Effect of sinter hardening on the microstructure, density, hardness and tensile properties of Astaloy 85Mo+0.7% graphite was investigated. For this purpose, Astaloy 85Mo, a pre-alloyed powder, was mixed with 0.7% UF4 ...Effect of sinter hardening on the microstructure, density, hardness and tensile properties of Astaloy 85Mo+0.7% graphite was investigated. For this purpose, Astaloy 85Mo, a pre-alloyed powder, was mixed with 0.7% UF4 graphite and then pressed in single action die and sintered at 1 120 ℃ for 30 min in N2-10%H2 atmosphere. Then samples were cooled from 0.5 to 3 ℃/s sintering temperature in accordance with different cooling rates. The difference in microstructure, hardness, density and tensile properties of the samples associated with different cooling rates from sintering temperature has been investigated. The results show that the microstructure remains bainitic by changing cooling rate, but it becomes finer and then the hardness and tensile strength of the samples will increase by increasing the cooling rate from sintering temperature.展开更多
By means of analysis technique such as scanning electron microscopy(SEM)equipped with energy dispersive spectroscopy(EDS),and transmission electron microscopy(TEM),deep metallurgy failure analysis for an early fractur...By means of analysis technique such as scanning electron microscopy(SEM)equipped with energy dispersive spectroscopy(EDS),and transmission electron microscopy(TEM),deep metallurgy failure analysis for an early fracture engine intake valve made of the martensite material of 85Cr18Mo2V was performed through macroscopical and microcosmic as well as chemical composition angles.According to the result of SEM,this valve belonged to fatigue fracture.The crack sources of dense micro-holes near the surface of intake valve and SiO2 impurity are the direct reasons to cause the valve failure.The EDS analysis for the fatigue source region approved that superfluous Si,O and Al impurity existed.The TEM observation of the slice cut from the region closing to the fracture surface showed that deep areas near the surface of valve were oxidized severely.The material structure got brittle due to the generation of Fe3O4.Cracks will be produced in these oxidation areas under high cycle fatigue loading.Consequently,the synthetical action of various factors finally caused the fracture of valve.展开更多
文摘Effect of sinter hardening on the microstructure, density, hardness and tensile properties of Astaloy 85Mo+0.7% graphite was investigated. For this purpose, Astaloy 85Mo, a pre-alloyed powder, was mixed with 0.7% UF4 graphite and then pressed in single action die and sintered at 1 120 ℃ for 30 min in N2-10%H2 atmosphere. Then samples were cooled from 0.5 to 3 ℃/s sintering temperature in accordance with different cooling rates. The difference in microstructure, hardness, density and tensile properties of the samples associated with different cooling rates from sintering temperature has been investigated. The results show that the microstructure remains bainitic by changing cooling rate, but it becomes finer and then the hardness and tensile strength of the samples will increase by increasing the cooling rate from sintering temperature.
基金NSFC(50975285,50735006)Advanced Maintenance Research Project(9140A270304090C8501)
文摘By means of analysis technique such as scanning electron microscopy(SEM)equipped with energy dispersive spectroscopy(EDS),and transmission electron microscopy(TEM),deep metallurgy failure analysis for an early fracture engine intake valve made of the martensite material of 85Cr18Mo2V was performed through macroscopical and microcosmic as well as chemical composition angles.According to the result of SEM,this valve belonged to fatigue fracture.The crack sources of dense micro-holes near the surface of intake valve and SiO2 impurity are the direct reasons to cause the valve failure.The EDS analysis for the fatigue source region approved that superfluous Si,O and Al impurity existed.The TEM observation of the slice cut from the region closing to the fracture surface showed that deep areas near the surface of valve were oxidized severely.The material structure got brittle due to the generation of Fe3O4.Cracks will be produced in these oxidation areas under high cycle fatigue loading.Consequently,the synthetical action of various factors finally caused the fracture of valve.
