In recent years, it has become necessary to develop lead substitutes, such as lead-free solder alloys, because of increased environmental concerns regarding the use of leaded materials. In addition, electronic components that use lead-free solder alloys will need to be smaller and usable at higher operating temperatures in next-generation semiconductor devices. Therefore, lead-free solder alloys must be made more reliable. In this work, tin-copper-nickel (Sn-Cu-Ni) solder alloys, Sn-Cu solder alloys, and Sn-Ni solder alloys, as well as 99.96 mass% pure Sn, were subjected to tensile testing. The results showed the effects of adding Cu and Ni to Sn on the high-temperature deformation behavior of the Sn-Cu-Ni solder alloys. For each alloy and Sn, the stress exponent was estimated to be >5. This result indicated that, in each sample, the high-temperature deformation was controlled by dislocation creep. Furthermore, the creep activation energy was dependent on stress, and was affected to the greatest extent when adding Cu.

The purpose of this study is to investigate the influence of Nb content of Ti-xNb-7Al alloys (x=20-35 mass%, abbreviated as xNbA) on β (bcc)→α″ (orthorhombic) transformation with tempering through microstructure, isothermal age-hardening, and shape change of a U-shaped specimen with heating. Full α″-martensite structure was obtained on the quenched 20 NbA. With increasing of Nb content, residual β-phase increased, and single β-phase was obtained in the alloys of more than 25 NbA. From the result, the M_S temperature commonly decreases with increasing of Nb content. The hardness of 20 NbA and 23 NbA rapidly increased in a few seconds by isothermal aging at 450°C, and the hardness of the alloys of more than 25 NbA abruptly increased after an incubation period for 30-60 s. No compositional distribution between α″ and matrix in the aged 23 NbA was found by STEM-EDS analysis, but the obvious distribution of Nb was detected in 35 NbA. U-shaped specimen of 20 NbA exhibited no shape change by heating. On the other hand, the specimen of 23 NbA composed of β+α″ phases showed the shape recovery (SR) first due to work induced α″→β inverse transformation, then deformed toward the bending direction (SA: shape advance) due to β→α″ transformation. The specimens of more than 28 NbA composed of single β-phase exhibited only SA without SR. The starting temperature of SA (M_SA: β→α″) with heating increases with increasing of Nb content. Merging M_S (upper) and M_SA (lower), it is proposed that the whole M_S of xNbA alloy forms a bow shape curve. It is suggested that the low Nb alloys inside the M_S curve transform immediately without atom diffusion by tempering at 450°C, but the higher Nb alloys outside the curve need an incubation period to distribute Nb concentration with atom diffusion, and martensitic α″ transformation will abruptly occur in the local domains less than 25 NbA which is the inside of the curve.

In this study, in order to improve the adhesion strength of diamond-like carbon (DLC) films, medium carbon steel specimens were treated by using an atmospheric-controlled induction heating fine particle peening (AIH-FPP) with Cr particles that have high affinity for DLC films. The AIH-FPP treated specimens were characterized using optical microscope, scanning electron microscope and energy dispersive X-ray spectrometer. It was found that a diffused layer of Cr was formed on the specimen surface that was treated with AIH-FPP. The modified layer was then coated with DLC films, and in order to investigate the adhesion strength of DLC films on the surface modified substrates, reciprocating wear and indentation tests were performed. It was revealed that a Cr diffused layer formed by AIH-FPP treatment improved the adhesion strength of DLC films against sliding loads and large plastic deformations. In addition, the adhesion strength of DLC films was improved by increasing the thickness of a Cr diffused layer and superior friction characteristics were maintained for a long time. These results suggest that a Cr diffused layer induced by AIH-FPP treatment is an effective method for improving the adhesion strength of DLC films.

