Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca,Mg-Sr and Mg-Ba systems.This investigation incorporated the difference in the‘Work ...Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca,Mg-Sr and Mg-Ba systems.This investigation incorporated the difference in the‘Work Function'(ΔWF)measured via Kelvin Probe Force Microscopy(KPFM),as a property directly affected by interatomic bond types,i.e.the electronic structure,nanoindentation measurements,and Stacking Fault Energy values reported in the literature.It was shown that the nano-hardness of the solid-solutionα-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba.Thus,it was shown,by also considering the nano-hardness levels,that SFE of a solid-solution is closely correlated with its‘Work Function'level.Nano-hardness measurements on the eutectics andΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys.Correlation withΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree,relatively simple atomic models and a number of assumptions.As asserted by this investigation,if the results of measurement techniques can be qualitatively correlated with those of the computational methods,it can be possible to evaluate the electronic structures in alloys,starting from binary systems,going to ternary and then multi-elemental systems.Our investigation has shown that such a qualitative correlation is possible.After all,the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level,that is,free electron density distributions.Our study indicated that the principles of‘electronic metallurgy'in developing multi-elemental alloy systems can be followed via practical experimental methods,i.e.ΔWF measurements using KPFM and nanoindentation.展开更多
Using first principles calculations combined with the quasiharmonic approach, we study the effects of temperature on the elastic constants, generalized stacking fault energies, and generalized planar fault energies of...Using first principles calculations combined with the quasiharmonic approach, we study the effects of temperature on the elastic constants, generalized stacking fault energies, and generalized planar fault energies of Ni3Al. The antiphase boundary energies, complex stacking fault energies, superlattice intrinsic stacking fault energies, and twinning energies decrease slightly with temperature. Temperature dependent anomalous yield stress of Ni3Al is predicted by the energybased criterion based on elastic anisotropy and antiphase boundary energies. It is found that p increases with temperature and this can give a more accurate description of the anomalous yield stress in Ni3Al. Furthermore, the predicted twinnablity of Ni3Al is also decreasing with temperature.展开更多
The effects of Cr and Al content were investigated on the stacking fault energy in austenitic Fe-31Mn-(0-7.26)Cr-0.96C and Fe-31Mn-(0-8.68)Al-0.85C alloys by the thermodynamic analysis. The results show that the addit...The effects of Cr and Al content were investigated on the stacking fault energy in austenitic Fe-31Mn-(0-7.26)Cr-0.96C and Fe-31Mn-(0-8.68)Al-0.85C alloys by the thermodynamic analysis. The results show that the additions of chromium or aluminum increase the non-magnetic component of the stacking fault energy in the γ-Fe-Mn alloys, and the effect of aluminum is larger than that of chromium. The change in the magnetic entropy caused in the antiferromagnetic transition increases the free energy difference between the γ and s phases in the γr-Fe-Mn alloys. The effects of chromium and aluminum on the magnetic component were discussed on the basis of the influence of both upon the antiferromagnetic transition in the γ-Fe-Mn alloys.展开更多
The genearlized planar fault energies of Al and Al-RE (RE = Sc, Y, Dy, Tb, Nd) alloys have been investigated using first-principles methods combined with a quasiharmonic approach. The stacking fault energies, unstab...The genearlized planar fault energies of Al and Al-RE (RE = Sc, Y, Dy, Tb, Nd) alloys have been investigated using first-principles methods combined with a quasiharmonic approach. The stacking fault energies, unstable stacking fault energies, and unstable twinning energies decrease slightly with increasing temperature. The ductility parameter D, the relative barrier difference Sut, and the twinnability τa of Al and Al-RE alloys at different temperatures have been determined. It is found that the ductilities of Al and Al alloys are nearly the same and the ductilities increase slightly with increasing temperature. The RE alloying elements make twinning more likely and the twinnabilities of Al and Al alloys decrease with increasing temperature.展开更多
The correlation between the creep rupture behaviour and the stacking fault energy of matrices of γ′strengthened superalloys has been studied dur- ing constant load creep.At high temperature and intermediate stress,t...The correlation between the creep rupture behaviour and the stacking fault energy of matrices of γ′strengthened superalloys has been studied dur- ing constant load creep.At high temperature and intermediate stress,the creep rupture time and strain strongly depend on the stacking fault energy of matrices rather than the creep friction stress,but at higher stress,the role of grain boundary carbides becomes more obvious. However,in the considerably extensive stress range investigated here,the mean creep rate is a power function of the stacking fault energy of matrices and the power index decreases with in- creasing initial applied stress.Particularly,at inter- mediate stresses the product of this index and the initial applied stress compensated by the shear modulus is same for two series of superalloys. Hence,this product may be a criterion predicting that the matrix deformation controls high tempera- ture creep rupture.展开更多
