray diffraction were used; at the FeO/Al₂O₃ and I/Al₂O₃ interfaces a newly formed reaction layer of about 6 m in thickness containing iron, aluminium and oxygen could be identified, but EPMA failed to reveal the Fe/FeO interface. Therefore, the interface of iron single crystals with FeO scale was investigated by Auger electron spectroscopy and X-ray photoelectron spectroscopy, and at the Fe/FeO interface formation of a transition layer with a thickness of several hundred nanometres was observed. Through the Fe/I interface, interdiffusion of iron occured. Fe/I/Fe and Al₂O₃/l/Al₂O₃ bonded materials had tensile strengths of 150 and 130 MPa, respectively, when an interlayer of Fe-25 mol% FeO was applied between both bonding pairs.     

Production, bonding strength and electrochemical behaviour of commercially pure Ti/Al2O3 brazed joints

The brazing of commercially pure titanium to Al₂O₃ has been studied. Two different brazing alloys within the Ag–Cu–Ti system and pure silver were selected as bonding agents. Titanium hydride (TiH2) additions were also tested, with the aim of improving the wetting of the ceramic surface by the melted brazing alloy. The mechanical and electrochemical behaviour of the produced joints was assessed, and related to chemical and morphological features resulting from an analysis by scanning electron microscopy and energy dispersive spectroscopy. It was possible to produce joints presenting high integrity, good strength and high resistance to corrosion. The best results were obtained when using an Ag–26Cu–3Ti brazing alloy. The addition of TiH₂ increased the mechanical properties, leading to a maximum bonding strength of 80±8 MPa, as determined in three-point bending tests. In most of the cases, for a maximum deflection of 5 mm, there was only a partial detachment of the ceramic/metal joints. The lowest values for the corrosion rates (i_corr=1.38 μA cm−2) determined in potentiodynamic experiments also correspond to the use of the Ag–26Cu–3Ti brazing alloy. The bonding strength and electrochemical results could be explained in terms of the different chemical compositions of the interfaces. The use of TiH₂ additions proved to be quite effective, allowing for the replacement of the usual metallizing and plating pre-treatments needed for the brazing of ceramics to metals. This revised version was published online in November 2006 with corrections to the Cover Date.     

基于CO2激光热效应的喷塑涂层界面结合强度研究

用CO2脉冲激光扫描AISI304-喷塑涂层的表面,分析喷塑涂层的破坏特征和断裂行为,研究了激光热效应下喷塑涂层的结合强度.结果表明,可用吸收的激光能量定量地表征涂层和基体之间的结合强度,聚烯烃喷塑涂层-AISI304的理论结合强度为19.9 MPa,当涂层中塑料与基体的溶度参数相近时,涂层与基材的结合界面附着力较强.     

Dynamic effect on strength in SiCf/SiCm composite

Loading rate dependence of mechanical properties of SiC fibre-reinforced SiC composites (SiC_f/SiC_m) has been experimentally investigated as to the fibre volume fraction and coating materials for SiC fibre. The composites consisting of monolithic SiC and SiC fibre (Hi-Nicalon) coated with Boron-Nitride (BN) or Carbon (C) with fibre volume fractions of 20, 30 and 40% were fabricated by polymer infiltration–pyrolysis (PIP) process. The stress–strain response and strength were measured in tension over a wide range of strain rate,10⁻⁴∼200 s⁻¹. It was shown that the higher volume fraction, the larger tensile strength regardless of the kind of coating and strain rate. The interface friction stress evaluated by the fibre pullout length that is measured through microscopic observations of fractured specimens is larger in dynamic loading than in static loading. The BN-coated fibre gave the composite superior tensile strength to the C-coated fibre. This trend results from the variety of the interface friction stress associated with the coating thickness.     

Investigation of bonding strength and sealing behavior of aluminum/stainless steel bonded at room temperature

This article reports the direct bonding of aluminum (Al) [99.999% (5N), 99% (2N)] and stainless steel SUS (304, 316) without heating for sealing in the ultra high vacuum (UHV) components. For bonding, the smooth surfaces of the Al and SUS specimens were activated using argon fast atom beam (Ar-FAB) for 1-60 and 60 min, respectively, in a background pressure of 6.0 × 10⁻⁵ Pa followed by close contact under an external pressure of 960 N. High bonding strength resulted in the bonded mates of Al and SUS304 activated for 30 and 60 min, respectively, due to the adhesion forces of the surface atoms. Tensile pulling tests showed bulk fractures in Al with impurity dependent bonding strength. The bonding strengths for the Al5N/SUS304 and Al2N/SUS304 specimens were higher than 60 and 100 MPa, respectively. For the sealing test, the smooth surface of the SUS316 flange containing a hole was bonded with Al after surface activation 60 and 30 min, respectively. Leak rates for Al5N/SUS316 and Al2N/SUS316 specimens were 1.5 × 10⁻¹¹ and 2.0 × 10⁻¹¹ Pa m³/s, respectively. These results satisfy the permissible leakage of a large-sized UHV chamber. Time dependence of the leak test behavior for both specimens shows a stable leak rate. Therefore, the sealing of Al/SUS316 may be utilized for the fabrication of corrosion free joints for fluid flow in the cooling of electron guns of small size equipment such as portable scanning electron microscopes in UHV pressure.     

