在整体式车辆稳定性轨迹跟踪控制架构的基础之上,设计了一种引入预瞄曲率信息的自适应预测时域非线性模型预测控制(NMPC).基于预瞄的参考路径曲率点列指导控制维度变化,提升控制器对于路径曲率的动态响应能力;进一步地,引入状态协调优...在整体式车辆稳定性轨迹跟踪控制架构的基础之上,设计了一种引入预瞄曲率信息的自适应预测时域非线性模型预测控制(NMPC).基于预瞄的参考路径曲率点列指导控制维度变化,提升控制器对于路径曲率的动态响应能力;进一步地,引入状态协调优化机制,使控制器显示耦合至上一控制周期的车辆状态空间,有效避免预测时域变化造成的多步优化问题解耦效应,抑制因控制输入突变对轨迹跟踪控制任务的影响.结合两种优化方法,有效改善固定预测时域策略在高曲率轨迹跟踪中因累计误差造成的跟踪精度下降问题.最后,基于MATLAB/Simulink-CarSim联合仿真平台对算法进行了验证.经计算,高速单移线工况下,该方法在侧向偏差均值/峰值、纵向偏差均值/峰值、航向偏差均值/峰值指标中,相较于固定预测时域NMPC同比降低36.17%/15.25%、11.55%/38.58%、6.13%/25.27%;高速双移线工况下,同比降低30.28%/29.77%、25.07%/3.85%、11.02%/2.68%.此外,在高速低附着工况中,该方法仍能保证良好的控制精度及侧向稳定性,其峰值侧向偏差为0.2017 m、峰值纵向偏差为0.9744 km h^(-1)、峰值航向偏差为1.1936°、峰值质心侧偏角为1.9074°.展开更多
The refinement of the as-cast grain structure in austenitic heat-resistant stainless steel depends on the formation of active solid nuclei during solidification.Titanium(Ti)additions successfully induced the formation...The refinement of the as-cast grain structure in austenitic heat-resistant stainless steel depends on the formation of active solid nuclei during solidification.Titanium(Ti)additions successfully induced the formation of Ti-containing inclusions,enhancing heterogeneous nucleation and promoting equiaxed dendritic growth in 347H stainless steel.Thermal simulation experiments indicated that the equiaxed crystal ratios increased notably with Ti content;samples with 0.06,0.12,and 0.36 wt.%Ti exhibited equiaxed ratios of 18%,24%,and 41%,respectively.Three primary inclusion types—TiN,Al_(2)O_(3)-TiN,and TiO_(x)-TiN—were identified at the cores of equiaxed dendrites,with nucleation core sizes predominantly ranging from 0.5 to 8μm.Among the tested samples,the 0.36 wt.%Ti addition produced the highest nucleation core density.Increasing Ti content significantly elevated dendrite tip undercooling from 2.6 K(0.06 wt.%Ti)to 10.8 K(0.36 wt.%Ti),accelerating solidification front instability and thus enhancing heterogeneous nucleation.Additionally,higher Ti content increased the divergence angle between adjacent columnar dendrites,further promoting the columnar-to-equiaxed transition(CET).展开更多
Different from previous attention on the austenization temperature or dwelling time of PH13-8Mo stainless steels,the effect of the cooling rate on the hierarchical microstructure and mechanical properties was revealed...Different from previous attention on the austenization temperature or dwelling time of PH13-8Mo stainless steels,the effect of the cooling rate on the hierarchical microstructure and mechanical properties was revealed.For all of water,oil,air and furnace cooling,there is almost-complete martensite with the favorable hardenability.The increase in cooling rate mainly increases the density of dislocation and residual strain in the as-solution annealed matrix.After aging treatment,the cooling rate dominates the ratio of high-angle grain boundaries(HAGBs)instead of the size of martensite blocks.The ratio of HAGBs continuously increases with the decreased cooling rate,while the width of blocks maintains 2.40-2.49μm.Meanwhile,more reversed austenite distributes at the martensite sub-grain boundaries.By comparison,the increased rate of water cooling contributes to a favorable precipitation of NiAl with fine size and dispersive distribution caused by more accumulated internal defects of vacancies and dislocations.With the decrease of cooling rate,NiAl precipitates exhibits a similar diameter of~7 nm while a larger inter-particle distance of~22 nm.In the case of low cooling rate(oil,air and furnace),the stable precipitation strengthening effect contributes to a high yield strength of~1.3 GPa and ultimate tensile strength of~1.4 GPa.The high-ratio HAGBs,reversed austenite and NiAl precipitates with larger-interparticle distance synergistically improve the impact toughness(V-notched Charpy impact energy of 100-110 J).展开更多
