The γ/γ＇ microstructure of a Re-containing Ni-based single crystal super alloy after a two-step aging was studied using scanning electron microscopy （SEM）,transmission electron microscopy （TEM） and scanning tra...The γ/γ＇ microstructure of a Re-containing Ni-based single crystal super alloy after a two-step aging was studied using scanning electron microscopy （SEM）,transmission electron microscopy （TEM） and scanning transmission electron microscopy （STEM）.The crystals were grown by the floating zone （FZ） method.Both cuboidal and spherical γ＇ precipitates were formed after a two-step aging.The size of the cuboidal γ＇ phases first increased and then decreased with the extension of the second-step aging time.Re,Co and Cr strongly concentrated in the γ phase whereas Ni and Al enriched in the γ＇ phase.Thermodynamic calculation by JMatPro was performed to explain the experimental observations.展开更多
The effects of γ/γ interfacial structures on continuous coarsening of the fully lamellar microstructure in Ti 48Al alloy aged at 1 150 ℃ were investigated by using transmission electron microscopy(TEM). Continuous ...The effects of γ/γ interfacial structures on continuous coarsening of the fully lamellar microstructure in Ti 48Al alloy aged at 1 150 ℃ were investigated by using transmission electron microscopy(TEM). Continuous lamellar coarsening can be achieved not only by migration of interface faults(such as ledges, edges and curved interfaces) but also by migration and decomposition of perfect γ/γ lamellar interfaces. Thermal grooves, initiative positions of interfacial dissociation, can frequently form at the triple point junctions between the 120° rotational ordered γ domain boundaries within γ lamellae and the lamellar interfaces. During the early stage of aging at 1 150 ℃, the interface migration and dissociation took place preferentially at the 120° rotational ordered lamellar interfaces. Comparing the relative thermal stability of the true twin, pseudo twin and 120° rotational ordered γ/γ lamellar interfaces shows that the 120° rotational ordered lamellar interface is the most unstable. The reason of this phenomenon was analyzed through the comparisons of the interfacial energies and atomic arrangements of the three types of γ/γ lamellar interfaces.展开更多
Based on analysis of three alloys with various Re contents, the effects of Re on the interfacial structure characteristic and interfacial dislocations ofγ/γ' in single crystal superalloys were investigated. A hi...Based on analysis of three alloys with various Re contents, the effects of Re on the interfacial structure characteristic and interfacial dislocations ofγ/γ' in single crystal superalloys were investigated. A high resolution transition electron microscopy (HRTEM) technique was used to detect the structure characteristic ofγ/γ' interface. The interfacial dislocations ofγ/γ' were analyzed with TEM. The results show that as Re content increases, the interfaces ofγ/γ' become orderly, the atomic arrangements at interfaces are more uniform, the number of mismatch dislocations increases and transition areas betweenγandγ' phases become narrow. That Re changes the interfacial structure promotes the formation of dense, regular and homogeneous interfacial dislocation networks in short time during creep at 1 100℃and 140 MPa, which results in strengthenedγ/γ' interface at elevated temperature.展开更多
基金Project(08dj1400402) supported by the Major Program for the Fundamental Research of Science and Technology Committee of the Shanghai Municipality,ChinaProject(09ZZ16) supported by Innovation Program of Shanghai Municipal Education Committee,China
文摘The γ/γ＇ microstructure of a Re-containing Ni-based single crystal super alloy after a two-step aging was studied using scanning electron microscopy （SEM）,transmission electron microscopy （TEM） and scanning transmission electron microscopy （STEM）.The crystals were grown by the floating zone （FZ） method.Both cuboidal and spherical γ＇ precipitates were formed after a two-step aging.The size of the cuboidal γ＇ phases first increased and then decreased with the extension of the second-step aging time.Re,Co and Cr strongly concentrated in the γ phase whereas Ni and Al enriched in the γ＇ phase.Thermodynamic calculation by JMatPro was performed to explain the experimental observations.
文摘The effects of γ/γ interfacial structures on continuous coarsening of the fully lamellar microstructure in Ti 48Al alloy aged at 1 150 ℃ were investigated by using transmission electron microscopy(TEM). Continuous lamellar coarsening can be achieved not only by migration of interface faults(such as ledges, edges and curved interfaces) but also by migration and decomposition of perfect γ/γ lamellar interfaces. Thermal grooves, initiative positions of interfacial dissociation, can frequently form at the triple point junctions between the 120° rotational ordered γ domain boundaries within γ lamellae and the lamellar interfaces. During the early stage of aging at 1 150 ℃, the interface migration and dissociation took place preferentially at the 120° rotational ordered lamellar interfaces. Comparing the relative thermal stability of the true twin, pseudo twin and 120° rotational ordered γ/γ lamellar interfaces shows that the 120° rotational ordered lamellar interface is the most unstable. The reason of this phenomenon was analyzed through the comparisons of the interfacial energies and atomic arrangements of the three types of γ/γ lamellar interfaces.
文摘Based on analysis of three alloys with various Re contents, the effects of Re on the interfacial structure characteristic and interfacial dislocations ofγ/γ' in single crystal superalloys were investigated. A high resolution transition electron microscopy (HRTEM) technique was used to detect the structure characteristic ofγ/γ' interface. The interfacial dislocations ofγ/γ' were analyzed with TEM. The results show that as Re content increases, the interfaces ofγ/γ' become orderly, the atomic arrangements at interfaces are more uniform, the number of mismatch dislocations increases and transition areas betweenγandγ' phases become narrow. That Re changes the interfacial structure promotes the formation of dense, regular and homogeneous interfacial dislocation networks in short time during creep at 1 100℃and 140 MPa, which results in strengthenedγ/γ' interface at elevated temperature.
