Thermal stability and strain rate sensitivity of ultrafine-grained(UFG)Fe produced by severe plastic deformation(SPD)were investigated.The UFG Fe was processed by equal-channel angular pressing(ECAP)via route Bc.After...Thermal stability and strain rate sensitivity of ultrafine-grained(UFG)Fe produced by severe plastic deformation(SPD)were investigated.The UFG Fe was processed by equal-channel angular pressing(ECAP)via route Bc.After 6 passes,the grain size of UFG Fe reaches 600 nm, as confirmed by means of electron back scatter diffraction(EBSD).Examination of micro-hardness and grain size of UFG Fe as a function of post-ECAP annealing temperature shows a transition from recovery to recrystallization.The critical transition temperature is approximately 500℃,and the material has a bimodal structure after annealing at this temperature.Deformation behaviors of ECAP Fe and ECAP + annealing Fe were studied under both quasi-static and dynamic compressive loadings.The UFG iron shows increased strength and reduced strain rate sensitivity compared with its coarse-grained counterparts.The appropriate post-ECAP annealing can increase strain hardening ability and cancel out thermal softening effect with only a small loss of strength under dynamic loading.展开更多
目的采用新型复合大塑性变形技术正挤压-等径角挤压工艺(FE-ECAP),研究5052铝合金在室温条件下的变形行为。方法基于有限元分析软件DEFORM-3D,在FE-ECAP工艺下对5052铝合金进行有限元模拟,研究变形过程中挤压载荷、等效应变、金属流动...目的采用新型复合大塑性变形技术正挤压-等径角挤压工艺(FE-ECAP),研究5052铝合金在室温条件下的变形行为。方法基于有限元分析软件DEFORM-3D,在FE-ECAP工艺下对5052铝合金进行有限元模拟,研究变形过程中挤压载荷、等效应变、金属流动速度等场量的分布规律。结果 5052铝合金在FE-ECAP变形过程中,挤压载荷曲线呈双峰形态分布,在挤压模口附近达到第一次峰值,第二次出现在转角处,挤压载荷值为347 k N,同时也是整个挤压过程的最大值;经过FE-ECAP变形后,等效应变大量累积,使得主要变形区达到了高度均匀的变形状态;坯料外转角处金属的流动速度值大于内转角处的流动速度值。结论根据以上结果分析,在FE-ECAP工艺下,为使变形坯料性能优越,应尽量提高坯料变形的均匀性。展开更多
To explore the temperature dependence of deformation behavior of BCC structural materials and the relevant effect of pre-annealing, commercially pure iron (CP Fe) produced by equal-channel angular pressing (ECAP) ...To explore the temperature dependence of deformation behavior of BCC structural materials and the relevant effect of pre-annealing, commercially pure iron (CP Fe) produced by equal-channel angular pressing (ECAP) is selected as the experimental material. The influences of deformation temperature T and pre-annealing on deformation behavior, surface deformation characteristics and substructures of ECAP Fe were systematically studied. The results show that ECAP Fe undergoes a remarkable strain softening stage after a rapid strain hardening during uniaxial compression, and the softening degree and the yield strength avs first decrease and then increase with raising temperature. Pre-annealing at 400 ℃ effectively weakens the strain softening degree and increases trys. To understand the influence of deformation temperature on deformation behavior, as well as the relevant pre-annealing effect, deformation and damage characteristics and dislocation structures are studied in detail. In a word, the strain softening of ECAP Fe is associated not only with internal structural instability, but also with temperature, and pre-annealing at 400 ℃ improves high-temperature me- chanical properties of ECAP Fe.展开更多
基金supported by the National Natural Science Foundation of China(11002151,110722432)973 Project(2010CB631004)
文摘Thermal stability and strain rate sensitivity of ultrafine-grained(UFG)Fe produced by severe plastic deformation(SPD)were investigated.The UFG Fe was processed by equal-channel angular pressing(ECAP)via route Bc.After 6 passes,the grain size of UFG Fe reaches 600 nm, as confirmed by means of electron back scatter diffraction(EBSD).Examination of micro-hardness and grain size of UFG Fe as a function of post-ECAP annealing temperature shows a transition from recovery to recrystallization.The critical transition temperature is approximately 500℃,and the material has a bimodal structure after annealing at this temperature.Deformation behaviors of ECAP Fe and ECAP + annealing Fe were studied under both quasi-static and dynamic compressive loadings.The UFG iron shows increased strength and reduced strain rate sensitivity compared with its coarse-grained counterparts.The appropriate post-ECAP annealing can increase strain hardening ability and cancel out thermal softening effect with only a small loss of strength under dynamic loading.
文摘目的采用新型复合大塑性变形技术正挤压-等径角挤压工艺(FE-ECAP),研究5052铝合金在室温条件下的变形行为。方法基于有限元分析软件DEFORM-3D,在FE-ECAP工艺下对5052铝合金进行有限元模拟,研究变形过程中挤压载荷、等效应变、金属流动速度等场量的分布规律。结果 5052铝合金在FE-ECAP变形过程中,挤压载荷曲线呈双峰形态分布,在挤压模口附近达到第一次峰值,第二次出现在转角处,挤压载荷值为347 k N,同时也是整个挤压过程的最大值;经过FE-ECAP变形后,等效应变大量累积,使得主要变形区达到了高度均匀的变形状态;坯料外转角处金属的流动速度值大于内转角处的流动速度值。结论根据以上结果分析,在FE-ECAP工艺下,为使变形坯料性能优越,应尽量提高坯料变形的均匀性。
基金financially supported by the National Natural Science Foundation of China (Nos. 51231002, 51271054, 51201077 and 50671023)the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20110042110017)the Fundamental Research Funds for the Central Universities of China (Nos. N110105001 and N120505001)
文摘To explore the temperature dependence of deformation behavior of BCC structural materials and the relevant effect of pre-annealing, commercially pure iron (CP Fe) produced by equal-channel angular pressing (ECAP) is selected as the experimental material. The influences of deformation temperature T and pre-annealing on deformation behavior, surface deformation characteristics and substructures of ECAP Fe were systematically studied. The results show that ECAP Fe undergoes a remarkable strain softening stage after a rapid strain hardening during uniaxial compression, and the softening degree and the yield strength avs first decrease and then increase with raising temperature. Pre-annealing at 400 ℃ effectively weakens the strain softening degree and increases trys. To understand the influence of deformation temperature on deformation behavior, as well as the relevant pre-annealing effect, deformation and damage characteristics and dislocation structures are studied in detail. In a word, the strain softening of ECAP Fe is associated not only with internal structural instability, but also with temperature, and pre-annealing at 400 ℃ improves high-temperature me- chanical properties of ECAP Fe.