Japanese Society of TribologistsActa Medica Okayama1881-21982042025Tribological Properties of Amorphous-SiC-Based Coatings on Al2O3 Substrates in Normal Saline212219ENTadashiShiotaFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityDaikiTaniyaGraduate School of Natural Science and Technology, Okayama UniversityKazumaShimazakiGraduate School of Natural Science and Technology, Okayama UniversityChiyuNakanoDepartment of Comprehensive Technical Solutions, Okayama UniversityYuyaOmiyaFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityMasahiroFujiiFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityAmorphous SiC (a-SiC)-based coatings containing not only Si–C bonds but also C–Si–O, C–C, and Si–O2 bonds were deposited on Al2O3 substrates via pulsed laser deposition. Sliding tests using SiC ceramic balls in normal saline revealed that the coating exhibited a low friction coefficient of 0.05-0.06 at a shorter running-in process than SiC bulk ceramic plates. The specific wear rate of the coating was also lower than that of the SiC plate. Reactive molecular dynamics simulations revealed that the C–Si–O bonds in the coating facilitated the generation of Si–O units, which contained Si–O bonds but no Si-C bonds, through tribochemical reactions with water, resulting in superior tribological properties in normal saline compared to those of SiC plates. These findings demonstrate that a-SiC-based coatings containing C–Si–O bonds are promising as low-friction and low-wear coatings for biomedical implants such as ceramic joint prostheses.No potential conflict of interest relevant to this article was reported.Japanese Society of TribologistsActa Medica Okayama1881-21982032025Water Lubrication of Polysiloxane-Containing Polyimide Coatings on Stainless Steel Substrates124129ENYuelinFanGraduate School of Environmental, Life, Natural Science and Technology, Okayama UniversityTadashiShiotaFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityYuyaOmiyaFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityMasahiroFujiiFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityThis study investigated the water-lubricated tribological properties of coatings made of a novel polysiloxane-containing polyimide (si-PI) material that was recently developed for the aerospace industry and can be diluted with the harmless and environmentally friendly ethanol or water. The si-PI coatings were deposited on stainless steel (JIS SUS304) substrates at curing temperatures ranging from 160C to 275C. Their water lubrication properties were measured by rubbing the coatings against each other in water at room temperature. The coatings exhibited lower friction than conventional polyimide materials, with a minimum friction coefficient of 0.04, which was lower than that of polytetrafluoroethylene (PTFE) measured under the same sliding conditions. Unlike the conventional polyimide, the coatings did not exhibit any obvious wear or damage. The results demonstrate that the si-PI coating is a promising low-friction and highly durable coating for water lubrication.No potential conflict of interest relevant to this article was reported.MDPIActa Medica Okayama2075-4701972019Effect of Lubrication and Forging Load on Surface Roughness, Residual Stress, and Deformation of Cold Forging Tools783ENNuwanKarunathilakaGraduate School of Natural Science and Technology, Okayama UniversityNaoyaTadaGraduate School of Natural Science and Technology, Okayama UniversityTakeshiUemoriGraduate School of Natural Science and Technology, Okayama UniversityRyotaHanamitsuGraduate School of Natural Science and Technology, Okayama UniversityMasahiroFujiiGraduate School of Natural Science and Technology, Okayama UniversityYuyaOmiyaGraduate School of Natural Science and Technology, Okayama UniversityMasahiroKawanoZeno Tech Co., LtdCold forging is a metal forming that which uses localized compressive force at room temperature. During the cold forging process, the tool is subjected to extremely high loads and abrasive wear. Lubrication plays an important role in cold forging to improve product quality and tool life by preventing direct metallic contact. Surface roughness and residual stress also greatly affects the service life of a tool. In this study, variations in surface roughness, residual stress, and specimen deformation with the number of cold forging cycles were investigated under different forging conditions. Specimens that were made of heat-treated SKH51 (59-61 HRC), a high-speed tool steel with a polished working surface, were used. The specimens were subjected to an upsetting process. Compressive residual stress, surface roughness, and specimen deformation showed a positive relationship with the number of forging cycles up to a certain limit and became almost constant in most of the forging conditions. A larger change in residual stress and surface roughness was observed at the center of the specimens in all the forging conditions. The effect of the magnitude of the forging load on the above discussed parameters is large when compared to the effect of the lubrication conditions.No potential conflict of interest relevant to this article was reported.