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.

Pure and 2 mol% yttria-doped zirconia nano-powders were synthesized via the precipitation method, using ZrOCl2

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.

Mechanical properties of in-situ toughened Al2O3/Fe3Al nano-/micro-composites were measured. Effects ofFe3Al content, sintering temperature and holding time on properties and microstructure of the composites wereinvestigated. The addition of Fe3Al nano-particles decreased the aspect ratio and grain size of Al2O3, and changedthe fracture mode of composites. The maximum bending strength and fracture toughness were 832 MPa and 7.96 MPa m1/2, which were obtained in Al2O3/5 wt.% Fe3Al sintered at 1530 8C and Al2O3/10 wt.% Fe3Al sintered at 1600 8C, respectively. Compared to monolithic alumina, the strength increased by 132% and the toughness increased by 73%. The improvement in the mechanical properties of the composites was attributed to the change in fracture mode from intergranular fracture to transgranular fracture, the "'in-situ reinforced effect" arising from the platelet grains of Al2O3 matrix, refined microstructure by dispersoids, as well as crack deflection and bridging of intergranular and intragranular Fe3Al.

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.