First-principles calculations based on the density functional theory（DFT） and ultra-soft pseudopotential are employed to study the atomic configuration and charge density of impurity P in Ni Al Σ5 grain boundary（G...First-principles calculations based on the density functional theory（DFT） and ultra-soft pseudopotential are employed to study the atomic configuration and charge density of impurity P in Ni Al Σ5 grain boundary（GB）. The negative segregation energy of a P atom proves that a P atom can easily segregate in the Ni Al GB. The atomic configuration and formation energy of the P atom in the Ni Al GB demonstrate that the P atom tends to occupy an interstitial site or substitute a Al atom depending on the Ni/Al atoms ratio. The P atom is preferable to staying in the Ni-rich environment in the Ni Al GB forming P–Ni bonds. Both of the charge density and the deformation charge imply that a P atom is more likely to bond with Ni atoms rather than with Al atoms. The density of states further exhibits the interactions between P atom and Ni atom, and the orbital electrons of P, Ni and Al atoms all contribute to P–Ni bonds in the Ni Al GB. It is worth noting that the P–Ni covalent bonds might embrittle the Ni Al GB and weakens the plasticity of the Ni Al intermetallics.展开更多
In this paper,we employ the first-principle total energy method to investigate the effect of P impurity on mechanical properties of NiA1 grain boundary(GB).According to"energy",the segregation of P atom in N...In this paper,we employ the first-principle total energy method to investigate the effect of P impurity on mechanical properties of NiA1 grain boundary(GB).According to"energy",the segregation of P atom in NiA1E5 GB reduces the cleavage energy and embrittlement potential,demonstrating that P impurity embrittles NiA1E5 GB.The first-principle computational tensile test is conducted to determine the theoretical tensile strength of NiA1E5 GB.It is demonstrated that the maximum idea/tensile strength of NiA1E5 GB with P atom segregation is 144.5 GPa,which is lower than that of the pure NiA1E5 GB(164.7 GPa).It is indicated that the segregation of P weakens the theoretical strength of NiA1E5 GB.The analysis of atomic configuration shows that the GB fracture is caused by the interfacial bond breaking.Moreover,P is identified to weaken the interactions between A1-A1 bonds and enhance Ni-Ni bonds.展开更多
The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to hig...The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to high-stress corrosion cracking(SCC)sensitivity due to the formation of high-density precipitates at grain boundaries(GBs).So far,it is still challenging to improve the strength of Al-Mg alloys without re-ducing SCC resistance.Herein,a nanostructured Al-5Mg-3 Zn alloy with a good yield strength of 336 MPa and good elongation was successfully produced.By dynamic plastic deformation and appropriate anneal-ing treatment,near-equiaxed nanograins were introduced in the nanostructured Al-5Mg-3 Zn alloy with a high proportion(71%)of the low-angle grain boundary.TEM statistical investigations show that the pre-cipitation of active T’phase at GBs has been greatly suppressed in the nanostructured Al-5Mg-3 Zn alloy at sensitized conditions,and the area fraction of GB precipitates is reduced from 72%to 21%,which sig-nificantly decreases the SCC susceptibility.This study provides guidance for developing advanced Al-Mg alloy with high SCC resistance.展开更多
Surface metal matrix composite is produced on the as cast Magnesium Rare Earth alloy-RZ 5 by single pass friction stir processing using various micro/nano sized reinforcement particles namely Boron Carbide(B_(4)C),Mul...Surface metal matrix composite is produced on the as cast Magnesium Rare Earth alloy-RZ 5 by single pass friction stir processing using various micro/nano sized reinforcement particles namely Boron Carbide(B_(4)C),Multi Walled Carbon Nano Tubes(MWCNTs),and a mixture of ZrO_(2)+Al_(2)O_(3)particles.Fine grained metal matrix composites having the grain size ranging 0.8μm to 1.87μm are achieved.Grain boundary pinning by the reinforcement particles has resulted in the transformation of coarse grained(∼81μm)base material into fine grained(<1μm)metal matrix composite.Finer grain structure and the presence of reinforcements at the stir zone have resulted in increased and improved mechanical properties of the developed composites.Microhardness ranging between 125 HV and 403 HV is achieved.Uni-axial Tensile Testing of the developed composites exhibited improvement in tensile strength.Metal matrix composites developed using various reinforcements exhibited an increase in strength ranges between 250 MPa and 320 MPa.展开更多
The microstructure evolution during annealing of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy was investigated. The results show that for the alloy compressed at 810 °C and 1.0 s^-1, deformation amount（height reduction） 20% an...The microstructure evolution during annealing of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy was investigated. The results show that for the alloy compressed at 810 °C and 1.0 s^-1, deformation amount（height reduction） 20% and 50% and annealed at 810 °C, thermal grooving by penetration of β phase is sufficient during the first 20 min annealing, resulting in a sharp increase in globularization fraction. The globularization fraction continuously increases with the increase of annealing time, and a height reduction of 50% leads to a near globular microstructure after annealing for 4 h. For the alloy with deformation amount of 50% by compressing at 810 °C, 0.01 s^-1, and then annealed at 810 °C, thermal grooving is limited during the first 20 min of annealing and large quantities of high-angle grain boundaries（HABs） remain. With long time annealing, the chain-like α grains are developed due to the HABs, termination migration and Ostwald ripening. The present results suggest that a higher strain rate and a larger height reduction are necessary before annealing to achieve a globular microstructure of Ti-5Al-2Sn-2Zr-4Mo-4Cr.展开更多
