We focused on the surface reinforcement of ligth weight casting alloys with Ni-AI intermetallic compounds by in-situ combustion reaction to improve the surface properties of non-ferrous casting components.In our previ...We focused on the surface reinforcement of ligth weight casting alloys with Ni-AI intermetallic compounds by in-situ combustion reaction to improve the surface properties of non-ferrous casting components.In our previous works,green compact of elemental Ni and Al powders were reacted to form Ni-3Al intermetallic compound by SHS （Self-propagating high temperature synthesis） reaction with the heat of molten Al alloy and simultaneously bonded with Al casting alloy.But some defects such as tiny cracks and porosities were remained in the reacted compact.So we applied pressure to prevent thermal cracks and fill up the pores with liquid Al alloy by squeeze casting process.The compressed Al alloy bonded with the Ni-3Al intermetallic compound was sectioned and observed by optical microscopy and scanning electron microscopy （SEM）.The stoichiometric compositions of the intermetallics formed around the bonded interface and in the reacted compact were identified by energy dispersive spectroscopy （EDS） and electron probe micro analysis （EPMA）. Si rich layer was formed on the Al alloy side near the bonded interface by the sequential solidification of Al alloy.The porosities observed in the reacted Ni-3Al compact were filled up with the liquid AI alloy.The Si particles from the molten Al alloy were detected in the pores of reacted Ni-3Al intermetallic compact.The Al casting alloy and Ni-3Al intermetallic compound were joined very soundly by applying pressure to the liquid Al alloy.展开更多
By use of the self-consistent method of linear muffin-tin orbitals with the atomic sphere approximation on the basis of density functional theory, the total energies and the electron-ic sTructures ofNi, Al, and their ...By use of the self-consistent method of linear muffin-tin orbitals with the atomic sphere approximation on the basis of density functional theory, the total energies and the electron-ic sTructures ofNi, Al, and their hydrides NiH. A1H and Ni3AlH are calculated. The theoretical excess energies and the lattice strains due to hydrogen absorption consequently obtained from the ah initio results indicate that Ni is a better hydrogen absorber than Al, an. the absorptivity of Ni3Al dramatically decreases owing to the repulsion between Al and H On the other hand, the changes of band structures due to hydrogenation are found to be remparkable except that tor Al. and they are shown to be the qualitative manifestation of existing conclusions from photoemission experiments.展开更多
A lot of work has been done to investigate the influence of irradiation on the structure and properties of nuclear reactor materials in high irradiation for the safety and reliability. Although the point defect surviv...A lot of work has been done to investigate the influence of irradiation on the structure and properties of nuclear reactor materials in high irradiation for the safety and reliability. Although the point defect survival and micromechanism by irradiation are important issues, the evolution of such a region is difficult to follow experimentally, so many results are展开更多
The hot deformation behavior of homogenized Nia Al-based alloy MX246A has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing on the MTS 81...The hot deformation behavior of homogenized Nia Al-based alloy MX246A has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing on the MTS 810 machine in the temperature range of 1 150--1225 ℃ and strain rate range of 0. 001-0.1 s-1. Microstructural obser- vation revealed striped secondary γ＇ phase which was vertical to compression axis, and precipitation of fine ternary γ＂ phase. The amount of striped secondary γ＇ phase reduced and that of fine ternary γ＇ phase increased with increasing temperature and decreasing strain rate. The material exhibited peak stress followed by flow softening, but no obvious steady-state flow behavior. Microstructural investigations have shown no dynamic recrystallization happened. TEM studies indicated that the flow softening was controUed by dynamic recovery mechanism.展开更多
文摘We focused on the surface reinforcement of ligth weight casting alloys with Ni-AI intermetallic compounds by in-situ combustion reaction to improve the surface properties of non-ferrous casting components.In our previous works,green compact of elemental Ni and Al powders were reacted to form Ni-3Al intermetallic compound by SHS （Self-propagating high temperature synthesis） reaction with the heat of molten Al alloy and simultaneously bonded with Al casting alloy.But some defects such as tiny cracks and porosities were remained in the reacted compact.So we applied pressure to prevent thermal cracks and fill up the pores with liquid Al alloy by squeeze casting process.The compressed Al alloy bonded with the Ni-3Al intermetallic compound was sectioned and observed by optical microscopy and scanning electron microscopy （SEM）.The stoichiometric compositions of the intermetallics formed around the bonded interface and in the reacted compact were identified by energy dispersive spectroscopy （EDS） and electron probe micro analysis （EPMA）. Si rich layer was formed on the Al alloy side near the bonded interface by the sequential solidification of Al alloy.The porosities observed in the reacted Ni-3Al compact were filled up with the liquid AI alloy.The Si particles from the molten Al alloy were detected in the pores of reacted Ni-3Al intermetallic compact.The Al casting alloy and Ni-3Al intermetallic compound were joined very soundly by applying pressure to the liquid Al alloy.
文摘By use of the self-consistent method of linear muffin-tin orbitals with the atomic sphere approximation on the basis of density functional theory, the total energies and the electron-ic sTructures ofNi, Al, and their hydrides NiH. A1H and Ni3AlH are calculated. The theoretical excess energies and the lattice strains due to hydrogen absorption consequently obtained from the ah initio results indicate that Ni is a better hydrogen absorber than Al, an. the absorptivity of Ni3Al dramatically decreases owing to the repulsion between Al and H On the other hand, the changes of band structures due to hydrogenation are found to be remparkable except that tor Al. and they are shown to be the qualitative manifestation of existing conclusions from photoemission experiments.
文摘A lot of work has been done to investigate the influence of irradiation on the structure and properties of nuclear reactor materials in high irradiation for the safety and reliability. Although the point defect survival and micromechanism by irradiation are important issues, the evolution of such a region is difficult to follow experimentally, so many results are
文摘The hot deformation behavior of homogenized Nia Al-based alloy MX246A has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing on the MTS 810 machine in the temperature range of 1 150--1225 ℃ and strain rate range of 0. 001-0.1 s-1. Microstructural obser- vation revealed striped secondary γ＇ phase which was vertical to compression axis, and precipitation of fine ternary γ＂ phase. The amount of striped secondary γ＇ phase reduced and that of fine ternary γ＇ phase increased with increasing temperature and decreasing strain rate. The material exhibited peak stress followed by flow softening, but no obvious steady-state flow behavior. Microstructural investigations have shown no dynamic recrystallization happened. TEM studies indicated that the flow softening was controUed by dynamic recovery mechanism.
