The evolution of stresses due to inhomogeneity in metal injection molding （MIM） parts during sintering was investigated. The sintering model of porous materials during densification process was developed based on th...The evolution of stresses due to inhomogeneity in metal injection molding （MIM） parts during sintering was investigated. The sintering model of porous materials during densification process was developed based on the continuum mechanics and thermal elasto-viseoplastic constitutive law. Model parameters were identified from the dilatometer sintering experiment. The real density distribution of green body was measured by X-ray computed tomography （CT）, which was regarded as the initial condition of sintering model. Numerical calculation of the above sintering model was carried out with the finite element soRware Abaqus, through the user-defined material mechanical behavior （UMAT）. The calculation results showed that shrinkages of low density regions were faster than those of high density regions during sintering, which led to internal stresses. Compressive stresses existed in high density regions and tensile stresses existed in low density regions. The densification of local regions depended on not only the initial density, but also the evolution of stresses during the sintering stage.展开更多
The reactive spontaneous infiltration of Al-activated TiO2 (anatase) was investigated. Pure Al powder was blended with TiO2 for activation. They were compacted into the preform and then sealed within 6060 alloy mould....The reactive spontaneous infiltration of Al-activated TiO2 (anatase) was investigated. Pure Al powder was blended with TiO2 for activation. They were compacted into the preform and then sealed within 6060 alloy mould. The activation and infiltration were carried out in 6060 alloy bath for 1 h and comparative sintering experiments were carried out in an argon protected environment under the same conditions of temperature and duration. X-ray diffraction analysis proved that the Al sealed environment was superior to the argon protection on activating the reaction between Al and TiO2. The blending ratio of TiO2 to Al and the temperature were found to play the most important role in infiltration by affecting infiltration and reaction kinetics. Three main types of microstructures were observed after infiltration: full infiltration, partial infiltration with the formation of cracks and no infiltration. The formation of these microstructures was explained on the basis of reaction kinetics and local volume changes due to the reactions. Ultimately, it is found that to obtain an overall good spontaneous infiltration, a TiO2 to Al blending ratio around 3:7 in volume and an infiltration temperature around 900 °C are the most suitable.展开更多
The reaction diffusion between Fe and Al during spark plasma sintering(SPS)was studied.Microstructural evolution wasinvestigated by X-ray diffraction(XRD)and scanning electron microscopy(SEM)and the sintering kinetics...The reaction diffusion between Fe and Al during spark plasma sintering(SPS)was studied.Microstructural evolution wasinvestigated by X-ray diffraction(XRD)and scanning electron microscopy(SEM)and the sintering kinetics was disclosed.The maininterphase of the SPS sample was Fe2Al5at773-873K.Ball-milling enabled a large number of lattice defects and grain boundariesthus the reaction kinetics was accelerated,although the direct current can also promote those defects.After milling,the phasetransformation kinetics was improved from0.207before mill to4.56×10-3.Besides,this work provided more details for thegeneration of Joule heating.The resistance offered to the electric path was considered to be the source of Joule heating,andparticularly the resistance offered by the different contact interfaces of die,punch,graphite foil and the sample played a leading rolefor the generation of Joule heating during spark plasma sintering.展开更多
基金Project(2011CB606306)supported by the National Basic Research Program of ChinaProject(FRF-TP-10-003B)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(51274040)supported by the National Natural Science Foundation of China
文摘The evolution of stresses due to inhomogeneity in metal injection molding （MIM） parts during sintering was investigated. The sintering model of porous materials during densification process was developed based on the continuum mechanics and thermal elasto-viseoplastic constitutive law. Model parameters were identified from the dilatometer sintering experiment. The real density distribution of green body was measured by X-ray computed tomography （CT）, which was regarded as the initial condition of sintering model. Numerical calculation of the above sintering model was carried out with the finite element soRware Abaqus, through the user-defined material mechanical behavior （UMAT）. The calculation results showed that shrinkages of low density regions were faster than those of high density regions during sintering, which led to internal stresses. Compressive stresses existed in high density regions and tensile stresses existed in low density regions. The densification of local regions depended on not only the initial density, but also the evolution of stresses during the sintering stage.
基金the Chinese Scholarship Council (CSC) for financial support (2010612033)
文摘The reactive spontaneous infiltration of Al-activated TiO2 (anatase) was investigated. Pure Al powder was blended with TiO2 for activation. They were compacted into the preform and then sealed within 6060 alloy mould. The activation and infiltration were carried out in 6060 alloy bath for 1 h and comparative sintering experiments were carried out in an argon protected environment under the same conditions of temperature and duration. X-ray diffraction analysis proved that the Al sealed environment was superior to the argon protection on activating the reaction between Al and TiO2. The blending ratio of TiO2 to Al and the temperature were found to play the most important role in infiltration by affecting infiltration and reaction kinetics. Three main types of microstructures were observed after infiltration: full infiltration, partial infiltration with the formation of cracks and no infiltration. The formation of these microstructures was explained on the basis of reaction kinetics and local volume changes due to the reactions. Ultimately, it is found that to obtain an overall good spontaneous infiltration, a TiO2 to Al blending ratio around 3:7 in volume and an infiltration temperature around 900 °C are the most suitable.
基金Projects(51474245,51571214)supported by the National Natural Science Foundation of ChinaProjects(2015GK3004,2015JC3006)supported by the Science and Technology Project of Hunan Province,China+3 种基金Project(2016YFB1100101)supported by the National Key Research and Development Program,ChinaProject(K1502003-11)supported by the Changsha Municipal Major Science and Technology Program,ChinaProject(CSUZC2015030)supported by the Open-End Fund for the Valuable and Precision Instruments of CSU,ChinaProjects(2015CX004,2016CX003)supported by the Project of Innovation-driven Plan in CSU,China
文摘The reaction diffusion between Fe and Al during spark plasma sintering(SPS)was studied.Microstructural evolution wasinvestigated by X-ray diffraction(XRD)and scanning electron microscopy(SEM)and the sintering kinetics was disclosed.The maininterphase of the SPS sample was Fe2Al5at773-873K.Ball-milling enabled a large number of lattice defects and grain boundariesthus the reaction kinetics was accelerated,although the direct current can also promote those defects.After milling,the phasetransformation kinetics was improved from0.207before mill to4.56×10-3.Besides,this work provided more details for thegeneration of Joule heating.The resistance offered to the electric path was considered to be the source of Joule heating,andparticularly the resistance offered by the different contact interfaces of die,punch,graphite foil and the sample played a leading rolefor the generation of Joule heating during spark plasma sintering.