Interfacial shear strength of a glass fiber/epoxy bonding in composites modified with carbon nanotubes

In recent years, carbon nanotubes (CNTs) grown on fibers have attracted a lot of interest as an additional reinforcing component in conventional fiber-reinforced composites to improve the properties of the fiber/matrix interface. Due to harsh growth conditions, the CNT-grafted fibers often exhibit degraded tensile properties. In the current study we explore an alternative approach to deliver CNTs to the fiber surface by dispersing CNTs in the fiber sizing formulation. This route takes advantage of the developed techniques for CNT dispersion in resins and introduces no damage to the fibers. We focus on unidirectional glass fiber/epoxy macro-composites where CNTs are introduced in three ways: (1) in the fiber sizing, (2) in the matrix and (3) in the fiber sizing and matrix simultaneously. Interfacial shear strength (IFSS) is investigated using single-fiber push-out microindentation. The results of the test reveal an increase of IFSS in all three cases. The maximum gain (over 90%) is achieved in the composite where CNTs are introduced solely in the fiber sizing.     

Post-deposition thermal treatments for improving the interconnection strength of a Ti-W/Au/Cu bonding system

The bonding combination of Ti-W/Au/Cu laminate strips deposited on an SiO₂/Si passivated substrate is strengthened through post-deposition age-hardening thermal treatment of the deposited metals in the amorphous state. For creating a copper layer of 10 m thickness at the top, both electrodeposition and physical vapour deposition (evaporation) methods are applied to obtain different strip properties. Peel tests, which can simulate the strip delamination process, are conducted to evaluate the strip-substrate bonding strength. A micro-mechanics analysis indicates that weak strip stiffness is a key cause for the frequent strip-substrate separations. Consequently, the laminate composite system is heated and cooled after deposition under different treatment conditions to strengthen the strip. The specimens are heated to a temperature of 220 to 400C, held there for a time and cooled quickly in air or water. The strengthening effect of the amorphous metals is obvious but complicated. The improved bonding strength will decrease again if the heating temperature is lower than 200C or the heating time is shorter than 50 min. At room temperature, indices of performance for strip-substrate bonding strength such as average peel force, peel energy and peak peel load continuously vary within approximately 100 h, depending upon the heating treatment history. Significant improvements of up to approximately 300% have been achieved according to peel strength tests. The sticking strength becomes so high after the thermal treatment that no part of a strip can initially leave its substrate during the tests.     

TiAl/40Cr钢扩散连接界面组织结构对接头强度的影响

扩散连接界面组织结构是影响连接性能的关键因素,不同的界面组织结构及生成相所决定的接合强度不同．本文研究了TiAl/40Cr钢的扩散连接,结果显示：连接温度过高及连接时间过长时,由于界面处形成了过多的TiC脆性层及Ti3Al FeAl FeAl2的金属间化合物混合层,接头拉伸强度低;当连接温度较低及连接时间较短时,界面紧密接触与元素扩散不充分,接头拉伸强度也较低．脆性TiC层的生成导致TiAl与40Cr钢之间的扩散连接性能较差,接头均破断于TiC层或TiC层与Ti3Al FeAl FeAl2的金属间化合物混合层之间．     

Using silane-functionalized graphene oxides for enhancing the interfacial bonding strength of carbon/epoxy composites

Silane-functionalized graphene oxides (sGOs) were fabricated with four different self-assembled monolayers (SAMs) to reinforce an epoxy adhesive, with the aim of improving the bonding strength of carbon/epoxy composites. The oxygen-containing groups on the surface of graphene oxide (GO) were converted by the SAMs to amine, epoxy, or alkyl groups. The successful reaction between the silane molecules of the SAMs and functional groups of GO was evidenced by the results of different characterization methods such as Fourier transform infrared spectroscopy. It was found that the average thickness of the sGO flakes was higher than that of GO flakes. The bonding strength of a carbon fiber/epoxy composite, tested with a single lap joint bonded with an epoxy adhesive, was increased by 53% after the addition of a sGO that contained amine groups. These results show that sGOs, especially those containing amine functional groups, can strengthen the interfacial bonding between the carbon fibers and epoxy adhesive.     

Pressure-assisted direct bonding of copper to silicon nitride for high thermal conductivity and strong interfacial bonding strength

To achieve superior thermal and mechanical properties of copper-bonded (Cu-bonded) Si₃N₄ substrate, a pressure-assisted direct bonded Cu (DBC) technique was applied to bond Cu foil with Si₃N₄ plate. The effects of oxide layer (SiO₂) thickness of Si₃N₄ plate on the microstructure, thermal and mechanical properties of the Si₃N₄-DBC samples were investigated. The successful bonding of Cu foil to Si₃N₄ plate was confirmed by the presence of the interfacial products of Cu₂MgSiO₄ and CuYO₂. Additionally, it was demonstrated that a thin SiO₂ layer can result in a discontinuous distribution of interfacial products while a thick one can lead to the formation of pores in SiO₂ layer. Notably, the sample prepared by Si₃N₄ plate with 5-μm-thickness SiO₂ layer and Cu foil with 5.9-μm-thickness oxide layer (Cu₂O) exhibited the optimally comprehensive properties with thermal conductivity of 92 W·m^?1·K^?1 and shearing strength of 102 MPa, which demonstrates significant promise for application in power electronic modules.

Graphical abstract