To study the effect of tempering temperature on strain hardening exponent and flow stress curve,one kind of 1000 MPa grade low carbon bainitic steel for construction machinery was designed,and the standard uniaxial te...To study the effect of tempering temperature on strain hardening exponent and flow stress curve,one kind of 1000 MPa grade low carbon bainitic steel for construction machinery was designed,and the standard uniaxial tensile tests were conducted at room temperature.A new flow stress model,which could predict the flow behavior of the tested steels at different tempering temperatures more efficiently,was established.The relationship between mobile dislocation density and strain hardening exponent was discussed based on the dislocation-stress relation.Arrhenius equation and an inverse proportional function were adopted to describe the mobile dislocation,and two mathematical models were established to describe the relationship between tempering temperature and strain hardening exponent.Nonlinear regression analysis was applied to the Arrhenius type model,hence,the activation energy was determined to be 37.6kJ/mol.Moreover,the square of correlation coefficient was 0.985,which indicated a high reliability between the fitted curve and experimental data.By comparison with the Arrhenius type curve,the general trend of the inverse proportional fitting curve was coincided with the experimental data points except of some fitting errors.Thus,the Arrhenius type model can be adopted to predict the strain hardening exponent at different tempering temperatures.展开更多
Yttria-stabilized zirconia(YSZ)coatings and Al_(2)O_(3)–YSZ coatings were prepared by atmospheric plasma spraying(APS).Their microstructural changes during thermal cycling were investigated via scanning electron micr...Yttria-stabilized zirconia(YSZ)coatings and Al_(2)O_(3)–YSZ coatings were prepared by atmospheric plasma spraying(APS).Their microstructural changes during thermal cycling were investigated via scanning electron microscopy(SEM)equipped with electron backscatter diffraction(EBSD)and X-ray diffraction(XRD).It was found that the microstructure and microstructure changes of the two coatings were different,including crystallinity,grain orientation,phase,and phase transition.These differences are closely related to the thermal cycle life of the coatings.There is a relationship between crystallinity and crack size.Changes in grain orientation are related to microscopic strain and cracks.Phase transition is the direct cause of coating failure.In this study,the relationship between the changes in the coating microstructure and the thermal cycle life is discussed in detail.The failure mechanism of the coating was comprehensively analyzed from a microscopic perspective.展开更多
文摘To study the effect of tempering temperature on strain hardening exponent and flow stress curve,one kind of 1000 MPa grade low carbon bainitic steel for construction machinery was designed,and the standard uniaxial tensile tests were conducted at room temperature.A new flow stress model,which could predict the flow behavior of the tested steels at different tempering temperatures more efficiently,was established.The relationship between mobile dislocation density and strain hardening exponent was discussed based on the dislocation-stress relation.Arrhenius equation and an inverse proportional function were adopted to describe the mobile dislocation,and two mathematical models were established to describe the relationship between tempering temperature and strain hardening exponent.Nonlinear regression analysis was applied to the Arrhenius type model,hence,the activation energy was determined to be 37.6kJ/mol.Moreover,the square of correlation coefficient was 0.985,which indicated a high reliability between the fitted curve and experimental data.By comparison with the Arrhenius type curve,the general trend of the inverse proportional fitting curve was coincided with the experimental data points except of some fitting errors.Thus,the Arrhenius type model can be adopted to predict the strain hardening exponent at different tempering temperatures.
基金This work is supported by the National Key Technologies R&D Program of China(No.2018YFB0704400)Shanghai Technical Platform for Testing on Inorganic Materials(No.19DZ2290700).
文摘Yttria-stabilized zirconia(YSZ)coatings and Al_(2)O_(3)–YSZ coatings were prepared by atmospheric plasma spraying(APS).Their microstructural changes during thermal cycling were investigated via scanning electron microscopy(SEM)equipped with electron backscatter diffraction(EBSD)and X-ray diffraction(XRD).It was found that the microstructure and microstructure changes of the two coatings were different,including crystallinity,grain orientation,phase,and phase transition.These differences are closely related to the thermal cycle life of the coatings.There is a relationship between crystallinity and crack size.Changes in grain orientation are related to microscopic strain and cracks.Phase transition is the direct cause of coating failure.In this study,the relationship between the changes in the coating microstructure and the thermal cycle life is discussed in detail.The failure mechanism of the coating was comprehensively analyzed from a microscopic perspective.
