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In order to study the variation of rare earth oxides during thermal failure of thermal barrier coatings, Eu2O3-doped YSZ coatings with 0.5 mol%, 1.0 mol% and 1.5 mol% were prepared by explosive spraying. SEM, XRD, EDS and microhardness tester were used to analyze the effect of different rare earth oxide doping content on the morphology, composition and mechanical properties of the coatings. The results showed that with the increase of rare earth oxide doping content, the porosity of the coatings decreased, and the microhardness and fracture toughness increased. When the doping amount of rare earth oxide is 1.0 mol%, the bonding strength and thermal cycle times of the coating are the highest, 33.4 Mpa and 185 times respectively. With the increase of the doping amount of rare earth, the luminous intensity of the sprayed coating increases. After thermal shock test, the luminous intensity of Eu2O3-doped YSZ coatings at 592 and 608 nm decreased to a certain extent.

In order to improve the erosion resistance and toughness of thermal barrier coatings, YSZ coatings, 20 vol%-AlBOw whisker modified YSZ coatings and 20 vol%-BNw whisker modified YSZ coatings were prepared by plasma spraying. The cross-section structure, morphology, composition and phase composition of coatings and powders were analyzed by SEM, EDS and XRD. The erosion resistance of three coatings was tested by self-made erosion tester. The crack growth resistance of coatings was tested and calculated by Vickers hardness tester. The results show that the density of the coating is improved by adding AlBOw and BNw. The whisker inhibits the crack propagation through the mechanisms of crack deflection, whisker pull-out and whisker bridging. The addition of whisker improves the erosion resistance of YSZ coating by 8.17% and 13.94%, which can effectively improve the service life of thermal barrier coating.

To enhance the fracture toughness and thermal shock resistance of the thermal barrier coatings (TBCs), detonation spraying has been used to prepare modified neodymium (Ⅲ) oxide (Nd2O3)-doped yttria-stabilized zirconia (YSZ) TBCs containing 20 vol% (D1 coating) and 30 vol% (D2 coating) of boron nitride whiskers (BNws). Analyses were performed using a scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and a microhardness tester to examine the manner in which the doping content of different rare earth oxides affected the coating morphology, composition, and mechanical properties. The results denoted that the porosity of the D2 coating was 47.9% higher than that of the D1 coating; the whisker content was 30 vol% in the former and 20 vol% in the latter. The increased porosity reduced the microhardness and bond strength of the coating. However, the fracture toughness (KIC) of the D2 coating was increased to 2.67 MPa·m1/2 because the whisker content was 8.5% higher than that in the D1 coating. The thermal cycling life of the D2 coating was 245 cycles, and its thermal shock resistance was 9.9% higher when compared with that of the D1 coating. A TBC with better overall performance was obtained when BNw reached 30 vol%.

In the conversion coatings, some uniformly distributed micro surface cracks always occur but the surface cracks behavior is rarely studied due to the frequent initiation in the real test conditions. In this work, computer simulation of micro surface cracks behavior and internal stresses generated in the anhydrous chemical conversion coating was carried out using the finite element method with the help of ABAQUS software. The Mises stress distribution, S11 stress variation, and the stress-time curves were obtained. The results show that the internal stresses generated in the conversion coating increase obviously with increasing time, and the stresses at the center and boundary of coating pieces are bigger than the ones in other areas while the S11 stresses around the center are bigger than the ones near the boundary. The cracks at the interface of coating pieces develop gradually and are as V-type cracks finally. The width of crack mouth opened is different since the contraction degree of each coating piece is different.

An experimental study and computer simulation on non-equilibrium grain-boundary segregation kinetics and the critical time for phosphorus in 12 CrlMoV steel (which is used in steam pipeline of ships) are put forward in this paper. The segregation level of phosphorus with solution temperature 1050°C at the isothermal holding temperature of 540°C, have been measured at grain-boundaries. A non-equilibrium grain-boundary segregation kinetics curve of phosphorus is given. The critical time for phosphorus non-equilibrium grain-boundary segregation is about 500 h at 540°C for the experimental steel. When the holding time is longer than 1500 h, non-equilibrium segregation disappears and the level of segregation reaches full equilibrium. The simulation using the kinetic equations of non-equilibrium grain-boundary segregation is in good accordance with the experimental observation for phosphorus in steel 12Cr1MoV. The non-equilibrium grain-boundary segregation kinetic model is therefore proved.

The non-equilibrium grain boundary segregation (NGS) concentrations of phosphorus in an industrial steel, 12Cr1MoV, at different solution temperatures, 1050 and 1300°C, were measured. The NGS kinetics curves of phosphorus at the isothermal holding temperature of 540°C are given. These results provide direct support for a NGS kinetic model, and also show that the higher the solution temperature, the higher the segregation concentration of phosphorus at the grain-boundaries, and also the longer the critical time.