In order to elucidate the action mechanism of environmentally benign lubricant additives on Fe-Cr-Ni alloys, tribological tests using a sulfur-containing extreme pressure additive (polysulfide) and various compositions of Fe-Cr-Ni alloy materials under boundary lubrication regime were carried out, and then their surfaces were analyzed quantitatively by means of X-ray photoelectron spectroscopy (XPS). The results exhibited that a boundary lubrication film comprising of iron sulfide (FeS or FeS2) was formed on the materials containing low Cr or Ni, whereas that of nickel sulfide (mainly NiS) was formed on the materials containing high Cr or Ni. A relatively thick oxide layer was detected beneath the boundary lubrication film, which indicates that oxidation most likely due to dissolved oxygen in the lubricant also occurs in conjunction with sulfuring under the boundary lubrication condition. Nickel sulfide showed lower hardness compared to iron sulfide, which may be the main cause of the high friction and adhesion during the friction test in the case of high Cr or Ni alloy.
This paper describes the effect of surrounding temperature on the behavior of cavitation formed in lubrication film. Point contact sliding tests were conducted in the vacuum chamber in which surrounding temperature and gas were controlled. Temperatures used in this study were in the range between 295 K and 350 K, and gases used were helium, argon, carbon dioxide and air. Two stage cavity growths, i.e. initial stage and second stage as reported in previous report, was found at elevated temperature. Although cavity length was not changed by temperature at initial time after its generation, the cavity length at higher temperature was longer than that at lower temperature in the second stage. Cavity growth in the second stage is affected by gas solubility; cavity length in temperature with higher gas solubility is longer. These results suggest that cavity growth in initial stage is related with rapid evolution of negative pressure at outlet of conjunction and that in second stage is related with gradual release of dissolved gas into cavity.
The purpose of this paper is to discuss the mechanism of wear phenomena about the diamond-like carbon (DLC) film due to the molybdenum dithio carbamate (Mo-DTC) by confirming the friction and wear properties between DLC films and the mating member with different oil adsorption properties under engine oil environment. Therefore, we prepared some DLC films produced by changing the feed gas composition using plasma CVD method, and selected iron and aluminum as mating member of DLC films because the oil-adsorbed ability were different. And we evaluated friction and wear properties using reciprocation tribometer. As a result, we found that the wear of the DLC film due to the Mo-DTC does not occur in the case of aluminum. We conducted a surface analysis by XPS to analyze the mechanism of DLC wear due to Mo-DTC. The results showed that the product ratio of MoO3 in the case of aluminum is small as compared with the case of the iron.
In this report, a procedure for significance test of rolling contact fatigue (RCF) life estimated by Weibull plots is introduced. This procedure generates results using random numbers followed by Weibull distribution (i.e. Weibull random number). The results can provide a relationship between the given number of test specimens and resultant significant differences at L10, L50 and L63.2 in RCF life test. This relationship is required to perform a significance test based on statistical logic. In addition, the relationship can apply to an estimation of the appropriate number of test specimen. In order to obtain the relationship without calculations by using Weibull random numbers, approximation equations are derived from a regression analysis for the significant differences calculated by using Weibull random numbers. The significance test using the approximation equations provides techniques that are easier to understand as compared with the general mathematical model, and they show enough flexibility to apply to several conditions for an arbitrary confidence level and different Weibull slopes. This new system will therefore eliminate the need for qualified experiences related to the statistical design and result interpretation for RCF life test.