The transformations between the phasesα_(2)(Ti_(3)Al)andω_(o)were investigated in a lamellar multiphase titanium aluminide alloy based onγ(TiAl).The paper complements an earlier investigation performed on the same ...The transformations between the phasesα_(2)(Ti_(3)Al)andω_(o)were investigated in a lamellar multiphase titanium aluminide alloy based onγ(TiAl).The paper complements an earlier investigation performed on the same material in which the importance of deformation-induced twin structures for theα_(2)→ω_(o) transformation was demonstrated.The present study shows that the reverse transformationω_(o)→α_(2) can also occur during high-temperature deformation.The transformation is probably triggered by constraint stresses,which exist between the different constituents due to the crystalline mismatch.The combined operation of mechanical twinning of theα_(2) phase and the reversible transformation fully converts theα_(2) lamellae into a mixture ofα_(2) andω_(o).This conversion greatly reduces the mechanical anisotropy existing in formerα_(2) lamellae.Regarding the technical use of the alloy,the stability of the converted structure with respect to further annealing was also examined.The reported processes occur at the nano-meter and sub nano-meter scale,thus,advanced characterization techniques were applied,such as high-resolution transmission electron microscopy(HRTEM)and atom probe tomography(APT).展开更多
本文研究了一种新型低密度(~6.24 g cm^(-3))双相AlTiVCoNi高熵合金,其组织结构由有序L21高熵金属间化合物、无序体心立方结构和纳米L21相多层次结构构成.该合金在1200℃+24 h热处理下未发生相结构转变,在此条件下具有优异的高温相结构...本文研究了一种新型低密度(~6.24 g cm^(-3))双相AlTiVCoNi高熵合金,其组织结构由有序L21高熵金属间化合物、无序体心立方结构和纳米L21相多层次结构构成.该合金在1200℃+24 h热处理下未发生相结构转变,在此条件下具有优异的高温相结构稳定性,其铸态和热处理态的压缩屈服强度相当,达到~1.6 GPa.另外,该合金在室温和600℃条件下表现出了优异的强塑性匹配和优异的比屈服强度,分别达到了约261和210 MPa g^(-1)cm^(3).该合金的超高强度主要源于有序L21相与体心立方相的半共格界面导致的一种强相结构稳定性和多层次结构的复合强化机制.该合金在800和1000℃压缩过程中出现了动态再结晶软化,使得其高温强度有所降低.这种“具有半共格界面L21+体心立方+纳米L21颗粒”的多层次结构设计为开发新型低密度耐高温高熵合金提供了一种新设计思路.展开更多
In modernβ-solidified TiAl alloys,the decomposition of α_(2) phase is frequently observed during heat treatment or high-temperature deformation of the alloys.In this study,high-temperature deformation and decomposit...In modernβ-solidified TiAl alloys,the decomposition of α_(2) phase is frequently observed during heat treatment or high-temperature deformation of the alloys.In this study,high-temperature deformation and decomposition mechanisms of α_(2) phase in a Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y alloy are investigated.In a sample deformed at 800℃,the precipitation ofβ_(o)(ω_(o))phase is observed within the equiaxed α_(2) phase.The nucleation ofω_(o) particles within theβ_(o) matrix indicates the α_(2)→β_(o)→ω_(o) transformation.In addition,numerous y phase precipitates form within theβ_(o)(ω)areas.The α_(2) lamellae decompose into ultrafine( α_(2)+γ)lamellae and coarsened y lamellae via α_(2)→ α_(2)+γand α_(2)→γtransformation,re-spectively.Moreover,theω_(o) phase nucleates within the ultrafine lamellae via α_(2)→ω_(o) transformation.However,in a sample deformed at 1000℃,the nucleation ofβ_(o) particles is sluggish,which is caused by the efficient release of the internal stress via dynamic recrystallization(DRX).These results indicate that complex phase transformations can be introduced by the decomposition of α_(2) phase in TiAl alloys with a high amount ofβ-stabilizing elements.展开更多
基金supported by the National Natural Science Foundation of China(contract No.51971175)Natural Science Basic Research Plan of Shaanxi Province(contract No.2020JM-097)+2 种基金State Key Laboratory of Advanced Metals and Materials(contract No.2020-ZD03)Research Fund of State Key Laboratory of Solidification Processing(contract No.2021-TS-05)the"111" Project(contract No.B20028)。
文摘The transformations between the phasesα_(2)(Ti_(3)Al)andω_(o)were investigated in a lamellar multiphase titanium aluminide alloy based onγ(TiAl).The paper complements an earlier investigation performed on the same material in which the importance of deformation-induced twin structures for theα_(2)→ω_(o) transformation was demonstrated.The present study shows that the reverse transformationω_(o)→α_(2) can also occur during high-temperature deformation.The transformation is probably triggered by constraint stresses,which exist between the different constituents due to the crystalline mismatch.The combined operation of mechanical twinning of theα_(2) phase and the reversible transformation fully converts theα_(2) lamellae into a mixture ofα_(2) andω_(o).This conversion greatly reduces the mechanical anisotropy existing in formerα_(2) lamellae.Regarding the technical use of the alloy,the stability of the converted structure with respect to further annealing was also examined.The reported processes occur at the nano-meter and sub nano-meter scale,thus,advanced characterization techniques were applied,such as high-resolution transmission electron microscopy(HRTEM)and atom probe tomography(APT).
