As-hot-rolled medium-entropy alloys(MEAs)with unevenly distributed grain sizes of face-centered cubic grains exhibit better yield strength without uniform elongation loss compared to cold-rolled and an-nealed ones.Suc...As-hot-rolled medium-entropy alloys(MEAs)with unevenly distributed grain sizes of face-centered cubic grains exhibit better yield strength without uniform elongation loss compared to cold-rolled and an-nealed ones.Successive operation of dynamic recrystallization(DRX)during several hot rolling passes leads to a wide range of grain sizes from submicrons to tens of micrometers due to the grain growth after nucleation:early recrystallized grains are coarser than recently recrystallized ones.Not only the grain size but internal dislocation density of the recently recrystallized grain is low.During the tensile deformation of the hot-rolled MEAs at-196 ℃,dislocation pile-ups in the relatively soft and fine DRX grains enhance yield stress and hetero-deformation-induced strain hardening.Thanks to the enhanced yield stress of the as-hot-rolled MEAs,stress-induced martensitic transformation easily occurs.Notably,partially DRXed MEAs hot-rolled at 800 ℃ have lower yield stress than fully DRXed ones,hot-rolled at 900 and 1000 ℃.This is attributed to the softening effect of the stress-induced body-centered cubic martensitic transformation in unrecrystallized coarse grains prior to the yielding,which lowers the yield stress of the partially DRXed ones.After yielding,the martensitic transformation facilitates strain hard-ening and early necking is precluded.This study presents a fresh outlook on the uneven distribution of grain sizes by hot rolling beneficial to mechanical responses of uniform elongation of~45%despite the as-rolled states with an advantage of simplified thermo-mechanical processes.展开更多
Thermodynamic properties of the charge density wave(CDW) transition in potassium blue bronze K 0.3 MoO 3 are investigated by the measurement of specific heat. A second order phase transition is observed at 177...Thermodynamic properties of the charge density wave(CDW) transition in potassium blue bronze K 0.3 MoO 3 are investigated by the measurement of specific heat. A second order phase transition is observed at 177.5 K. The specific heat jump, and enthalpy and entropy changes associated with the transition are estimated. The results suggest that the lattice plays an important role in thermodynamics for this compound. Analysis of the data near CDW transition shows that width of critical region is about 6 K and the critical behavior belongs to the universality class of the three dimensional XY model.展开更多
基金POSCO(No.2021Y037)Nano&Material Technology Development Program through the National Research Foundation of Korea(NRF)funded by Ministry of Science and ICT(No.RS-2023-00281246)+1 种基金National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIP)(Nos.NRF–2021R1A2C3006662 and NRF-2022R1F1A1073796)J.L.acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(No.RS-2023-00276120).
文摘As-hot-rolled medium-entropy alloys(MEAs)with unevenly distributed grain sizes of face-centered cubic grains exhibit better yield strength without uniform elongation loss compared to cold-rolled and an-nealed ones.Successive operation of dynamic recrystallization(DRX)during several hot rolling passes leads to a wide range of grain sizes from submicrons to tens of micrometers due to the grain growth after nucleation:early recrystallized grains are coarser than recently recrystallized ones.Not only the grain size but internal dislocation density of the recently recrystallized grain is low.During the tensile deformation of the hot-rolled MEAs at-196 ℃,dislocation pile-ups in the relatively soft and fine DRX grains enhance yield stress and hetero-deformation-induced strain hardening.Thanks to the enhanced yield stress of the as-hot-rolled MEAs,stress-induced martensitic transformation easily occurs.Notably,partially DRXed MEAs hot-rolled at 800 ℃ have lower yield stress than fully DRXed ones,hot-rolled at 900 and 1000 ℃.This is attributed to the softening effect of the stress-induced body-centered cubic martensitic transformation in unrecrystallized coarse grains prior to the yielding,which lowers the yield stress of the partially DRXed ones.After yielding,the martensitic transformation facilitates strain hard-ening and early necking is precluded.This study presents a fresh outlook on the uneven distribution of grain sizes by hot rolling beneficial to mechanical responses of uniform elongation of~45%despite the as-rolled states with an advantage of simplified thermo-mechanical processes.
文摘Thermodynamic properties of the charge density wave(CDW) transition in potassium blue bronze K 0.3 MoO 3 are investigated by the measurement of specific heat. A second order phase transition is observed at 177.5 K. The specific heat jump, and enthalpy and entropy changes associated with the transition are estimated. The results suggest that the lattice plays an important role in thermodynamics for this compound. Analysis of the data near CDW transition shows that width of critical region is about 6 K and the critical behavior belongs to the universality class of the three dimensional XY model.
