The mechanism of oxide inclusions in fatigue crack initiation in the very-high cycle fatigue (VHCF) regime was clarified by subjecting bearing steels deoxidized by Al (Al-deoxidized steel) and Si (Si-deoxidized steel) to ultrasonic tension-compression fatigue tests (stress ratio, R = −1) and analyzing the characteristics of the detected inclusions. Results show that the main types of inclusions in Si-and Al-deoxidized steels are silicate and calcium aluminate, respectively. The content of calcium aluminate inclusions larger than 15 µm in Si-deoxidized steel is lower than that in Al-deoxidized steel, and the difference observed may be attributed to different inclusion generation processes during melting. Despite differences in their cleanliness and total oxygen contents, the Si-and Al-deoxidized steels show similar VHCF lives. The factors causing fatigue failure in these steels reveal distinct differences. Calcium aluminate inclusions are responsible for the cracks in Al-deoxidized steel. By comparison, most fatigue cracks in Si-deoxidized steel are triggered by the inhomogeneity of a steel matrix, which indicates that the damage mechanisms of the steel matrix can be a critical issue for this type of steel. A minor portion of the cracks in Si-deoxidized steel could be attributed to different types of inclusions. The mechanisms of fatigue fracture caused by calcium aluminate and silicate inclusions were further analyzed. Calcium aluminate inclusions first separate from the steel matrix and then trigger crack generation. Silicate inclusions and the steel matrix are closely combined in a fatigue process; thus, these inclusions have mild effects on the fatigue life of bearing steels. Si/Mn deoxidation is an effective method to produce high-quality bearing steel with a long fatigue life and good liquid steel fluidity.

In this paper, aramid fiber (AF)/ethylene‐propylene‐diene monomer (EPDM) microcellular foams added with different content of AF are prepared by the supercritical foaming method. The effect of the AF content on the rheological behavior, mechanical properties, thermal properties and cellular structure of the AF/EPDM microcellular foams has been systematically studied. The research illustrates that compared with pure EPDM, the AF/EPDM matrix has greater viscosity and modulus, which is conducive to reduce the cell size and increase its density. And the thermal stability of EPDM foams is improved with the addition of aramid fiber. Meanwhile, when the content of AF is added to 1 wt%, the AF/EPDM microcellular foam exhibits a relatively low thermal diffusion coefficient and apparent density with the thermal conductivity to 0.06 W/mK. When the AF is added to 5 wt%, the tensile strength of the AF/EPDM microcellular foam increases to 1.95 MPa, which is improved by 47% compared with that of the pure EPDM foam. Furthermore, when the compressive strain reaches to 50%, the compressive strength of the AF/EPDM microcellular foam is 0.48 MPa, improved by 296% compared with that of the pure EPDM foam.

The CaO‐MgO‐Al2O3‐SiO2 (CMAS) corrosion of thermal barrier coatings (TBCs) is a crucial problem for the lifetime of blades and vanes of jet engine and gas turbine at high operating temperature. Although many new alternative materials for TBCs have been developed in recent years, their application is limited by the CMAS corrosion. On the other hand, the composition difference of CMAS between regions makes solving this problem very difficult. Therefore, in this study, the yearly composition changes of sand‐dust around Beijing area were investigated. The high‐temperature corrosion behavior of air‐plasma‐sprayed 8YSZ and newly developed (LaxYb1−x)2Zr2O7 TBCs by the representative sand‐dust of Beijing was investigated. In comparison, a universally used CaO‐riched composition of simulated silicate deposit was also adopted for the TBCs corrosion test. It is found that the (LaxYb1−x)2Zr2O7 TBCs performs much better anti‐corrosion behavior than that of 8YSZ, both by Beijing sand‐dust and simulated one. Particularly, Yb2Zr2O7 TBCs appear to be the optimum material against silicate deposits attack. The mechanism of silicate deposits corrosion has also been discussed.