基金the supports from the Fundamental Research Funds for the Central Universities(FRF-MP-19-013)Guangdong Basic and Applied Basic Research Foundation(2019B1515120020)+6 种基金the State Key Laboratory for Advanced Metals and Materials,the University of Science and Technology Beijing(2020Z-08)the Funds for Creative Research Groups of China(51921001)the National Natural Science Foundation of China(51801128)Guangdong Basic and Applied Basic Research Foundation(2021A1515012278 and 2022A1515010288)the supports from the National Natural Science Foundation of China(51871015 and 52171151)the supports from the National Science Foundation(DMR-1611180 and 1809640)the US Army Research Office(W911NF13-1-0438 and W911NF-19-2-0049)。
文摘本文研究了一种新型低密度(~6.24 g cm^(-3))双相AlTiVCoNi高熵合金,其组织结构由有序L21高熵金属间化合物、无序体心立方结构和纳米L21相多层次结构构成.该合金在1200℃+24 h热处理下未发生相结构转变,在此条件下具有优异的高温相结构稳定性,其铸态和热处理态的压缩屈服强度相当,达到~1.6 GPa.另外,该合金在室温和600℃条件下表现出了优异的强塑性匹配和优异的比屈服强度,分别达到了约261和210 MPa g^(-1)cm^(3).该合金的超高强度主要源于有序L21相与体心立方相的半共格界面导致的一种强相结构稳定性和多层次结构的复合强化机制.该合金在800和1000℃压缩过程中出现了动态再结晶软化,使得其高温强度有所降低.这种“具有半共格界面L21+体心立方+纳米L21颗粒”的多层次结构设计为开发新型低密度耐高温高熵合金提供了一种新设计思路.
基金supported in part by the Nationa Natural Science Foundation of China (51471025, 51671020, 51471024 and 11771407)the Department of Energy (DOE), Office of Fossil Energy, National Energy Technology Laboratory (DE-FE-0011194)+1 种基金the support from the US Army Research Office project (W911NF-13-1-0438)the support from the National Science Foundation (DMR-1611180 and 1809640)
基金supported by the National Natural Science Foundation of China (No. 51971175)the Natural Science Basic Research Plan of Shaanxi Province (No. 2020JM-097)+2 种基金the State Key Laboratory of Solidification Processing (No. 2021-TS-05)the State Key Laboratory of Advanced Metals and Materials (No. 2020-ZD03)the “111” Project (No. B20028)。
文摘In modernβ-solidified TiAl alloys,the decomposition of α_(2) phase is frequently observed during heat treatment or high-temperature deformation of the alloys.In this study,high-temperature deformation and decomposition mechanisms of α_(2) phase in a Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y alloy are investigated.In a sample deformed at 800℃,the precipitation ofβ_(o)(ω_(o))phase is observed within the equiaxed α_(2) phase.The nucleation ofω_(o) particles within theβ_(o) matrix indicates the α_(2)→β_(o)→ω_(o) transformation.In addition,numerous y phase precipitates form within theβ_(o)(ω)areas.The α_(2) lamellae decompose into ultrafine( α_(2)+γ)lamellae and coarsened y lamellae via α_(2)→ α_(2)+γand α_(2)→γtransformation,re-spectively.Moreover,theω_(o) phase nucleates within the ultrafine lamellae via α_(2)→ω_(o) transformation.However,in a sample deformed at 1000℃,the nucleation ofβ_(o) particles is sluggish,which is caused by the efficient release of the internal stress via dynamic recrystallization(DRX).These results indicate that complex phase transformations can be introduced by the decomposition of α_(2) phase in TiAl alloys with a high amount ofβ-stabilizing elements.
