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.

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.

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.

The (A1N, TiN)-A12O3 composites were fabricated by reaction sintering powder mixtures containing 10-30 wt.% (A1, Ti)-Al2O3 at 1420-1520℃ in nitrogen. It was found that the densification and mechanical properties of the sintered composites depended strongly on the A1, Ti contents of the starting powder and hot pressing parameters. Reaction sintering 20 wt.% (A1, Ti)-Al2O3 powder in nitrogen in 1520℃ for 30 min yields (A1N, TiN)-Al2O3 composites with the best mechanical properties, with a hardness HRA of 94.1, bending strength of 687 MPa, and fracture toughness of 6.5 MPa ml/2. Microstructure analysis indicated that TiN is present as well dispersed particulates within a matrix of A1203. The A1N identified by XRD was not directly observed, but probably resides at the A12O3 grain boundary. The fracture mode of these composites was observed to be transgranular.

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.