Brittleness is a dominant issue that restricts potential applications of Mg_2Si intermetallic compounds(IMC). In this paper, guided by first-principles calculations, we found that Al doping will enhance the ductility ...Brittleness is a dominant issue that restricts potential applications of Mg_2Si intermetallic compounds(IMC). In this paper, guided by first-principles calculations, we found that Al doping will enhance the ductility of Mg_2Si. The underlying mechanism is that Al doping could reduce the electronic exchange effect between Mg and Si atoms, and increase the volume module/shear modulus ratio, both of which are beneficial to the deformation capability of Mg_2Si. Experimental investigations were then carried out to verify the calculation results with Al doping contents ranging from Al-free to 10 wt%. Results showed that the obtained ductile-brittle transition temperature of the Mg_2Si–Al alloy decreased and the corresponding ductility increased. Specifically, the ductile-brittle transition temperature could be reduced by about 100℃. When the content of Al reached 6 wt%, α-Al phase started to precipitate, and the ductile-brittle transition temperature of the alloy no longer decreased.展开更多
The dynamic fracture toughness of a mild steel has been studied at different loading rates andtemperatures.The material exhibits a transition from tough to brittle fracture with the chang-ing loading rate alone.Analys...The dynamic fracture toughness of a mild steel has been studied at different loading rates andtemperatures.The material exhibits a transition from tough to brittle fracture with the chang-ing loading rate alone.Analysis of the fracture process by the theory of thermal activationsuggests that the fracture activation energy approximates to the bond energy of the{100}of aunit cell.The toughness can be resolved into two parts,J-（fd）=J<sub>a</sub>+J<sub>l</sub>,where J<sub>a</sub> is the athermalpart,being independent on temperature and loading rate,whileJ<sub>l</sub>=（K/K<sub>o</sub>）<sup>1/n</sup>exp（Q<sub>f</sub>/nkT）,which controls the fracture process is temperature and load-ing rate dependent.The transition of fracture mechanism caused by both temperature andloading rate is associated with the thermal movement of atoms.展开更多
Based on the observation of the deep bore cores sampled from the State of Cali-fornia, USA, preferred arranged particulate concentration belts were found in the ultra-slipping lamellae. And the same phenomenon was fou...Based on the observation of the deep bore cores sampled from the State of Cali-fornia, USA, preferred arranged particulate concentration belts were found in the ultra-slipping lamellae. And the same phenomenon was found again later in the bore cores from the petroleum basin in the Northern Shaanxi Province. It may be the product of the dynamic processes involv-ing tumbling, grinding and compresso-shearing functions, so the spherical particulates with ul-tra-size of nm and mm are called grinding grain. The formation of the grinding grains is related with the ductile-brittle deformation, the lateral pressure of the slipping, and the very low grade of dynamic metamorphism of the rocks. Based on the systematic analysis, it is indicated that some elements like Nb and Ta are enriched in the grinding grains in the granitic rocks because of the chemical differentiation, and that the slipping lamellae bearing grinding grains in mudstone with smear efficiency prove a perfect seal for oil and gas reservoirs. Meanwhile, the paper provides bases for the studies on the fast stick-slip movement and shear paradigm.展开更多
Magneto-plasticity occurs when a weak magnetic field alters material plasticity and offers a viable solution to enhance ductile-mode cutting of brittle materials.This study demonstrates the susceptibility of non-magne...Magneto-plasticity occurs when a weak magnetic field alters material plasticity and offers a viable solution to enhance ductile-mode cutting of brittle materials.This study demonstrates the susceptibility of non-magnetic single-crystal calcium fluoride(CaF_(2))to the magneto-plastic effect.The influence of magneto-plasticity on CaF_(2) was confirmed in micro-deformation tests under a weak magnetic field of 20 mT.The surface pile-up effect was weakened by 10-15 nm along with an enlarged plastic zone and suppressed crack propagation under the influence of the magnetic field.Micro-cutting tests along different crystal orientations on the(111)plane of CaF_(2) revealed an increase in the ductile-brittle transition of the machined surface with the aid of magneto-plasticity where the largest increase in ductile-brittle transition occurred along the[112]orientation from 512 nm to a range of 664-806 nm.Meanwhile,the subsurface damage layer was concurrently thinner under magnetic influence.An anisotropic