To elucidate the synergistic effect of gelatin, thiourea and chloride ions on the surface roughness, throwing power and polarization curves for Cu deposition from electrorefining solution, Cu electrodeposition was performed at a current density of 200 A·m^-2 and 5×10⁵ C·m^-2 of charge in an unagitated sulfate solution containing 0.708 mol・dm^-3 of CuSO₄ and 2.04 mol・dm^-3 of H₂SO₄ at a temperature of 60°C. In solutions containing three kinds of additives such as gelatin, thiourea and chloride ions, the surface roughness of deposited Cu decreased with increasing the concentration of thiouea and gelatin and decreasing the chloride ions. On the other hand, the throwing power of deposited Cu was improved with decrease in thiourea and increase in gelatin in solutions containing three kinds of additives. The throwing power of deposited Cu was significantly improved in solution containing both gelatin and chloride ions. The polarization resistance dE/di for Cu deposition increased in solution containing both gelatin and chloride ions, which resulting in improvement of throwing power of Cu deposition. As small amounts of thiourea have a depolarization effect on Cu deposition, a leveling effect is expected owing to the promotion of deposition at recesses.

In order to analyze combustion synthesis of Cu-Al intermetallic compounds, Cu/Al premixed compacts were quenched during combustion synthesis, and the micro-structure was analyzed. And, in dipping experiments of Cu wire and Cu plate into molten Al, the formation reactions between solid Cu and molten Al were also investigated. A piece of Cu wire was put into a crucible, and Al powder was filled around the Cu wire. The crucible was inserted in a quartz tube, and was vacuum-sealed with 10^-3Pa vacuum degree. The capsule was kept at 800-1000°C for 0-90 min. using an electric furnace. After the holding time, the cross-sections were observed by an optical microscope and SEM-EDX. Additionally, the dipping experiment of Cu plates into molten Al were also investigated by same method as Cu wire experiment.

From the quenching of Cu/Al premixed compacts during the combustion synthesis, Cu₃Al formation reaction between Cu particles and molten Al could be observed. The formation reaction was also found in the dipping experiments of Cu wire and Cu plate into molten Al. However, the formation rate and the composition of Cu₃Al synthesized was depend on the contact surface shape between Solid Cu and molten Al. Furthermore, kinetics equations were derived for the Cu₃Al formation reaction.

To reduce the weight of 20 vol% Al₂O₃-particle-dispersed Mg (Al₂O₃/Mg) compacts produced by spark plasma sintering (SPS), which are much harder than practical high strength AZ91 Mg alloys, 20/0/20 vol% laminated SPS compacts sandwiching a lightweight 0 vol% Al₂O₃/Mg (0 vol%) layer between two 20 vol% Al₂O₃/Mg (20 vol%) layers were fabricated by a mechanical milling/SPS process, and their microstructures and mechanical properties were investigated. The density of the 20/0/20 vol% laminated SPS compacts was 1.88 Mg·m^-3, and they could be lightened to approximately 80% of the weight of equivalent 20 vol% SPS compacts. The 20/0/20 vol% laminated SPS compacts had a slightly higher hardness than the 20 vol% SPS compacts and a much higher hardness than AZ91 alloys. The bending strength of the 20/0/20 vol% laminated SPS compacts was almost the same as that of the 20 vol% SPS compacts, and was higher than the value calculated from those of the 20 and 0 vol% SPS compacts using the rule of mixtures. A new phase appeared at the flat interface between the 20 and 0 vol% layers with excellent adhesion to the adjoining layers, so this phase probably had a beneficial effect on the bending strength of the 20/0/20 vol% laminated SPS compacts. The new phase generated a monotonically decreasing hardness gradient from the 20 vol% layer to the 0 vol% layer and was formed by diffusion of Al and O from the 20 vol% layer and diffusion of Mg from the 0 vol% layer. The new phase most likely consisted of αMg, MgO, and Mg₁₇Al₁₂, and the concentrations of Al in the αMg, MgO, and Mg₁₇Al₁₂ components of this phase were considered to decrease from the 20 vol% layer to the 0 vol% layer.

Mater. Trans. 58（2017） 206-210に掲載