To evaluate the influence of hybrid surface modification processing on the rolling contact fatigue life, we used a roller pitting test comprising a combination of high strengthening by Super Rapid Induction heating and Quenching (SRIQ) and improvement of the tribological quality by a Diamond Like Carbon (DLC) membrane. The applicability of the process to a small gear was examined. Results show that the rolling contact fatigue life of the SRIQ+DLC specimen was longer than that of SRIQ specimen at all loads. Subsequent SEM observation of fractures showed that many micro-surface cracks and pittings along with pitting caused fracturing of the SRIQ specimen. However, the SRIQ+DLC specimen showed few micro-surface cracks aside from the pitting causing fracture. Many internal cracks were found. Based on these results, we infer that improvement of the rolling contact fatigue life is introduced by retarding of the generation of surface damage attributable to the decrease of tangential stress brought by superior low friction and excellent wear resistance of the DLC membrane. Therefore, SRIQ+DLC compound surface modification, which improves tribological and fatigue properties, is suggested as effective for improving rolling contact fatigue life. Regarding SRIQ, it is possible also for the discharge of carbon dioxide to produce a substantial decrease in comparison to other heat treatment processes. It can contribute also to protection of the terrestrial environment. It might be said that a new hybrid surface modification process has been produced.
In order to evaluate the cracking strength of a gas nitrided layer on a tool steel substrate, four-point bending tests were performed on two specimens nitrided by different companies. The results showed that cracks were introduced in a direction perpendicular to the loading direction after the beginning of plastic deformation of the substrate. In addition, the number of cracks increased with increasing bending load. Nanoindentation tests of the nitrided layer revealed that the indentation hardness and modulus increased as a result of nitriding. Moreover, both the indentation hardness and modulus remained nearly constant throughout the compound layer but decreased gradually with increasing distance from the surface in the diffusion layer. The cracking strength of the compound layer was evaluated by extrapolating the cracking strain from the crack interval-strain relationship obtained from the four-point bending tests.
Single-crystalline diamond or a sintered diamond cutting tools are used for precision processing and for difficult processing materials because diamond is the hardest known material. Nevertheless, natural and synthesized diamonds are so expensive that their industrial applications are limited. Diamond films can be synthesized inexpensively using chemical vapor deposition (CVD), but synthesized diamond film has a rugged surface and a dull cutting edge, causing severe problems when used as a cutting tool. As described in this paper, the cutting edge of a diamond-coated cutting tool was reshaped to a sharpened form using electric discharge machining. To do so, the hot-filament CVD diamond film was made electrically conductive by doping with boron. The performance of this cutting tool was investigated using wood processing. Results show that the diamond-coated cutting tool prepared in this study was superior to a normal diamond-coated one in terms of cutting power consumption.
Fluid flow around an n-butyl acetate / aqueous ZnSO4 interface was visualized using Schlieren method and Mach-Zehnder interferometry during Zn electrodeposition. Results showed that fluid flows were introduced into both the organic liquid and the electrolyte solution after applying potential. The fluid flow observed in the organic liquid was considered to be attributable to the temperature increase by Joule heating at the growth front during Zn electrodeposition. However, the fluid flow observed in the electrolyte solution was considered to be attributable to electro-osmotic flow and Marangoni convection. We speculated that the vigorous fluid flow attributable to electro-osmotic flow and Marangoni convection in the electrolyte solution can enhance Zn2+ transportation to the growth front of Zn deposits, producing rapid and preferential growth along the liquid-liquid interface.