The stacking fault probability of CoNi alloys with different contents of Ni was measured by X ray diffraction methods. The results show that the stacking fault decreases with increasing Ni content and with increasing ...The stacking fault probability of CoNi alloys with different contents of Ni was measured by X ray diffraction methods. The results show that the stacking fault decreases with increasing Ni content and with increasing temperature. The thermodynamical calculation has found an equation that can express the stacking fault energy γ of CoNi at temperature T . The phase equilibrium temperature depends on the composition of the certain alloy. The relationship between stacking fault energy γ and stacking fault probability P sf is determined.展开更多
Chemical randomness and the associated energy fluctuation are essential features of multi-principal ele-ment alloys(MPEAs).Due to these features,nanoscale stacking fault energy(SFE)fluctuation is a natural and indepen...Chemical randomness and the associated energy fluctuation are essential features of multi-principal ele-ment alloys(MPEAs).Due to these features,nanoscale stacking fault energy(SFE)fluctuation is a natural and independent contribution to strengthening MPEAs.However,existing models for conventional alloys(i.e.,alloys with one principal element)cannot be applied to MPEAs.The extreme values of SFEs required by such models are unknown for MPEAs,which need to calculate the nanoscale volume relevant to the SFE fluctuation.In the present work,we developed an analytic model to evaluate the strengthening ef-fect through the SFE fluctuation,profuse in MPEAs.The model has no adjustable parameters,and all parameters can be determined from experiments and ab initio calculations.This model explains available experimental observations and provides insightful guidance for designing new MPEAs based on the SFE fluctuation.It generally applies to MPEAs in random states and with chemical short-range order.展开更多
The variation of stacking fault energy(SFE)in a number of binary Cu alloys is predicted through considering the Suzuki segregation by the full potential linearly augmented plane wave(FPLAPW)method.The calculated resul...The variation of stacking fault energy(SFE)in a number of binary Cu alloys is predicted through considering the Suzuki segregation by the full potential linearly augmented plane wave(FPLAPW)method.The calculated results show that some solute atoms(Mg,Al,Si,Zn,Ga,Ge,Cd,Sn,and Pb),which prefer to form the Suzuki segregation,may decrease the value of SFE;while the others(Ti,Mn,Fe,Ni,Zr,Ag,and Au),which do not cause the Suzuki segregation may not decrease the SFE.Furthermore,it is interesting to find that the former alloying elements are located on the right of Cu group while the latter on the left of Cu group in the periodic table of elements.The intrinsic reasons for the new findings can be traced down to the valences electronic structure of solute and Cu atoms,i.e.,the similarity of valence electronic structure between solute and Cu atoms increases the value of SFE,while the difference decreases the value of SFE.展开更多
Texture and microstructure evolution in two kinds of the twinning induced plasticity (TWIP) steels (Fe-Mn- Si-AI and Fe-Mn-C) with diverse stacking fault energies during tensile testing were investigated by interr...Texture and microstructure evolution in two kinds of the twinning induced plasticity (TWIP) steels (Fe-Mn- Si-AI and Fe-Mn-C) with diverse stacking fault energies during tensile testing were investigated by interrupted testing. The strain-hardening rate curves of the two steels were quite similar, but the texture characterization curves (maximum of pole density measured by X-ray diffraction) were varied. According to the curvature of max pole density curves, the evolution of the texture and the microstructure can be divided into three stages: low strain stage, medium stage and high stage. In low strain stage the difference of the microstructure came from the intensity of dislocation, which was much smaller in Fe-Mn-Si-AI. The main difference of the microstructure in medium and high strain stages originated from the numbers of activated twin systems. There were more than one twin systems activated in Fe-Mn-C, while only a single twin system activated in Fe-Mn-Si-AI. Texture showed various differences in the whole tensile process because it was affected by their micromechanism, such as concentration of the dislocation and the activation of twin systems. Texture in low strain stage was connected with annealing twin; the evolution ofthe texture was mainly induced by deformation twin generation. More than one activated twin systems in medium and high stages may counteract each other in the view of concentration of the grain orientations.展开更多
The influence of temperatures on the stacking fault energies and deformation mechanism of a Re- containing single crystal nickel-based superalloy during creep at elevated temperatures was investigated by means of calc...The influence of temperatures on the stacking fault energies and deformation mechanism of a Re- containing single crystal nickel-based superalloy during creep at elevated temperatures was investigated by means of calculating the stacking fault energy of alloy, measuring creep properties and performing contrast analysis of dislocation configuration. The results show that the alloy at 760 ℃ possesses lower stacking fault energy, and the stacking fault of alloy increases with increasing temperature. The defor- mation mechanism of alloy during creep at 760 ℃ is 7' phase sheared by 〈110〉 super-dislocations, which may be decomposed to form the configuration of Shockley partials plus super-lattice intrinsic stacking fault, while the deformation mechanism of alloy during creep at 1070 ℃ is the screw or edge super- dislocations shearing into the rafted 7' phase. But during creep at 7(50 and 980 ℃, some super- dislocations shearing into 7' phase may cross-slip from the {111} to {100} planes to form the K-W locks with non-plane core structure, which may restrain the dislocations slipping to enhance the creep resis- tance of alloy at high temperature. The interaction between the Re and other elements may decrease the diffusion rate of atoms to improve the microstructure stability, which is thought to be the main reason why the K-W locks are to be kept in the Re-containing superalloy during creep at 980 ℃.展开更多