Cold deformation treatment of Cu-bearing stainless steel through a cold rolling process combined with electric pulse treatment(EPT)can significantly improve the microstructure and formability of cold-rolled Cu-bearing...Cold deformation treatment of Cu-bearing stainless steel through a cold rolling process combined with electric pulse treatment(EPT)can significantly improve the microstructure and formability of cold-rolled Cu-bearing stainless steel.The microstructure after EPT was characterized by scanning electron microscopy,transmission electron microscopy,and in-situ tensile testing.It is found that compared with conventional heat treatment,EPT process can significantly promote the nucleation rate and mobility at grain boundaries of the deformed samples,greatly accelerating the recovery and static recrystallization of Cu-bearing stainless steel samples at lower temperatures and contributing to the recovery of anisotropy and the re-molding of deformed samples.Microstructural characterization and theoretical analyses show that the rapid recrystallization during EPT process is caused not only by Joule heating effects but also by non-thermal effects that accelerate grain boundary migration and dislocation destruction and regeneration.In addition,EPT process significantly accelerated the nucleation and precipitation growth of Cu-rich phase.The coarsening of Cu-rich phase during EPT process is due to not only the high vacancy diffusion coefficient under the action of the electric pulse but also the increase in the vacancy diffusion flux induced by the electromigration in the process of the electric pulse.展开更多
To elucidate the accelerated degradation mechanisms of metallic interconnects in operational solid oxide fuel cells,the oxidation behavior of FSS430 ferritic stainless steel under the coupling of simultaneous electric...To elucidate the accelerated degradation mechanisms of metallic interconnects in operational solid oxide fuel cells,the oxidation behavior of FSS430 ferritic stainless steel under the coupling of simultaneous electrical current and high-temperature exposure is investigated.Isothermal thermogravimetric analysis was employed to quantify oxidation kinetics,complemented by microstructural characterization using X-ray diffraction,scanning electron microscopy with energy-dispersive spectroscopy and transmission electron microscopy.Experimental results demonstrate that the applied current dramatically enhances oxidation rates,increasing specific mass gain from 0.25 mg/cm^(2)(0 A/cm^(2))to 5.20 mg/cm^(2)(0.2 A/cm^(2))and oxide scale thickness from 1.87 to 15.62μm after 200 h.This acceleration originates from current-induced electromigration forces that promote cationic transport through the oxide layer.The quantitative relationships between current density and oxidation parameters are established,enabling predictive modeling of interconnector degradation in solid oxide fuel cell(SOFC)systems.展开更多
350 keV He^(+) ions were injected into laser powder bed fusion(LPBF)-processed 304L stainless steel and traditional rolled 304L stainless steel with a flux of 1×10^(17) ions/cm^(2) at room temperature,followed by...350 keV He^(+) ions were injected into laser powder bed fusion(LPBF)-processed 304L stainless steel and traditional rolled 304L stainless steel with a flux of 1×10^(17) ions/cm^(2) at room temperature,followed by annealing at 750℃ for 10,100,and 300 h,respectively.The results showed that material swelling due to helium bubble coarsening was almost not observed in either the LPBF or rolled samples after 10 h of annealing duration.Rapid coarsening and swelling of bubbles occurred in the rolled samples,but only moderate bubble growth occurred in the LPBF sample after annealing for 100 h.After annealing for 300 h,the helium bubbles in both samples tended to grow steadily.For 10 h of annealing,the irradiated samples were in a disequilibrium state,and the apparent activation energy(E^(act))calculated by the Arrhenius model determined that helium atoms tended to diffuse through the displacement mechanism,and helium bubbles grew under the migration and coalescence(MC)mechanism.With annealing times over 100 h,the high-density dislocations and nano-oxide particles in the LPBF sample still had a strong trapping effect on the movement and growth of helium bubbles.After annealing for 300 h,the cellular subgrains in the LPBF sample decomposed,and the nano-oxide particles had no trapping effect on the helium bubbles.At this time,the dislocation structure played a primary role in suppressing the growth of helium bubbles,and the radiation resistance of the LPBF sample remained superior to that of the rolled samples.展开更多
