The precipitation sequence of η（MgZn2） phase along low-angle grain boundaries in Al-Zn-Mg-Cu alloy was investigated by examining samples aged at 135 ℃ for various times from 5 min to 6 h. High resolution transmiss...The precipitation sequence of η（MgZn2） phase along low-angle grain boundaries in Al-Zn-Mg-Cu alloy was investigated by examining samples aged at 135 ℃ for various times from 5 min to 6 h. High resolution transmission electron microscopy （HRTEM） observations and energy dispersive X-ray spectroscopy （EDX） analysis indicate that the precipitation sequence of η phase along low-angle grain boundaries should be supersaturated solid solution （SSS）→vacancy-rich clusters （VRC）→GP Ⅱ zones→η＇→η. Based on the theory of non-equilibrium grain boundary segregation （NGS） and non-equilibrium grain boundary co-segregation （NGCS）, the excessive solute elements gradually segregate to the grain boundaries by the diffusion of the solute-vacancy complex during aging treatment. The grain boundary segregation plays an important role in the nucleation and growth of VRC, GP Ⅱ zones, η＇ phase as well as η phase.展开更多
Based on the phase field theory, the phase precipitation sequence of Ni75A110Cr15 alloy and the free energy of each phase were studied. Moreover, the interatomic potentials of Llo phase, L12 phase and DO22 phase chang...Based on the phase field theory, the phase precipitation sequence of Ni75A110Cr15 alloy and the free energy of each phase were studied. Moreover, the interatomic potentials of Llo phase, L12 phase and DO22 phase changing with temperature and concen- trations were computed through utilizing the interatomic potentials equations induced by Khachaturyan＇s relational equations between the interatomic potentials and the long-range order （LRO） parameters. Results match preceding work and demonstrate that the phase precipitation sequence of Ni75AlloCr15 alloy is the disordered phase -L10 pre-precipitation phase -L12 equilibrium phase -L12＋DO22 equilibrium phase. Free energies of Llo pre-precipitation phase are higher and interatomic potentials are smaller than those of L12 equilibrium phase; therefore, it is concluded that Llo phase is unstable, and phase transformation would occur to L12 which is more stable; L12 phase precipitates earlier than DO22 phase because L12＇s interaction potentials are larger than DO22＇s.展开更多
Based on the available experimental phase equilibrium relations and aging precipitation sequences,the Mg–Gd–Y ternary system has been thermodynamically re-assessed by means of CALPHAD technique.To simulate the exper...Based on the available experimental phase equilibrium relations and aging precipitation sequences,the Mg–Gd–Y ternary system has been thermodynamically re-assessed by means of CALPHAD technique.To simulate the experimentally reported aging precipitation sequence,α(Mg)_(SS)(supersaturated)→GP zones(D019-type,metastable)→β’-Mg_(7)Gd(c-bco,metastable)→β_(1)-Mg_(3)Gd(fcc,metastable)→β-Mg_(5)Gd(fcc,stable)near the Mg–Gd side,andα(Mg)SS(supersaturated)→β’-Mg_(7)Y(c-bco,metastable)→β-Mg_(24)Y_(5)(bcc,stable)near the Mg–Y side,the effective nucleation driving forces obtained by deducting the nucleation resistances from the thermodynamic driving forces are calculated and analyzed.Two metastable components,GP zones(D019-type)andβ’(c-bco)ordered fromα(Mg)_(SS),do not exist in the stable equilibrium phase diagram but appear in the annealing process of typical alloys.The Redlich–Kister equations are adopted to describe three solution phases,Liquid,HCP_A3 and BCC_A2.The intermediate compounds Mg_(2)Y,Mg_(24)Y_(5),Mg_(2)Gd,Mg_(3)Gd and Mg_(5)Gd are expressed by the formulas of(Mg,Y)_(2/3)(Gd,Mg,Y)_(1/3),Mg_(24/29)(Gd,Mg,Y)_(4/29)Y1/29,(Gd,Mg)_(2/3)(Gd,Mg,Y)_(1/3),(Gd,Mg)_(3/4)(Gd,Mg,Y)_(1/4)and Mg_(5/6)(Gd,Mg,Y)_(1/6),respectively.In particular,the two-sublattice models(Gd,Mg,Y)_(1/2)(Gd,Mg,Y)_(1/2),(Gd,Mg,Y)_(3/4)(Gd,Mg,Y)_(1/4)and(Gd,Mg,Y)_(7/8)(Gd,Mg,Y)_(1/8)have been respectively used to describe the stable Mg(Gd,Y)(BCC_B2)alloy compound as well as the metastable GP zones(D019-type)andβ’(c-bco)phase,in order to cope with the order-disorder transitions.A set of self-consistent thermodynamic parameters has been obtained to ensure the thermodynamic calculations well consistent with the reported experimental data,containing not only the stable equilibrium phase diagram but also the aging precipitation sequence.展开更多