The influence of carbon content on the stacking fault energy (SFE) of Fe-20Mn-3Cu twinning-induced plasticity (TWIP) steel was investigated by means of X-ray diffraction peak-shift method and thermodynamic modelin...The influence of carbon content on the stacking fault energy (SFE) of Fe-20Mn-3Cu twinning-induced plasticity (TWIP) steel was investigated by means of X-ray diffraction peak-shift method and thermodynamic modeling. The experimental result indicated that the stacking fault probability decreases with increasing carbon addition, the SFE increases linearly when the carbon content in mass percent is between 0.23 M and 1.41%. The thermody namic calculation results showed that the SFE varied from 22.40 to 29.64 mJ ~ m 2 when the carbon content in mass percent changes from 0.23 % to 1.41%. The XRD analysis revealed that all steels were fully austenitic before and after deformation, which suggested that TWIP effect is the predominant mechanism during the tensile deformation process of Fe-20Mn-3Cu-XC steels.展开更多
As a typical configuration in plastic deformations, dislocation arrays possess a large variation of the separation of the partial dislocation pairs in face-centered cubic(fcc) metals. This can be manifested convenie...As a typical configuration in plastic deformations, dislocation arrays possess a large variation of the separation of the partial dislocation pairs in face-centered cubic(fcc) metals. This can be manifested conveniently by an effective stacking fault energy(SFE). The effective SFE of dislocation arrays is described within the elastic theory of dislocations and verified by atomistic simulations. The atomistic modeling results reveal that the general formulae of the effective SFE can give a reasonably satisfactory prediction for all dislocation types, especially for edge dislocation arrays. Furthermore, the predicted variation of the effective SFE is consistent with several previous experiments, in which the measured SFE is not definite, changing with dislocation density. Our approach could provide better understandings of cross-slip and the competition between slip and twinning during plastic deformations in fcc metals.展开更多
Silicon is an essential alloying element in quenching and partitioning(Q&P)steels,because it is known to suppress carbide precipitation during partitioning step and promote carbon partitioning to stabilize austeni...Silicon is an essential alloying element in quenching and partitioning(Q&P)steels,because it is known to suppress carbide precipitation during partitioning step and promote carbon partitioning to stabilize austenite.When 2 wt%Si was added to 10Mn-2Al-0.2C steel,the size and fraction of the carbides formed during partitioning became smaller than in the Si-free counterpart.Moreover,the suppression of carbide formation promoted C partitioning into austenite as expected.However,austenite stability was always lower with Si under the equivalent partitioning condition because Si effectively decreased the stacking fault energy of austenite.As partitioning progressed,the both yield and tensile strengths of the Si-added steel exceeded that of the Si-free steel with the similar ductility level.This was because Si was an effective solid solution strengthener,and the austenite in the Si-added steel exhibited the appropriate stability to gradually transform into martensite throughout the deformation.The resulting strengthening effect compensated for the softening caused by martensite recovery.Consequently,strain hardening rate decreased continuously throughout deformation,which resulted in high tensile strength and ductility.展开更多
The uniaxial ratcheting behaviors of several metals with different crystal structures or values of fault energy were observed by the stress-controlled cyclic tests at room temperature. The prescribed metals included 3...The uniaxial ratcheting behaviors of several metals with different crystal structures or values of fault energy were observed by the stress-controlled cyclic tests at room temperature. The prescribed metals included 316L stainless steel, pure copper, pure aluminum, and ordinary 20# carbon steel. The effects of applied mean stress, stress amplitude and stress ratio on the uniaxial ratcheting were also investigated. The observations show that different crystal structures or values of fault energy result in more or less different ratcheting behaviors for the prescribed metals. The different ratcheting behaviors are partially caused by the variation of dislocation mobility.展开更多
Assessing the stacking fault forming probability(P_(sf)) and stacking fault energy(SFE)in medium-or highMn base structural materials can anticipate and elucidate the microstructural evolution before and after deformat...Assessing the stacking fault forming probability(P_(sf)) and stacking fault energy(SFE)in medium-or highMn base structural materials can anticipate and elucidate the microstructural evolution before and after deformation.Typically,these two parameters have been determined from theoretical calculations and empirical results.However,the estimation of SFE values in Fe–Mn–C ternary systems is a longstanding debate due to the complicated nature of carbon:that is,whether the carbon doping indeed plays an important role in the formation of stacking faults;and how the amount of carbon atoms exist at grain boundaries or at internal grains with respect to the nominal carbon doping contents.Herein,the use of atom probe tomography and transmission electron microscopy(TEM)unveils the influence of carbondoping contents on the structural properties of dual-phase Fe–17 Mn–x C(x=0–1.56 at%)steels,such as carbon segregation free energy at grain boundaries,carbon concentration in grain interior,interplanar D-spacings,and mean width of intrinsic stacking faults,which are essential for SFE estimation.We next determined the Psfvalues by two different methods,viz.,reciprocal-space electron diffraction measurements and stacking fault width measurements in real-space TEM images.Then,SFEs in the Fe–17 Mn–x C systems were calculated on the basis of the generally-known SFE equations.We found that the high amount of carbon doping gives rise to the increased SFE from 8.6 to 13.5 m J/m^(2)with non-linear variation.This SFE trend varies inversely with the mean width of localized stacking faults,which pass through both other stacking faults and pre-existingε-martensite plates without much difficulty at their intersecting zones.The high amount of carbon doping acts twofold,through increasing the segregation free energy(due to more carbon at grain boundaries)and large lattice expansion(due to increased soluble carbon at internal grains).The experimental data obtained here strengthens the composition-dependent SFE maps for predicting the deformation structure and mechanical response of other carbon-doped high-Mn alloy compositions.展开更多
