The austenite(γ)reversely transformed from lath martensite(LM),lath bainite(LB),granular bainite(GB)and pearlite+ferrite(P+F)in a high-strength steel was studied at high temperatures using in-situ electron backscatte...The austenite(γ)reversely transformed from lath martensite(LM),lath bainite(LB),granular bainite(GB)and pearlite+ferrite(P+F)in a high-strength steel was studied at high temperatures using in-situ electron backscatter diffraction(EBSD).The memory effect of initial γ significantly affects the nucleation of the reverted γ in LM and GB structures,while a weak influence on that of LB and P+F structures.This results in a significant difference in γ grain size after complete austenitization,with the first two obtaining larger γ grains while the latter two are relatively small.Crystallographic analysis revealed that the reverted γ with acicular morphology(γA),most of which maintained the same orientation with the prior γ,dominated the reaustenitization behavior of LM and GB structures through preferential nucleation within γ grains and coalesced growth modes.Although globular reverted γ(γ_(G))with random orientation or large deviation from the prior γ can nucleate at the grain boundaries or within the grains,it is difficult for it to grow and play a role in segmenting and refining the prior γ due to the inhibition of γ_(A) coalescing.For LB and P+F structures,the nucleation rate of intragranular γ_(G) increases with increasing temperature,and always shows a random orientation.These γ_(G) grains can coarsen simultaneously with the intergranular γ_(G),ultimately playing a role in jointly dividing and refining the finalγgrains.Research also found that the differences in the effects of four different microstructures on revertedγnucleation are closely related to the variant selection of the matrix structure,as well as the content and size of cementite(θ).High density of block boundaries induced by weakening of variant selection and many fineθformed in the lath are the key to promoting LB structure to obtain more intragranular γ_(G) formation,as well as the important role of the large-sized θ in P+F structure.展开更多
A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hard...A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by insitu electron backscatter diffraction(EBSD)observations coupled with transmission electron microscopy(TEM)characterization and fracture morphologies at both 298 and 77 K.It is found that kernel average misorientation(KAM)mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations(GNDs)at 77 K.The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems,which is consistent with the results of potential slip systems calculated by Taylor axes.Furthermore,dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K.This temperature-mediated activation of dislocations facilitates the increased dislocations,thus enhancing the strain hardening capacity and ductility of the alloy.This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications.展开更多
The effects of various heat treatments on the microstructures and mechanical properties of as-built selective laser melted Inconel 718 alloy were investigated through conventional and quasi-in-situ tensile tests.The c...The effects of various heat treatments on the microstructures and mechanical properties of as-built selective laser melted Inconel 718 alloy were investigated through conventional and quasi-in-situ tensile tests.The corresponding heat treatment processes include direct aging(DA),solution+aging(SA),and homogenization+aging(HA).The DA and SA samples preserve the melt pool configuration and grain size stability,while the precipitated phase characteristics reveal the refinement of the long-strip Laves phase and the appearance of theδphase,respectively.The HA process induces recrystallization and grain coarsening.The specimens exhibit enhanced strength concomitant with diminished elongation,which is likely attributed to the reduction of the geometrically necessary dislocation density and the intensified precipitation of theγ′′phase after heat treatment.Tensile plastic deformation displays notable strain concentration along grain boundaries.The dimensional alterations in precipitated phases were measured to quantitatively determine the impact of grain boundary,dislocation and precipitation strengthening on the yield strength after heat treatment.Precipitation strengthening encompasses coherent,order,and Orowan strengthening.A remarkable agreement is revealed between theoretical predictions and experimental results.Insights are offered for optimizing heat treatment processes to comprehend microstructural evolution effect on the mechanical properties of additive-manufactured metals.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52271089 and 52001023)the Basic Research and Application Basic Research Foundation of Guangdong Province(Nos.2022A1515240016 and 2023B1515250006)the Fundamental Research Funds for the Central Universities(No.FRF-BD-23-01).
文摘The austenite(γ)reversely transformed from lath martensite(LM),lath bainite(LB),granular bainite(GB)and pearlite+ferrite(P+F)in a high-strength steel was studied at high temperatures using in-situ electron backscatter diffraction(EBSD).The memory effect of initial γ significantly affects the nucleation of the reverted γ in LM and GB structures,while a weak influence on that of LB and P+F structures.This results in a significant difference in γ grain size after complete austenitization,with the first two obtaining larger γ grains while the latter two are relatively small.Crystallographic analysis revealed that the reverted γ with acicular morphology(γA),most of which maintained the same orientation with the prior γ,dominated the reaustenitization behavior of LM and GB structures through preferential nucleation within γ grains and coalesced growth modes.Although globular reverted γ(γ_(G))with random orientation or large deviation from the prior γ can nucleate at the grain boundaries or within the grains,it is difficult for it to grow and play a role in segmenting and refining the prior γ due to the inhibition of γ_(A) coalescing.For LB and P+F structures,the nucleation rate of intragranular γ_(G) increases with increasing temperature,and always shows a random orientation.These γ_(G) grains can coarsen simultaneously with the intergranular γ_(G),ultimately playing a role in jointly dividing and refining the finalγgrains.Research also found that the differences in the effects of four different microstructures on revertedγnucleation are closely related to the variant selection of the matrix structure,as well as the content and size of cementite(θ).High density of block boundaries induced by weakening of variant selection and many fineθformed in the lath are the key to promoting LB structure to obtain more intragranular γ_(G) formation,as well as the important role of the large-sized θ in P+F structure.
基金supported by the National Natural Science Foundation of China(Grant Nos.92263201,51927801,and 52001160)the National Key Research and Development Program of China(Grant No.2020YFA0405900).
文摘A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by insitu electron backscatter diffraction(EBSD)observations coupled with transmission electron microscopy(TEM)characterization and fracture morphologies at both 298 and 77 K.It is found that kernel average misorientation(KAM)mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations(GNDs)at 77 K.The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems,which is consistent with the results of potential slip systems calculated by Taylor axes.Furthermore,dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K.This temperature-mediated activation of dislocations facilitates the increased dislocations,thus enhancing the strain hardening capacity and ductility of the alloy.This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications.
基金supported by the National Natural Science Foundation of China(NSFC)under Grant Nos.U24A2037,52130002,52321001.
文摘The effects of various heat treatments on the microstructures and mechanical properties of as-built selective laser melted Inconel 718 alloy were investigated through conventional and quasi-in-situ tensile tests.The corresponding heat treatment processes include direct aging(DA),solution+aging(SA),and homogenization+aging(HA).The DA and SA samples preserve the melt pool configuration and grain size stability,while the precipitated phase characteristics reveal the refinement of the long-strip Laves phase and the appearance of theδphase,respectively.The HA process induces recrystallization and grain coarsening.The specimens exhibit enhanced strength concomitant with diminished elongation,which is likely attributed to the reduction of the geometrically necessary dislocation density and the intensified precipitation of theγ′′phase after heat treatment.Tensile plastic deformation displays notable strain concentration along grain boundaries.The dimensional alterations in precipitated phases were measured to quantitatively determine the impact of grain boundary,dislocation and precipitation strengthening on the yield strength after heat treatment.Precipitation strengthening encompasses coherent,order,and Orowan strengthening.A remarkable agreement is revealed between theoretical predictions and experimental results.Insights are offered for optimizing heat treatment processes to comprehend microstructural evolution effect on the mechanical properties of additive-manufactured metals.
