AlSi10Mg alloy products with a hydrogen content of approximately 3.9 or 5.6 cm³/100g-Al of hydrogen were fabricated by selective laser melting (SLM) using normal (as-received) and moist powders, and their non-reversible dimensional changes during heat treatment at 473 or 803 K were investigated. The linear dimensional change arising from the heat treatment at 473 K was approximately 0.22％ by 3.6 ks and remained constant thereafter. This behavior was independent of the amount of hydrogen in the SLM products, suggesting that the dimensional changes at 473 K were induced by precipitation of Si phase from the α-Al phase. However, the linear dimensional changes during the heat treatment at 803 K were comparatively large and continued to increase during the heat treatment. At the same time, the linear dimensional changes at 803 K also showed a dependence on the amount of hydrogen in the SLM products. These phenomena indicated that the porosity expansion and precipitation of Si phase occurred simultaneously at 803 K. For the SLM product with a hydrogen content of approximately 3.9 cm³/100g-Al, the linear dimensional change during the heat treatment at 803 K was 0.867％ at 18 ks, of which 0.116％ and 0.751％ were estimated to have been induced by the precipitation of Si phase and the porosity expansion, respectively. From gas analyses using different methods, it was elucidated that the hydrogen desorbed from the powder and was entrapped in the SLM products at the time of laser scanning, and then enriched to the porosities during the heat treatment at 803 K, causing the porosity expansion.

Mater. Trans. 64 (2023) 697-706に掲載

To improve wear resistance and adhesion, a hard film of titanium carbide (TiC) is usually prepared by a plasma chemical vapor deposition technique. Microwave sheath-voltage combination plasma (MVP) is a method to generate high-density plasma. In the present study, TiC coatings were prepared by MVP and the processing conditions were examined to reveal the effect on film deposition speed. The TiC coatings were deposited in a reactor using a TiCl₄-CH₄-H₂-Ar gas mixture. The phase identifications, binding energy analysis, coating composition, and friction coefficient were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and ball-on-disk friction tester, respectively. TiC was detected by XRD. As the flow rate of the raw material gas increased, the film deposition rate increased. The maximum deposition rate of the films was 9.0 µm/h. By changing the film deposition conditions, it is considered that higher speed film deposition of TiC will be possible.

The microstructural change and fracture by repeated gas nitriding and gas nitrocarburizing of SUS304 jig were investigated in this study. It was found that an oxide layer which was formed owing to high-temperature oxidation of the microstructure near the surface, was easily detached from the surface layer. Also, many micro voids in the oxide layer were observed. Beneath the oxide layer, a compound layer containing mainly nitrides was identified. A carbon diffusion region was observed in the matrix adjacent to the interface between the compound layer and the matrix. It was considered that the fine voids and uneven surfaces induced under loading stress during both treatments were the crack initiation points, which coalesced for the development of cracking. The fractured surface exhibits a sequence of brittle and ductile fracture patterns as the microstructure changes from the surface to the interior.