In this study, Ti-Zr-Sc sintered alloys with excellent biocompatibility were fabricated from the elemental mixture of pure Ti, ZrH₂ and ScH₂ powders, and their microstructures and mechanical properties were investigated to clarify the strengthening mechanism. In particular, the effect of scandium (Sc) used as the third alloying element on the strengthening behavior by grain refinement, oxygen (O) and Sc solid solution, and Sc₂O₃ particle dispersion was quantitatively evaluated by using the theoretical strengthening models. 0.2% YS of Ti-Zr-Sc alloys decreased with Sc content in the range of 0∼1.0 at.% Sc, and increased in the range of 1.0∼2.5 at.% Sc. In the former, the added Sc elements reacted with O solutes to form Sc₂O₃ particles and resulted in a significant decrease of O solid solution strengthening effect. On the other hand, when Sc content was over 1.0 at.%, the strengthening effects by both Sc solid solution and Sc₂O₃ dispersion were effective, and cause a remarkable increment of 0.2% YS of Ti-Zr-Sc sintered alloys.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 482–491, https://doi.org/10.2497/jjspm.23-00067. The citation in reference 35 is corrected.

In this study, nanostructure formation and age-hardening behavior of an Al-6Zn-0.75Mg alloy were investigated by varying cooling conditions during solution heat treatment. For the sample furnace-cooled from 723 K to around 303 K, the hardness after cooling was higher than the hardness after quenching of the WQ sample, and the maximum hardness was equivalent to that of the WQ sample. On the other hand, samples taken out of the furnace at around 373 K during furnace cooling showed a slower hardening rate and a relatively lower maximum hardness. Microstructure observations at as quenched (A.Q.) and as cooled (A.C.) state showed nanostructures in the FC-303 K sample that were considered to have formed during furnace cooling, which is consistent with the structure reported as GP(I) with TCO structure. Clusters and GP zones formed during furnace cooling tend to form at temperatures below 373 K, suggesting that they contribute to age hardening.

This Paper was Originally Published in Japanese in J. JILM 75 (2025) 74–82. The abstract is slightly modified. The citation in reference 13 is corrected.

In metastable β titanium alloys, superelasticity induced by martensitic transformation can be achieved by lowering the phase stability of the β phase. However, reducing the stability of the β phase also promotes the formation of the isothermal ω phase, which suppresses martensitic transformation and leads to embrittlement. The addition of Sn and Al effectively inhibits the formation of the isothermal ω phase; however, these elements also promote the formation of the isothermal α′′ phase in β-type titanium alloys. In this study, we conducted aging heat treatment on two Ti-Cr-Sn alloys exhibiting superelasticity at room temperature and investigated the resulting aging products and mechanical properties. In alloys with low Sn concentrations, aging at low temperatures led to the formation of the isothermal ω phase, whereas in alloys with high Sn concentrations, the isothermal α′′ phase formed instead of the isothermal ω phase. Both alloys in which the isothermal ω phase formed and those in which the isothermal α′′ phase formed exhibited a loss of superelasticity and significant embrittlement.

In this study, α-Ti alloys with supersaturated iron (Fe) elements were fabricated by laser powder bed fusion, and their microstructures and mechanical properties were investigated to clarify the strengthening mechanism. The formation of β-Ti was not confirmed in the LPBF prepared Ti-Fe alloy, and Fe was solid soluted in the α-Ti grain. With solid solution of Fe, the α-Ti grain became fine, and the width of α-Ti lath was 530 nm with solid solution of 2 wt% Fe. 0.2% YS of LPBF Ti-Fe alloys increased with solid solution of Fe while maintaining a high elongation at break. The tensile strength of the Ti-2 wt% Fe alloy increased by 600 MPa compared to Ti-0 wt% Fe. The strengthening mechanism of LPBF Ti-Fe alloys was quantitatively clarified as Fe solid solution strengthening and grain refinement strengthening.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy, Advanced Publication by J-STAGE, https://doi.org/10.2497/jjspm.23-00068. The main text is slightly modified. The citation in Table 2 is corrected.

