Fe3Al intermetallic-A12O3 ceramic graded coatings were produced by plasma spray. The microstructure and composition distribution were studied by techniques including metallurgical microscope, SEM, XRD and electron probe. The adhesive strength, micro-hardness and thermal-shock resistance of the coatings were also tested. The results showed that although the compositions of graded coatings were designed gradient transition, the composition and structure varied continuously and there were no abrupt structure changes and macro-interfaces. The structure of graded coatings exhibited macro-inhomogeneity and micro-continuity. The gradient distribution of coating composition improved adhesive strength and thermal-shock resistance of the coatings. The highest micro-hardness of coatings was obtained in the composition area of containing 75 wt.% A1203. The weakest point of the substrate-coating system was the interface between the substrate and the coating.

Fe3Al nano-particles and commercial purity Al2O3 powders were used as raw materials to fabricate in situ reinforced Al2O3/Fe3Al nano/micro-composites. Densification and microstructure were studied. The Al2O3 matrix grains were characterized by platelet grains. The Fe3Al particles inhibited the grain growth of Al2O3 grains and limited the densification of the composites. In Al2O3/Fe3Al composites, the Fe3Al particles were uniformly dispersed in the Al2O3 matrix. The major Fe3Al micro-particles, about 1 mm in average size, existed at Al2O3 grain boundaries, and the Fe3Al nano-particles were found embedded in the matrix grains. The grain size of the intragranular particles ranged from several to several hundred nanometers. The grain size and aspect ratio of Al2O3 platelet grains and distribution of intragranular Fe3Al could be optimized by controlling the Fe3Al contents and sintering process. The in situ formed Al2O3 platelet grains, as well as Fe3Al dispersoids, were beneficial to the increase of the mechanical properties of alumina.

Nanometer zirconia powders were prepared by the precipitation method at different pHs and different reaction temperatures. X-ray results show that monoclinic zirconia is favored at pH 4 while tetragonal zirconia is favored at pH 9.5 at room temperature, and monoclinic zirconia is also favored at pH 9.5 and 70℃ reaction temperature, with the slow addition of alkali. Four models of zirconium complexes were applied to simulate the structural monomers in different pH solutions. Geometric parameters and Mulliken charge population were calculated by optimizing these complexes using the density functional theory (DFT/B3LYP). Theoretical analyses show that if Model I ([Zr(OH)2(H2O)4]2þ monomers) is favored in the aqueous precursor solution, it will be preferentially polymerized into monoclinic precursor structure irrespective of slow or quick alkali addition. Contrarily, if Model IV ([Zr(OH)7]32 monomers) is major in the aqueous precursor solution, tetragonal precursor structures are favored irrespective of slow or quick alkali addition. When Model II ([Zr(OH)4(H2O)2]0 monomers) and Model III ([Zr(OH)6]22 monomers), respectively, predominate in the aqueous precursor solution, they will be preferentially polymerized into tetragonal precursor structure at slow alkali addition, however, for quick alkali addition, they will be preferentially polymerized into monoclinic precursor structure. Our theoretical models well explain the present experimental results as well as previous experimental results, and allow building up a correlation between aqueous precursor structures and crystalline phases of zirconia.

Based on the empirical electron theory of solids and molecules, analysis of valence electron structures is made on Fe3Al intermetallic compounds. The bonding complex model of the DO3 cell is set up. Some preliminary attempts to discover the relationship between alloy composition, structure and properties and the Fe3Al alloy phase valence electron structure are presented.

The paper contains the results of a preliminary study of SiCw-reinforced Al2TiO5 matrix composites. With the increase in the SiC whisker content, the bending strength of composites also increased. For the 7 wt.% SiCw composition, the strength had increased by 170% from the value for Al2TiO5ceramic without notable alteration of thermal expansion coefficient.