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
The isothermal compression of M50 steel is carried out on a Gleeble-3500 thermo-mechanical simulator in temperature range of 1 223-1 423 K and strain rates range of 10-70 s^-1. The results show that the carbides play ...The isothermal compression of M50 steel is carried out on a Gleeble-3500 thermo-mechanical simulator in temperature range of 1 223-1 423 K and strain rates range of 10-70 s^-1. The results show that the carbides play a significant role in the flow behavior and microstructure evolution during isothermal compression of M50 steel. The average apparent activation energy for deformation in isothermal compression of M50 steel is （281.1±42.6） kJ·mol^-1 at the strains of 0.4-0.8. The dynamic recrystallization of austenite grains occurs in isothermal compression of M50 steel at 1 363 K and 1 393 K, enhancing with the increase of strain rate and/or strain. The volume fraction of the carbides decreases with the increase of deformation temperature during isothermal compression of M50 steel and the fine carbides inhibit the dynamic recrystallization of austenite grain. With the occurrence of dynamic recrystallization, the austenite grains are refined, leading to a minor increase in the flow stress and apparent activation energy for deformation in isothermal compression of M50 steel. The austenite grains begin to coarsen at 1 423 K and dynamic recrystallization is limited. Hot working of M50 steel should not be performed above 1 393 K in order to achieve good workability.展开更多
Isothermal compression of Ti-6Al-4V alloy was conducted in the deformation temperature range of 1093-1303 K, the strain rates of 0.001, 0.01, 0.1, 1.0, and 10.0 s-1, and the height reductions of 20%-60% with an interv...Isothermal compression of Ti-6Al-4V alloy was conducted in the deformation temperature range of 1093-1303 K, the strain rates of 0.001, 0.01, 0.1, 1.0, and 10.0 s-1, and the height reductions of 20%-60% with an interval of 10%. After compression, the effect of the processing parameters including deformation temperature, strain rate, and height reduction on the flow stress and the microstructure was investigated. The grain size of primary a phase was measured using an OLYMPUS PMG3 microscope with the quantitative metallography SISC IAS V8.0 image analysis software. A model of grain size in isothermal compression of Ti-6A1-4V alloy was developed using fuzzy neural net- work （FNN） with back-propagation （BP） learning algorithm. The maximum difference and the average difference between the predicted and the experimental grain sizes of primary a phase are 13.31% and 7.62% for the sampled data, and 16.48% and 6.97% for the non-sampled data, respectively. It can be concluded that the present model with high prediction precision can be used to predict the grain size in isothermal compression of Ti-6Al-4V alloy.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.
文摘采用Gleeble-1500热模拟试验机对V-5Cr-5Ti合金进行了热模拟压缩试验。研究了V-5Cr-5Ti合金在变形温度为1373~1493 K、应变速率为0.1~30.0 s-1工艺条件下的流变行为,建立了合金高温变形的流变应力模型和加工图,并观察了合金变形后的金相组织。研究结果表明：流变应力和峰值应变随变形温度的降低和应变速率的提高而增大。以热模拟压缩试验为基础,通过对真应力-应变曲线的分析与计算得到了V-5Cr-5Ti合金的热变形激活能Q值为468.25 k J·mol-1,建立了V-5Cr-5Ti合金高温变形的流变应力模型。同时,建立了描述V-5Cr-5Ti合金热加工性能的热加工图,其由3部分组成,即Ⅰ变形安全区,Ⅱ变形安全区以及流变失稳区,其中流变失稳区呈对角线连续分布。在绘制、分析V-5Cr-5Ti合金的热加工图的基础上,结合组织分析得出,V-5Cr-5Ti合金最适合在Ⅱ变形安全区内采用液压机进行变形加工。
文摘The isothermal compression of M50 steel is carried out on a Gleeble-3500 thermo-mechanical simulator in temperature range of 1 223-1 423 K and strain rates range of 10-70 s^-1. The results show that the carbides play a significant role in the flow behavior and microstructure evolution during isothermal compression of M50 steel. The average apparent activation energy for deformation in isothermal compression of M50 steel is （281.1±42.6） kJ·mol^-1 at the strains of 0.4-0.8. The dynamic recrystallization of austenite grains occurs in isothermal compression of M50 steel at 1 363 K and 1 393 K, enhancing with the increase of strain rate and/or strain. The volume fraction of the carbides decreases with the increase of deformation temperature during isothermal compression of M50 steel and the fine carbides inhibit the dynamic recrystallization of austenite grain. With the occurrence of dynamic recrystallization, the austenite grains are refined, leading to a minor increase in the flow stress and apparent activation energy for deformation in isothermal compression of M50 steel. The austenite grains begin to coarsen at 1 423 K and dynamic recrystallization is limited. Hot working of M50 steel should not be performed above 1 393 K in order to achieve good workability.
基金financially supported by the National Natural Science Foundation of China (No.50975234)
文摘Isothermal compression of Ti-6Al-4V alloy was conducted in the deformation temperature range of 1093-1303 K, the strain rates of 0.001, 0.01, 0.1, 1.0, and 10.0 s-1, and the height reductions of 20%-60% with an interval of 10%. After compression, the effect of the processing parameters including deformation temperature, strain rate, and height reduction on the flow stress and the microstructure was investigated. The grain size of primary a phase was measured using an OLYMPUS PMG3 microscope with the quantitative metallography SISC IAS V8.0 image analysis software. A model of grain size in isothermal compression of Ti-6A1-4V alloy was developed using fuzzy neural net- work （FNN） with back-propagation （BP） learning algorithm. The maximum difference and the average difference between the predicted and the experimental grain sizes of primary a phase are 13.31% and 7.62% for the sampled data, and 16.48% and 6.97% for the non-sampled data, respectively. It can be concluded that the present model with high prediction precision can be used to predict the grain size in isothermal compression of Ti-6Al-4V alloy.
