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In this paper, the pure MCrAlY coating and nano-Al2O3 particles reinforced MCrAlY graded coating were prepared on TiAl base intermetallic alloy substrates by laser cladding process. Furthermore, the microstructure characterization, microhardness and wear resistance of the two kinds of MCrAlY coating were comparatively investigated with scanning electron microscope (SEM), HXD-1000TC hardness tester and MM-200 block-on-ring dry sliding wear tester. The results show that the laser-clad pure MCrAlY coating has a dendrite crystals characteristic. However, the graded composite MCrAlY coating consists of fine equiaxed grains because of addition of nanometer ceramic particles. Moreover, the grain size becomes small with increasing the nano-Al2O3 content in the coating. The microhardness and wear resistance of the composite coating is higher than that of the pure coating. The mainly wear mechanism of the pure MCrAlY coating is abrasive and delamination, while the mainly wear mechanism of the composites graded MCrAlY coating is abrasive.

Nano-SiC/MCrAlY graded coating was prepared by laser multi-layer cladding on TiAl base intermetallic alloy using composite MCrAlY powders with 1%, 2%, and 3% nano-SiC particles (mass fraction) in turn. The microstructure and microhardness of the composite coating were analyzed by means of scanning electron microscope (SEM) and Vickers microhardness tester. The results show that the microstructure of the composite coating was refined and composed of fine equiaxed grains because of addition of nanometer SiC particles, and the crystal size becomes small with increasing the nano-SiC content in the coating. In addition, due to small size and formation heat of the nano-SiC particles, SiC particles decompose and form new carbides in the coating after laser cladding. The hardness of the composite MCrAlY coating is obviously improved due to enhancement of multi-carbide and refinement of structure.

It has attracted very strong interests in enhancing the wear resistance of the TiAl intermetallic alloy. In this paper, both plasma-sprayed conventional and nanostructured ZrO2-7wt.%Y2O3 thermal barrier coatings (TBCs) were prepared on TiAl alloy, and microhardness of coating were investigated. Meanwhile, the dry sliding friction tests on the substrate, the traditional coating, and the nanostructured coating were evaluated by ball-on-disk tribometer at room temperature. The results show that the microhardness of nanostructured coating is higher than that of the conventional one. Lower friction coefficient and higher wear resistance than the original TiAl alloy is achieved in the coatings under wear test conditions. Due to the existence of nanostructured microstructures, the nanostructured coating exhibits the lowest friction coefficient, and the best wear resistance. The wear mechanism of the original TiAl substrate is severe adhesive wear. However, the wear mechanisms of the TBCs are mild ploughing and severe adhesion.

In this study, conventional and nanostructured MCrAlY/ZrO2-7wt.%Y2O3 double-layer thermal barrier coatings (TBCs) were fabricated on TiAl base intermetallic alloy substrates by the plasma spraying technique. The microstructural characterization and thermal insulation capability of the two types of coatings were comparatively researched. The results show that the conventional ceramic coating has a typical lamellar stacking characteristic. However, the nanostructured coating exhibits a bimodal microstructure, which is composed of both fully melted regions and partially melted regions (remained nanoparticles). The nanostructured TBCs has higher thermal barrier effect than the traditional one. The temperature drops of the nanostructured TBCs at 1100 oC increases 53% compared with that of the conventional TBCs.

In this study, ZrO2-7wt.%Y2O3 thermal barrier coatings (TBCs) were prepared on TiAl base intermetallic alloy substrates by plasma spraying process. After that, the plasma-sprayed TBCs were laser remelted using a CO2 laser. Influences of laser remelting on the microstructure and solid particle erosion characterization of the coatings were researched. Meanwhile, the erosion damage modes of the two types of TBCs were discussed. The results show that the as-sprayed TBC has a typical lamellar stacking characteristic. The lamellar defect of the plasma-sprayed coating is erased, and the compactness of the coating is improved significantly after laser remelting. The laser-remelted coating consists of column-like crystals along the direction of the heat current. The laser-remelted coating had better erosion resistance than the as-sprayed coating. Owing to the limited bonding at the interfaces between lamellar, the spalling of the sprayed splats from the lamellar interface is mainly attributed to the erosion failure of the as-sprayed coating. In addition, crushing of brittle ceramic coating is also responsible for the erosion damage of the plasma-sprayed TBC. In contrast, cracking occurs within region near the surface of the laser-remelted layer and that erosion occurs mainly by removal of these small blocks. Moreover, the laser-remelted has evident mciro-cutting marks and shows some ductile erosion characteristic.

Abstract. In this work, conventional and nanostructured Al2O3-13wt.%TiO2 coatings were deposited by the plasma spraying technique. The microstructures of the two types of coatings were analyzed, and the solid particle erosion behaviors of the two coatings were comparatively researched in an erosion tester. Meanwhile, the erosion failure mechanisms of the coatings were discussed. The results show that the traditional coating has laminated structure and some pores. However, the nanostructured coating possesses a denser structure and not obviously lamellar-like structure, and exhibits a bimodal microstructure consisted of fully melted regions and partially melted regions. Owing to the compact microstructure and remained nano-particles, the nanostructured coating had a better erosion wear resistance than the conventional coating. Eroded morphology analysis indicates the main erosion mass loss of the coatings is attributed to lamellar spalling of the sprayed splats and fracture of brittle ceramic particles. In addition, the nanostructued coating has some impact craters and plough marks. In terms of the erosion mechanism, the conventional ceramic coating is dominated by brittle erosion, while the nanostructured ceramic coating is dominated by brittle erosion as well as ductile erosion to some extent.

Nanostructured ceramic bulk materials were achieved from nano-Al2O3 ceramic powders via direct selective laser sintering (SLS). SLS as a non-traditional machining technology of Rapid Prototyping was introduced and compared with other ceramic forming technologies. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied to analyze the microstructure of the ceramic bulk materials. These results demonstrated that the nano-Al2O3 ceramic powders can be sintered into bulk materials maintained nanostructure with some technological parameters. It was found that the nanostructured ceramic bulk exhibited unique microstructure and was free formed rapidly by this sintering technology.