The mechanical behavior of Fes Si based alloy with B2 structure was studied by tension and fracture toughness test in various testing media. The fracture strength σb of Fe3Si alloy decreased in the following order: o...The mechanical behavior of Fes Si based alloy with B2 structure was studied by tension and fracture toughness test in various testing media. The fracture strength σb of Fe3Si alloy decreased in the following order: oxygen, air and hydrogen respectively. The fracture toughness in different testing environment showed that KIC in oxygen is 11.5±0.3MPa·m1/2, and is 8.6±0.4MPa·ml/2 in distilled water. The reduction of fracture toughness is contributed to the environmental reaction of Si with water. Addition of Al element in Fe3Si is not beneficial to improve the intrinsic ductility of Fe-14Si-3Al alloy. The scattering phenomenon of fracture strength was found, and explained by fracture mechanics. It was found by means of SEM that the fracture mode changed from transgranular in oxygen to intergranular in hydrogen gas and distilled water.展开更多
The microstructural stability of lamellar TiAl base alloys at high temperatures was studied by conventional and high resolution transmission electron microscopy. The influence of substructures on the thermal stability...The microstructural stability of lamellar TiAl base alloys at high temperatures was studied by conventional and high resolution transmission electron microscopy. The influence of substructures on the thermal stability of lamellar structure was emphasized. These substructures produced by thermal mechanical treatments include the interfacial dislocations and ledges, the subgrain boundaries, the impinged T(Q) twins and misorientated lamellar interfaces. The microstructural change of three kinds of lamellar TiAl base alloys containing differents type and densities of substructures were compared during exposure at 800~1 000 ℃. It was found that the existence of such substructures could accelerate the degeneration of lamellar structure, leading to the rapid necking and break up of α 2 plates, the coarsening of γ plates, and the formation of new γ grains. As a result, the lamellar structure with substructures started to degenerate after thermal exposure at 800℃ for 4.5 h. While only slight coarsening was observed at the colony boundaries in the lamellar structure without substructures even after exposure at 900 ℃ for 7 d.展开更多
High-resolution transmission electron microscope (HRTEM) was employed to investigate the deformation-induced α2→γ phase transformation phenomenon in a hot deformed Ti-45Al-10Nb alloy. Such a tronsformation can be n...High-resolution transmission electron microscope (HRTEM) was employed to investigate the deformation-induced α2→γ phase transformation phenomenon in a hot deformed Ti-45Al-10Nb alloy. Such a tronsformation can be nucleated either at α2/γ interfaces or at stacking faults on the basal planes of the α2 phase. The growth of deformation-induced γplate is accomplished by the motion of α/6<100> Shockley partials on alternate basal planes (0001)α2, and the α/6<100> Shockley partials move in coordination rather than sweep on (0001)α2 plane one by one. It appears that no atom transportation is involved in this stress-induced α2→γ transfromation.展开更多
文摘The mechanical behavior of Fes Si based alloy with B2 structure was studied by tension and fracture toughness test in various testing media. The fracture strength σb of Fe3Si alloy decreased in the following order: oxygen, air and hydrogen respectively. The fracture toughness in different testing environment showed that KIC in oxygen is 11.5±0.3MPa·m1/2, and is 8.6±0.4MPa·ml/2 in distilled water. The reduction of fracture toughness is contributed to the environmental reaction of Si with water. Addition of Al element in Fe3Si is not beneficial to improve the intrinsic ductility of Fe-14Si-3Al alloy. The scattering phenomenon of fracture strength was found, and explained by fracture mechanics. It was found by means of SEM that the fracture mode changed from transgranular in oxygen to intergranular in hydrogen gas and distilled water.
文摘The microstructural stability of lamellar TiAl base alloys at high temperatures was studied by conventional and high resolution transmission electron microscopy. The influence of substructures on the thermal stability of lamellar structure was emphasized. These substructures produced by thermal mechanical treatments include the interfacial dislocations and ledges, the subgrain boundaries, the impinged T(Q) twins and misorientated lamellar interfaces. The microstructural change of three kinds of lamellar TiAl base alloys containing differents type and densities of substructures were compared during exposure at 800~1 000 ℃. It was found that the existence of such substructures could accelerate the degeneration of lamellar structure, leading to the rapid necking and break up of α 2 plates, the coarsening of γ plates, and the formation of new γ grains. As a result, the lamellar structure with substructures started to degenerate after thermal exposure at 800℃ for 4.5 h. While only slight coarsening was observed at the colony boundaries in the lamellar structure without substructures even after exposure at 900 ℃ for 7 d.
文摘High-resolution transmission electron microscope (HRTEM) was employed to investigate the deformation-induced α2→γ phase transformation phenomenon in a hot deformed Ti-45Al-10Nb alloy. Such a tronsformation can be nucleated either at α2/γ interfaces or at stacking faults on the basal planes of the α2 phase. The growth of deformation-induced γplate is accomplished by the motion of α/6<100> Shockley partials on alternate basal planes (0001)α2, and the α/6<100> Shockley partials move in coordination rather than sweep on (0001)α2 plane one by one. It appears that no atom transportation is involved in this stress-induced α2→γ transfromation.