In this paper,a comprehensive understanding of stable and metastable phase equilibria in binary Mg-Gd system was conducted with an aid of the CALculation of PHAse Diagram(CALPHAD)modeling.Firstly,thermodynamic descrip...In this paper,a comprehensive understanding of stable and metastable phase equilibria in binary Mg-Gd system was conducted with an aid of the CALculation of PHAse Diagram(CALPHAD)modeling.Firstly,thermodynamic descriptions of all the stable phases in the Mg-Gd system were re-assessed by considering all the experimental data in the literature.The discrepancy between the phase equilibria and thermochemical properties existing in the previous assessments was eliminated,and the better agreement with the experimental data was achieved in the present assessment.Secondly,the Gibbs energies for metastable β"-Mg3Gd and β"-Mg7Gd were constructed based on the first-principles and CALPHAD computed results as well as their correlation,and then incorporated into the CALPHAD descriptions.The model-predicted solvuses of(Mg)in equilibrium with the metastable β"-Mg7Gd and β'-Mg7Gd compounds showed very good agreement with the limited experimental data.Finally,the presently obtained thermodynamic descriptions of both stable and metastable phases in the binary Mg-Gd system were further validated by realizing the quantitative Scheil-Gulliver solidification simulations of 5 as-cast Mg-Gd alloys,and the successful prediction of the precipitation sequences in Mg-15Gd and Mg-12Gd alloys during the aging process.展开更多
The age hardening behavior of gravity cast B356 aluminum alloy was investigated by differential scanning calorimetry(DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were se...The age hardening behavior of gravity cast B356 aluminum alloy was investigated by differential scanning calorimetry(DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were selected, namely 155, 165 and 180 °C, with heat treatment time from 40 min to 32 h. DSC analysis results show that cluster formation begins below room temperature(at around-10 °C). Since cluster formation influences the subsequent precipitation of the main strengthening β'' phase, it can be inferred that a delay between solutionizing and artificial aging has a detrimental effect on the mechanical properties of the alloy. It was also confirmed that the hardness and the tensile properties of the alloy reach the maximum values when β'' phase is completely developed during the artificial aging. This happens after 16 h for samples aged at 155 °C, after 6 h for samples aged at 165 °C and after 4 h for samples aged at 180 °C. A subsequent decrease of the mechanical properties, observed only in the sample aged at the highest temperature, with increasing aging time can be associated with the transformation of the coherent β'' phase into the semi-coherent β' phase. Finally, the activation energy associated with the precipitation of β'' phase was calculated to be 57.2 k J/mol.展开更多
The differences of the microstructure and mechanical property between metal mould and sand mould cast Mg-10Gd-3Y-Zr alloy were investigated both under as-cast condition and after solution heat treatment. In the as-cas...The differences of the microstructure and mechanical property between metal mould and sand mould cast Mg-10Gd-3Y-Zr alloy were investigated both under as-cast condition and after solution heat treatment. In the as-cast specimens, the microstructure is similar and composed of a-Mg solid solution and eutectic compound of a-Mg＋ Mg24（Gd,Y）5; whereas the grain size using metal mould and sand mould is 27 pm and 71 IJm, respectively. The eutectic compound of metal mould cast alloy was completely dissolved after solution treated at 500℃ for 8 h, however it needs higher temperature （525 ℃） and longer time （12 h） to achieve the absolute dissolving under sand mould condition. In contrast to metal mould, the peak time of sand mould alloy aged at 225℃ and 250℃ of was advanced by 4 h and 6 h, respectively. The precipitation reaction sequence in sand mould cast Mg-10Gd-3Y-Zr alloy during isothermal ageing at 250℃ follows S.S.S.S.→β（D010）→β′（cboc）→β1（fcc）→β（fcc）, which is similar to that in the alloy cast using metal mould.展开更多
