Significant two-way shape memory effect(TWSME)was achieved in single crystals of single-phase multielement Ni42-x Cu8 Cox Mn37 Ga13(8≤x≤12)alloys by performing thermomechanical training.However,anomalous dependence ...Significant two-way shape memory effect(TWSME)was achieved in single crystals of single-phase multielement Ni42-x Cu8 Cox Mn37 Ga13(8≤x≤12)alloys by performing thermomechanical training.However,anomalous dependence of the martensitic transformation temperature span on Co content was observed.Before training,quite a narrow temperature span of the martensitic transformation,nearly independent of the Co content,was observed in all single crystals.After training the temperature span was still narrow for 8≤x≤10.9 but was obviously expanded for 10.9<x≤12.High-resolution transmission electron microscopy revealed that at the atomic scale,there exists incommensurate modulated structure in the single phase single crystals,as evidenced by nonperiodic satellite spots in the selected area electronic diffraction patterns.Moreover,the modulated wave vector of the satellite spots was increased by higher Co contents.Combining first principal calculations it was considered that the incommensurate modulated structure originates from the formation of Co-Co pairs.After training arrays of ordered dislocations with the same Burgers vector were introduced for 8≤x≤10.9 but the network of dislocations was formed for 10.9<x≤12.Based on analysis of transmission electron microscopy,geometric phase,thermodynamics,and Landau theory,it was considered that the austenite/martensite phase interface was pinned by the network of dislocations,expanding the temperature span of the martensitic transformation.This work supplies new insights for understanding the microstructure and martensitic transformation of Ni-Mn-Ga-based alloys.展开更多
Multi-principal-element alloys(MPEAs)are attracting increasing attentions because of their high strength and ductility,high fracture toughness,excellent corrosion resistance,outstanding thermal-softening resistance an...Multi-principal-element alloys(MPEAs)are attracting increasing attentions because of their high strength and ductility,high fracture toughness,excellent corrosion resistance,outstanding thermal-softening resistance and high oxidation resistance.Moreover,gradient structures(GSs)have been shown to be effective in alleviating the strength-ductility trade-off although strength and ductility are mutually exclusive properties for metals,which provides an opportunity for developing highperformance MPEAs.Here,we summarized four processing methods for creating GSs in MPEAs,including rotationally accelerated shot peening(RASP),ultra-precision machining technology(UPMT),cyclic dynamic torsion(CDT),and ultrasonic surface rolling processing(USRP).Principles,advantages,disadvantages,and typical applications of these methods are discussed in this work.展开更多
Reducing the size of the lamellar structures and increasing the number of twin structures are both effective strategies for enhancing the ductility and fracture toughness ofγ-TiAl alloys.Hot isostatic pressing combin...Reducing the size of the lamellar structures and increasing the number of twin structures are both effective strategies for enhancing the ductility and fracture toughness ofγ-TiAl alloys.Hot isostatic pressing combined with heat treatment is an promising method to optimize the microstructure of TiAl alloys and improve their mechanical properties.However,systematic investigations into the microstructural evolution under high temperature pressure/external stress are limited.In this study,by integrating phase field simulations and CALPHAD thermodynamic database,a unique microstructural response to external stress during aging process is revealed.With the increase of external stress,the size of the lamellar structure initially decreases but then increases,while the number of twin structures initially rises but then decreases,showing nonlinear relationships.An increase in external stress shifts the free energy curves,altering the position of c0(the intersection position between free energies ofα_(2)andγ),which leads to a change in the nucleation mechanism from classical nucleation to pseudo-spinodal decomposition and influences the final microstructure ofγprecipitates.Further simulations indicate a linear correlation between optimal external stress and varying Al content.A deeper analysis indicates that the observed variations in the size and twin structures can be attributed to the interplay among the growth rate of existing variants,the competitive nucleation rates of twinned variants and the redistribution of composition under different external stresses.Our findings provide new insights into optimizing microstructures by pressure/external stress in precipitation processes.展开更多
A series of material parameters are derived from atomistic simulations and implemented into a phase field（PF） model to simulate void evolution in body-centered cubic（bcc） iron subjected to different irradiation do...A series of material parameters are derived from atomistic simulations and implemented into a phase field（PF） model to simulate void evolution in body-centered cubic（bcc） iron subjected to different irradiation doses at different temperatures.The simulation results show good agreement with experimental observations — the porosity as a function of temperature varies in a bell-shaped manner and the void density monotonically decreases with increasing temperatures; both porosity and void density increase with increasing irradiation dose at the same temperature. Analysis reveals that the evolution of void number and size is determined by the interplay among the production, diffusion and recombination of vacancy and interstitial.展开更多
基金support from the National Key Research and Development Program of China(Grant No.2021YFB3501402)the National Natural Science Foundation of China(Grant Nos.52250313 and 52121001)Yang Liu and Chen Si acknowledge financial support from the National Natural Science Foundation of China(Grant No.12274013).
