Ni-based alloy was transient liquid phase bonded using a BNi-2 interlayer. The effect of bonding parameters on the microstructures and mechanical properties of the joints was investigated. With the increase of bonding...Ni-based alloy was transient liquid phase bonded using a BNi-2 interlayer. The effect of bonding parameters on the microstructures and mechanical properties of the joints was investigated. With the increase of bonding temperature or time, the number of Ni-rich and Cr-rich borides and the grain size of precipitation zone decrease. Higher bonding temperature or longer bonding time is beneficial to the diffusion of melting point depressant elements (B and Si) from the PZ to the base metal and atomic interdiffusion between the base metal and the joint. The chemical composition and microstructure of the joints bonded at 1170 ℃ for 24 h are comparable to the base metal. The shear test results show that both the room and elevated temperature shear-strengths of the joints increase with increasing bonding time. However, the effect of bonding time on elevated temperature tensile-shear strength is greater than on room temperature tensile-shear strength.展开更多
This investigation was carried out to study the effect of aggregate roughness on ITZ (interfacial transition zone) at same water/cement ratio and the influence of silica fume on the bond strength. On the experimenta...This investigation was carried out to study the effect of aggregate roughness on ITZ (interfacial transition zone) at same water/cement ratio and the influence of silica fume on the bond strength. On the experimental side, two types of aggregates (limestone and granite) were used, which were prepared with broken surface. Cement (Type I) was used with same w/c ratio for all batches. In order to study the effect of silica fume on the bond, the same mixes were produced with 8% silica fume. Three different tests were performed: "pull a part", Brazilian test and compressive strength test. The specimens for Brazilian and compressive strength were tested after 28 days, while the "pull a part" specimens were tested after 29 days. The result showed that the bond strength is influenced by the surface roughness of aggregate. For the same mix, limestone recorded higher bond strength than granite. Moreover, the bond strength is increased by adding the silica fume.展开更多
We study the fluctuation-activated transition process in a system of two coupled forced bistable oscillators with a mismatch σ in the force constants. As the coupling strength μ is increased, the transition pathway ...We study the fluctuation-activated transition process in a system of two coupled forced bistable oscillators with a mismatch σ in the force constants. As the coupling strength μ is increased, the transition pathway undergoes four stages changes from a two-step process with two candidate pathways to a mixture of a two-step pathway and a one-step pathway to a one-step process with also two candidate pathways and then to a one-step process with a single pathway.Interestingly, we find that the total transition rate depends nonmonotonically on σ in the weak coupling: a maximal rate appears in an intermediate magnitude of σ. Moreover, the rate also exhibits an unexpected maximum as a function ofμ. The results are in an excellent agreement with our numerical simulations by forward flux sampling.展开更多
This paper presents experimental studies on bypass transition of separated boundary layer on low-pressure turbine airfoils,focusing on the effects of freestream turbulence on the transition process.Hot-wire probe meas...This paper presents experimental studies on bypass transition of separated boundary layer on low-pressure turbine airfoils,focusing on the effects of freestream turbulence on the transition process.Hot-wire probe measurements are performed on the suction side of an airfoil in the low-pressure linear turbine cascade at several Reynolds number conditions.Freestream turbulence is enhanced by use of turbulence grid located upstream of the cascade.The results of this experimental study show that the location of boundary layer separation does not strongly de-pend on the freestream turbulence level.However,as the freestream turbulence level increases,the size of separa-tion bubble becomes small and the location of turbulent transition moves upstream.The size of separation bubble becomes small as the Reynolds number increases.At low freestream turbulence intensity,the velocity fluctuation due to Kelvin-Helmholtz instability is observed clearly in the shear layer of the separation bubble.At high frees-tream turbulence intensity,the streak structures appear upstream of the separation location,indicating bypass transition of attached boundary layer occurs at high Reynolds number.展开更多
The Cu Cr/1Cr18Ni9 Ti bi-metal materials were prepared by the solid-liquid bonding method. The microstructures, mechanical properties and formation mechanism of the bonding interface were studied. The results show tha...The Cu Cr/1Cr18Ni9 Ti bi-metal materials were prepared by the solid-liquid bonding method. The microstructures, mechanical properties and formation mechanism of the bonding interface were studied. The results show that there exists a serrated transition layer with a certain width at the interface of Cu Cr/1Cr18Ni9 Ti bi-metal materials, and the transition layer consists of Fe-based and Cu-based solid solutions. The elastic modulus and hardness reach the maximum values at the interface closing to the 1Cr18Ni9 Ti zone. The bonding temperature has a significant effect on the width and morphology of the transition layer. The interfacial bonding strength is at least 30% higher than that of the Cu Cr alloy, and the tensile fracture occurs at the side of the Cu Cr alloy rather than at the bonding interface.展开更多
基金Projects (50975062, 51105107, 51275135, 51021002) supported by the National Natural Science Foundation of ChinaProject (QC2011C044) supported by the Natural Science Foundation of Heilongjiang Province, China+1 种基金Project (20112302130005) supported by Specialized Research Fund for the Doctoral Program of Higher Education, ChinaProject (20100471027) supported by the Postdoctoral Science Foundation of China
文摘Ni-based alloy was transient liquid phase bonded using a BNi-2 interlayer. The effect of bonding parameters on the microstructures and mechanical properties of the joints was investigated. With the increase of bonding temperature or time, the number of Ni-rich and Cr-rich borides and the grain size of precipitation zone decrease. Higher bonding temperature or longer bonding time is beneficial to the diffusion of melting point depressant elements (B and Si) from the PZ to the base metal and atomic interdiffusion between the base metal and the joint. The chemical composition and microstructure of the joints bonded at 1170 ℃ for 24 h are comparable to the base metal. The shear test results show that both the room and elevated temperature shear-strengths of the joints increase with increasing bonding time. However, the effect of bonding time on elevated temperature tensile-shear strength is greater than on room temperature tensile-shear strength.
