Shinji Fukumoto

Hydrolysis behavior of aluminum nitride in various solutions

The AlN powder was immersed in deionized water, HCl aq, NaOH aq and H3PO4 aq to investigate their hydrolysis behavior at 283 to 373 K. The pH of the solutions were not varied at the initial stage in the case of deionized water, and they increased abruptly after the incubation time with evolution of NH3. Time until the evolution of NH3 decreased with increasing temperature. The hydrolysis at the higher temperature was different from at the lower. Below 351 K a crystalline bayerite was produced on the surface of AlN particle, while a crystalline boehmite was produced at higher than 351 K. The AlN powder was hydrolyzed more efficiently in HCl aq and NaOH aq compared with in the deionized water. While, H3PO4 aq restrained hydrolysis of AlN powder.

Friction welding process of 5052 aluminium alloy to 304 stainless steel

AbstractType 5052 aluminium alloy was joined to type 304 austenitic stainless steel via a continuous drive friction welding process. The joint strength increased, and then decreased after reaching a maximum value, with increasing friction time. Joint strength depended on the size and shape of the tensile testpiece. Friction weldability could be estimated by electrical resistmetry. The process of friction welding between the aluminium alloy and the stainless steel is proposed to evolve as follows: welding progresses from the outer to the inner region; an unbonded region is retained at the centre of the weld interface with shorter friction time; longer friction time causes the formation of an intermetallic reaction layer at the weld interface; and the reaction layer grows as the friction time increases. When the thickness of the reaction layer increased above a critical value, the joint was brittle and fractured at the weld interface. The joint was sound when there was no unbonded region and a thin reaction...

Surface modification of titanium by nitrogen ion implantation

Abstract Nitrogen ions were implanted in high purity titanium at various doses. The nitride phase, TiN, was identified using either grazing incidence X-ray analysis or transmission electron microscopy. AES depth profile of nitrogen was altered from Gaussian-like to a rectangle with increasing nitrogen doses. Both dissolved nitrogen and tendency to form TiN increased precipitates with increasing nitrogen doses. These TiN precipitates that size were several tens of nm were observed at a lower dose. They grew larger as nitrogen dose increased. The dynamic ultra-microhardness rose to a thickness of within 200 nm of the surface owing to TiN formation, resulting in improved wear resistance of titanium. The wear volume was minimum at a dose of 5×10 21 N 2 + m −2 .

Amorphization by friction welding between 5052 aluminum alloy and 304 stainless steel

The joining of dissimilar metals such as aluminum/stainless steel is a very important technique. In the case of fusion welding of an Fe-Al system, excess formation of brittle intermetallic compounds degrades the joint. Since friction welding is one of the solid-state bonding procedures, few intermetallic compounds are formed at the weld interface. However, in the Al-Fe system, the solid solubility is almost nil, so some intermetallic compounds will be formed in spite of the friction welding. In the present study, microstructure of the friction weld interface between Al-Mg alloy and austenitic stainless steel was investigated by high resolution transmission electron microscopy and the mechanism of friction welding was examined.

Friction welding of TiNi alloy to stainless steel using Ni interlayer

Abstract Friction welding was carried out between TiNi alloy and austenitic stainless steel with and without a Ni interlayer. When TiNi alloy was welded to stainless steel without the Ni interlayer, a large amount of brittle Fe2Ti intermetallic compound was formed at the weld interface. The formation of this brittle compound led to degradation of the joint strength. The Ni interlayer changed the microstructures at the weld interface and improved the joint strength. A fracture occurred at the interface between Ni and TiNi. The interface between Ni and TiNi was free from Fe2Ti and consisted of mainly TiNi3 and TiNi. After TiNi3 was formed as the reaction layer, a eutectic reaction occurred between the TiNi3 and TiNi base alloy. A reaction layer with a eutectic structure tends to form at the periphery, where the temperature would be higher than that of the central region.

Dynamic recrystallisation phenomena of commercial purity aluminium during friction welding

Abstract The microstructures of commercial purity aluminium near the friction weld interface were observed by transmission electron microscopy. Large plastic deformation of aluminium occurred near the weld interface and the microstructure of the aluminium was oriented from the centre to the periphery of the weld nugget. The aluminium grains were refined, and there were many recrystallised grains which were almost dislocation free. The refined grains, which were of size ~ 1 νm, formed very near the weld interface. The grain boundary was estimated to be a large angle tilt boundary. The refined grains were mainly formed by dynamic recrystallisation during the upset stage of the welding cycle. A large amount of shear strain and heat were introduced during the friction stage, and dynamic recrystallisation started during the upset stage. Grain growth occurred during air cooling after the upset stage. The grain size was larger in the central region than in the periphery owing to the variation in temperature. The Vickers microhardness of aluminium near the weld interface increased owing to the microstructural refinement.

Laser-beam welding of SiC fibre-reinforced Ti-6Al-4V composite

Three- and ten-ply SiC fibre-reinforced Ti-6Al-4V composites were joined using a laser beam. With a 300 μm thick Ti-6Al-4V filler metal, fully penetrated welds without apparent fibre damage, could be obtained in welding directions both parallel and transverse to the fibre direction by controlling the welding heat input. Excess heat input resulted in the decomposition of SiC and subsequent TiC formation, and also caused degradation of joint strength. The welding of the three-ply composite in which full penetration was achieved at lower laser power, exhibited higher flexibility in heat input than that of the ten-ply composite. Heat treatment at 1173 K after welding improved the joint strength because of the homogenization of the weld metal and decomposition of TiC. The strengths of the transverse weld joints after the heat treatment were approximately 650 and 550 MPa for the three- and ten-ply composites, respectively. With the welding direction parallel to the fibre direction, the strengths both parallel and transverse to the weld joint were equivalent to those of the base plate.

Small-Scale Resistance Welding of Crossed TiNi Fine Wire

Resistance microwelding of fine crossed wires is of increasing industrial importance for medical devices, but the understanding of the process is very limited. A study has been carried on the feasibility of small-scale resistance welding of crossed TiNi fine wire. Welding mechanism is similar to that of small-scale resistance welding of crossed Ni wire, which is mainly four stages (wire cold deformation, surface melting, molten phase squeeze-out and, solid-state bonding). The optimum microstructure and welding parameters were proposed.

Estimation of current path area during small scale resistance spot welding of bulk metallic glass to stainless steel

Abstract The current path area is a significant factor in estimating the temperature distribution via numerical modelling for resistance spot welding. This paper presents a method for the estimation of the current path area at the faying surface during small scale resistance spot welding between bulk metallic glass and stainless steel. Observation of cross-sections and fracture surfaces reveals the welding process at the faying surface for both dissimilar and similar welding. The equipotential surface that depends on the difference between the contact area of the electrode-to-sheet and sheet-to-sheet interfaces is estimated by numerical modelling. The current path area at the faying surface is estimated by measuring the electric potential between the sheets, taking into account the current distribution.

Bonding of copper to silicon chips using vapor-deposited tin film

A bonding process between a Cu plate and a Si chip using a vapor-deposited tin film has been developed. The microstructures of the bond interface and the reliability during thermal cyclic tests were investigated. Intermetallic compounds (IMCs) of Cu3Sn and/or Au- Cu-Sn were formed at the bond interface. The stress concentration initiated fracture in the IMC layer at the corners of the bond area and the initial cracks in the IMC layer propagated through the Al layer in the metallized layer on the Si chip. Joints using a deposited tin film showed much longer lifetime than solder joints.