influence of the magnetic field relative to the single-crystal orientation and the cutting direction was also observed.An analytical model was derived to determine an orientation factor M that successfully describes the anisotropy while considering the single-crystal dislocation behaviour,material fracture toughness,and the orientation of the magnetic field.Previously suggested theoretical mechanism of magneto-plasticity via formation of non-singlet electronic states in defected configurations was confirmed with density functional theory calculations.The successful findings on the influence of a weak magnetic field on plasticity present an opportunity for the adoption of magnetic-assisted micro-cutting of non-magnetic materials.展开更多
In the present work,we have employed machine learning(ML)techniques to evaluate ductile-brittle(DB)behaviors in intermetallic compounds(IMCs)which can form magnesium(Mg)alloys.This procedure was mainly conducted by a ...In the present work,we have employed machine learning(ML)techniques to evaluate ductile-brittle(DB)behaviors in intermetallic compounds(IMCs)which can form magnesium(Mg)alloys.This procedure was mainly conducted by a proxy-based method,where the ratio of shear(G)/bulk(B)moduli was used as a proxy to identify whether the compound is ductile or brittle.Starting from compounds information(composition and crystal structure)and their moduli,as found in open databases(AFLOW),ML-based models were built,and those models were used to predict the moduli in other compounds,and accordingly,to foresee the ductile-brittle behaviors of these new compounds.The results reached in the present work showed that the built models can effectively catch the elastic moduli of new compounds.This was confirmed through moduli calculations done by density functional theory(DFT)on some compounds,where the DFT calculations were consistent with the ML prediction.A further confirmation on the reliability of the built ML models was considered through relating between the DB behavior in MgBe_(13) and MgPd_(2),as evaluated by the ML-predicted moduli,and the nature of chemical bonding in these two compounds,which in turn,was investigated by the charge density distribution(CDD)and electron localization function(ELF)obtained by DFT methodology.The ML-evaluated DB behaviors of the two compounds was also consistent with the DFT calculations of CDD and ELF.These findings and confirmations gave legitimacy to the built model to be employed in further prediction processes.Indeed,as examples,the DB characteristics were investigated in IMCs that might from in three Mg alloy series,involving AZ,ZX and WE.展开更多
In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting dir...In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting direction of resultant force. Anisotropic characteristics of crack morphology and ductility of machining depending on cutting direction were explained in detail with modified fracture cleavage and plastic deformation parameters. Through the analysis, it was concluded that crack morphologies were mainly determined by the interaction of multiple fracture systems activated while, critical depth of cut was determined by the dominant plastic deformation parameter. In addition to this, by using proportionality relationship between magnitude of resultant force and depth of cut in the ductile region, an empirical model for critical depth of cut was developed.展开更多
The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and theeffect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-basesuperallovs have been investigated t...The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and theeffect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-basesuperallovs have been investigated to propose the theoretical basis of search for an optimum ofmechanical properties of the high temperature coating on Ni-base alloys.展开更多
In this paper,the damage state of a torsional prestrained steel isexamined by means of the concepts of continuum damage mechanics and then thetensile properties and fracture ductility of two kinds of steels under vari...In this paper,the damage state of a torsional prestrained steel isexamined by means of the concepts of continuum damage mechanics and then thetensile properties and fracture ductility of two kinds of steels under various torsionalprestrained conditions are investigated from both macroscopic and microscopic points ofvery slight as contrasted with tensile damage;(2)after torsional prestraining,bothyielding strength and ultimate tensile strength become higher for 20 steel and lower for40Cr steel;(3)when the torsional prestrain exceeds a critical value,that is about70% of pure torsional shear fracture strain,the ductile-brittle transition of tensilefracture behavior may initiates.Moreover,the advantages and applicable conditions oftorsional prestrain strengthening technique are also discussed.展开更多