文摘This investigation was carried out to study the effect of aggregate roughness on ITZ (interfacial transition zone) at same water/cement ratio and the influence of silica fume on the bond strength. On the experimental side, two types of aggregates (limestone and granite) were used, which were prepared with broken surface. Cement (Type I) was used with same w/c ratio for all batches. In order to study the effect of silica fume on the bond, the same mixes were produced with 8% silica fume. Three different tests were performed: "pull a part", Brazilian test and compressive strength test. The specimens for Brazilian and compressive strength were tested after 28 days, while the "pull a part" specimens were tested after 29 days. The result showed that the bond strength is influenced by the surface roughness of aggregate. For the same mix, limestone recorded higher bond strength than granite. Moreover, the bond strength is increased by adding the silica fume.
基金Supported by Natural Science Foundation of China under Grant Nos.11205002,11475003,21125313"211 project"of Anhui University under Grant No.02303319-33190133
文摘We study the fluctuation-activated transition process in a system of two coupled forced bistable oscillators with a mismatch σ in the force constants. As the coupling strength μ is increased, the transition pathway undergoes four stages changes from a two-step process with two candidate pathways to a mixture of a two-step pathway and a one-step pathway to a one-step process with also two candidate pathways and then to a one-step process with a single pathway.Interestingly, we find that the total transition rate depends nonmonotonically on σ in the weak coupling: a maximal rate appears in an intermediate magnitude of σ. Moreover, the rate also exhibits an unexpected maximum as a function ofμ. The results are in an excellent agreement with our numerical simulations by forward flux sampling.
文摘This paper presents experimental studies on bypass transition of separated boundary layer on low-pressure turbine airfoils,focusing on the effects of freestream turbulence on the transition process.Hot-wire probe measurements are performed on the suction side of an airfoil in the low-pressure linear turbine cascade at several Reynolds number conditions.Freestream turbulence is enhanced by use of turbulence grid located upstream of the cascade.The results of this experimental study show that the location of boundary layer separation does not strongly de-pend on the freestream turbulence level.However,as the freestream turbulence level increases,the size of separa-tion bubble becomes small and the location of turbulent transition moves upstream.The size of separation bubble becomes small as the Reynolds number increases.At low freestream turbulence intensity,the velocity fluctuation due to Kelvin-Helmholtz instability is observed clearly in the shear layer of the separation bubble.At high frees-tream turbulence intensity,the streak structures appear upstream of the separation location,indicating bypass transition of attached boundary layer occurs at high Reynolds number.
基金supported by the National Natural Science Foundation of China(Grant No.51371139)Science and Technique Innovation Program of Shaanxi Province(Grant No.2012KTCQ01-14)+1 种基金Pivot Innovation Team of Shaanxi Electric Materials and the Infiltration Technique(Grant No.2012KCT-25)Shaanxi Provincial Project of Special Foundation of Key Disciplines
文摘The Cu Cr/1Cr18Ni9 Ti bi-metal materials were prepared by the solid-liquid bonding method. The microstructures, mechanical properties and formation mechanism of the bonding interface were studied. The results show that there exists a serrated transition layer with a certain width at the interface of Cu Cr/1Cr18Ni9 Ti bi-metal materials, and the transition layer consists of Fe-based and Cu-based solid solutions. The elastic modulus and hardness reach the maximum values at the interface closing to the 1Cr18Ni9 Ti zone. The bonding temperature has a significant effect on the width and morphology of the transition layer. The interfacial bonding strength is at least 30% higher than that of the Cu Cr alloy, and the tensile fracture occurs at the side of the Cu Cr alloy rather than at the bonding interface.