Fractographic analysis of fracture surfaces helps to improve the performance of mechanical pieces. In order to determine the causes that generated the fracture, it is necessary to classify a fracture into a failure mode. Experts in fractographic classification use visual evidence of textures and surface marks to determine the failure classification. The fractographic images for this task are obtained using a Scanning Election Microscope (SEM). With new advances in machine learning and artificial intelligence, specifically with deep learning and Convolution Neural Networks (CNN) becoming accessible, it is becoming possible to automate fractographic classification. This study aimed to improve the accuracy of fractographic classification using CNN by considering the material types. We proposed a Stepwise Selection of Source Classes (SSSC) to perform transfer learning considering the material types. The proposed method was applied to classifying fractographic SEM images into seven groups of fracture surfaces in alloy steels, austenitic stainless steels, and copper and copper alloys. The existing method, which does not distinguish the material types, achieved an average accuracy of 92.4%, while the proposed method improved the average accuracy to 98.7%.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 72 (2023) 376–383.

The assessment of residual stress in rolled and hydrogenated multiphase Nb-TiNi alloys is important because such materials consist of B2-TiNi and bcc-Nb phases having different mechanical properties. The present work demonstrates that residual stress in cold-rolled and heat treated Nb₁₉Ti₄₀Ni₄₁ (mol%) alloys can be determined using the cos α method, and investigates factors affecting residual stress in hydrogenated and dehydrogenated Nb₁₉Ti₄₀Ni₄₁ alloys. The stress in the sample which was cold rolled and annealed at 1373 K followed by furnace cooling is very low. However, compressive stress was observed in both the Nb and TiNi phases after hydrogenation and dehydrogenation cycling due to the different lattice expansions of the two phases. Variations in total stress and macrostress were found to correlate with the volume change of the Nb phase while variations in pseudo-macro stress were associated with changes in the mechanical properties of this phase.

In this study, the relationships of the microstructures, the hardness distributions and the residual stress distributions with the laser scanning patterns were systematically investigated for a martensitic stainless steel SUS420J2 fabricated by laser powder bed fusion (AM material). The microstructures of the AM materials were consisted of mainly the needle-shaped α′ phase, with the retained γ phase and the fine cementite particles. There was the Kurdjumov-Sachs relationship between the (011) plane of the α′ phase and the (111) plane of the retained γ phase. The hardness of the AM materials was higher than that of the wrought material which was quenched and tempered. All AM materials had similar hardness since there were no significant differences in their microstructures, even though the scanning patterns were different. It was experimentally shown that the residual stresses of the AM materials can be reduced by changing the laser scanning patterns. Especially, the residual stress value was reduced by 75% using the chessboard-type scanning pattern with the alternating scanning directions and shifting the pattern.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 73 (2024) 743–750.

The relationship between pouring temperature and carburized microstructure of 1%Nb-added SCH13A heat-resistant cast steel manufactured by the self-hardening mold casting process at pouring temperatures of 1753 K, 1823 K and 1883 K was investigated. The creep properties of these materials subjected to repeated carburizing and quenching treatment were also examined. As a result, with increasing pouring temperature, the carburized depth decreases and the carbon concentration distribution in the carburized layer increases. A relative comparison of the creep properties revealed that the volume of primary carbides and the number of voids and micro-cracks in carbides generated due to repeated vacuum carburizing quenching treatment affects the creep rupture time. Creep rupture time of the carburized samples is shorter than that of the as-cast samples. Additionally, pouring at 1823 K exhibits the longest rupture time among the samples poured at the three different temperatures.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 269–278.

