Based on the empirical electron theory of solids andmolecules, analysis of valence electron structures is applied to the Fe3Al intermetallic compounds. The bonding complex model of the DO3 cell is set up. Some preliminary attempts at revealing the relationship between alloy composition-structure-properties and the Fe3Al alloy phase valence electron structure are prescnted.

On the basis of analyzing the formation mechanism of thermal stress in coatings, according to practical thermal conditions and mechanical principle, the calculating model that can estimate thermal stress of coatings during fabricating process is established. Through observing the microstructure of coatings by SEM, the thermal mechanical behavior and its effect on the properties of coatings are studied. The results show that, in graded coatings, parameters of thermal mechanical behavior and fabrication stress change with the compositions. The largest stress exists in the bottom layer and the thermal stress decrease from the substrate to the surface. In graded coatings, the highest stress and the average stress are both lower in coatings. The gradient distribution of coatings' composition can effectively reduce thermal stress during fabrication process.

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.

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.

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.