Aging behavior of Mg-3.6Y-0.5Zr and Mg-2.TNd-0.5Zr alloys was investigated by microhardness measurement and transmission electron microscopy.In the case of Mg-Y-Zr alloy,the presence ofβ″phase,a major strength- ener...Aging behavior of Mg-3.6Y-0.5Zr and Mg-2.TNd-0.5Zr alloys was investigated by microhardness measurement and transmission electron microscopy.In the case of Mg-Y-Zr alloy,the presence ofβ″phase,a major strength- ener,having base centered orthorhombic structure with its lattice constants of a-（β″）=0.64 nm,b-（β″）=2.22 nm, and c-（β″）=0.52 nm was identified.In the case of Mg-Nd-Zr alloy aged at 250℃,the presence ofβ″andβ′phases was identified.The crystal structure ofβ″phase was found to be DO-（19） and its orientation relationships with Mg matrix were [0001]-（β″）//[0001]-（Mg） and [01（？）0]-（β″）//[01（？）0]-（Mg）.Theβ′phase had face centered cubic structure and its orientation relationships with Mg matrix were [011]-（β′）//[0001]-（Mg） and [（？）1（？）]β′//[（？）110]）-（Mg）. The Mg-2.TNd-0.5Zr alloy showed higher hardness compared with Mg-3.6Y-0.5Zr alloy.展开更多
Wavelet method is often used in analyzing trend and period of time sequence. When using wavelet method one serious problem is different chosen wavelet basis and scale would lead to different results. Sometimes, the re...Wavelet method is often used in analyzing trend and period of time sequence. When using wavelet method one serious problem is different chosen wavelet basis and scale would lead to different results. Sometimes, the results vary greatly. To overcome this problem and to improve the accuracy and efficiency, a new method denoted by Natural-based Wavelet Method is introduced and extended. It can be proved that the proposed method in fact is a special class of discrete wavelet. At first, two numerical examples are designed to show the capacity of the novel method. Second, this method is applied to a precipitation series. According to wavelet analysis and short-range precipitation prediction, this precipitation exists a faintly increasing trend. Through the analysis, the studied precipitation has two major periods: 11 and 41 years. The results validate that the Natural-based Wavelet Method used in application of multi-complicated observed data is suitable. It is easy to write the source code of the proposed method. When new information appears, new information can be easily added into the original sequence, this is another advantage of the proposed method.展开更多
This study analyzes the evolution of carbides in the tempering process of a newly developed semi-high speed steel cold forged roll with nitrogen addition using a transmission electron microscope （TEM） equipped with ...This study analyzes the evolution of carbides in the tempering process of a newly developed semi-high speed steel cold forged roll with nitrogen addition using a transmission electron microscope （TEM） equipped with an energy dispersive X-ray （EDX）. The precipitation sequence of the carbides was identified in the entire tempering process and it can be expressed as M3C→M3C ＋ M （C, N）Ⅱ→M（ C, N）Ⅱ → M7C3Ⅱ ＋ M23 C6. The secondary hardening in the tempering process was mainly due to the dispersed precipitation of fine M（ C, N）n particles. The dissolution of M3 C tempered at high temperatures induced the precipitation and coarsening of M7 C31/ and M23 C6.展开更多
Studies have shown that microalloying Cu-Ni-Sn alloys using Al inhibits discontinuous precipitation reactions;however,the mechanism has not been investigated yet.Thus,this study explored the properties and precipitati...Studies have shown that microalloying Cu-Ni-Sn alloys using Al inhibits discontinuous precipitation reactions;however,the mechanism has not been investigated yet.Thus,this study explored the properties and precipitation evolution of Cu-15Ni-8Sn alloys without and with 1 wt%Al(Cu-15Ni-8Sn-1Al)during ageing at 500℃ through X-ray diffraction(XRD),scanning electron microscopy and high-angle annular dark-field scanning transmission electron microscopy.The results revealed that in Cu-15Ni-8Sn alloy,DO_(22)ordering first occurred after spinodal decomposition,subsequently transitioning to an L1_(2)ordering phase,during which the discontinuous precipitates gradually nucleated at the grain boundaries and formed ingrains.The alloy hardness increased sharply with ordering and then decreased rapidly after reaching its peak value,due to the dominance of the discontinuous precipitation reaction.However,the DO_(22)ordered phase