Binder jetting (BJT) holds enormous promise as an additive manufacturing technique due to its high throughput and low-cost equipment. The ability to fabricate geometrically complex parts from aluminum alloy via BJT would have a significant impact on the development of high-performance machine components and heat-dissipation devices. However, processing printed objects by sintering of aluminum alloy is difficult due to the surface oxide layer that covers the powder particles, which prevents the final parts from reaching a sufficiently high density. In order to investigate the sintering mechanism for controlling the quality of sintered parts, we directly observed the sintering behavior of pure Al and Al-10%Si-0.4%Mg (mass%) alloy using an in situ scanning electron microscopy system equipped with a heating stage. It is found that the surface roughness of the powder particles is reduced above their melting or solidus temperature. Subsequently, the liquid ruptures the oxide layer and forms necks between the particles.

In recent years, materials infomatics (MI), a technology that combines materials engineering and machine learning, has become popular and is used for discovering new materials. In this research, we aimed to verify whether MI can be applied to the problem of “development and maintenance of technology,” which is becoming more difficult due to the decrease in the number of engineers caused by the declining birthrate and aging population in Japan. We selected “discrimination of optical electron microscope images” as the verification target, and used Convolutional Neural Networks (CNNs) as the machine learning technology to discriminate between seven types of sintered metal objects under different sintering conditions, hoping for general applicability to the discrimination problem, and confirmed a discrimination accuracy of 98.5%. In addition, we verified the effectiveness of using pseudo-samples for the discrimination problem using Generative Adversarial Networks (GANs) in the hope of improving accuracy by increasing the number of samples, and confirmed the improvement of accuracy by adding pseudo-samples to the training data.

Silicon carbide (SiC) powders have been synthesized by microwave-heating of mixtures of silicon (Si) and graphite (C) powders embedded in graphite powder (susceptor). The influence of the mixing composition of these powders on the SiC formation has been investigated. For 1-min heating, the products qualitatively followed the rules of the Si-C phase diagram, depending on the Si/C mixing ratio. For heating periods of 10 min or longer, however, almost single-phase β-SiC powders have been obtained irrespective of the Si/C mixing ratio, not being in accordance with the phase diagram. This result suggests that the initial mixing ratio was not retained during the carbonization for long heating periods. A comparative experiment using an electrical furnace, providing thermally equilibrium heating, also confirmed the rapid carbonization of solid Si at 1673 K in a carbon monoxide (CO) atmosphere. These results suggest that the carbonization occurs mainly via solid-state reaction among the neighboring Si/C particles for an early stage of the heating period, followed by the gas-solid reaction between CO gas and solid silicon for the subsequent heating period. The latter mechanism contributes to the carbonization independent of the Si/C mixing ratio and the long-distance mass transfer of extra carbon from the susceptor.

WC-Ni composite hard coatings were prepared by the complex method consist of wet plating and gas carburizing. The coatings conducted only gas carburizing after wet plating indicated that the microstructure composed of random-oriented fine needle like WC crystal surrounded by Ni matrix. Whereas the coatings conducted both reduction heat treatment and gas carburizing after wet plating showed that the microstructure composed of specific-oriented columnar WC crystal surrounded by Ni matrix. This fact suggested that the changing of fabrication procedure of the coatings, which occurred difference of WC crystal formation process, was able to control microstructure of the coatings. The coatings conducted both reduction heat treatment and gas carburizing after wet plating also demonstrated that the significant improvement of its mechanical properties compared to the coatings conducted only gas carburizing after wet plating.