The comparative study of submerged arc welding(SAW)and laser hybrid welding(LHW)was carried out for a 690 MPa high strength steel with thickness of 20 mm.Microstructure and ductile–brittle transition temperature(DBTT...The comparative study of submerged arc welding(SAW)and laser hybrid welding(LHW)was carried out for a 690 MPa high strength steel with thickness of 20 mm.Microstructure and ductile–brittle transition temperature(DBTT)evolution in welded zone were elucidated from the aspect of crystallographic structure,particularly,digitization and visualization of 24 variants.The impact toughness of each micro zone in LHW joint is better than that of SAW,in which the DBTT of equivalent fusion line and heat-affected zone(HAZ)can reach−70 and−80℃,while that of SAW is only−50℃.LHW technology induces narrowing of the HAZ and refining of the microstructure obtained in weld metal and HAZ.Meanwhile,the austenite grain size and transformation driving force in the coarse grained heat-affected zone(CGHAZ)are reduced and increased,respectively.It makes variant selection mechanism occurring in CGHAZ of LHW dominate by close-packed plane grouping,which promotes lath bainite formation with high density of high angle grain boundary,especially block boundary dominated by V1/V2 pair.While for SAW,the lower transformation driving force inferred from the large amount of retained austenite in CGHAZ induces Bain grouping of variants,and thus triggers the brittle crack propagating straightly in granular bainite,resulting in lower impact toughness and higher DBTT.展开更多
Based on the knowledge of the shallow-level mylonitization of detrital rocks and intrusive rocks, the poorly-known cataclastic rheology of carbonate rocks is discussed compre-hensively in this paper. The cases taken f...Based on the knowledge of the shallow-level mylonitization of detrital rocks and intrusive rocks, the poorly-known cataclastic rheology of carbonate rocks is discussed compre-hensively in this paper. The cases taken from eastern China are analyzed in various aspects including ductile-brittle fault zone, rock texture and structure, clastomylonite layer, leucocratic stress minerals, and frictional dynamometamorphism. It is proposed that the cataclastic flow structure represented by clastomylonite texture is a cooling pattern of flow assemblage charac-terized by cooling metamorphism, cooling mylonite and cooling stress minerals. Such a pattern is formed generally in mildly reducing physicochemical environments, and is commonly related to regional tectonism and mesothermal and epithermal mineralization.展开更多
基金financially supported by the National Key Research and Development Program of China (No. 2016YFB0700500)the National Natural Science Foundation of China (No. 51574027)
文摘Brittleness is a dominant issue that restricts potential applications of Mg_2Si intermetallic compounds(IMC). In this paper, guided by first-principles calculations, we found that Al doping will enhance the ductility of Mg_2Si. The underlying mechanism is that Al doping could reduce the electronic exchange effect between Mg and Si atoms, and increase the volume module/shear modulus ratio, both of which are beneficial to the deformation capability of Mg_2Si. Experimental investigations were then carried out to verify the calculation results with Al doping contents ranging from Al-free to 10 wt%. Results showed that the obtained ductile-brittle transition temperature of the Mg_2Si–Al alloy decreased and the corresponding ductility increased. Specifically, the ductile-brittle transition temperature could be reduced by about 100℃. When the content of Al reached 6 wt%, α-Al phase started to precipitate, and the ductile-brittle transition temperature of the alloy no longer decreased.
文摘The dynamic fracture toughness of a mild steel has been studied at different loading rates andtemperatures.The material exhibits a transition from tough to brittle fracture with the chang-ing loading rate alone.Analysis of the fracture process by the theory of thermal activationsuggests that the fracture activation energy approximates to the bond energy of the{100}of aunit cell.The toughness can be resolved into two parts,J-（fd）=J<sub>a</sub>+J<sub>l</sub>,where J<sub>a</sub> is the athermalpart,being independent on temperature and loading rate,whileJ<sub>l</sub>=（K/K<sub>o</sub>）<sup>1/n</sup>exp（Q<sub>f</sub>/nkT）,which controls the fracture process is temperature and load-ing rate dependent.The transition of fracture mechanism caused by both temperature andloading rate is associated with the thermal movement of atoms.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 40173001, 40003002 and 40172072) the State Key Laboratory of Oil/Gas Reservoir Geology and Exploitation.
