Hot hammer forging is a useful manufacturing process for producing mechanical parts with excellent mechanical properties. One of the problems in this forming process is seizure between die and work-piece. It does not only decrease quality of the products and the productivity but also put a worker in danger. In order to avoid the seizure in forging process, sulfonitriding to die surface has been often applied. The surface treatment provides a nitrided zone with a sulfide layer as a top layer. The nitrided zone has higher hardness of the die while the sulfide layer improves anti-seizure ability and decreases the friction coefficient. The sulfide layer on the die surface is constituted of Iron sulfide (FeS). However, mechanical and physical properties of FeS have not been investigated yet. In the present study, pulsed electric current sintering of FeS powder was studied to fabricate dense sintered bodies of bulk FeS for evaluating physical and mechanical properties. Some mechanical properties such as Vickers hardness and fracture tougŠess of sintered FeS were evaluated in the present report.

Electrodeposition of Zn-polyethyleneimine composite was performed at current density of 100-12000 A·m^-2 and a charge of 4.8×10⁵ C·m^-2 in an agitated sulfate solution containing 1.84 mol·dm^-3 of ZnSO₄ and 4 g·dm^-3 of polyethyleneimine at pH 1.8 and at 313 K, and the deposition behavior and its micro structure were investigated. The films deposited at current densities above 4000 A・m^-2 from the solution containing polyethyleneimine exhibited the gloss, and the gloss was highest with polyethyleneimine of higher molecular weight of 70000. The preferred orientation of deposited Zn changed from {0001} to {1120} and {1010} with polyethyleneimine, and the size of Zn platelet crystals deceased with increasing the molecular weight of polyethyleneimine and current density. The deposition of Zn was polarized with polyethyleneimine, and the degree of polarization became larger at higher current density region with polyethyleneimine of higher molecular weight of 70000. With increasing the molecular weight of polyethyleneimine and current density, the content of C and N in deposited films increased, indicating the increase in adsorption ability of polyethyleneimine onto cathode. Polyethyleneimine somewhat suppressed the rise of pH at cathode layer during deposition, or showed the buffer action of pH. During deposition, H⁺ ions are detached from the polyethyleneimine due to rise of pH at cathode layer and, as a result, the lone pairs of electron in N atom increased, which resulted in increase in adsorption ability of polyethyleneimine onto cathode.

The surface reforming of Ti wire by powder metallurgy was investigated in this study. Pure Ni powder, Ni/Ti powder and Ni/Al powder were used as coating materials. A piece of Ti wire (φ=1.0 mm) was placed in an alumina crucible, and coating materials (Ni powder, Ni/Ti premixed powder, Ni/Al premixed powder) were filled around the Ti wire. The alumina crucible was vacuum sealed in a quartz tube with 2 ×10^-3 Pa. The quartz tube was heated in an electric furnace for 60 min. For the test piece obtained, microstructure, phase and Vickers hardness were measured. A uniform compound layer was formed when the Ni / Al premixed powder was used as the coating material. The intermetallic compound layer was consisted of (Ti₃Al+NiTi), (Ti₃Al+Ti₂Ni+τ₄) phases. The surface reforming of Ti wire was able to be performed by dipping heat of Ti wire into Ni/Al premixed powder.

In our previous paper, dipping experiments of Cu wires and Cu plates into molten Al were investigated to analyze the combustion synthesis of Cu-Al intermetallic compounds. From the dipping experiments, it was found that Cu₃Al compound layers were formed between the Cu base metal and the molten Al. The compound formation reactions were able to be almost simulated by calculating the cylindrical model and the flat plate reaction model. However, there are a few differences between Cu wire dipping experiment and Cu plate dipping experiment. Al concentration of Cu₃Al compound phase formed in the Cu wire are higher than that of Cu plate. For the reaction parameters, diffusion coefficient of Al in Cu plate dipping experiment is also higher than that of Cu wire dipping experiment.

For the dipping experiment of Cu wire, the reaction parameters are,

For the dipping experiment of Cu plate, the reaction parameters are,

From analyzing the cylindrical model and the flat plate reaction model, it is guessed the differences were caused by the contact area of Cu/Cu₃Al/Al interface and Al concentration of Cu₃Al phase formed in Cu wires and Cu plates.

