The purpose of this study was to evaluate the corrosion resistance of experimental dental Ti-Ag alloys in 0.9% NaCl solution. Open-circuit potential (OCP) measurement and elution tests of the alloys with 5-30% Ag were performed. The amounts of both Ti and Ag ions released from the alloys with Ag≤20% were below the detection limit. A very small amount of Ti ions was released from some of the 22.5% Ag specimens and some of the 25% Ag specimens. The time for the Ti-Ag alloys with 5-25% Ag to become the stable potential was earlier than that for titanium, and the OCP of the alloys was higher than that of titanium. These results indicated that the corrosion resistance of the alloys with 5-25% Ag was equivalent to that of titanium. On the other hand, it was suggested that the precipitation of TiAg deteriorated the corrosion resistance of Ti-Ag alloys because TiAg dissolved preferentially in the NaCl solution. Ti-Ag alloys with 5-25% Ag can be used not only as dental restorative materials but also as dental implant materials.
Basic mechanisms of generating a surface modified layer formed by a previously developed atmospheric controlled IH-FPP system, consisting of induction heating system and fine particle peening system, were investigated. Three types of specimen treated at 900°C in argon with Cr, Al2O3 and Cu shot particles were prepared. Surface microstructures of the treated commercial-grade pure iron were characterized with a scanning electron microscope (SEM), an energy dispersive X-ray spectrometer (EDX) and an X-ray diffraction analysis (XRD). When treatment was carried out using Cr particles, the transferred layer and the diffused layer of the shot-particle element formed at the treated surface. This was because the radius of Cr atom was almost the same as that of the Fe, thus forming a solid solution in the substrate. Conversely, when the treatment was applied using chemically stable Al2O3 particles, a transferred layer only was observed. In the case of Cu particles, adhesion occurred due to the low melting temperature of Cu particles, resulting in the formation of a thick adhesive layer such as that generated by thermal spraying. These results suggest that the characteristics of the modified layer, generated by the atmospheric controlled IH-FPP treatment system, can be controlled by varying the shot particles and other processing parameters.
Closed cell nickel titanium (NiTi) alloy foams were made by combustion synthesis with the help of both foaming agent and endothermic agent powders. Nickel, titanium, the foaming agent (ZrH2) and the endothermic agent (TiB2) powders were mixed and pressed at room temperature into cylindrical compacts. By heating these powder compacts up to an ignition temperature of the combustion reaction, NiTi alloy specimens are made. In this method, pores in the specimens are made by the gas generation from the foaming agent during melting of NiTi alloy due to the high heat of combustion reaction. Cell wall rupture of these foams caused by the gas generation is successfully prevented by the endothermic agent addition which increases the viscosity of molten NiTi alloy. An optimum amount of endothermic agent addition turned out to be in between 30 and 35 vol%. This volume fraction range is close to the one that makes adiabatic temperature of the combustion reaction below melting point of NiTi alloy. Specimens made by the addition of 40 vol% endothermic agent did not foam sufficiently. Porosity of the NiTi alloy foams increased by increasing the additive amount of the foaming agent by 1 mass%. Cell wall rupture and large pore formation became remarkable by increasing the foaming agent addition.
We have confirmed the effectiveness of ultra-high purity plating material on the formation of low resistivity Cu wires for 22 nm level ULSIs using 8 inch wafer. The resistivity of the 30 nm wide Cu wires formed by ultra-high purity process is found to be 30% lower than those for Cu wires fabricated by the conventional process. It was also found that the grain size of the ultra- high purity processed Cu wires is larger than that of the conventional processed Cu wires by 30%, and the grain size is much more uniform. This innovative new process is expected to be one of the powerful candidates as the Cu wire forming process for 22 nm level ULSIs.
The tin-zinc binary alloy is one of the candidates for lead-free solder and plating. In order to investigate the evolution of solidified structure of the tin-zinc binary eutectic alloy, the unidirectional solidification technique has been applied using a Bridgman type furnace. The primary β-tin is obtained as dendritic structure. On the other hand, the primary zinc is obtained as plate crystal because of high anisotropy in surface tension. Coupled-zone is found to be extended to tin-rich side and to be rather symmetric. The lamella spacing in coupled zone agrees with Jackson-Hunt model. Furthermore, the broken-lamellar to fibrous transition has been observed at high growth velocity.
The transformation phenomena of α→γ during intercritical annealing and of γ→α during subsequent cooling are important to achieve precise control over the mechanical properties of low-carbon cold-rolled Dual Phase steels. Taking advantage of multi-component diffusion simulation, this paper aims to investigate the partition of Si and Mn at the early stages of α→γ and γ→α transformation. The steel with the chemical composition of 0.13 mass% C-1.4 mass% Si-2.0 mass% Mn was intercritically annealed at 800°C for 0∼1000s, then air-cooled to 600∼800°C, followed by water-quenching. Its microstructural observation and elemental analysis were conducted using a field emission electron probe microanalyser. At the early stages of the α→γ transformation during annealing at 800°C, substitutional alloying elements such as Mn and Si are hardly partitioned. Even if the volume fraction of γ is the same before cooling, the γ→α transformation kinetics differs depending on the Mn concentration in γ. The diffusion simulation shows similar tendency with the experimental data.
Ni electrodeposition was galvanostatically conducted over the current density range of 1-5000 A/m2 in unagitated sulfamate and Watt's solutions containing polyethylene glycol (PEG) or saccharin at 323 and 313 K, respectively, to examine the effect of the content of C and S in deposits and texture on the hardness of the deposited Ni. The content of C in Ni deposited from Watt's solutions containing PEG was significantly larger than that from the sulfamate solutions. There was little difference in S content in deposits between sulfamate and Watt's solutions containing saccharin except for 2000 A/m2. The hardness of deposited Ni increased with C and S content in deposits, and the degree of increase in hardness decreased at S contents above 0.02 mass%. The texture of deposited Ni changed from the field-oriented texture type to the unoriented dispersed type when C and S were codeposited with Ni by addition of PEG and saccharin. The hardness of unoriented dispersed type of Ni was larger than that of the field-oriented texture type.
Intense plastic strain is imparted into disk- and ring-shape samples using high-pressure torsion (HPT) which is known as a typical process of severe plastic deformation. The grain size is refined to the submicrometer and/or nanometer range. The grain refinement is also achieved using high-pressure sliding (HPS) which was developed recently for rectangular sheet samples under high pressure as in HPT. However, the samples with the thickness thinner than 1 mm are usually used for both HPT and HPS processes but no attempt has been made for samples with the thickness thicker than 1 mm. This study is then initiated to investigate how homogeneously the strain is developed and the grain refinement is achieved in the thicker samples. High purity Al (99.99%) is used with ring-shape and rectangular sheet samples having thicknesses of 2 and 4 mm. It is shown that a region of intense plastic strain develops at the center height and expands to both upper and lower edges with straining. The grain refinement is achieved at such an intense plastic region with dislocation-free grains with the sizes of a few micrometers.