The hot deformation behaviors of Ni18 Cr9 Co9 Fe5 Nb3 Mo superalloy were explored in the formation temperature range free ofγ’phase with various strain rates applied.The hot deformation behaviors are initially model...The hot deformation behaviors of Ni18 Cr9 Co9 Fe5 Nb3 Mo superalloy were explored in the formation temperature range free ofγ’phase with various strain rates applied.The hot deformation behaviors are initially modeled with Arrhenius equation which gives an average activation energy of 581.1 kJ mol^(-1).A modified Arrhenius approach,including the updated Zener-Hollomon parameter is proposed to consider the change of activation ene rgy under different deformation conditions which turns out a relatively accurate computation for activation energy of hot deformation,i.e.,the standard variance for modified model calculated in the covered deformation condition is just 35.4%of that for Arrhenius equation.The modified model also proposes a map for activation ene rgy which ranges from 571.5-589.0 kJ mol^(-1)for various deformation conditions.Microstructural features of the representative superalloy specimens were characterized by electron backscattered diffraction(EBSD)techniques in order to clarify the influence of activation energy on the microstructural formation.It is found that the Ni-based superalloy samples with higher activation energy are promoted by the degree of dynamic recrystallization which suggests that the rise in activation energy gives either a better recrystallization rate or finer grains.展开更多
LiFePO_(4)has normal olivine-structured(a-LFP)and high pressure(b-LFP)phases,with the former being one of the cathode materials for commercial Li-ion batteries.Despite extensive focus on the respective electrochemical...LiFePO_(4)has normal olivine-structured(a-LFP)and high pressure(b-LFP)phases,with the former being one of the cathode materials for commercial Li-ion batteries.Despite extensive focus on the respective electrochemical properties of the two phases,there is a lack of comparative studies on their electronic and magnetic properties,and the origin of the structural phase transition remains unclear.By combining first-principles calculations with molecular dynamics simulations,we find that the anisotropic compression of Li-O bonds drives the structural phase transition from a-LFP to b-LFP at a critical pressure of 20 GPa,while b-LFP undergoes a transition from semiconductor to metal due to Fe^(3+)generated during delithiation.Their antiferromagnetic(AFM)ground states are predicted to arise from the negative magnetic exchange interactions between nearest and next-nearest neighbor sites,with the corresponding N'eel temperature showing significant enhancement under pressure.Furthermore,compared with a-LFP,b-LFP shows increases in bulk,shear,and Young’s moduli of 8%,13%,and 12%,respectively.These findings enrich the physical property data of LiFePO_(4)phase compounds,providing knowledge for expanding the application scenarios of the a-LFP phase under special operating conditions such as high pressure.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52034004 and 51975404)。
文摘The hot deformation behaviors of Ni18 Cr9 Co9 Fe5 Nb3 Mo superalloy were explored in the formation temperature range free ofγ’phase with various strain rates applied.The hot deformation behaviors are initially modeled with Arrhenius equation which gives an average activation energy of 581.1 kJ mol^(-1).A modified Arrhenius approach,including the updated Zener-Hollomon parameter is proposed to consider the change of activation ene rgy under different deformation conditions which turns out a relatively accurate computation for activation energy of hot deformation,i.e.,the standard variance for modified model calculated in the covered deformation condition is just 35.4%of that for Arrhenius equation.The modified model also proposes a map for activation ene rgy which ranges from 571.5-589.0 kJ mol^(-1)for various deformation conditions.Microstructural features of the representative superalloy specimens were characterized by electron backscattered diffraction(EBSD)techniques in order to clarify the influence of activation energy on the microstructural formation.It is found that the Ni-based superalloy samples with higher activation energy are promoted by the degree of dynamic recrystallization which suggests that the rise in activation energy gives either a better recrystallization rate or finer grains.
基金supported by the National Natural Science Foundation of China(Grant No.12304089)the start-up foundation from Shanghai University。
文摘LiFePO_(4)has normal olivine-structured(a-LFP)and high pressure(b-LFP)phases,with the former being one of the cathode materials for commercial Li-ion batteries.Despite extensive focus on the respective electrochemical properties of the two phases,there is a lack of comparative studies on their electronic and magnetic properties,and the origin of the structural phase transition remains unclear.By combining first-principles calculations with molecular dynamics simulations,we find that the anisotropic compression of Li-O bonds drives the structural phase transition from a-LFP to b-LFP at a critical pressure of 20 GPa,while b-LFP undergoes a transition from semiconductor to metal due to Fe^(3+)generated during delithiation.Their antiferromagnetic(AFM)ground states are predicted to arise from the negative magnetic exchange interactions between nearest and next-nearest neighbor sites,with the corresponding N'eel temperature showing significant enhancement under pressure.Furthermore,compared with a-LFP,b-LFP shows increases in bulk,shear,and Young’s moduli of 8%,13%,and 12%,respectively.These findings enrich the physical property data of LiFePO_(4)phase compounds,providing knowledge for expanding the application scenarios of the a-LFP phase under special operating conditions such as high pressure.