文摘在整体式车辆稳定性轨迹跟踪控制架构的基础之上,设计了一种引入预瞄曲率信息的自适应预测时域非线性模型预测控制(NMPC).基于预瞄的参考路径曲率点列指导控制维度变化,提升控制器对于路径曲率的动态响应能力;进一步地,引入状态协调优化机制,使控制器显示耦合至上一控制周期的车辆状态空间,有效避免预测时域变化造成的多步优化问题解耦效应,抑制因控制输入突变对轨迹跟踪控制任务的影响.结合两种优化方法,有效改善固定预测时域策略在高曲率轨迹跟踪中因累计误差造成的跟踪精度下降问题.最后,基于MATLAB/Simulink-CarSim联合仿真平台对算法进行了验证.经计算,高速单移线工况下,该方法在侧向偏差均值/峰值、纵向偏差均值/峰值、航向偏差均值/峰值指标中,相较于固定预测时域NMPC同比降低36.17%/15.25%、11.55%/38.58%、6.13%/25.27%;高速双移线工况下,同比降低30.28%/29.77%、25.07%/3.85%、11.02%/2.68%.此外,在高速低附着工况中,该方法仍能保证良好的控制精度及侧向稳定性,其峰值侧向偏差为0.2017 m、峰值纵向偏差为0.9744 km h^(-1)、峰值航向偏差为1.1936°、峰值质心侧偏角为1.9074°.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB3700602)the Jiaxing Key Research and Development Program(Grant No.2022BZ10010).
文摘The refinement of the as-cast grain structure in austenitic heat-resistant stainless steel depends on the formation of active solid nuclei during solidification.Titanium(Ti)additions successfully induced the formation of Ti-containing inclusions,enhancing heterogeneous nucleation and promoting equiaxed dendritic growth in 347H stainless steel.Thermal simulation experiments indicated that the equiaxed crystal ratios increased notably with Ti content;samples with 0.06,0.12,and 0.36 wt.%Ti exhibited equiaxed ratios of 18%,24%,and 41%,respectively.Three primary inclusion types—TiN,Al_(2)O_(3)-TiN,and TiO_(x)-TiN—were identified at the cores of equiaxed dendrites,with nucleation core sizes predominantly ranging from 0.5 to 8μm.Among the tested samples,the 0.36 wt.%Ti addition produced the highest nucleation core density.Increasing Ti content significantly elevated dendrite tip undercooling from 2.6 K(0.06 wt.%Ti)to 10.8 K(0.36 wt.%Ti),accelerating solidification front instability and thus enhancing heterogeneous nucleation.Additionally,higher Ti content increased the divergence angle between adjacent columnar dendrites,further promoting the columnar-to-equiaxed transition(CET).
基金supported by the National Key Research and Development Program(Grant No.2024YFB3714200)the National Natural Science Foundation of China(Grant Nos.52173305,52233017,52203384,U244120568 and U2441261)+1 种基金the Key Program of the Chinese Academy of Sciences(Grant No.RCJJ-145-24-40)LingChuang Research Project of China National Nuclear Corporation,and Special Funds for Science and Technology Planning of Jiangsu Province(No.BZ2024059).
文摘Different from previous attention on the austenization temperature or dwelling time of PH13-8Mo stainless steels,the effect of the cooling rate on the hierarchical microstructure and mechanical properties was revealed.For all of water,oil,air and furnace cooling,there is almost-complete martensite with the favorable hardenability.The increase in cooling rate mainly increases the density of dislocation and residual strain in the as-solution annealed matrix.After aging treatment,the cooling rate dominates the ratio of high-angle grain boundaries(HAGBs)instead of the size of martensite blocks.The ratio of HAGBs continuously increases with the decreased cooling rate,while the width of blocks maintains 2.40-2.49μm.Meanwhile,more reversed austenite distributes at the martensite sub-grain boundaries.By comparison,the increased rate of water cooling contributes to a favorable precipitation of NiAl with fine size and dispersive distribution caused by more accumulated internal defects of vacancies and dislocations.With the decrease of cooling rate,NiAl precipitates exhibits a similar diameter of~7 nm while a larger inter-particle distance of~22 nm.In the case of low cooling rate(oil,air and furnace),the stable precipitation strengthening effect contributes to a high yield strength of~1.3 GPa and ultimate tensile strength of~1.4 GPa.The high-ratio HAGBs,reversed austenite and NiAl precipitates with larger-interparticle distance synergistically improve the impact toughness(V-notched Charpy impact energy of 100-110 J).
