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

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.

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.

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 (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.