The hot deformation characteristics of Rene88DT superalloy with directionally solidified micro- structure produced by electroslag remelting continuous directionally solidification （ESR-CDS） were studied in the tempe...The hot deformation characteristics of Rene88DT superalloy with directionally solidified micro- structure produced by electroslag remelting continuous directionally solidification （ESR-CDS） were studied in the temperature range of 1,040-1,140 ℃ and strain rate range of 0.001-1.000 s-1 by hot compression tests. Flow curves for Rene88DT alloy with initial directionally solidified （DS） microstructure exhibit pronounced peak stresses at the early stage of deformation followed by the occurrence of dynamic softening phenomenon. Rene88DT alloy with DS micro- structure shows higher flow peak stresses compared with HIPed P/M superalloy FGH4096, but the disparities in peak stresses between ESR-CDSed Rene88DT and HIPed P/M superalloy FGH4096 reduce as temperature increases. The improvement of hot workability of DS alloy with columnar grains avoiding the maximum shear stress comes true. A hot deformation constitutive equation as a function of strain that describes the dependence of flow stress on strain rate and temperature is established. Hot deformation apparent acti- vation energy （Q） varies not only with the strain rate and temperature but also with strain. The strain rate sensitivity exponent （m） map is established at the strain of 0.8, which reveals that global dynamic recrystallization （DRX） shows a relatively high m value in a large strain compression. Optimum parameters are predicted in two regions： T = 1,100-1,130 ℃, ε = 0.100-1.000 s-1 and T = 1,080- 1,100 ℃, ε = 0.010-100 s-1, which is based on pro- cessing maps and deformation microstructure observations.展开更多
Isothermal crystallization process of polymers in a confined volume was simulated in the case of instantaneous nucleation by use of the Monte Carlo method.The influence of sample thickness on some kinetic parameters o...Isothermal crystallization process of polymers in a confined volume was simulated in the case of instantaneous nucleation by use of the Monte Carlo method.The influence of sample thickness on some kinetic parameters of crystallization was quantitatively evaluated.It was found that there was a critical thickness value.Influence of thickness on the crystallization behavior was only found for samples of thickness near and less than the critical value.For thick samples the Avrami plot showed straight lines with a turning point at the late stage of crystallization due to the secondary crystallization.When the thickness was near or less than the critical value a primary turning point appeared in the Avrami plot at the very beginning of the crystallization process.A model was proposed to explain the mechanism of this phenomenon.According to this model the critical thickness value is related to the nucleation density or the average distance between adjacent nuclei,and the primary turning point is an indication of a transformation of crystal growth geometry from a three-dimensional mode to a two-dimensional one.Analysis of experimental results of PEO isothermally crystallized at 53.5℃ was consistent with the proposed model.展开更多
基金financially supported by the Military Supporting Project (No. JPPT125GJGG11)
文摘The hot deformation characteristics of Rene88DT superalloy with directionally solidified micro- structure produced by electroslag remelting continuous directionally solidification （ESR-CDS） were studied in the temperature range of 1,040-1,140 ℃ and strain rate range of 0.001-1.000 s-1 by hot compression tests. Flow curves for Rene88DT alloy with initial directionally solidified （DS） microstructure exhibit pronounced peak stresses at the early stage of deformation followed by the occurrence of dynamic softening phenomenon. Rene88DT alloy with DS micro- structure shows higher flow peak stresses compared with HIPed P/M superalloy FGH4096, but the disparities in peak stresses between ESR-CDSed Rene88DT and HIPed P/M superalloy FGH4096 reduce as temperature increases. The improvement of hot workability of DS alloy with columnar grains avoiding the maximum shear stress comes true. A hot deformation constitutive equation as a function of strain that describes the dependence of flow stress on strain rate and temperature is established. Hot deformation apparent acti- vation energy （Q） varies not only with the strain rate and temperature but also with strain. The strain rate sensitivity exponent （m） map is established at the strain of 0.8, which reveals that global dynamic recrystallization （DRX） shows a relatively high m value in a large strain compression. Optimum parameters are predicted in two regions： T = 1,100-1,130 ℃, ε = 0.100-1.000 s-1 and T = 1,080- 1,100 ℃, ε = 0.010-100 s-1, which is based on pro- cessing maps and deformation microstructure observations.
文摘Isothermal crystallization process of polymers in a confined volume was simulated in the case of instantaneous nucleation by use of the Monte Carlo method.The influence of sample thickness on some kinetic parameters of crystallization was quantitatively evaluated.It was found that there was a critical thickness value.Influence of thickness on the crystallization behavior was only found for samples of thickness near and less than the critical value.For thick samples the Avrami plot showed straight lines with a turning point at the late stage of crystallization due to the secondary crystallization.When the thickness was near or less than the critical value a primary turning point appeared in the Avrami plot at the very beginning of the crystallization process.A model was proposed to explain the mechanism of this phenomenon.According to this model the critical thickness value is related to the nucleation density or the average distance between adjacent nuclei,and the primary turning point is an indication of a transformation of crystal growth geometry from a three-dimensional mode to a two-dimensional one.Analysis of experimental results of PEO isothermally crystallized at 53.5℃ was consistent with the proposed model.
