Medium-entropy alloys(MEAs)have garnered significant interest due to their unique mechanical prop-erties,but phase instabilities such as the formation of brittle sigma(σ)phase during annealing pose challenges to thei...Medium-entropy alloys(MEAs)have garnered significant interest due to their unique mechanical prop-erties,but phase instabilities such as the formation of brittle sigma(σ)phase during annealing pose challenges to their practical application.This study investigates the microstructural evolution and me-chanical behavior of an 80%cold-rolled Fe_(45)Co_(35)Cr_(10)V_(10)MEA that was isochronally annealed between 100℃ and 900℃ for 300 s and characterized using hardness indentations,in-situ X-ray diffraction,and thermodynamic calculations,with high-resolution electron microscopy detailing microstructural evo-lution at 625℃,675℃,and 725℃.The results show increases in Vickers hardness between 500℃ and 625℃,attributed to the nucleation of a Cr-and V-rich sigma(σ)phase,primarily at the bcc grain boundaries.Beyond 625℃,the hardness decreased due toσ-phase dissolution,recovery of bcc and fcc phases,bcc→fcc phase reversion,and recrystallization of the reverted fcc phase.Scanning-transmission electron microscopy and transmission Kikuchi diffraction revealed a Kurdjumov-Sachs orientation rela-tionship(OR)at 675℃ and a near Nishiyama-Wassermann OR at 725℃ for bcc-fcc interfaces,whereas bcc-σand fcc-σinterfaces showed no dominant OR.In addition toσphase,two types of bcc phase were identified at 625℃.Type 1 bcc initially retained a near-nominal composition and a disordered crystal structure from deformation-induced bcc martensite but gradually became Fe-enriched and Cr-and V-depleted up to 725℃.In contrast,Type 2 bcc phase was Fe-depleted and Co-enriched at 625℃ but dis-appeared at 675℃,coinciding with the onset of bcc→fcc phase reversion.This phase also exhibited B2-like chemical short-range ordering,with alternating FeCo-rich and CrV-rich domains.This study provides insights into the complex phase transformation occurring between 500℃ and 725℃ in a Fe_(45)Co_(35)Cr_(10)V_(10)MEA,which can be leveraged to design alloys with optimized mechanical properties for practical appli-cations.展开更多
A transformation-induced plasticity phenomenon in Fe65(CoCrMnNi)35 medium-entropy alloy was investigated.According to the X-ray diffraction patterns,the as-cast specimen contains a single-phase face-centered cubic(fcc...A transformation-induced plasticity phenomenon in Fe65(CoCrMnNi)35 medium-entropy alloy was investigated.According to the X-ray diffraction patterns,the as-cast specimen contains a single-phase face-centered cubic(fcc),while low-temperature annealing at 500℃and 600℃leads to the introduction of a body-centered cubic(bcc)phase as a secondary phase.Further increment of the annealing temperature to above 700℃eliminates the bcc phase,and the microstructure was found to contain a single-phase fcc.At 20%true strain,an fcc-to-bcc phase transformation is observed;whereas,at 28%true strain,an fccto-hcp phase transformation takes place as an additional deformation mechanism.This strain-induced phase transformation phenomenon leads to improved tensile properties of this alloy.展开更多
The evolution of strain hardening behavior of the Fe_(50)(CoCrMnNi)_(50) medium-entropy alloy as a function of the fraction of recrystallized microstructure and the grain size was studied using the Hollomon and Ludwig...The evolution of strain hardening behavior of the Fe_(50)(CoCrMnNi)_(50) medium-entropy alloy as a function of the fraction of recrystallized microstructure and the grain size was studied using the Hollomon and Ludwigson equations.The specimens under study were partially recrystallized,fully recrystallized with ultrafine-grained microstructure,and fully recrystallized with coarse grains.The yield strength decreases steadily as the fraction of recry stallized micro structure and grain size increases due to the recovery process and the Hall-Petch effect.Interestingly,the bimodal grain distribution was found to have a significant impact on strain hardening during plastic deformation.For instance,the highest ultimate tensile strength was exhibited by a 0.97 μm specimen,which was observed to contain a bimodal grain distribution.Furthermore,using the Ludwigson equation,the effect of the bimodal grain distribution was established from the behavior of K_(2) and n_(1) curves.These curves tend to show very high values in the specimens with a bimodal grain distribution compared to those that show a homogenous grain distribution.Additionally,the bimodal grain distribution contributes to the extensive Luders strain observed in the 0.97 μm specimen,which induces a significant deviation of the Hollomon equation at lower strains.展开更多
基金provided by the Nano and Material Technology Development Program(RS-2023-00281246)via the National Research Foundation of Korea,Ministry of Science and ICT,KoreaThe JEOL JSM-7001F,JEOL ARM 200F,and FEI Helios G3 CX FIB-SEM were funded by the Australian Research Council-Linkage,Infrastructure,Equipment and Facilities GrantsNos.LE0882613,LE120100104 andLE160100063,respectivelyThe Oxford Instruments 80 mm2 X-Max EDS detector and the JEOL JEM F200 were funded via the 2012 UOW Major Equipment Grant and 2019 UOW Equipment Replacement Grant schemes,respectively.