基金supported by the National Natural Science Foundation of China(Nos.52305401 and 52475391)National Key Research and Development Program of China(2024YFB3714301)+1 种基金the Fundamental Research Program of Shanxi Province(202303011211004,TZLH20230818001)Engineering Research Center of the Ministry of Education.
文摘Cold deformation treatment of Cu-bearing stainless steel through a cold rolling process combined with electric pulse treatment(EPT)can significantly improve the microstructure and formability of cold-rolled Cu-bearing stainless steel.The microstructure after EPT was characterized by scanning electron microscopy,transmission electron microscopy,and in-situ tensile testing.It is found that compared with conventional heat treatment,EPT process can significantly promote the nucleation rate and mobility at grain boundaries of the deformed samples,greatly accelerating the recovery and static recrystallization of Cu-bearing stainless steel samples at lower temperatures and contributing to the recovery of anisotropy and the re-molding of deformed samples.Microstructural characterization and theoretical analyses show that the rapid recrystallization during EPT process is caused not only by Joule heating effects but also by non-thermal effects that accelerate grain boundary migration and dislocation destruction and regeneration.In addition,EPT process significantly accelerated the nucleation and precipitation growth of Cu-rich phase.The coarsening of Cu-rich phase during EPT process is due to not only the high vacancy diffusion coefficient under the action of the electric pulse but also the increase in the vacancy diffusion flux induced by the electromigration in the process of the electric pulse.
基金supported by Natural Science Foundation of Wuhan(2024040701010051)Natural Science Foundation of Hubei(2023AFB111)and National Natural Science Foundation of China(52401108).
文摘To elucidate the accelerated degradation mechanisms of metallic interconnects in operational solid oxide fuel cells,the oxidation behavior of FSS430 ferritic stainless steel under the coupling of simultaneous electrical current and high-temperature exposure is investigated.Isothermal thermogravimetric analysis was employed to quantify oxidation kinetics,complemented by microstructural characterization using X-ray diffraction,scanning electron microscopy with energy-dispersive spectroscopy and transmission electron microscopy.Experimental results demonstrate that the applied current dramatically enhances oxidation rates,increasing specific mass gain from 0.25 mg/cm^(2)(0 A/cm^(2))to 5.20 mg/cm^(2)(0.2 A/cm^(2))and oxide scale thickness from 1.87 to 15.62μm after 200 h.This acceleration originates from current-induced electromigration forces that promote cationic transport through the oxide layer.The quantitative relationships between current density and oxidation parameters are established,enabling predictive modeling of interconnector degradation in solid oxide fuel cell(SOFC)systems.
基金supported by the National Natural Science Foundation of China(Nos.U22B2067 and 52073176).
文摘350 keV He^(+) ions were injected into laser powder bed fusion(LPBF)-processed 304L stainless steel and traditional rolled 304L stainless steel with a flux of 1×10^(17) ions/cm^(2) at room temperature,followed by annealing at 750℃ for 10,100,and 300 h,respectively.The results showed that material swelling due to helium bubble coarsening was almost not observed in either the LPBF or rolled samples after 10 h of annealing duration.Rapid coarsening and swelling of bubbles occurred in the rolled samples,but only moderate bubble growth occurred in the LPBF sample after annealing for 100 h.After annealing for 300 h,the helium bubbles in both samples tended to grow steadily.For 10 h of annealing,the irradiated samples were in a disequilibrium state,and the apparent activation energy(E^(act))calculated by the Arrhenius model determined that helium atoms tended to diffuse through the displacement mechanism,and helium bubbles grew under the migration and coalescence(MC)mechanism.With annealing times over 100 h,the high-density dislocations and nano-oxide particles in the LPBF sample still had a strong trapping effect on the movement and growth of helium bubbles.After annealing for 300 h,the cellular subgrains in the LPBF sample decomposed,and the nano-oxide particles had no trapping effect on the helium bubbles.At this time,the dislocation structure played a primary role in suppressing the growth of helium bubbles,and the radiation resistance of the LPBF sample remained superior to that of the rolled samples.