did not appear during the ageing of Cu-15Ni-8Sn-1Al alloy,and a Ni_(3)(Al_(x),Sn_(1-x))intermetallic compound with L1_(2)structure was formed,consuming Ni and Sn atoms,thereby significantly suppressing the discontinuous precipitation reaction and improving the stability during prolonged ageing.The tensile strength(yield strength)of Cu-15Ni-8Sn and Cu-15Ni-8Sn-1Al alloys at peak hardness were 855(755)and 936 MPa(892 MPa),respectively,and their main strengthening mechanisms were solid solution strengthening and precipitation strengthening.The addition of 1 wt%Al effectively improved the precipitation strengthening effect of Cu-Ni-Sn alloys but severely decreased the ductility.展开更多
The precipitation characteristics and mechanism of vanadium carbides during isothermal transformation at 650℃ in aV-microalloyed medium-carbon steel were investigated through scanning electron microscopy and transmis...The precipitation characteristics and mechanism of vanadium carbides during isothermal transformation at 650℃ in aV-microalloyed medium-carbon steel were investigated through scanning electron microscopy and transmission electronmicroscopy as well as dilatometry test. Five morphologies of vanadium carbides were found to precipitate at differentnucleation sites during the transformation. Two kinds of interphase precipitation form simultaneously in both pro-eutectoidand pearlitic ferrites. The linear arrays of fine interphase precipitates are parallel to the γ/α interface, and the fine needles ofinterphase precipitates are perpendicular to the 7/ct interface. The vanadium carbides of long or short fibers, coarse particlesand fine particles form in both pro-eutectoid and pearlitic ferrites, displaying different precipitation distributions andorientation relationships with ferrite. The precipitation mechanisms of vanadium carbide precipitates with different modeswere proposed, and the precipitation sequence of various vanadium carbide precipitates was finally ascertained.展开更多
基金Project(51071122)supported by the National Natural Science Foundation of ChinaProject(B08040)supported by the Program of Introducing Talents of Discipline to Universities,China("111"Project)
文摘The precipitation sequence of η（MgZn2） phase along low-angle grain boundaries in Al-Zn-Mg-Cu alloy was investigated by examining samples aged at 135 ℃ for various times from 5 min to 6 h. High resolution transmission electron microscopy （HRTEM） observations and energy dispersive X-ray spectroscopy （EDX） analysis indicate that the precipitation sequence of η phase along low-angle grain boundaries should be supersaturated solid solution （SSS）→vacancy-rich clusters （VRC）→GP Ⅱ zones→η＇→η. Based on the theory of non-equilibrium grain boundary segregation （NGS） and non-equilibrium grain boundary co-segregation （NGCS）, the excessive solute elements gradually segregate to the grain boundaries by the diffusion of the solute-vacancy complex during aging treatment. The grain boundary segregation plays an important role in the nucleation and growth of VRC, GP Ⅱ zones, η＇ phase as well as η phase.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10902086, 51075335 and 50875217)the Basic Re-search Fund of the Northwestern Polytechnical University (Grant No. JC201005)the Doctoral Foundation of Northwestern Polytechnical University (Grant No. CX201103)
文摘Based on the phase field theory, the phase precipitation sequence of Ni75A110Cr15 alloy and the free energy of each phase were studied. Moreover, the interatomic potentials of Llo phase, L12 phase and DO22 phase changing with temperature and concen- trations were computed through utilizing the interatomic potentials equations induced by Khachaturyan＇s relational equations between the interatomic potentials and the long-range order （LRO） parameters. Results match preceding work and demonstrate that the phase precipitation sequence of Ni75AlloCr15 alloy is the disordered phase -L10 pre-precipitation phase -L12 equilibrium phase -L12＋DO22 equilibrium phase. Free energies of Llo pre-precipitation phase are higher and interatomic potentials are smaller than those of L12 equilibrium phase; therefore, it is concluded that Llo phase is unstable, and phase transformation would occur to L12 which is more stable; L12 phase precipitates earlier than DO22 phase because L12＇s interaction potentials are larger than DO22＇s.