文摘Based on the observation of the deep bore cores sampled from the State of Cali-fornia, USA, preferred arranged particulate concentration belts were found in the ultra-slipping lamellae. And the same phenomenon was found again later in the bore cores from the petroleum basin in the Northern Shaanxi Province. It may be the product of the dynamic processes involv-ing tumbling, grinding and compresso-shearing functions, so the spherical particulates with ul-tra-size of nm and mm are called grinding grain. The formation of the grinding grains is related with the ductile-brittle deformation, the lateral pressure of the slipping, and the very low grade of dynamic metamorphism of the rocks. Based on the systematic analysis, it is indicated that some elements like Nb and Ta are enriched in the grinding grains in the granitic rocks because of the chemical differentiation, and that the slipping lamellae bearing grinding grains in mudstone with smear efficiency prove a perfect seal for oil and gas reservoirs. Meanwhile, the paper provides bases for the studies on the fast stick-slip movement and shear paradigm.
基金supported by the Ministry of Education,Singapore,under its Academic Research Funds(Grant Nos.:MOE-T2EP50120-0010,MOE-T2EP50220-0010)the funding from the Ministère des Relations Internationales et de la Francophonie du Québec,Coopération Québec-Singapour,with which this work was partially supported。
文摘Magneto-plasticity occurs when a weak magnetic field alters material plasticity and offers a viable solution to enhance ductile-mode cutting of brittle materials.This study demonstrates the susceptibility of non-magnetic single-crystal calcium fluoride(CaF_(2))to the magneto-plastic effect.The influence of magneto-plasticity on CaF_(2) was confirmed in micro-deformation tests under a weak magnetic field of 20 mT.The surface pile-up effect was weakened by 10-15 nm along with an enlarged plastic zone and suppressed crack propagation under the influence of the magnetic field.Micro-cutting tests along different crystal orientations on the(111)plane of CaF_(2) revealed an increase in the ductile-brittle transition of the machined surface with the aid of magneto-plasticity where the largest increase in ductile-brittle transition occurred along the[112]orientation from 512 nm to a range of 664-806 nm.Meanwhile,the subsurface damage layer was concurrently thinner under magnetic influence.An anisotropic influence of the magnetic field relative to the single-crystal orientation and the cutting direction was also observed.An analytical model was derived to determine an orientation factor M that successfully describes the anisotropy while considering the single-crystal dislocation behaviour,material fracture toughness,and the orientation of the magnetic field.Previously suggested theoretical mechanism of magneto-plasticity via formation of non-singlet electronic states in defected configurations was confirmed with density functional theory calculations.The successful findings on the influence of a weak magnetic field on plasticity present an opportunity for the adoption of magnetic-assisted micro-cutting of non-magnetic materials.
基金supported by National Research Foundation(NRF)of South Korea(2020R1A2C1004720)。
文摘In the present work,we have employed machine learning(ML)techniques to evaluate ductile-brittle(DB)behaviors in intermetallic compounds(IMCs)which can form magnesium(Mg)alloys.This procedure was mainly conducted by a proxy-based method,where the ratio of shear(G)/bulk(B)moduli was used as a proxy to identify whether the compound is ductile or brittle.Starting from compounds information(composition and crystal structure)and their moduli,as found in open databases(AFLOW),ML-based models were built,and those models were used to predict the moduli in other compounds,and accordingly,to foresee the ductile-brittle behaviors of these new compounds.The results reached in the present work showed that the built models can effectively catch the elastic moduli of new compounds.This was confirmed through moduli calculations done by density functional theory(DFT)on some compounds,where the DFT calculations were consistent with the ML prediction.A further confirmation on the reliability of the built ML models was considered through relating between the DB behavior in MgBe_(13) and MgPd_(2),as evaluated by the ML-predicted moduli,and the nature of chemical bonding in these two compounds,which in turn,was investigated by the charge density distribution(CDD)and electron localization function(ELF)obtained by DFT methodology.The ML-evaluated DB behaviors of the two compounds was also consistent with the DFT calculations of CDD and ELF.These findings and confirmations gave legitimacy to the built model to be employed in further prediction processes.Indeed,as examples,the DB characteristics were investigated in IMCs that might from in three Mg alloy series,involving AZ,ZX and WE.