Based on wavelet packet decomposition (WPD) algorithm and Teager energy operator (TEO), a novel gearbox fault detection and diagnosis method is proposed. Its process is expatiated after the principles of WPD and T...Based on wavelet packet decomposition (WPD) algorithm and Teager energy operator (TEO), a novel gearbox fault detection and diagnosis method is proposed. Its process is expatiated after the principles of WPD and TEO modulation are introduced respectively. The preprocessed sigaaal is interpolated with the cubic spline function, then expanded over the selected basis wavelets. Grouping its wavelet packet components of the signal based on the minimum entropy criterion, the interpolated signal can be decomposed into its dominant components with nearly distinct fault frequency contents. To extract the demodulation information of each dominant component, TEO is used. The performance of the proposed method is assessed by means of several tests on vibration signals collected from the gearbox mounted on a heavy truck. It is proved that hybrid WPD-TEO method is effective and robust for detecting and diagnosing localized gearbox faults.展开更多
Although many methods have been applied to diagnose the gear thult currently, the sensitivity of them is not very good. In order to make the diagnosis methods have more excellent integrated ability in such aspects as ...Although many methods have been applied to diagnose the gear thult currently, the sensitivity of them is not very good. In order to make the diagnosis methods have more excellent integrated ability in such aspects as precision, sensitivity, reliability and compact algorithm, and so on, and enlightened by the energy operator separation algorithm (EOSA), a new demodulation method which is optimizing energy operator separation algorithm (OEOSA) is presented. In the algorithm, the non-linear differential operator is utilized to its differential equation: Choosing the unit impulse response length of filter and fixing the weighting coefficient for inportant points. The method has been applied in diagnosing tooth broden and fatiguing crack of gear faults successfully. It provides demodulation analysis of machine signal with a new approach.展开更多
The stacking fault energies of Ti-46Al-8.5Nb-0.2W alloy at 298 K and 1273 K were determined. The principle for the determination of the stacking fault energies is based on the fact that the stacking fault energy and t...The stacking fault energies of Ti-46Al-8.5Nb-0.2W alloy at 298 K and 1273 K were determined. The principle for the determination of the stacking fault energies is based on the fact that the stacking fault energy and the elastic interaction energy acting on the dissociated partial dislocations are equal. After the compress deformations with the strain of 0.2% at 298 K and 1273 K, and water quench to maintain the dislocation structures deformed at 1273 K, the dissociation distances between two partial dislocations were determined by weak beam transmission electron microscopy (WBTEM) technique. Based on these dissociation distances and the corresponding calculation method, the stacking fault energies were determined to be 77-81 mJ/m2 at 298 K and to be 57-60mJ/m2 at 1273 K respectively.展开更多
We analyze the influences of interstitial atoms on the generalized stacking fault energy (GSFE), strength, and ductility of Ni by first-principles calculations. Surface energies and GSFE curves are calculated for t...We analyze the influences of interstitial atoms on the generalized stacking fault energy (GSFE), strength, and ductility of Ni by first-principles calculations. Surface energies and GSFE curves are calculated for the (112) (111) and / 101) ( 1 1 1) systems. Because of the anisotropy of the single crystal, the addition of interstitials tends to promote the strength of Ni by slipping along the (10T) direction while facilitating plastic deformation by slipping along the (115) direction. There is a different impact on the mechanical behavior of Ni when the interstitials are located in the slip plane. The evaluation of the Rice criterion reveals that the addition of the interstitials H and O increases the brittleness in Ni and promotes the probability of cleavage fracture, while the addition of S and N tends to increase the ductility. Besides, P, H, and S have a negligible effect on the deformation tendency in Ni, while the tendency of partial dislocation is more prominent with the addition of N and O. The addition of interstitial atoms tends to increase the high-energy barrier γmax, thereby the second partial resulting from the dislocation tends to reside and move on to the next layer.展开更多
The stacking fault energies of Ti-46Al-8.5Nb-0.2W alloy at 298 K and 1273 Kwere determined. The principle for the determination of the stacking fault energies is based on thefact that the stacking fault energy and the...The stacking fault energies of Ti-46Al-8.5Nb-0.2W alloy at 298 K and 1273 Kwere determined. The principle for the determination of the stacking fault energies is based on thefact that the stacking fault energy and the elastic interaction energy acting on the dissociatedpartial dislocations are equal. After the compress deformations with the strain of 0.2% at 298 K and1273 K, and water quench to maintain the dislocation structures deformed at 1273 K, thedissociation distances between two partial dislocations were determined by weak beam transmissionelectron microscopy (WBTEM) technique. Based on these dissociation distances and the correspondingcalculation method, the stacking fault energies were determined to be 77-81 mJ/m^2 at 298 K and tobe 57-60mJ/m^2 at 1273 K respectively.展开更多