基金the National Key Research and Development Program of China(No.2016YFB0701201)the National Natural Science Foundation of China(No.52071011)for the financial supports.
文摘Based on the available experimental phase equilibrium relations and aging precipitation sequences,the Mg–Gd–Y ternary system has been thermodynamically re-assessed by means of CALPHAD technique.To simulate the experimentally reported aging precipitation sequence,α(Mg)_(SS)(supersaturated)→GP zones(D019-type,metastable)→β’-Mg_(7)Gd(c-bco,metastable)→β_(1)-Mg_(3)Gd(fcc,metastable)→β-Mg_(5)Gd(fcc,stable)near the Mg–Gd side,andα(Mg)SS(supersaturated)→β’-Mg_(7)Y(c-bco,metastable)→β-Mg_(24)Y_(5)(bcc,stable)near the Mg–Y side,the effective nucleation driving forces obtained by deducting the nucleation resistances from the thermodynamic driving forces are calculated and analyzed.Two metastable components,GP zones(D019-type)andβ’(c-bco)ordered fromα(Mg)_(SS),do not exist in the stable equilibrium phase diagram but appear in the annealing process of typical alloys.The Redlich–Kister equations are adopted to describe three solution phases,Liquid,HCP_A3 and BCC_A2.The intermediate compounds Mg_(2)Y,Mg_(24)Y_(5),Mg_(2)Gd,Mg_(3)Gd and Mg_(5)Gd are expressed by the formulas of(Mg,Y)_(2/3)(Gd,Mg,Y)_(1/3),Mg_(24/29)(Gd,Mg,Y)_(4/29)Y1/29,(Gd,Mg)_(2/3)(Gd,Mg,Y)_(1/3),(Gd,Mg)_(3/4)(Gd,Mg,Y)_(1/4)and Mg_(5/6)(Gd,Mg,Y)_(1/6),respectively.In particular,the two-sublattice models(Gd,Mg,Y)_(1/2)(Gd,Mg,Y)_(1/2),(Gd,Mg,Y)_(3/4)(Gd,Mg,Y)_(1/4)and(Gd,Mg,Y)_(7/8)(Gd,Mg,Y)_(1/8)have been respectively used to describe the stable Mg(Gd,Y)(BCC_B2)alloy compound as well as the metastable GP zones(D019-type)andβ’(c-bco)phase,in order to cope with the order-disorder transitions.A set of self-consistent thermodynamic parameters has been obtained to ensure the thermodynamic calculations well consistent with the reported experimental data,containing not only the stable equilibrium phase diagram but also the aging precipitation sequence.
基金The financial support from the National Key Research and Development Program of China(Grant no.2016YFB0301101)the Hunan Provincial Science and Technology Program of China(Grant no.2017RS3002)-Huxiang Youth Talent Plan+2 种基金the Youth Talent Project of Innovation-driven Plan at Central South University(Grant no.2019XZ027)the Hebei Provincial Science and Technology Program of China(Grant no.BJ2018026)-Outstanding Young Talents Plan is acknowledgedYing Tang acknowledges the financial support from the Yuanguang fellowship released by Hebei University of Technology.
文摘In this paper,a comprehensive understanding of stable and metastable phase equilibria in binary Mg-Gd system was conducted with an aid of the CALculation of PHAse Diagram(CALPHAD)modeling.Firstly,thermodynamic descriptions of all the stable phases in the Mg-Gd system were re-assessed by considering all the experimental data in the literature.The discrepancy between the phase equilibria and thermochemical properties existing in the previous assessments was eliminated,and the better agreement with the experimental data was achieved in the present assessment.Secondly,the Gibbs energies for metastable β"-Mg3Gd and β"-Mg7Gd were constructed based on the first-principles and CALPHAD computed results as well as their correlation,and then incorporated into the CALPHAD descriptions.The model-predicted solvuses of(Mg)in equilibrium with the metastable β"-Mg7Gd and β'-Mg7Gd compounds showed very good agreement with the limited experimental data.Finally,the presently obtained thermodynamic descriptions of both stable and metastable phases in the binary Mg-Gd system were further validated by realizing the quantitative Scheil-Gulliver solidification simulations of 5 as-cast Mg-Gd alloys,and the successful prediction of the precipitation sequences in Mg-15Gd and Mg-12Gd alloys during the aging process.
