Ti−Zr alloys(oxygen content 0.42−0.54 wt.%)were prepared via powder metallurgy and hot working.The results indicate that the Ti−Zr alloys exhibit Zr-rich and Zr-lean areas with the sameα-phase structure,and the Zr-ri...Ti−Zr alloys(oxygen content 0.42−0.54 wt.%)were prepared via powder metallurgy and hot working.The results indicate that the Ti−Zr alloys exhibit Zr-rich and Zr-lean areas with the sameα-phase structure,and the Zr-rich area shows a slightly higher oxygen content and a much finer grain size.The Ti−Zr alloys present a good combination of high strength(σs=700−900 MPa)and total elongation(>20%),and solid solution strengthening of oxygen plays a major role.Zr does not influence much the oxygen-induced brittleness due to its high structural similarity to Ti.Therefore,the high value of 0.54 wt.%is still within the critical oxygen content for the ductile-to-brittle transition of Ti and does not degrade the ductility.展开更多
It is know from literature that small additions(<1 wt%)of Ca,Al and Zn significantly improve the intrinsic ductility of Mg.The exact role of each element,both qualitatively and quantitatively,and their combined eff...It is know from literature that small additions(<1 wt%)of Ca,Al and Zn significantly improve the intrinsic ductility of Mg.The exact role of each element,both qualitatively and quantitatively,and their combined effects,however,are poorly understood.Here we achieved a much clearer view on the quantitative role of each element with respect to ductility improvement and on the collaborative effect,particularly of Ca and Zn in Mg.Some of our findings and conclusions are in disagreement with data and interpretation found in literature.Four different alloys,namely,Mg-0.1 Ca,Mg-0.1 Ca-1 Al,Mg-0.05 Ca-1 Al,Mg-0.1 Ca-2 Al-1 Zn(all are in wt%)were selected for this investigation.All alloys were treated such that approx.similar grain sizes and textures were obtained.This largely excludes the effect of extrinsic factors on ductility.EBSD-guided slip trace analyses reveal that the addition of Ca eases activation of prismatic and pyramidal II slip systems.Using in-situ deformation experiments in SEM and atom probe tomography observations of grain boundaries direct evidence is given for the individual and synergetic effects of Ca and Zn on grain boundary cohesion as an important contribution to improve the ductility of these alloys.We conclude that Ca reduces the slip anisotropy and ameliorates ductility,however,the weak grain boundary cohesion in the Mg-0.1 wt%Ca alloy limits the material’s tensile ductility.The addition of Zn alters the Ca segregation at the grain boundaries and helps to retain their cohesive strength,an effect which thus enables higher ductility and strength.The further addition of Al primarily improves the strength.The results show that the balanced influence of reduced slip anisotropy on the one hand and increased grain boundary cohesion on the other hand allow to design a high strength high ductility rare-earth free Mg alloy.展开更多
The microstructural evolution of a metastable face centered cubic(FCC)Fe40Co20Cr20Mn10Ni10high-entropy alloy(HEA)under both tension and compression is systemically investigated.The results show much higher level of ma...The microstructural evolution of a metastable face centered cubic(FCC)Fe40Co20Cr20Mn10Ni10high-entropy alloy(HEA)under both tension and compression is systemically investigated.The results show much higher level of martensite phase transformation from FCC structure to hexagonal closed packed(HCP)structure under compression than tension,indicating a distinct tension-compression asymmetry.The compressive tests underwent higher true stresses,which further provided stronger driving forces to trigger the phase transformation than those in tensile tests.Except for the martensite phase transformation,dislocation planar slip prevails in both tension and compression,along with the occasional formation of mechanical twins.Dislocation slip dominates the whole tensile deformation,while both dislocation motions and martensite phase transformation play critical roles in the compressive deformation.The martensite phase transformation is preferred to nucleate at grain or subgrain boundaries due to a medium stacking fault energy(SFE)of^20 m J m^-2.The formation of HCP phase via partial dislocation emission from low-angle grain boundaries offers additional pathways for martensite phase transformation.Our study thus remarkably benefits the understanding of the deformation mechanisms of metastable HEAs.展开更多
Nanoscale L12-type ordered structures are widely used in face-centered cubic(FCC)alloys to exploit their hardening capacity and thereby improve mechanical properties.These fine-scale particles are typically fully cohe...Nanoscale L12-type ordered structures are widely used in face-centered cubic(FCC)alloys to exploit their hardening capacity and thereby improve mechanical properties.These fine-scale particles are typically fully coherent with matrix with the same atomic configuration disregarding chemical species,which makes them challenging to be characterized.Spatial distribution maps(SDMs)are used to probe local order by interrogating the three-dimensional(3D)distribution of atoms within reconstructed atom probe tomography(APT)data.However,it is almost impossible to manually analyze the complete point cloud(>10 million)in search for the partial crystallographic information retained within the data.Here,we proposed an intelligent L1_(2)-ordered structure recognition method based on convolutional neural networks(CNNs).The SDMs of a simulated L1_(2)-ordered structure and the FCC matrix were firstly generated.These simulated images combined with a small amount of experimental data were used to train a CNN-based L1_(2)-ordered structure recognition model.Finally,the approach was successfully applied to reveal the 3D distribution of L1_(2)–typeδ′–Al3(LiMg)nanoparticles with an average radius of 2.54 nm in a FCC Al-Li-Mg system.The minimum radius of detectable nanodomain is even down to 5Å.The proposed CNN-APT method is promising to be extended to recognize other nanoscale ordered structures and even more-challenging short-range ordered phenomena in the near future.展开更多
基金Project(51625404)supported by the National Natural Science Foundation for Distinguished Young Scholar of China。
文摘Ti−Zr alloys(oxygen content 0.42−0.54 wt.%)were prepared via powder metallurgy and hot working.The results indicate that the Ti−Zr alloys exhibit Zr-rich and Zr-lean areas with the sameα-phase structure,and the Zr-rich area shows a slightly higher oxygen content and a much finer grain size.The Ti−Zr alloys present a good combination of high strength(σs=700−900 MPa)and total elongation(>20%),and solid solution strengthening of oxygen plays a major role.Zr does not influence much the oxygen-induced brittleness due to its high structural similarity to Ti.Therefore,the high value of 0.54 wt.%is still within the critical oxygen content for the ductile-to-brittle transition of Ti and does not degrade the ductility.
