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To study the impact of rare earth oxide doping on the thermal failure of thermal barrier coatings, 0.5 mol%, 1.0 mol% and 1.5 mol% Nd2O3-doped YSZ coatings were prepared by explosive spraying. SEM, XRD, EDS and microhardness testing were used to analyse the effect of different rare earth oxide doping contents on the morphology, composition and mechanical properties of the coatings. With an increase in the Nd2O3 doping content, the porosity of the coatings was reduced. The decrease in the porosity increased the compactness of the coatings and improved the microhardness and fracture toughness. The bonding strength and thermal shock resistance of the coatings were the highest among the samples herein when the rare earth doping content was 1.0 mol%, and the values were 37.6 MPa and 200 times, respectively. The thermal shock failure mode of the coating was mainly due to the exfoliation of the inner layer of the ceramic layer. The luminous intensity of the coating increased with increasing rare earth oxide doping content, and the emission spectrum of the Nd2O3-modified YSZ coating after the thermal shock test produced a new emission peak at 594 nm, which decreased at 708 nm.

To improve the crack propagation resistance of YSZ thermal barrier coatings during the thermal cycle, three kinds of thermal barrier coatings were prepared by atmospheric plasma spraying: YSZ, AlBOw-modified YSZ and BNW-modified YSZ. SEM, EDS and XRD were used to analyse the morphology, composition and phase composition of the sprayed powder and coating section. The phase structures of the YSZ, YSZ+AlBOw and YSZ+BNw coatings were t' phase. The cross-section of the coating presents a layered structure with pores inside. The porosity values of the YSZ, YSZ+AlBOw and YSZ+BNw coatings are 10.33%, 14.17% and 12.52%, respectively. The thermal shock resistance of three groups of coatings after 5 min at 1000 °C was analysed. The failure behaviour of the coatings after several thermal cycles was studied. The results show that the thermal shock resistance of the coatings with AlBOw is slightly lower than that of the YSZ coatings. The thermal shock resistance of the BNw coatings is 62.2% higher than that of the YSZ coatings. The whisker inhibits the crack propagation and prolongs the life of the coatings via crack deflection, whisker pull-out and whisker bridging.

In order to expand the application of polyimide resin matrix composites in the hot stage components of aeroengine, YSZ-based thermal protective composite coating was prepared on the surface of polyimide-based composites by detonation gun spraying. Sandblasting, sandpaper polishing and laser ablation were used to improve the surface roughness of the composites matrix. Bond bottom layer (Al, Cu, Zn), NiCoCrAl intermediate transition layer and YSZ top layer were matching with different thickness. The cross-section structure of the composite coating observed by SEM shows that the composite coatings of 0.1 mm Al bottom layer, 0.1 mm NiCoCrAl transition layer and 0.3 mm YSZ top layer are the best thickness matching for thermal protection of polyimide-based composite materials. There is no thermal damage to the surface and interior of the substrate during the preparation of the coating. The cross-section structure of the coating is uniform, and the interface between the layers is closely bonded and no micro-damage, Cracks and holes appear. After sandblasting, the bonding strength of the coating is 16.5 MPa by lattice laser texture treatment. The structure and thermal insulation properties of the composite coating are the best at 800 °C. The thermal conductivity is 1.46 W/(m·K), the specific heat capacity is 0.58 J/(g·K), and the thermal expansion coefficient is 7.89 × 10-6/K.

To reduce the friction coefficient of cobalt-cemented tungsten carbide (WC-12Co) wear-resistant coatings, graphene was compounded into WC-12Co powder via wet ball milling and spray granulation. Self-lubricating and wear-resistant graphene coatings were prepared via detonation gun spraying. The presence, morphologies, and phase compositions of graphene in the powders and coatings that are obtained through different powder preparation processes were analyzed. The analysis was performed using the following technologies: energy-dispersive X-ray-spectroscopy (EDXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The mechanical properties of the coatings were studied using a microhardness tester and a universal drawing machine. The friction and wear properties of the coatings were studied using an SRV-4 friction and wear tester. The results showed that the graphene content in the WC-12Co coating modified with graphene was higher than that without modification; graphene was embedded in the structure in a transparent and thin-layer state. The adhesive strength of this coating at approximately 25 °C was approximately 60.33 MPa, and the hardness was approximately 984 HV0.3. After high-temperature treatment, the adhesive strength and hardness of the graphene oxide (GO)/WC-12Co coating decreased slightly (the lowest adhesive strength of 53.16 MPa was observed after treatment at 400 °C, and the lowest hardness of approximately 837 HV0.3 was observed after treatment at 300 °C). Compared to the friction coefficient (0.6) of the WC-12Co coating obtained at room temperature, the friction coefficient of the GO/WC-12Co coating was decreased by approximately 50% of that value. The graphene-modified coating was continuously exposed to the wear tracks on the surface of the contacting materials during friction, and a lubricating film was formed in the microareas in which the wear tracks were present. The coating exhibited improved self-lubricating and wear-resistant effects compared to the unmodified WC-12Co coating. The results of this study demonstrated that graphene could be effective in self-lubrication and wear-reduction in a temperature range of 100–200 °C, as a friction coefficient of 0.3 was maintained.

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.

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.

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%.

Microstructure, mechanical property and oxidation resistance of MCrAlYX coatings prepared by detonation gun (D-gun) and HVOF spraying were investigated. Lamellar microstructure and uniform microstructure formed in D-gun sprayed MCrAlYX coating and HVOF sprayed coating, respectively. Element redistribution and formation of new phase took place during the detonation process. Besides, the porosity of D-gun sprayed coating was much lower than that of HVOF sprayed coating. On the mechanical property, the micro-hardnesses of the two coatings were in the same level (∼HV 910). However, D-gun sprayed MCrAlYX coating exhibited larger standard deviation of microhardness due to its lamellar microstructure, and exhibited better bend bonding strength owing to the existence of residual compressive stress between the layers and particles. Meanwhile, due to the much more compact microstructure, D-gun sprayed MCrAlYX coating showed superior oxidation resistance to the HVOF sprayed coating. The continuous dense protective layer can form earlier in D-gun sprayed coating and thus suppress further oxidation and control the oxide thickness at a relatively low level.

Al 2 O 3 /Au nano-laminated composite coatings were prepared by means of magnetron sputtering. The coating was compact and comprised of nano-laminated Al 2 O 3 and Au layers. High temperature cyclic oxidation test was employed to investigate the oxidation resistance of the composite coatings. The results revealed that the applied Al 2 O 3 /Au nano-laminated composite coatings improved the oxidation and spallation resistance of the stainless steel substrate significantly. The mechanism accounting for oxidation resistance was related with the suppression of inward oxygen diffusion and selective oxidation of Cr in the substrate. The mechanism accounting for spallation resistance was attributed to the relaxation of thermal stress by the nano-laminated structure.