On developing a graphitic white iron for metal-to-metal wear systems

This research addressed heat dissipation issues related to the adhesive wear observed in metal-to-metal wear systems, by developing a graphitic white iron to increase thermal diffusivity of the wear components. One of the premium materials commonly used in current metal-to-metal wear systems is Fe15Mo18Cr and field returned parts were characterized as part of this study. Failure analysis showed that white layers were formed on the wearing surface due to frictional heating and surface deformation. These white layers were extremely brittle and could be fractured easily during use, which in turn led to micro-galling defects that caused parts leakage. Increasing thermal diffusivity of the material was recommended to improve the performance of wear components. A new alloy, graphitic white iron, was developed for metal-to-metal wear systems by introducing 3.2-9.6 vol.% graphite flakes into white irons, to increase thermal diffusivity and reduce friction and frictional heating. Graphite volume percent was quantitatively investigated. It turned out that, at 200 °C, thermal diffusivity increased by ~114% with increasing graphite to 7.6 vol.%. Abrasive and adhesive wear resistance was measured by dry sand/rubber wheel test and block on ring test, respectively. Empirical models were established to predict graphite volume percent for any given composition, and a Hashin-Shtrikman model was used to predict the thermal diffusivity of the multiphase alloy. Abrasive and adhesive wear resistance was found to depend upon composite hardness and graphite volume percent. It was found that 1 vol.% graphite was equivalent to an increase of 2.33 HRC and 2.66 HRC in composite hardness with respect to abrasive wear resistance and adhesive wear resistance, respectively”--Abstract, page iv

Cosmological constraints from Radial Baryon Acoustic Oscillation measurements and Observational Hubble data

We use the Radial Baryon Acoustic Oscillation (RBAO) measurements, distant type Ia supernovae (SNe Ia), the observational $H(z)$ data (OHD) and the Cosmic Microwave Background (CMB) shift parameter data to constrain cosmological parameters of $\Lambda$CDM and XCDM cosmologies and further examine the role of OHD and SNe Ia data in cosmological constraints. We marginalize the likelihood function over $h$ by integrating the probability density $P\propto e^{-\chi^{2}/2}$ to obtain the best fitting results and the confidence regions in the $\Omega_{m}-\Omega_{\Lambda}$ plane.With the combination analysis for both of the {\rm $\Lambda$}CDM and XCDM models, we find that the confidence regions of 68.3%, 95.4% and 99.7% levels using OHD+RBAO+CMB data are in good agreement with that of SNe Ia+RBAO+CMB data which is consistent with the result of Lin et al's work. With more data of OHD, we can probably constrain the cosmological parameters using OHD data instead of SNe Ia data in the future.Comment: 8 pages, 6 figures, 2 tables, accepted for publication in Physics Letters