基金funded by Regione Lombardia-MIUR (Research Program "2 MILLIMETRI" ID 30152773)
文摘The age hardening behavior of gravity cast B356 aluminum alloy was investigated by differential scanning calorimetry(DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were selected, namely 155, 165 and 180 °C, with heat treatment time from 40 min to 32 h. DSC analysis results show that cluster formation begins below room temperature(at around-10 °C). Since cluster formation influences the subsequent precipitation of the main strengthening β'' phase, it can be inferred that a delay between solutionizing and artificial aging has a detrimental effect on the mechanical properties of the alloy. It was also confirmed that the hardness and the tensile properties of the alloy reach the maximum values when β'' phase is completely developed during the artificial aging. This happens after 16 h for samples aged at 155 °C, after 6 h for samples aged at 165 °C and after 4 h for samples aged at 180 °C. A subsequent decrease of the mechanical properties, observed only in the sample aged at the highest temperature, with increasing aging time can be associated with the transformation of the coherent β'' phase into the semi-coherent β' phase. Finally, the activation energy associated with the precipitation of β'' phase was calculated to be 57.2 k J/mol.
基金funded by the National Basic Research Program of China under contract No.2007CB613701National Key Technology R&D Program of China under contract No.2006BAE04B07-2Program of Shanghai Subject Chief Scientist under contract No.08XD14020
文摘The differences of the microstructure and mechanical property between metal mould and sand mould cast Mg-10Gd-3Y-Zr alloy were investigated both under as-cast condition and after solution heat treatment. In the as-cast specimens, the microstructure is similar and composed of a-Mg solid solution and eutectic compound of a-Mg＋ Mg24（Gd,Y）5; whereas the grain size using metal mould and sand mould is 27 pm and 71 IJm, respectively. The eutectic compound of metal mould cast alloy was completely dissolved after solution treated at 500℃ for 8 h, however it needs higher temperature （525 ℃） and longer time （12 h） to achieve the absolute dissolving under sand mould condition. In contrast to metal mould, the peak time of sand mould alloy aged at 225℃ and 250℃ of was advanced by 4 h and 6 h, respectively. The precipitation reaction sequence in sand mould cast Mg-10Gd-3Y-Zr alloy during isothermal ageing at 250℃ follows S.S.S.S.→β（D010）→β′（cboc）→β1（fcc）→β（fcc）, which is similar to that in the alloy cast using metal mould.
文摘Aging behavior of Mg-3.6Y-0.5Zr and Mg-2.TNd-0.5Zr alloys was investigated by microhardness measurement and transmission electron microscopy.In the case of Mg-Y-Zr alloy,the presence ofβ″phase,a major strength- ener,having base centered orthorhombic structure with its lattice constants of a-（β″）=0.64 nm,b-（β″）=2.22 nm, and c-（β″）=0.52 nm was identified.In the case of Mg-Nd-Zr alloy aged at 250℃,the presence ofβ″andβ′phases was identified.The crystal structure ofβ″phase was found to be DO-（19） and its orientation relationships with Mg matrix were [0001]-（β″）//[0001]-（Mg） and [01（？）0]-（β″）//[01（？）0]-（Mg）.Theβ′phase had face centered cubic structure and its orientation relationships with Mg matrix were [011]-（β′）//[0001]-（Mg） and [（？）1（？）]β′//[（？）110]）-（Mg）. The Mg-2.TNd-0.5Zr alloy showed higher hardness compared with Mg-3.6Y-0.5Zr alloy.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.11461026,11361024,51378206 and 11661036)the Provincial Natural Science Foundation(Grant No.2017BAB201009)
文摘Wavelet method is often used in analyzing trend and period of time sequence. When using wavelet method one serious problem is different chosen wavelet basis and scale would lead to different results. Sometimes, the results vary greatly. To overcome this problem and to improve the accuracy and efficiency, a new method denoted by Natural-based Wavelet Method is introduced and extended. It can be proved that the proposed method in fact is a special class of discrete wavelet. At first, two numerical examples are designed to show the capacity of the novel method. Second, this method is applied to a precipitation series. According to wavelet analysis and short-range precipitation prediction, this precipitation exists a faintly increasing trend. Through the analysis, the studied precipitation has two major periods: 11 and 41 years. The results validate that the Natural-based Wavelet Method used in application of multi-complicated observed data is suitable. It is easy to write the source code of the proposed method. When new information appears, new information can be easily added into the original sequence, this is another advantage of the proposed method.