基金financial support for this work provided by Eski sehir Technical University Scientific Research Projects Unit with Grant Number 20DRP059support provided by the Turkish Ministry of Science,Industry and Technology under the SANTEZ Project 0286.STZ.2013±2。
文摘Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca,Mg-Sr and Mg-Ba systems.This investigation incorporated the difference in the‘Work Function'(ΔWF)measured via Kelvin Probe Force Microscopy(KPFM),as a property directly affected by interatomic bond types,i.e.the electronic structure,nanoindentation measurements,and Stacking Fault Energy values reported in the literature.It was shown that the nano-hardness of the solid-solutionα-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba.Thus,it was shown,by also considering the nano-hardness levels,that SFE of a solid-solution is closely correlated with its‘Work Function'level.Nano-hardness measurements on the eutectics andΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys.Correlation withΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree,relatively simple atomic models and a number of assumptions.As asserted by this investigation,if the results of measurement techniques can be qualitatively correlated with those of the computational methods,it can be possible to evaluate the electronic structures in alloys,starting from binary systems,going to ternary and then multi-elemental systems.Our investigation has shown that such a qualitative correlation is possible.After all,the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level,that is,free electron density distributions.Our study indicated that the principles of‘electronic metallurgy'in developing multi-elemental alloy systems can be followed via practical experimental methods,i.e.ΔWF measurements using KPFM and nanoindentation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11104361 and 11304403)the Fundamental Research Funds for the Central Universities,China(Grant Nos.CQDXWL2014003 and CDJZR14328801)
文摘Using first principles calculations combined with the quasiharmonic approach, we study the effects of temperature on the elastic constants, generalized stacking fault energies, and generalized planar fault energies of Ni3Al. The antiphase boundary energies, complex stacking fault energies, superlattice intrinsic stacking fault energies, and twinning energies decrease slightly with temperature. Temperature dependent anomalous yield stress of Ni3Al is predicted by the energybased criterion based on elastic anisotropy and antiphase boundary energies. It is found that p increases with temperature and this can give a more accurate description of the anomalous yield stress in Ni3Al. Furthermore, the predicted twinnablity of Ni3Al is also decreasing with temperature.
文摘The effects of Cr and Al content were investigated on the stacking fault energy in austenitic Fe-31Mn-(0-7.26)Cr-0.96C and Fe-31Mn-(0-8.68)Al-0.85C alloys by the thermodynamic analysis. The results show that the additions of chromium or aluminum increase the non-magnetic component of the stacking fault energy in the γ-Fe-Mn alloys, and the effect of aluminum is larger than that of chromium. The change in the magnetic entropy caused in the antiferromagnetic transition increases the free energy difference between the γ and s phases in the γr-Fe-Mn alloys. The effects of chromium and aluminum on the magnetic component were discussed on the basis of the influence of both upon the antiferromagnetic transition in the γ-Fe-Mn alloys.
基金supported by the National Natural Science Foundation of China(Grant Nos.11104361 and 11304403)the Fundamental Research Funds for the Central Universities,China(Grant No.CQDXWL2012015)
文摘The genearlized planar fault energies of Al and Al-RE (RE = Sc, Y, Dy, Tb, Nd) alloys have been investigated using first-principles methods combined with a quasiharmonic approach. The stacking fault energies, unstable stacking fault energies, and unstable twinning energies decrease slightly with increasing temperature. The ductility parameter D, the relative barrier difference Sut, and the twinnability τa of Al and Al-RE alloys at different temperatures have been determined. It is found that the ductilities of Al and Al alloys are nearly the same and the ductilities increase slightly with increasing temperature. The RE alloying elements make twinning more likely and the twinnabilities of Al and Al alloys decrease with increasing temperature.
文摘The correlation between the creep rupture behaviour and the stacking fault energy of matrices of γ′strengthened superalloys has been studied dur- ing constant load creep.At high temperature and intermediate stress,the creep rupture time and strain strongly depend on the stacking fault energy of matrices rather than the creep friction stress,but at higher stress,the role of grain boundary carbides becomes more obvious. However,in the considerably extensive stress range investigated here,the mean creep rate is a power function of the stacking fault energy of matrices and the power index decreases with in- creasing initial applied stress.Particularly,at inter- mediate stresses the product of this index and the initial applied stress compensated by the shear modulus is same for two series of superalloys. Hence,this product may be a criterion predicting that the matrix deformation controls high tempera- ture creep rupture.
文摘The stacking fault probability of CoNi alloys with different contents of Ni was measured by X ray diffraction methods. The results show that the stacking fault decreases with increasing Ni content and with increasing temperature. The thermodynamical calculation has found an equation that can express the stacking fault energy γ of CoNi at temperature T . The phase equilibrium temperature depends on the composition of the certain alloy. The relationship between stacking fault energy γ and stacking fault probability P sf is determined.
