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Based on the wear resistance application scenarios of the heat surface tubes, fans and other components of popwer station boiler, coatings were prepared on the substrate 20G steel by high velocity arc - spraying technology with the application of two kinds of FeCr - based coating materials containing different carbon and rare earth element contents. Subsequently, the microscopic morphology and phase composition of the coatings were characterized through optical microscope (OM), scanning electron microscope (SEM), X - ray diffractometer (XRD) and white light interferometer system, and the mechanical and wear resistance properties of the coatings were tested through Vickers microhardness, tensile bonding strength, ball - disk friction and wear tests. Results showed that the microstructure of these two coatings was a typical lamellar structure. As B, C and other hard phase elements were distributed in FeCr solid solution, the microhardness of the coatings was much higher than that of the substrate. Furthermore, the high carbon content and the addition of rare earth elements contributed to a decrease of the porosity of the coatings from 2.22±0.47% to 0.92±0.13%, an increase of the microhardness from 8.05±0.53 GPa to 10.47±0.68 GPa, and a reduction of the wear weight loss by 40%. Judging from the wear morphology of the coatings, high microhardness and low porosity made the wear mechanism changed from adhesive wear to abrasive wear. In general, applying FeCr - based coatings to protect the wear surfaces could effectively solve the wear problem of the boiler parts of the power station, and thus ensure the safe and stable operation of the boiler units.

The large scale construction of both military and civil infrastructures located in Nansha reefs and offshore marine areas, South China Sea, has raised the seismic safety a challenging issue for the projects in the region. The influences of fines content (FC) on the liquefaction characteristics of saturated terrestrial quartz sands have been extensively studied, but the corresponding research on saturated coral sands in reclaimed coral islands is less involved. Using the GDS hollow cylinder torsion shear apparatus, a series of isotropically consolidated undrained cyclic tests have been performed on saturated coral sand sampled from the Nansha Islands, South China Sea. The samples are prescribed with the stress path formed under the 90° jump rotation of principal stress with various cyclic loading directions. The influences of the inclination angle (αd) of the major principal stress and fines content FC on the liquefaction characteristics of saturated coral sand are investigated. It has been discovered that, regarding the zero effective stress state as initial liquefaction criterion, the liquefaction resistance of saturated coral sand decreases with the increase of αd for 0°≤αd≤45° and FC for 0%≤FC≤30%. The correlation among the generalized shear strain amplitude (γga), the fines content FC, and the revolution of residual excess pore water pressure of saturated coral soil has been clearified. By introducing a unit cyclic stress ratio USR as a new index for liquefaction resistance and based on binary medium theory, the expression between the unit cyclic stress ratio USR15, inducing initial liquefaction in 15 cycles, and the equivalent skeleton void ratio e*sk for the saturated sands is established for the test. The theory is validated by the experimental data in the literature.

The physical and engineering mechanical behaviors between coral sand and terrigenous sandy soils are considerably different. To study these behaviours, a series of undrained multistage strain-controlled cyclic triaxial tests were conducted on saturated coral sand from Nansha Islands, South China Sea. The influence of effective confining pressure 0 p and relative density Dr on the dynamic shear modulus and damping ratio of coral sand was studied. Compared with the test results of coral sand and terrigenous sandy soil and gravel, significant differences were found in the maximum shear modulus Gmax, the shapes and the upper and lower boundaries of shear modulus ratio G/Gmax curves, reference shear strains 0  , the shapes and the upper and lower boundaries of damping ratio  curves. The maximum shear modulus Gmax of coral sand is higher than that of terrigenous sandy soil and gravel, and the Gmax of coral sand predicted by empirical equations of terrigenous sandy soil is underestimated by 30%. The nonlinearity of coral sand is slightly weaker than that of terrigenous sandy soil and gravel. The empirical formulas for predicting G/Gmax and  of terrigenous sandy soil and gravel are not applicable for Nansha coral sand. The empirical formulas for predicting G/Gmax and  of coral sand are proposed.