The phase equilibria in Co-rich region of Co-Ti-Ta system were studied.The microstructure and XRD analysis together with EDS determination show that L12 type Co3Ti phase and Laves_C36_Co3Ta phase get equilibrium with ...The phase equilibria in Co-rich region of Co-Ti-Ta system were studied.The microstructure and XRD analysis together with EDS determination show that L12 type Co3Ti phase and Laves_C36_Co3Ta phase get equilibrium with α-Co phase from 1 000 to 1 200 ℃.The Co3Ti phase possesses a solubility of Ta higher than 10%,and the addition of Ta stabilizes the Co3Ti phase.The isothermal sections of the Co-Ti-Ta system in the Co-rich region at 1 000,1 100 and 1 200 ℃ were constructed according to the result.展开更多
IN617B nickel-base superalloy is considered as a good candidate material in 700℃advanced ultrasupercritical coal-fired power plants.The effect of Ta addition on solidification microstructure and element segregation o...IN617B nickel-base superalloy is considered as a good candidate material in 700℃advanced ultrasupercritical coal-fired power plants.The effect of Ta addition on solidification microstructure and element segregation of IN617B alloy was investigated by OM,SEM,TEM,EDS,EPMA and thermodynamic calculation.The results showed that the solidification microstructure exhibited a dendritic segregation pattern with many primary carbides distributed in interdendritic regions,such as network M_(6)C,lath M_(23)C_(6) and granular Ti(C,N).The addition of Ta promoted the precipitation of Ta-rich MC significantly inhibiting the precipitation of M_(6)C and M_(23)C_(6),and reduced the segregation degree of Al,Mo and Ti alloying elements.The addition of Ta decreased the melting temperature of MC carbide,but did not impact the solidification path,that was,L→γmatrix→MC or Ti(C,N)→M_(6)C→M_(23)C_(6),where MC and Ti(C,N)tended to form symbiotic microstructure with M_(6)C.This study will provide theoretical basis and data support for the alloy optimization and casting structure control of IN617B nickel-based superalloy.展开更多
Taking Ta–W alloy system as an example, the concentration formulae of alloy genes of DO3-type alloys in BCC structures were derived on the basis of the theory of alloy genes and the number of coordination atoms. The ...Taking Ta–W alloy system as an example, the concentration formulae of alloy genes of DO3-type alloys in BCC structures were derived on the basis of the theory of alloy genes and the number of coordination atoms. The concentrations of alloy genes of DO3-TaW3 and DO3-Ta3W ordered alloys were calculated as functions of composition xW and ordering degree (s). When s=smax, the concentrations of alloy genes of stoichiometric DO3-TaW3 compound are equal to those of alloys, that is, x8^Ta=0.25(at),x4^W=0.5(at),x8^W=0.25(at)The concentrations of alloy genes of stoichiometric DO3-Ta3W compound are also equal to those of alloys, that is,x0^Ta=0.25(at),x4^Ta=0.5(at),x0^W=0.25(at). As ordering degree decreases, alloy genes of DO3-TaW3 and DO3-Ta3W ordered alloys will split. And the degree of splitting of alloy genes increases with the ordering degree decreasing. The atomic states and properties of DO3-TaW3 and DO3-Ta3W ordered alloys were calculated as a function of composition xW. The reason was pointed out that preparation of DO3-TaW3 and DO3-Ta3W intermetallic compounds is difficult due to small differences in their cohesive energies. It will provide theoretical guidance for the scientific designation to new candidate for ultra- high-temperature materials in areo-engine applications.展开更多
基金Project (50771027) supported by the National Natural Science Foundation of China
文摘The phase equilibria in Co-rich region of Co-Ti-Ta system were studied.The microstructure and XRD analysis together with EDS determination show that L12 type Co3Ti phase and Laves_C36_Co3Ta phase get equilibrium with α-Co phase from 1 000 to 1 200 ℃.The Co3Ti phase possesses a solubility of Ta higher than 10%,and the addition of Ta stabilizes the Co3Ti phase.The isothermal sections of the Co-Ti-Ta system in the Co-rich region at 1 000,1 100 and 1 200 ℃ were constructed according to the result.
文摘IN617B nickel-base superalloy is considered as a good candidate material in 700℃advanced ultrasupercritical coal-fired power plants.The effect of Ta addition on solidification microstructure and element segregation of IN617B alloy was investigated by OM,SEM,TEM,EDS,EPMA and thermodynamic calculation.The results showed that the solidification microstructure exhibited a dendritic segregation pattern with many primary carbides distributed in interdendritic regions,such as network M_(6)C,lath M_(23)C_(6) and granular Ti(C,N).The addition of Ta promoted the precipitation of Ta-rich MC significantly inhibiting the precipitation of M_(6)C and M_(23)C_(6),and reduced the segregation degree of Al,Mo and Ti alloying elements.The addition of Ta decreased the melting temperature of MC carbide,but did not impact the solidification path,that was,L→γmatrix→MC or Ti(C,N)→M_(6)C→M_(23)C_(6),where MC and Ti(C,N)tended to form symbiotic microstructure with M_(6)C.This study will provide theoretical basis and data support for the alloy optimization and casting structure control of IN617B nickel-based superalloy.
基金Project(50954006) supported by the National Natural Science Foundation of ChinaProject(2014-12) supported by the Environmental Protection Department of Hunan,China+1 种基金Project(2016TP1007) supported by the Hunan Provincial Science and Technology Plan Project,ChinaProject(2016-01) supported by the Development and Reform Commission of Hunan Province,China
文摘Taking Ta–W alloy system as an example, the concentration formulae of alloy genes of DO3-type alloys in BCC structures were derived on the basis of the theory of alloy genes and the number of coordination atoms. The concentrations of alloy genes of DO3-TaW3 and DO3-Ta3W ordered alloys were calculated as functions of composition xW and ordering degree (s). When s=smax, the concentrations of alloy genes of stoichiometric DO3-TaW3 compound are equal to those of alloys, that is, x8^Ta=0.25(at),x4^W=0.5(at),x8^W=0.25(at)The concentrations of alloy genes of stoichiometric DO3-Ta3W compound are also equal to those of alloys, that is,x0^Ta=0.25(at),x4^Ta=0.5(at),x0^W=0.25(at). As ordering degree decreases, alloy genes of DO3-TaW3 and DO3-Ta3W ordered alloys will split. And the degree of splitting of alloy genes increases with the ordering degree decreasing. The atomic states and properties of DO3-TaW3 and DO3-Ta3W ordered alloys were calculated as a function of composition xW. The reason was pointed out that preparation of DO3-TaW3 and DO3-Ta3W intermetallic compounds is difficult due to small differences in their cohesive energies. It will provide theoretical guidance for the scientific designation to new candidate for ultra- high-temperature materials in areo-engine applications.