Bonding of aluminum alloys and steel is of immense interest to different applications. In this study, we aim to determine the optimal conditions for diffusion bonding of Hardox 400 steel with Aluminum Alloy AA7020 using tin as the interlayer. Three loads: 150, 250 and 350 N, four temperatures: 400, 450, 500 and 550°C, and three times: 2, 4 and 6 hr were used. The optimal case for these conditions was evaluated using the double shear test, where it appeared that temperature and applied load have an important role in determining the shear stress, while time has a minor effect. The temperature of 550°C and the load of 350 N gave the best results at a time of 4 hr. To investigate the effect of the type of interlayer, steel and copper were used for this purpose under the optimal welding conditions, and the results revealed that the shear stress was low for both of them compared to tin, which appeared to be the best. To evaluate the effect of temperature at the constant load of 350 N and time 4 hr using tin as interlayer, microscopic examination, micro-hardness test and wear test were adopted. The results show that the increasing of process temperature led to improve the mechanical properties of joint and corrosion resistance due to more diffusion of atoms and Interfacial Transition Zone (ITZ) layer would be more thickened.

Green sand molding is a casting method that uses bentonite as a binder and is the most widely used technique for producing cast products. Green sand molding uses a green sand mold as the main mold while incorporating various other molds, such as shell or cold box molds for the core. When the core is heated by molten metal, it disintegrates into sand and mixes with green sand. The addition of cores increases the total sand volume, leading to overflow beyond the casting line capacity, and resulting in waste sand. This waste sand is subsequently reclaimed and processed into reusable reclaimed sand. Integrating the reclaimed sand into core production can establish a sustainable recycling system within the casting industry. Two primary methods for regenerating waste sand are thermal-mechanical and mechanical reclamations. Thermal-mechanical reclamation is more suitable for shell mold, whereas mechanical reclamation is more suitable for cold box mold. This distinction has led to a confusion in the application of reclaimed sand and has hindered the development of a circular recycling system. Furthermore, the underlying cause of this difference remains unclear.

This study considers residual bentonite in reclaimed sand as a critical factor contributing to the observed discrepancies in the mold performance. In shell mold, the residual bentonite causes a considerable degradation of the shell mold strength. This strength degradation is attributed to an intercalation reaction between the shell mold binder (guest) and bentonite (host). In cold box mold, bentonite residue does not cause a notable deterioration of the mold strength. In this case, the intercalation reaction is observed to a very limited extent and is not as pronounced as in shell mold. By applying the results of this study to the reclamation method, a reclamation line that facilitates a circular recycling structure can be established.

Hot-extruded AZX611Mg alloy was multi-directionally forged under decreasing-temperature conditions (dMDFed) and followed by room-temperature MDFing (rMDFing). Coarse initial grains were gradually fragmented by dynamic recrystallization during dMDFing and ultrafine-grained structure was homogeneously developed over the cumulative strain of ΣΔε = 4.8. Additional rMDFing contributed to further grain fragmentation due to kinking and mechanical twinning. Nevertheless, coarse precipitates in the as-hot-extruded samples and newly formed fine precipitates during dMDFing impeded twinning. The achieved grain size appeared rather larger than that of the dMDFed AZ61Mg alloy. While mechanical properties were drastically improved by simple dMDFing or rMDFing, the combined processes of dMDFing and rMDFing were not so effective to induce additional strengthening. This was attributed to complicatedly combined effects of impediment of twinning by precipitates to grain fragmentation and fracture caused by stress concentration at around precipitates/matrices.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 88 (2024) 119–127.

High-strength joints used in timber structures are increasing to utilize the shear properties of wood. Thus, it is important to understand the long-term shear performance. Therefore, we proposed the tensile shear testing method to investigate the long-term shear performance of wood. This testing method is to apply stabilized axial load for a long-term and to be able to measure the shear deformation. In order to evaluate the method, the results were compared with results of JIS block shear test. As a result, the mean value of shear strength in the proposed method was 30% lower than the block shear test. The reason for the small results of the proposed method is that the specimen has two shear face and breaks at the weak side, and the shear face is affected by rotation due to the tensile deformation of the perpendicular to grain direction. Therefore, the coefficient of variation of 6.8% in the proposed method shows smaller than 11.1% in the block shear test. And the shear strength value of the proposed method was little bit higher than one of the four-point-bending type shear test methods, and all specimens were shown the shear failure. Based on these results, the proposed method was judged to be useful as a shear test method.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 72 (2023) 737–742. The reference list is corrected.