文摘Medium-entropy alloys(MEAs)have garnered significant interest due to their unique mechanical prop-erties,but phase instabilities such as the formation of brittle sigma(σ)phase during annealing pose challenges to their practical application.This study investigates the microstructural evolution and me-chanical behavior of an 80%cold-rolled Fe_(45)Co_(35)Cr_(10)V_(10)MEA that was isochronally annealed between 100℃ and 900℃ for 300 s and characterized using hardness indentations,in-situ X-ray diffraction,and thermodynamic calculations,with high-resolution electron microscopy detailing microstructural evo-lution at 625℃,675℃,and 725℃.The results show increases in Vickers hardness between 500℃ and 625℃,attributed to the nucleation of a Cr-and V-rich sigma(σ)phase,primarily at the bcc grain boundaries.Beyond 625℃,the hardness decreased due toσ-phase dissolution,recovery of bcc and fcc phases,bcc→fcc phase reversion,and recrystallization of the reverted fcc phase.Scanning-transmission electron microscopy and transmission Kikuchi diffraction revealed a Kurdjumov-Sachs orientation rela-tionship(OR)at 675℃ and a near Nishiyama-Wassermann OR at 725℃ for bcc-fcc interfaces,whereas bcc-σand fcc-σinterfaces showed no dominant OR.In addition toσphase,two types of bcc phase were identified at 625℃.Type 1 bcc initially retained a near-nominal composition and a disordered crystal structure from deformation-induced bcc martensite but gradually became Fe-enriched and Cr-and V-depleted up to 725℃.In contrast,Type 2 bcc phase was Fe-depleted and Co-enriched at 625℃ but dis-appeared at 675℃,coinciding with the onset of bcc→fcc phase reversion.This phase also exhibited B2-like chemical short-range ordering,with alternating FeCo-rich and CrV-rich domains.This study provides insights into the complex phase transformation occurring between 500℃ and 725℃ in a Fe_(45)Co_(35)Cr_(10)V_(10)MEA,which can be leveraged to design alloys with optimized mechanical properties for practical appli-cations.
基金the National Research Foundation of Korea(No.NRF-2015R1C1A1A01052856)。
文摘A transformation-induced plasticity phenomenon in Fe65(CoCrMnNi)35 medium-entropy alloy was investigated.According to the X-ray diffraction patterns,the as-cast specimen contains a single-phase face-centered cubic(fcc),while low-temperature annealing at 500℃and 600℃leads to the introduction of a body-centered cubic(bcc)phase as a secondary phase.Further increment of the annealing temperature to above 700℃eliminates the bcc phase,and the microstructure was found to contain a single-phase fcc.At 20%true strain,an fcc-to-bcc phase transformation is observed;whereas,at 28%true strain,an fccto-hcp phase transformation takes place as an additional deformation mechanism.This strain-induced phase transformation phenomenon leads to improved tensile properties of this alloy.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.NRF-2019R1A2C1088535)。
文摘The evolution of strain hardening behavior of the Fe_(50)(CoCrMnNi)_(50) medium-entropy alloy as a function of the fraction of recrystallized microstructure and the grain size was studied using the Hollomon and Ludwigson equations.The specimens under study were partially recrystallized,fully recrystallized with ultrafine-grained microstructure,and fully recrystallized with coarse grains.The yield strength decreases steadily as the fraction of recry stallized micro structure and grain size increases due to the recovery process and the Hall-Petch effect.Interestingly,the bimodal grain distribution was found to have a significant impact on strain hardening during plastic deformation.For instance,the highest ultimate tensile strength was exhibited by a 0.97 μm specimen,which was observed to contain a bimodal grain distribution.Furthermore,using the Ludwigson equation,the effect of the bimodal grain distribution was established from the behavior of K_(2) and n_(1) curves.These curves tend to show very high values in the specimens with a bimodal grain distribution compared to those that show a homogenous grain distribution.Additionally,the bimodal grain distribution contributes to the extensive Luders strain observed in the 0.97 μm specimen,which induces a significant deviation of the Hollomon equation at lower strains.