基金supported by the NSF under grant No. CMMI-1844821。
文摘In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting direction of resultant force. Anisotropic characteristics of crack morphology and ductility of machining depending on cutting direction were explained in detail with modified fracture cleavage and plastic deformation parameters. Through the analysis, it was concluded that crack morphologies were mainly determined by the interaction of multiple fracture systems activated while, critical depth of cut was determined by the dominant plastic deformation parameter. In addition to this, by using proportionality relationship between magnitude of resultant force and depth of cut in the ductile region, an empirical model for critical depth of cut was developed.
文摘The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and theeffect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-basesuperallovs have been investigated to propose the theoretical basis of search for an optimum ofmechanical properties of the high temperature coating on Ni-base alloys.
文摘In this paper,the damage state of a torsional prestrained steel isexamined by means of the concepts of continuum damage mechanics and then thetensile properties and fracture ductility of two kinds of steels under various torsionalprestrained conditions are investigated from both macroscopic and microscopic points ofvery slight as contrasted with tensile damage;(2)after torsional prestraining,bothyielding strength and ultimate tensile strength become higher for 20 steel and lower for40Cr steel;(3)when the torsional prestrain exceeds a critical value,that is about70% of pure torsional shear fracture strain,the ductile-brittle transition of tensilefracture behavior may initiates.Moreover,the advantages and applicable conditions oftorsional prestrain strengthening technique are also discussed.
基金financially supported by the National Natural Science Foundation of China(No.52001023)the Special Fund for Science and Technology Project of Guangdong Province(No.SDZX2020008)the Key Research and Development Program of Shandong Province,China(No.2019JZZY020238).
文摘The comparative study of submerged arc welding(SAW)and laser hybrid welding(LHW)was carried out for a 690 MPa high strength steel with thickness of 20 mm.Microstructure and ductile–brittle transition temperature(DBTT)evolution in welded zone were elucidated from the aspect of crystallographic structure,particularly,digitization and visualization of 24 variants.The impact toughness of each micro zone in LHW joint is better than that of SAW,in which the DBTT of equivalent fusion line and heat-affected zone(HAZ)can reach−70 and−80℃,while that of SAW is only−50℃.LHW technology induces narrowing of the HAZ and refining of the microstructure obtained in weld metal and HAZ.Meanwhile,the austenite grain size and transformation driving force in the coarse grained heat-affected zone(CGHAZ)are reduced and increased,respectively.It makes variant selection mechanism occurring in CGHAZ of LHW dominate by close-packed plane grouping,which promotes lath bainite formation with high density of high angle grain boundary,especially block boundary dominated by V1/V2 pair.While for SAW,the lower transformation driving force inferred from the large amount of retained austenite in CGHAZ induces Bain grouping of variants,and thus triggers the brittle crack propagating straightly in granular bainite,resulting in lower impact toughness and higher DBTT.
基金the Ntional Natural Science Foundation of China(Grant Nos.40372092,40373024,40172067 , 40172034) the State Key Laboratory of Geology and Exploitation Engineering of Petroleum Reservoir
文摘Based on the knowledge of the shallow-level mylonitization of detrital rocks and intrusive rocks, the poorly-known cataclastic rheology of carbonate rocks is discussed compre-hensively in this paper. The cases taken from eastern China are analyzed in various aspects including ductile-brittle fault zone, rock texture and structure, clastomylonite layer, leucocratic stress minerals, and frictional dynamometamorphism. It is proposed that the cataclastic flow structure represented by clastomylonite texture is a cooling pattern of flow assemblage charac-terized by cooling metamorphism, cooling mylonite and cooling stress minerals. Such a pattern is formed generally in mildly reducing physicochemical environments, and is commonly related to regional tectonism and mesothermal and epithermal mineralization.