文摘Significant two-way shape memory effect(TWSME)was achieved in single crystals of single-phase multielement Ni42-x Cu8 Cox Mn37 Ga13(8≤x≤12)alloys by performing thermomechanical training.However,anomalous dependence of the martensitic transformation temperature span on Co content was observed.Before training,quite a narrow temperature span of the martensitic transformation,nearly independent of the Co content,was observed in all single crystals.After training the temperature span was still narrow for 8≤x≤10.9 but was obviously expanded for 10.9<x≤12.High-resolution transmission electron microscopy revealed that at the atomic scale,there exists incommensurate modulated structure in the single phase single crystals,as evidenced by nonperiodic satellite spots in the selected area electronic diffraction patterns.Moreover,the modulated wave vector of the satellite spots was increased by higher Co contents.Combining first principal calculations it was considered that the incommensurate modulated structure originates from the formation of Co-Co pairs.After training arrays of ordered dislocations with the same Burgers vector were introduced for 8≤x≤10.9 but the network of dislocations was formed for 10.9<x≤12.Based on analysis of transmission electron microscopy,geometric phase,thermodynamics,and Landau theory,it was considered that the austenite/martensite phase interface was pinned by the network of dislocations,expanding the temperature span of the martensitic transformation.This work supplies new insights for understanding the microstructure and martensitic transformation of Ni-Mn-Ga-based alloys.
基金the support of Qilu Young Talent Program from Shandong University and the State Key Lab of Advanced Metals and Materials (No.2021-Z10)the financial support from the Scientific Research Program Funded by Shaanxi Provincial Education Department (No.19JK0039)
文摘Multi-principal-element alloys(MPEAs)are attracting increasing attentions because of their high strength and ductility,high fracture toughness,excellent corrosion resistance,outstanding thermal-softening resistance and high oxidation resistance.Moreover,gradient structures(GSs)have been shown to be effective in alleviating the strength-ductility trade-off although strength and ductility are mutually exclusive properties for metals,which provides an opportunity for developing highperformance MPEAs.Here,we summarized four processing methods for creating GSs in MPEAs,including rotationally accelerated shot peening(RASP),ultra-precision machining technology(UPMT),cyclic dynamic torsion(CDT),and ultrasonic surface rolling processing(USRP).Principles,advantages,disadvantages,and typical applications of these methods are discussed in this work.
基金supported by the National Key Research and Development Program of China(No.2021YFB3702603)the Outstanding Youth Fund of Shaanxi Province(No.2024JC-JCQN-45)+3 种基金the Scientist+Engineer Teams in Shaanxi’s Qin Chuangyuan Initiative(No.2023KXJ-183)the National Natural Science Foundation of China(No.52171012)111 Project(No.BP2018008),the GHfundA(No.202302019461)“H2”High-Performance Cluster.
文摘Reducing the size of the lamellar structures and increasing the number of twin structures are both effective strategies for enhancing the ductility and fracture toughness ofγ-TiAl alloys.Hot isostatic pressing combined with heat treatment is an promising method to optimize the microstructure of TiAl alloys and improve their mechanical properties.However,systematic investigations into the microstructural evolution under high temperature pressure/external stress are limited.In this study,by integrating phase field simulations and CALPHAD thermodynamic database,a unique microstructural response to external stress during aging process is revealed.With the increase of external stress,the size of the lamellar structure initially decreases but then increases,while the number of twin structures initially rises but then decreases,showing nonlinear relationships.An increase in external stress shifts the free energy curves,altering the position of c0(the intersection position between free energies ofα_(2)andγ),which leads to a change in the nucleation mechanism from classical nucleation to pseudo-spinodal decomposition and influences the final microstructure ofγprecipitates.Further simulations indicate a linear correlation between optimal external stress and varying Al content.A deeper analysis indicates that the observed variations in the size and twin structures can be attributed to the interplay among the growth rate of existing variants,the competitive nucleation rates of twinned variants and the redistribution of composition under different external stresses.Our findings provide new insights into optimizing microstructures by pressure/external stress in precipitation processes.
基金Project supported by the National Magnetic Confinement Fusion Energy Research Project of China(Grant No.2015GB118001)the Fundamental Research Funds for the Central Universities,China(Grant No.DUT16RC(3)052)+1 种基金the National Basic Research Program of China(Grant No.2012CB619402)the NETL Project(Grant No.DE-FE0027776)
文摘A series of material parameters are derived from atomistic simulations and implemented into a phase field（PF） model to simulate void evolution in body-centered cubic（bcc） iron subjected to different irradiation doses at different temperatures.The simulation results show good agreement with experimental observations — the porosity as a function of temperature varies in a bell-shaped manner and the void density monotonically decreases with increasing temperatures; both porosity and void density increase with increasing irradiation dose at the same temperature. Analysis reveals that the evolution of void number and size is determined by the interplay among the production, diffusion and recombination of vacancy and interstitial.