基金sponsored by the U.S.Department of En-ergy,Office of Science,Basic Energy Sciences,Materials Science and Engineering Divisionsupported by the Office of Science of the U.S.Department of Energy under Contract No.DE-AC05-00OR22725+2 种基金the supports from(1)the National Science Foundation(DMR-1611180 and 1809640)with program directors,Drs.J.Yang,G.Shifletthe US Army Research Office(W911NF-13-1-0438 and W911NF-19-2-0049)with program managers,Drs.M.P.Bakas,S.N.Math-audhuthe support of U.S.Na-tional Science Foundation under grant DMR-1804320.
文摘Chemical randomness and the associated energy fluctuation are essential features of multi-principal ele-ment alloys(MPEAs).Due to these features,nanoscale stacking fault energy(SFE)fluctuation is a natural and independent contribution to strengthening MPEAs.However,existing models for conventional alloys(i.e.,alloys with one principal element)cannot be applied to MPEAs.The extreme values of SFEs required by such models are unknown for MPEAs,which need to calculate the nanoscale volume relevant to the SFE fluctuation.In the present work,we developed an analytic model to evaluate the strengthening ef-fect through the SFE fluctuation,profuse in MPEAs.The model has no adjustable parameters,and all parameters can be determined from experiments and ab initio calculations.This model explains available experimental observations and provides insightful guidance for designing new MPEAs based on the SFE fluctuation.It generally applies to MPEAs in random states and with chemical short-range order.
基金financially supported by the National Natural Science Foundation of China(Nos.51871223,51571198 and 51790482)the LiaoNing Revitalization Talents Program(No.XLYC1808027)。
文摘The variation of stacking fault energy(SFE)in a number of binary Cu alloys is predicted through considering the Suzuki segregation by the full potential linearly augmented plane wave(FPLAPW)method.The calculated results show that some solute atoms(Mg,Al,Si,Zn,Ga,Ge,Cd,Sn,and Pb),which prefer to form the Suzuki segregation,may decrease the value of SFE;while the others(Ti,Mn,Fe,Ni,Zr,Ag,and Au),which do not cause the Suzuki segregation may not decrease the SFE.Furthermore,it is interesting to find that the former alloying elements are located on the right of Cu group while the latter on the left of Cu group in the periodic table of elements.The intrinsic reasons for the new findings can be traced down to the valences electronic structure of solute and Cu atoms,i.e.,the similarity of valence electronic structure between solute and Cu atoms increases the value of SFE,while the difference decreases the value of SFE.
基金financially supported by the National Natural Science Foundation of China(No.50804005)Special Fund from the Central Collegiate Basic Scientific Research Bursary of China(No.FRF-TP-11-005B)
文摘Texture and microstructure evolution in two kinds of the twinning induced plasticity (TWIP) steels (Fe-Mn- Si-AI and Fe-Mn-C) with diverse stacking fault energies during tensile testing were investigated by interrupted testing. The strain-hardening rate curves of the two steels were quite similar, but the texture characterization curves (maximum of pole density measured by X-ray diffraction) were varied. According to the curvature of max pole density curves, the evolution of the texture and the microstructure can be divided into three stages: low strain stage, medium stage and high stage. In low strain stage the difference of the microstructure came from the intensity of dislocation, which was much smaller in Fe-Mn-Si-AI. The main difference of the microstructure in medium and high strain stages originated from the numbers of activated twin systems. There were more than one twin systems activated in Fe-Mn-C, while only a single twin system activated in Fe-Mn-Si-AI. Texture showed various differences in the whole tensile process because it was affected by their micromechanism, such as concentration of the dislocation and the activation of twin systems. Texture in low strain stage was connected with annealing twin; the evolution ofthe texture was mainly induced by deformation twin generation. More than one activated twin systems in medium and high stages may counteract each other in the view of concentration of the grain orientations.
基金supported by the National Natural Science Foundation of China (Grant No. 51271125)
文摘The influence of temperatures on the stacking fault energies and deformation mechanism of a Re- containing single crystal nickel-based superalloy during creep at elevated temperatures was investigated by means of calculating the stacking fault energy of alloy, measuring creep properties and performing contrast analysis of dislocation configuration. The results show that the alloy at 760 ℃ possesses lower stacking fault energy, and the stacking fault of alloy increases with increasing temperature. The defor- mation mechanism of alloy during creep at 760 ℃ is 7' phase sheared by 〈110〉 super-dislocations, which may be decomposed to form the configuration of Shockley partials plus super-lattice intrinsic stacking fault, while the deformation mechanism of alloy during creep at 1070 ℃ is the screw or edge super- dislocations shearing into the rafted 7' phase. But during creep at 7(50 and 980 ℃, some super- dislocations shearing into 7' phase may cross-slip from the {111} to {100} planes to form the K-W locks with non-plane core structure, which may restrain the dislocations slipping to enhance the creep resis- tance of alloy at high temperature. The interaction between the Re and other elements may decrease the diffusion rate of atoms to improve the microstructure stability, which is thought to be the main reason why the K-W locks are to be kept in the Re-containing superalloy during creep at 980 ℃.
