The Al-Cu alloy is a historical model alloy system in the physical metallurgy of engineering aluminum al-loys.Nevertheless,a few fundamental phenomena of phase transformation occurring in this simple alloy are still n...The Al-Cu alloy is a historical model alloy system in the physical metallurgy of engineering aluminum al-loys.Nevertheless,a few fundamental phenomena of phase transformation occurring in this simple alloy are still not adequately understood.Among all,for instance,the formation mechanisms of its key harden-ingθ'-phase remain mysterious.There is strong evidence thatθ'-precipitates can form from a different high-temperature precipitation pathway,while their formation mechanism via the conventional pathway well-known since 1938 remains to be clarified.Using state-of-the-art electron microscopy,here we report a secondary high-temperature precipitation pathway ofθ'-precipitates.It is demonstrated that led by a secondary high-temperature precursor,namedθ'_(S-HTP),very fineθ'-precipitates can form in the unde-formed bulk Al-Cu alloys at elevated temperatures(≥250℃).Interestingly is that with Sc-microalloying the surviving rate of meta-stableθ'_(S-HTP) precipitates increases drastically and the formedθ'-precipitates become much finer,significantly enhancing the alloys’strength and thermal stability.It is also revealed that aθ'_(S-HTP) precipitate can genetically evolve into aθ'-precipitate without having to change its mor-phology and orientation.Our study provides new insights into understanding the industry bulk alloys’microstructures and properties.展开更多
Al-Cu binary alloys are important and interesting industry materials.Up to date,the formation mechanisms of the key strengthening precipitates,namedθ’-phase,in the alloys are still controversial.Here,we report that ...Al-Cu binary alloys are important and interesting industry materials.Up to date,the formation mechanisms of the key strengthening precipitates,namedθ’-phase,in the alloys are still controversial.Here,we report that for non-deformed bulk Al-Cu alloys theθ’-phase actually has its own direct precursors that can form only at elevated aging temperature(>ca.200℃).These high-temperature precursors have the same plate-like morphology as theθ’-phase precipitates but rather different structures.Atomicresolution imaging reveals that they have a tetragonal structure with a=0.405 nm and c=1.213 nm,and an average composition of Al_(5-x)Cu_(1+x)(0≤x<1),being fully coherent with the Al-lattice.This precursor phase may initiate with a composition of Al5 Cu and evolve locally towards Al_(4)Cu_(2)in composition,eventually leading to a consequent structural transformation into theθ’-phase(Al4 Cu2=Al2 Cu).There are evidences that because of their genetic links in structure,such a high-temperature precursor may transform to theθ’-phase without having to change their morphology and interface structure.Our study reveals a well-defined and previously hidden precipitation scenario for theθ’-phase to form in Al-Cu alloys at an elevated aging temperature.展开更多
The missing wedge effect in electron tomography introduces various types of artifacts in the tomograms and lowers the reconstruction resolution and quality.The artifacts produced in tomographic reconstruction of bulk ...The missing wedge effect in electron tomography introduces various types of artifacts in the tomograms and lowers the reconstruction resolution and quality.The artifacts produced in tomographic reconstruction of bulk materials can be very severe,particularly for sintered bulk ceramic materials in which there are often nano-pores or pore-like microstructure features.Here,we report a neural network algebraic reconstruction algorithm with no prior knowledge to perform electron tomography for a sintered SiC material with nano carbon zones.The results show that the proposed algorithm has a great suppressive effect on the missing wedge artifacts and a high tolerance for noise.The information in the missing wedge can be partly recovered by this technique.Thus,both the shape of the bulk SiC specimen and its irregular inner pore-like features are correctly retrieved in the obtained 3D image.Our study shows the effectiveness of the neural network algorithm for improving the reconstruction accuracy of electron tomography,in order to reveal sophisticated 3D microstructures generally existing in sintered ceramic materials.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51831004 and 52171006).