Martensitic transformation behavior during cooling and heating of Ti-15V-7Al was investigated. The alloy was heated at 1050°C under a vacuum and quenched into an iced water. The structure of the quenched specimen consist of most β-phase and a small quantity of α” martensite at near grain boundaries. The elastic bent strip using a jig exhibited spontaneous shape change into the bending direction with heating. By sub zero treatment using LN₂, some martensites were newly formed at around prior martensites formed by quench, but no martensite was formed at the single β region. The martensite formation by the sub zero treatment exhibited a time dependence. Even tempering at 550°C for a few second dramatically induced coarse martensites all over the specimen. All martensites, formed by the quenching, the sub zero treatment, or the tempering, disappeared completely by the heat treatment at 200°C for 300 s, and turned into a single β phase. However, the coarse martensites were regenerated again from the single β phase by the tempering at 550°C for a short time, which means the martensite behavior in the range of 200~550°C is reversible. Continuous isothermal aging at 550°C led to a remarkable hardening through the process of β→coarse α”→fine α”→β+fine α. Both the Ms curve and the free energy model with a spinodal decomposition of α, which can explain the martensite formation at low and high temperatures, were proposed.

The yield strength and work hardening of Al-Mg-Si alloys are related to the concentration of solute atoms. This study was carried out to clarify the effect of two kinds of solute atoms on these properties in terms of a linear combination of contributions from a solid solution. Tensile tests were conducted with Al and with Al-0.62Mg-0.32Si, Al-0.65Mg-0.81Si, Al-2.4Mg and Al-4.4Mg (mass%) alloys in solid solution. Work hardening was analysed using the Kocks–Mecking model, yielding two parameters which indicate the storage and recovery of dislocations in the material. The yield strength could not be expressed as a linear combination of solute atom concentrations, but the amount of dislocation storage and dynamic recovery could be expressed as such linear combinations. In the high-strain region, the Kocks–Mecking model no longer applies, and the maximum stress at which the model failed increased with increasing concentrations of solute atoms. It is generally known that an interaction between strain fields around solute atoms and quenched-in vacancies can affect the yield strength owing to dislocation motion and that these atoms can retard the development of microstructure in high-strain regions. A linear combination of contributions from solid solutions is possible only for the storage and recovery of dislocations in the low-strain region.

The Takamatsuzuka tumulus was constructed in the 7-8^th centuries at Asuka in the current Nara Prefecture. The mural is painted on the stucco plastered over the tuff wall. The stucco is apparently rough due to degradation, and therefore, the mural surface is also rough. The purpose of this research is to clarify the causative factor of the degradation observed in the stucco materials scientifically. Surface and inner morphology of the stucco are observed using a computerized X-ray tomograph (CT), a scanning electron microscope, and a transmission electron microscope. Impurity elements are analyzed by means of energy dispersive X-ray spectroscopy. Many tunnel-like voids are observed in the stucco. Two-dimensional macroscopic-void areas observed by CT account for approximately 15 percent of the total area. Furthermore, a great many voids in micrometer-size are observed. Numerous small CaCO₃ crystals grow from the tunnel wall, and impurity content of the grown crystal is lower than that of the stucco matrix. This shows that the grown crystal is purified in the process of recrystallization. It is thought that the tunnel is formed by the dissolution of stucco constituents into water during the wet season. Then the small crystals grow by recrystallization from water containing stucco constituents during the dry season.

To enhance the mechanical properties of Mg alloys, we have fabricated Mg/TiC composites by reinforcing the Mg matrix composed of nanosize crystal grains with 20 vol% TiC nanoparticles. The Mg/TiC nanocomposites were fabricated by mechanical milling (MM) and spark plasma sintering (SPS). The TiC nanoparticles were produced by mechanical alloying (MA). The effects of the applied pressure and holding time during SPS on the mechanical properties of this nanocomposite were investigated. Microstructure observations and elemental analysis show that the TiC particles (TiC_p) in the nanocomposites have an ultrafine microstructure with an average particle size of approximately 9 nm and they aggregate within the Mg matrix. The Vickers hardness of the nanocomposites increases to 150 HV when the SPS applied pressure and holding time are increased. However, the increase in the hardness is accompanied by a decrease in the bending strength. The main factors for the improvement of the mechanical properties of the 20 vol% TiC_p/Mg nanocomposite are considered to be the density and compressive residual stress.

Mater. Trans. 59（2018） 82-87に掲載