基金Item Sponsored by Industry-University Cooperation Major Program of Science and Technology Department of Fujian Province of China(2011H6012)Key Program of Science and Technology Department of Fujian Province of China(2011H0001)
文摘The influence of carbon content on the stacking fault energy (SFE) of Fe-20Mn-3Cu twinning-induced plasticity (TWIP) steel was investigated by means of X-ray diffraction peak-shift method and thermodynamic modeling. The experimental result indicated that the stacking fault probability decreases with increasing carbon addition, the SFE increases linearly when the carbon content in mass percent is between 0.23 M and 1.41%. The thermody namic calculation results showed that the SFE varied from 22.40 to 29.64 mJ ~ m 2 when the carbon content in mass percent changes from 0.23 % to 1.41%. The XRD analysis revealed that all steels were fully austenitic before and after deformation, which suggested that TWIP effect is the predominant mechanism during the tensile deformation process of Fe-20Mn-3Cu-XC steels.
基金support of this work by the Program of ‘‘One Hundred Talented People’’ of the Chinese Academy of Sciences (JBY) and the National Natural Science Foundation of China (Nos. 51571198, 51771206, 51331007, 51501197 and 51401207)
文摘As a typical configuration in plastic deformations, dislocation arrays possess a large variation of the separation of the partial dislocation pairs in face-centered cubic(fcc) metals. This can be manifested conveniently by an effective stacking fault energy(SFE). The effective SFE of dislocation arrays is described within the elastic theory of dislocations and verified by atomistic simulations. The atomistic modeling results reveal that the general formulae of the effective SFE can give a reasonably satisfactory prediction for all dislocation types, especially for edge dislocation arrays. Furthermore, the predicted variation of the effective SFE is consistent with several previous experiments, in which the measured SFE is not definite, changing with dislocation density. Our approach could provide better understandings of cross-slip and the competition between slip and twinning during plastic deformations in fcc metals.
基金POSCO(Pohang,Republic of Korea)for the financial supportsupported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(2019R1I1A3A0106262212).
文摘Silicon is an essential alloying element in quenching and partitioning(Q&P)steels,because it is known to suppress carbide precipitation during partitioning step and promote carbon partitioning to stabilize austenite.When 2 wt%Si was added to 10Mn-2Al-0.2C steel,the size and fraction of the carbides formed during partitioning became smaller than in the Si-free counterpart.Moreover,the suppression of carbide formation promoted C partitioning into austenite as expected.However,austenite stability was always lower with Si under the equivalent partitioning condition because Si effectively decreased the stacking fault energy of austenite.As partitioning progressed,the both yield and tensile strengths of the Si-added steel exceeded that of the Si-free steel with the similar ductility level.This was because Si was an effective solid solution strengthener,and the austenite in the Si-added steel exhibited the appropriate stability to gradually transform into martensite throughout the deformation.The resulting strengthening effect compensated for the softening caused by martensite recovery.Consequently,strain hardening rate decreased continuously throughout deformation,which resulted in high tensile strength and ductility.
基金support of the National Natural Science Foundation of China (Grant No. 10772153)
文摘The uniaxial ratcheting behaviors of several metals with different crystal structures or values of fault energy were observed by the stress-controlled cyclic tests at room temperature. The prescribed metals included 316L stainless steel, pure copper, pure aluminum, and ordinary 20# carbon steel. The effects of applied mean stress, stress amplitude and stress ratio on the uniaxial ratcheting were also investigated. The observations show that different crystal structures or values of fault energy result in more or less different ratcheting behaviors for the prescribed metals. The different ratcheting behaviors are partially caused by the variation of dislocation mobility.
基金the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(2020R1A4A3079417)(No.2021R1A2C4002622)by the Future Material Discovery Program of the NRFfunded by the MSIP of Korea(No.2021M3D1A1021236)。
文摘Assessing the stacking fault forming probability(P_(sf)) and stacking fault energy(SFE)in medium-or highMn base structural materials can anticipate and elucidate the microstructural evolution before and after deformation.Typically,these two parameters have been determined from theoretical calculations and empirical results.However,the estimation of SFE values in Fe–Mn–C ternary systems is a longstanding debate due to the complicated nature of carbon:that is,whether the carbon doping indeed plays an important role in the formation of stacking faults;and how the amount of carbon atoms exist at grain boundaries or at internal grains with respect to the nominal carbon doping contents.Herein,the use of atom probe tomography and transmission electron microscopy(TEM)unveils the influence of carbondoping contents on the structural properties of dual-phase Fe–17 Mn–x C(x=0–1.56 at%)steels,such as carbon segregation free energy at grain boundaries,carbon concentration in grain interior,interplanar D-spacings,and mean width of intrinsic stacking faults,which are essential for SFE estimation.We next determined the Psfvalues by two different methods,viz.,reciprocal-space electron diffraction measurements and stacking fault width measurements in real-space TEM images.Then,SFEs in the Fe–17 Mn–x C systems were calculated on the basis of the generally-known SFE equations.We found that the high amount of carbon doping gives rise to the increased SFE from 8.6 to 13.5 m J/m^(2)with non-linear variation.This SFE trend varies inversely with the mean width of localized stacking faults,which pass through both other stacking faults and pre-existingε-martensite plates without much difficulty at their intersecting zones.The high amount of carbon doping acts twofold,through increasing the segregation free energy(due to more carbon at grain boundaries)and large lattice expansion(due to increased soluble carbon at internal grains).The experimental data obtained here strengthens the composition-dependent SFE maps for predicting the deformation structure and mechanical response of other carbon-doped high-Mn alloy compositions.