基金the financial support by the international doctoral school IMPRS,Surmat。
文摘It is know from literature that small additions(<1 wt%)of Ca,Al and Zn significantly improve the intrinsic ductility of Mg.The exact role of each element,both qualitatively and quantitatively,and their combined effects,however,are poorly understood.Here we achieved a much clearer view on the quantitative role of each element with respect to ductility improvement and on the collaborative effect,particularly of Ca and Zn in Mg.Some of our findings and conclusions are in disagreement with data and interpretation found in literature.Four different alloys,namely,Mg-0.1 Ca,Mg-0.1 Ca-1 Al,Mg-0.05 Ca-1 Al,Mg-0.1 Ca-2 Al-1 Zn(all are in wt%)were selected for this investigation.All alloys were treated such that approx.similar grain sizes and textures were obtained.This largely excludes the effect of extrinsic factors on ductility.EBSD-guided slip trace analyses reveal that the addition of Ca eases activation of prismatic and pyramidal II slip systems.Using in-situ deformation experiments in SEM and atom probe tomography observations of grain boundaries direct evidence is given for the individual and synergetic effects of Ca and Zn on grain boundary cohesion as an important contribution to improve the ductility of these alloys.We conclude that Ca reduces the slip anisotropy and ameliorates ductility,however,the weak grain boundary cohesion in the Mg-0.1 wt%Ca alloy limits the material’s tensile ductility.The addition of Zn alters the Ca segregation at the grain boundaries and helps to retain their cohesive strength,an effect which thus enables higher ductility and strength.The further addition of Al primarily improves the strength.The results show that the balanced influence of reduced slip anisotropy on the one hand and increased grain boundary cohesion on the other hand allow to design a high strength high ductility rare-earth free Mg alloy.
基金supported by the National Natural Science Foundation of China(51971247)the open Foundation of State Key Laboratory of Powder Metallurgy at Central South University,Changsha,China。
文摘The microstructural evolution of a metastable face centered cubic(FCC)Fe40Co20Cr20Mn10Ni10high-entropy alloy(HEA)under both tension and compression is systemically investigated.The results show much higher level of martensite phase transformation from FCC structure to hexagonal closed packed(HCP)structure under compression than tension,indicating a distinct tension-compression asymmetry.The compressive tests underwent higher true stresses,which further provided stronger driving forces to trigger the phase transformation than those in tensile tests.Except for the martensite phase transformation,dislocation planar slip prevails in both tension and compression,along with the occasional formation of mechanical twins.Dislocation slip dominates the whole tensile deformation,while both dislocation motions and martensite phase transformation play critical roles in the compressive deformation.The martensite phase transformation is preferred to nucleate at grain or subgrain boundaries due to a medium stacking fault energy(SFE)of^20 m J m^-2.The formation of HCP phase via partial dislocation emission from low-angle grain boundaries offers additional pathways for martensite phase transformation.Our study thus remarkably benefits the understanding of the deformation mechanisms of metastable HEAs.
文摘Nanoscale L12-type ordered structures are widely used in face-centered cubic(FCC)alloys to exploit their hardening capacity and thereby improve mechanical properties.These fine-scale particles are typically fully coherent with matrix with the same atomic configuration disregarding chemical species,which makes them challenging to be characterized.Spatial distribution maps(SDMs)are used to probe local order by interrogating the three-dimensional(3D)distribution of atoms within reconstructed atom probe tomography(APT)data.However,it is almost impossible to manually analyze the complete point cloud(>10 million)in search for the partial crystallographic information retained within the data.Here,we proposed an intelligent L1_(2)-ordered structure recognition method based on convolutional neural networks(CNNs).The SDMs of a simulated L1_(2)-ordered structure and the FCC matrix were firstly generated.These simulated images combined with a small amount of experimental data were used to train a CNN-based L1_(2)-ordered structure recognition model.Finally,the approach was successfully applied to reveal the 3D distribution of L1_(2)–typeδ′–Al3(LiMg)nanoparticles with an average radius of 2.54 nm in a FCC Al-Li-Mg system.The minimum radius of detectable nanodomain is even down to 5Å.The proposed CNN-APT method is promising to be extended to recognize other nanoscale ordered structures and even more-challenging short-range ordered phenomena in the near future.