A CoCe/ZSM-5 catalyst was prepared by ultrasonic-assisted impregnation for the catalytic combustion of toluene.To study the effect of Na+on catalytic performance of CoCe/ZSM-5 catalysts,a series of different Si/Al ZSM...A CoCe/ZSM-5 catalyst was prepared by ultrasonic-assisted impregnation for the catalytic combustion of toluene.To study the effect of Na+on catalytic performance of CoCe/ZSM-5 catalysts,a series of different Si/Al ZSM-5 zeolites and catalysts doped with Na were synthesized.The experimental results show that 0.71 wt%Na+can inhibit active growth,generate more active small crystal grains,and promote improvement of the catalytic activity by the grain boundary segregation block mechanism,and the catalyst with 0.71 wt%of Na shows toluene conversion of 90 vol%at 250℃.Over 0.71 wt%of Na+content will neutralize the acid centre of the catalyst,lowering the specific surface area of the catalyst and resulting in a gradual decrease in the catalytic activity.展开更多
Electrical additive manufacturing can improve manufacturing efficiency and reduce the cost of 16MND5 reactor pres-sure vessel steel. Impact tests were conducted to compare the impact toughness of 16MND5 steels manufac...Electrical additive manufacturing can improve manufacturing efficiency and reduce the cost of 16MND5 reactor pres-sure vessel steel. Impact tests were conducted to compare the impact toughness of 16MND5 steels manufactured by the electrical additive manufacturing and conventional forging, respectively. It is found that the impact toughness of electrical additive manufacturing specimen was slightly higher than that of conventional forging specimen. The characterizations of microstructure show that there were large ferrites and carbides in electrical additive manufacturing specimen. The fracture mechanisms of electrical additive manufacturing specimen were that microvoids or microcracks were prone to nucleate at the large ferrite/bainite interface and large carbide/bainitic ferrite interface, where the stress concentration was high. In addi-tion, the block size and high-angle grain boundaries played a vital role in hindering crack propagation of electrical additive manufacturing specimen, helping to improve the impact energy and leading to a low ductile–brittle transition temperature. The results suggest that the electrical additive manufacturing technology was an effective method to enhance the impact toughness of 16MND5 steel.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.51201181)the Scientific Research Fund of Civil Aviation University of China(Grant No.08QD14X)
文摘First-principles calculations based on the density functional theory（DFT） and ultra-soft pseudopotential are employed to study the atomic configuration and charge density of impurity P in Ni Al Σ5 grain boundary（GB）. The negative segregation energy of a P atom proves that a P atom can easily segregate in the Ni Al GB. The atomic configuration and formation energy of the P atom in the Ni Al GB demonstrate that the P atom tends to occupy an interstitial site or substitute a Al atom depending on the Ni/Al atoms ratio. The P atom is preferable to staying in the Ni-rich environment in the Ni Al GB forming P–Ni bonds. Both of the charge density and the deformation charge imply that a P atom is more likely to bond with Ni atoms rather than with Al atoms. The density of states further exhibits the interactions between P atom and Ni atom, and the orbital electrons of P, Ni and Al atoms all contribute to P–Ni bonds in the Ni Al GB. It is worth noting that the P–Ni covalent bonds might embrittle the Ni Al GB and weakens the plasticity of the Ni Al intermetallics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11404396 and 51201181)the Subject Construction Fund of Civil Aviation University of China(Grant No.000032041102)
文摘In this paper,we employ the first-principle total energy method to investigate the effect of P impurity on mechanical properties of NiA1 grain boundary(GB).According to"energy",the segregation of P atom in NiA1E5 GB reduces the cleavage energy and embrittlement potential,demonstrating that P impurity embrittles NiA1E5 GB.The first-principle computational tensile test is conducted to determine the theoretical tensile strength of NiA1E5 GB.It is demonstrated that the maximum idea/tensile strength of NiA1E5 GB with P atom segregation is 144.5 GPa,which is lower than that of the pure NiA1E5 GB(164.7 GPa).It is indicated that the segregation of P weakens the theoretical strength of NiA1E5 GB.The analysis of atomic configuration shows that the GB fracture is caused by the interfacial bond breaking.Moreover,P is identified to weaken the interactions between A1-A1 bonds and enhance Ni-Ni bonds.
基金This research was financially supported by the National Nat-ural Science Foundation of China(Grant No.52171088)the Young Elite Scientists Sponsorship Program by CAST(grant No.2022QNRC001).We thank X.Si for assistance in sample prepara-tion.