Although magnesium and magnesium alloys are known as biodegradable medical metals with proper mechanical properties and bio-compatibility, the rapid degradation rate limits their clinical applications. In this paper, Fe₇₈Si₉B₁₃ amorphous coatings were prepared on the surface of ZK60A magnesium alloy by using the cold gas dynamic spraying (CGDS) technology. Microstructure, mechanical properties, corrosion resistance, and the degradation behavior of the coatings were investigated. Results show that the coating prepared at 5 MPa and 1073 K has the maximum coating thickness, the lowest porosity, the highest microhardness and contact angle, the most positive corrosion potential, the smallest corrosion current density, and a relatively high volume fraction of amorphous phase. Immersion corrosion experiments show that the degradation rate of the optimal coating is 0.15 mm/a, meeting the requirement of the bone implant material. Degradation behavior analysis shows that bone-like apatite nucleates and rapidly grows into bone-like hydroxyapatite when the sample is immersed in simulated body fluids solution for several days, demonstrating strong biological activity and osteoinductivity of the coating. Furthermore, although pits occurred, electrochemical impedance spectra shows that the coating still keeps a good corrosion resistance immersed in SBF for 15 days.

Geopolymers are attracting attention as an environmentally friendly alternative to cement. In this study, compressive strength tests were conducted on geopolymer pastes using fly ash and blast furnace slag as active fillers. Sodium hydroxide solution and sodium silicate were used as alkaline activators. Raman spectroscopy was also employed to investigate its potential for analyzing Ca-enriched geopolymers. These results indicated that calcium aluminosilicate hydrate was formed by 7-day in the environment containing a certain amount of soluble Si in NaOH solution. This was reinforced by the formation of magnesium aluminosilicate hydrate and sodium aluminosilicate hydrate by 28-day, which may contribute to higher compressive strength. Moreover, the coexistence of high-polymerized silicates and relatively low-polymerized silicates is thought to enhance the physical entanglement of the silicates and to increase the compressive strength. These findings suggest that Raman spectroscopy is a useful tool for microstructural analysis of Ca-enriched geopolymers.

This study presents the synthesis and characterization of CeO₂ particles using tea residue extract as a phytomediated approach. The synthesized CeO₂ sample was conducted to test its application in the catalytic combustion of diesel soot. The thermal behavior of the as-prepared sample was evaluated by TGA/DTG. Two main weight-loss steps were identified due to the evaporation of adsorbed water and the elimination of residual organic materials. The XRD pattern showed high-intensity peaks consistent with the fluorite-type structure of CeO₂ (JCPDS 34-0394) and a crystallite size was determined to be 9.51 ± 0.06 nm. Raman spectroscopy provided the main F_2g mode at 463 cm⁻¹ with a defect-induced mode at 600 cm⁻¹, confirming the Ce-O₈ vibration and tetrahedral symmetry. A signal of EPR spectra (g = 2.003) at room temperature indicated the presence of oxygen vacancy in the sample. XPS investigation further confirmed the coexistence of Ce⁴⁺ and Ce³⁺ ions and the oxygen vacancies presence on the synthesized CeO₂ samples, demonstrating the oxygen vacancies presence and Ce³⁺ species, which are crucial for catalytic activity. The synthesized CeO₂ exhibited superior soot catalytic combustion performance in the tight contact operation, with T₅₀ and T₉₀ at 440°C and 485°C, respectively. The higher catalytic activity was contributed to the larger surface area and higher concentration of oxygen vacancies. Activation energy analysis revealed lower energy barriers for soot conversion with the synthesized CeO₂ compared to commercial and direct combustion (DC) samples, highlighting its potential for diesel soot control applications.