基金supported by the Baosteel Group Corporation Project (R05DSES220)
文摘This study analyzes the evolution of carbides in the tempering process of a newly developed semi-high speed steel cold forged roll with nitrogen addition using a transmission electron microscope （TEM） equipped with an energy dispersive X-ray （EDX）. The precipitation sequence of the carbides was identified in the entire tempering process and it can be expressed as M3C→M3C ＋ M （C, N）Ⅱ→M（ C, N）Ⅱ → M7C3Ⅱ ＋ M23 C6. The secondary hardening in the tempering process was mainly due to the dispersed precipitation of fine M（ C, N）n particles. The dissolution of M3 C tempered at high temperatures induced the precipitation and coarsening of M7 C31/ and M23 C6.
基金financially supported by the National Natural Science Foundation of China(No.52271038)the Technological Innovation 2025&Major Special Project of Ningbo(No.2021Z084)。
文摘Studies have shown that microalloying Cu-Ni-Sn alloys using Al inhibits discontinuous precipitation reactions;however,the mechanism has not been investigated yet.Thus,this study explored the properties and precipitation evolution of Cu-15Ni-8Sn alloys without and with 1 wt%Al(Cu-15Ni-8Sn-1Al)during ageing at 500℃ through X-ray diffraction(XRD),scanning electron microscopy and high-angle annular dark-field scanning transmission electron microscopy.The results revealed that in Cu-15Ni-8Sn alloy,DO_(22)ordering first occurred after spinodal decomposition,subsequently transitioning to an L1_(2)ordering phase,during which the discontinuous precipitates gradually nucleated at the grain boundaries and formed ingrains.The alloy hardness increased sharply with ordering and then decreased rapidly after reaching its peak value,due to the dominance of the discontinuous precipitation reaction.However,the DO_(22)ordered phase did not appear during the ageing of Cu-15Ni-8Sn-1Al alloy,and a Ni_(3)(Al_(x),Sn_(1-x))intermetallic compound with L1_(2)structure was formed,consuming Ni and Sn atoms,thereby significantly suppressing the discontinuous precipitation reaction and improving the stability during prolonged ageing.The tensile strength(yield strength)of Cu-15Ni-8Sn and Cu-15Ni-8Sn-1Al alloys at peak hardness were 855(755)and 936 MPa(892 MPa),respectively,and their main strengthening mechanisms were solid solution strengthening and precipitation strengthening.The addition of 1 wt%Al effectively improved the precipitation strengthening effect of Cu-Ni-Sn alloys but severely decreased the ductility.
文摘The precipitation characteristics and mechanism of vanadium carbides during isothermal transformation at 650℃ in aV-microalloyed medium-carbon steel were investigated through scanning electron microscopy and transmission electronmicroscopy as well as dilatometry test. Five morphologies of vanadium carbides were found to precipitate at differentnucleation sites during the transformation. Two kinds of interphase precipitation form simultaneously in both pro-eutectoidand pearlitic ferrites. The linear arrays of fine interphase precipitates are parallel to the γ/α interface, and the fine needles ofinterphase precipitates are perpendicular to the 7/ct interface. The vanadium carbides of long or short fibers, coarse particlesand fine particles form in both pro-eutectoid and pearlitic ferrites, displaying different precipitation distributions andorientation relationships with ferrite. The precipitation mechanisms of vanadium carbide precipitates with different modeswere proposed, and the precipitation sequence of various vanadium carbide precipitates was finally ascertained.