文摘The Al-Cu alloy is a historical model alloy system in the physical metallurgy of engineering aluminum al-loys.Nevertheless,a few fundamental phenomena of phase transformation occurring in this simple alloy are still not adequately understood.Among all,for instance,the formation mechanisms of its key harden-ingθ'-phase remain mysterious.There is strong evidence thatθ'-precipitates can form from a different high-temperature precipitation pathway,while their formation mechanism via the conventional pathway well-known since 1938 remains to be clarified.Using state-of-the-art electron microscopy,here we report a secondary high-temperature precipitation pathway ofθ'-precipitates.It is demonstrated that led by a secondary high-temperature precursor,namedθ'_(S-HTP),very fineθ'-precipitates can form in the unde-formed bulk Al-Cu alloys at elevated temperatures(≥250℃).Interestingly is that with Sc-microalloying the surviving rate of meta-stableθ'_(S-HTP) precipitates increases drastically and the formedθ'-precipitates become much finer,significantly enhancing the alloys’strength and thermal stability.It is also revealed that aθ'_(S-HTP) precipitate can genetically evolve into aθ'-precipitate without having to change its mor-phology and orientation.Our study provides new insights into understanding the industry bulk alloys’microstructures and properties.
基金the National Natural Science Foundation of China(Nos.51831004,51801060,51671082,11427806,51471067)the National Key Research and Development Program of China(No.2016YFB0300801)。
文摘Al-Cu binary alloys are important and interesting industry materials.Up to date,the formation mechanisms of the key strengthening precipitates,namedθ’-phase,in the alloys are still controversial.Here,we report that for non-deformed bulk Al-Cu alloys theθ’-phase actually has its own direct precursors that can form only at elevated aging temperature(>ca.200℃).These high-temperature precursors have the same plate-like morphology as theθ’-phase precipitates but rather different structures.Atomicresolution imaging reveals that they have a tetragonal structure with a=0.405 nm and c=1.213 nm,and an average composition of Al_(5-x)Cu_(1+x)(0≤x<1),being fully coherent with the Al-lattice.This precursor phase may initiate with a composition of Al5 Cu and evolve locally towards Al_(4)Cu_(2)in composition,eventually leading to a consequent structural transformation into theθ’-phase(Al4 Cu2=Al2 Cu).There are evidences that because of their genetic links in structure,such a high-temperature precursor may transform to theθ’-phase without having to change their morphology and interface structure.Our study reveals a well-defined and previously hidden precipitation scenario for theθ’-phase to form in Al-Cu alloys at an elevated aging temperature.
基金financially supported by the National Natural Science Foundation of China(Nos.51831004,11904093,11427806,51671082,51471067)the National Key Research and Development Program of China(No.2016YFB0300801)+2 种基金the Major Science and Technology Program of Changsha(kq1804010)the National Key Laboratory Foundation of National Defense Science and Technology(No.6142907190402)financial support from Aid Program for Innovative Group of National University of Defense Technology。
文摘The missing wedge effect in electron tomography introduces various types of artifacts in the tomograms and lowers the reconstruction resolution and quality.The artifacts produced in tomographic reconstruction of bulk materials can be very severe,particularly for sintered bulk ceramic materials in which there are often nano-pores or pore-like microstructure features.Here,we report a neural network algebraic reconstruction algorithm with no prior knowledge to perform electron tomography for a sintered SiC material with nano carbon zones.The results show that the proposed algorithm has a great suppressive effect on the missing wedge artifacts and a high tolerance for noise.The information in the missing wedge can be partly recovered by this technique.Thus,both the shape of the bulk SiC specimen and its irregular inner pore-like features are correctly retrieved in the obtained 3D image.Our study shows the effectiveness of the neural network algorithm for improving the reconstruction accuracy of electron tomography,in order to reveal sophisticated 3D microstructures generally existing in sintered ceramic materials.