基金This project is supported by National Natural Science Foundation of China (No.50605065)Natural Science Foundation Project of CQ CSTC (No.2007BB2142)
文摘Based on wavelet packet decomposition (WPD) algorithm and Teager energy operator (TEO), a novel gearbox fault detection and diagnosis method is proposed. Its process is expatiated after the principles of WPD and TEO modulation are introduced respectively. The preprocessed sigaaal is interpolated with the cubic spline function, then expanded over the selected basis wavelets. Grouping its wavelet packet components of the signal based on the minimum entropy criterion, the interpolated signal can be decomposed into its dominant components with nearly distinct fault frequency contents. To extract the demodulation information of each dominant component, TEO is used. The performance of the proposed method is assessed by means of several tests on vibration signals collected from the gearbox mounted on a heavy truck. It is proved that hybrid WPD-TEO method is effective and robust for detecting and diagnosing localized gearbox faults.
基金This project is supported by National Ministry of Education of China (No.020616)Science and Technology Project of Municipal Educational Committee of Chongqing(No.030602)Scientific Research Foundation of Chongqing Institute of Technology(No.2004ZD10).
文摘Although many methods have been applied to diagnose the gear thult currently, the sensitivity of them is not very good. In order to make the diagnosis methods have more excellent integrated ability in such aspects as precision, sensitivity, reliability and compact algorithm, and so on, and enlightened by the energy operator separation algorithm (EOSA), a new demodulation method which is optimizing energy operator separation algorithm (OEOSA) is presented. In the algorithm, the non-linear differential operator is utilized to its differential equation: Choosing the unit impulse response length of filter and fixing the weighting coefficient for inportant points. The method has been applied in diagnosing tooth broden and fatiguing crack of gear faults successfully. It provides demodulation analysis of machine signal with a new approach.
文摘The stacking fault energies of Ti-46Al-8.5Nb-0.2W alloy at 298 K and 1273 K were determined. The principle for the determination of the stacking fault energies is based on the fact that the stacking fault energy and the elastic interaction energy acting on the dissociated partial dislocations are equal. After the compress deformations with the strain of 0.2% at 298 K and 1273 K, and water quench to maintain the dislocation structures deformed at 1273 K, the dissociation distances between two partial dislocations were determined by weak beam transmission electron microscopy (WBTEM) technique. Based on these dissociation distances and the corresponding calculation method, the stacking fault energies were determined to be 77-81 mJ/m2 at 298 K and to be 57-60mJ/m2 at 1273 K respectively.
基金supported by the National Natural Science Foundation of China(Grant No 51371123)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.2013140211003)+1 种基金the Natural Science Foundation of Shanxi Science Technological Commission,China(Grant No.2014011002)the Scientific and Technological Research Program of Chongqing Municipal Education Commission,China(Grant No.KJ131315)
文摘We analyze the influences of interstitial atoms on the generalized stacking fault energy (GSFE), strength, and ductility of Ni by first-principles calculations. Surface energies and GSFE curves are calculated for the (112) (111) and / 101) ( 1 1 1) systems. Because of the anisotropy of the single crystal, the addition of interstitials tends to promote the strength of Ni by slipping along the (10T) direction while facilitating plastic deformation by slipping along the (115) direction. There is a different impact on the mechanical behavior of Ni when the interstitials are located in the slip plane. The evaluation of the Rice criterion reveals that the addition of the interstitials H and O increases the brittleness in Ni and promotes the probability of cleavage fracture, while the addition of S and N tends to increase the ductility. Besides, P, H, and S have a negligible effect on the deformation tendency in Ni, while the tendency of partial dislocation is more prominent with the addition of N and O. The addition of interstitial atoms tends to increase the high-energy barrier γmax, thereby the second partial resulting from the dislocation tends to reside and move on to the next layer.
基金The work was financial supported by the National Natural Science Foundation of China (No.59895151).
文摘The stacking fault energies of Ti-46Al-8.5Nb-0.2W alloy at 298 K and 1273 Kwere determined. The principle for the determination of the stacking fault energies is based on thefact that the stacking fault energy and the elastic interaction energy acting on the dissociatedpartial dislocations are equal. After the compress deformations with the strain of 0.2% at 298 K and1273 K, and water quench to maintain the dislocation structures deformed at 1273 K, thedissociation distances between two partial dislocations were determined by weak beam transmissionelectron microscopy (WBTEM) technique. Based on these dissociation distances and the correspondingcalculation method, the stacking fault energies were determined to be 77-81 mJ/m^2 at 298 K and tobe 57-60mJ/m^2 at 1273 K respectively.