文摘The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to high-stress corrosion cracking(SCC)sensitivity due to the formation of high-density precipitates at grain boundaries(GBs).So far,it is still challenging to improve the strength of Al-Mg alloys without re-ducing SCC resistance.Herein,a nanostructured Al-5Mg-3 Zn alloy with a good yield strength of 336 MPa and good elongation was successfully produced.By dynamic plastic deformation and appropriate anneal-ing treatment,near-equiaxed nanograins were introduced in the nanostructured Al-5Mg-3 Zn alloy with a high proportion(71%)of the low-angle grain boundary.TEM statistical investigations show that the pre-cipitation of active T’phase at GBs has been greatly suppressed in the nanostructured Al-5Mg-3 Zn alloy at sensitized conditions,and the area fraction of GB precipitates is reduced from 72%to 21%,which sig-nificantly decreases the SCC susceptibility.This study provides guidance for developing advanced Al-Mg alloy with high SCC resistance.
文摘Surface metal matrix composite is produced on the as cast Magnesium Rare Earth alloy-RZ 5 by single pass friction stir processing using various micro/nano sized reinforcement particles namely Boron Carbide(B_(4)C),Multi Walled Carbon Nano Tubes(MWCNTs),and a mixture of ZrO_(2)+Al_(2)O_(3)particles.Fine grained metal matrix composites having the grain size ranging 0.8μm to 1.87μm are achieved.Grain boundary pinning by the reinforcement particles has resulted in the transformation of coarse grained(∼81μm)base material into fine grained(<1μm)metal matrix composite.Finer grain structure and the presence of reinforcements at the stir zone have resulted in increased and improved mechanical properties of the developed composites.Microhardness ranging between 125 HV and 403 HV is achieved.Uni-axial Tensile Testing of the developed composites exhibited improvement in tensile strength.Metal matrix composites developed using various reinforcements exhibited an increase in strength ranges between 250 MPa and 320 MPa.
基金Project(51275416)supported by the National Natural Science Foundation of ChinaProject(KP201513)supported by the Fund of the State Key Laboratory of Solidification Processing in NWPU,China
文摘The microstructure evolution during annealing of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy was investigated. The results show that for the alloy compressed at 810 °C and 1.0 s^-1, deformation amount（height reduction） 20% and 50% and annealed at 810 °C, thermal grooving by penetration of β phase is sufficient during the first 20 min annealing, resulting in a sharp increase in globularization fraction. The globularization fraction continuously increases with the increase of annealing time, and a height reduction of 50% leads to a near globular microstructure after annealing for 4 h. For the alloy with deformation amount of 50% by compressing at 810 °C, 0.01 s^-1, and then annealed at 810 °C, thermal grooving is limited during the first 20 min of annealing and large quantities of high-angle grain boundaries（HABs） remain. With long time annealing, the chain-like α grains are developed due to the HABs, termination migration and Ostwald ripening. The present results suggest that a higher strain rate and a larger height reduction are necessary before annealing to achieve a globular microstructure of Ti-5Al-2Sn-2Zr-4Mo-4Cr.
基金Project supported by Science and Technology Department of Jiangsu Province(BE2016769).
文摘A CoCe/ZSM-5 catalyst was prepared by ultrasonic-assisted impregnation for the catalytic combustion of toluene.To study the effect of Na+on catalytic performance of CoCe/ZSM-5 catalysts,a series of different Si/Al ZSM-5 zeolites and catalysts doped with Na were synthesized.The experimental results show that 0.71 wt%Na+can inhibit active growth,generate more active small crystal grains,and promote improvement of the catalytic activity by the grain boundary segregation block mechanism,and the catalyst with 0.71 wt%of Na shows toluene conversion of 90 vol%at 250℃.Over 0.71 wt%of Na+content will neutralize the acid centre of the catalyst,lowering the specific surface area of the catalyst and resulting in a gradual decrease in the catalytic activity.
基金This work was financially supported by the Nuclear Power Technology Innovation Center(HDLCXZX-2018-HD-027-03)Science and Technology on Reactor System Design Technology Laboratory(HT-KFKT-02-2017006).
文摘Electrical additive manufacturing can improve manufacturing efficiency and reduce the cost of 16MND5 reactor pres-sure vessel steel. Impact tests were conducted to compare the impact toughness of 16MND5 steels manufactured by the electrical additive manufacturing and conventional forging, respectively. It is found that the impact toughness of electrical additive manufacturing specimen was slightly higher than that of conventional forging specimen. The characterizations of microstructure show that there were large ferrites and carbides in electrical additive manufacturing specimen. The fracture mechanisms of electrical additive manufacturing specimen were that microvoids or microcracks were prone to nucleate at the large ferrite/bainite interface and large carbide/bainitic ferrite interface, where the stress concentration was high. In addi-tion, the block size and high-angle grain boundaries played a vital role in hindering crack propagation of electrical additive manufacturing specimen, helping to improve the impact energy and leading to a low ductile–brittle transition temperature. The results suggest that the electrical additive manufacturing technology was an effective method to enhance the impact toughness of 16MND5 steel.
