The effect of T6heat treatment on the fracture strength and reliability of AM60B alloy was studied.The tensile specimens were poured at three different temperatures of670,685and700?C for different holding times of5,10...The effect of T6heat treatment on the fracture strength and reliability of AM60B alloy was studied.The tensile specimens were poured at three different temperatures of670,685and700?C for different holding times of5,10and15min.The fluidity test was also conducted to determine the fluidity length under different pouring temperatures and holding times.According to the results,the optimum pouring temperature and holding time were determined as685?C and10min,respectively.SEM fractography of the tensile specimens reveals that the entrained oxides and oxide-related porosities are the main factors responsible for the reduction of fracture strength under the non-optimal casting conditions.The Weibull statistical approach was used to quantify the scatter of fracture strength in as-cast and heat-treated conditions.For this purpose,T6schedule was applied to the specimens prepared under the optimal casting condition.It is found that,despite minor effect on the average fracture strength,T6heat treatment improves the reliability of castings,where the Weibull modulus is increased by75%.According to the microstructural and fractography observations,this improvement is related to the evolution of more uniform microstructure and the elimination of coarse brittleβ-particles in heat-treated samples.展开更多
Let X be a C1 vector field on a compact boundaryless Riemannian manifold M（dim M≥2）,and A a compact invariant set of X.Suppose that A has a hyperbolic splitting,i.e.,T∧M = Es Eu with Es uniformly contracting and E...Let X be a C1 vector field on a compact boundaryless Riemannian manifold M（dim M≥2）,and A a compact invariant set of X.Suppose that A has a hyperbolic splitting,i.e.,T∧M = Es Eu with Es uniformly contracting and Eu uniformly expanding.We prove that if,in addition,A is chain transitive,then the hyperbolic splitting is continuous,i.e.,A is a hyperbolic set.In general,when A is not necessarily chain transitive,the chain recurrent part is a hyperbolic set.Furthermore,we show that if the whole manifold M admits a hyperbolic splitting,then X has no singularity,and the flow is Anosov.展开更多
文摘The effect of T6heat treatment on the fracture strength and reliability of AM60B alloy was studied.The tensile specimens were poured at three different temperatures of670,685and700?C for different holding times of5,10and15min.The fluidity test was also conducted to determine the fluidity length under different pouring temperatures and holding times.According to the results,the optimum pouring temperature and holding time were determined as685?C and10min,respectively.SEM fractography of the tensile specimens reveals that the entrained oxides and oxide-related porosities are the main factors responsible for the reduction of fracture strength under the non-optimal casting conditions.The Weibull statistical approach was used to quantify the scatter of fracture strength in as-cast and heat-treated conditions.For this purpose,T6schedule was applied to the specimens prepared under the optimal casting condition.It is found that,despite minor effect on the average fracture strength,T6heat treatment improves the reliability of castings,where the Weibull modulus is increased by75%.According to the microstructural and fractography observations,this improvement is related to the evolution of more uniform microstructure and the elimination of coarse brittleβ-particles in heat-treated samples.
基金supported by the State Key Development Program for Basic Research of China(973 Project)(Grant No.2011CB808002)National Natural Science Foundation of China(Grant Nos.11025101 and 11231001)
文摘Let X be a C1 vector field on a compact boundaryless Riemannian manifold M（dim M≥2）,and A a compact invariant set of X.Suppose that A has a hyperbolic splitting,i.e.,T∧M = Es Eu with Es uniformly contracting and Eu uniformly expanding.We prove that if,in addition,A is chain transitive,then the hyperbolic splitting is continuous,i.e.,A is a hyperbolic set.In general,when A is not necessarily chain transitive,the chain recurrent part is a hyperbolic set.Furthermore,we show that if the whole manifold M admits a hyperbolic splitting,then X has no singularity,and the flow is Anosov.
