This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduc...This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction （XRD）, respectively. Our results show that the average grain size of samples decreases from about 830 nm to 127 nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.展开更多
A low carbon hypoeutectoid steel(0.19 wt%C)with proeutectoid ferrite and pearlite dual-components was subjected to surface plastic deformation via pipe inner surface grinding(PISG)at room temperature.The deformation m...A low carbon hypoeutectoid steel(0.19 wt%C)with proeutectoid ferrite and pearlite dual-components was subjected to surface plastic deformation via pipe inner surface grinding(PISG)at room temperature.The deformation microstructures for each component were systematically characterized along depth,and the patterns of structural evolution toward nanometer regime as well as the governing parameters were addressed.Proeutectoid ferrite grains were refined down to 17 nm,and the pattern covering a length scale of 4–5 orders of magnitude from micron-to nanometer-scale follows:formation of cellular dislocation structure(CDS),elongated dislocation structure(EDS),ultrafine lamellar structure(UFL)and finally the nanolaminated structure(NL).The pearlite experiences the deformation and refinement,and finally the transforming the ultrafine pearlite(UFP)into nanolaminated pearlite(NLP)with the ferrite lamellae as thin as 20 nm.Refinement for both UFL(UFP)and NL(NLP)can be realized via forming novel extended boundaries within ferrite lamellae.A critical lattice curvature of~2.8°is required for forming such extended boundary,corresponding to a minimum strain gradient of 0.25μm^(-1)for a 100 nm-thick lamella.Refinement below size limit(expressed by lamellar thickness d_Tin nm)is correlated with the strain gradient(χ,inμm^(-1))by:d_T=12.5/x.Refinement contributions from strain gradient caused by PISG processing and material heterogeneity were discussed.展开更多
The high performance magnesium alloy was investigated by adding B2O3 in magnesium and magnesium alloys. Experiments include adding B2O3 in Mg, Mg-Al and Mg-RE alloys, respectively, studying the effects of B2O3 on the ...The high performance magnesium alloy was investigated by adding B2O3 in magnesium and magnesium alloys. Experiments include adding B2O3 in Mg, Mg-Al and Mg-RE alloys, respectively, studying the effects of B2O3 on the microstructure, were studied measuring the change of grain size and microhardness of the materials, discussing the change of grain size, morphology and distribution. The results show that adding 3% or 6%(mass fraction) B2O3 in Mg can bring twinning in Mg, adding B2O3 in Mg-Al alloys and Mg-RE alloys can refine the alloy grain size. Adding 3%B2O3 in Mg-6Al alloys can refine the average grain size by about 5μm, with the average hardness increased by 13.3% (53.3-60.4 HV0.03); adding 6%B2O3 in Mg-6Al alloys can refine the average grain size by about 13μm, with the average hardness increased by 15.8% (53.3-61.73 HV0.03); adding 3% and 6%B2O3 into Mg-6RE alloys can refine the grain size by about 5 and 9μm, respectively, with the average hardness decreased to HV0.03 64.66 and HV0.03 57.86, respectively from HV0.03 88.57. In the Mg-6Al alloy the content of aluminum is increased, while in the Mg-6RE alloy the content of oxygen is decreased. It can be concluded that it is beneficial to develop Mg-Al-B-O particle reinforce composite alloys, and it is feasible to develop nanometer crystallization of block material by Mg-B-O-RE.展开更多
To reveal the formation and characteristics of metallic iron grains in coal-based reduction, oolitic iron ore was isothermally re- duced in various reduction times at various reduction temperatures. The microstructure...To reveal the formation and characteristics of metallic iron grains in coal-based reduction, oolitic iron ore was isothermally re- duced in various reduction times at various reduction temperatures. The microstructure and size of the metallic iron phase were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and a Bgrimm process mineralogy analyzer. In the results, the re- duced Fe separates from the ore and forms metallic iron protuberances, and then the subsequent reduced Fe diffuses to the protuberances and grows into metallic iron grains. Most of the metallic iron grains exist in the quasi-spherical shape and inlaid in the slag matrix. The cumula- tive frequency of metallic iron grain size is markedly influenced by both reduction time and temperature. With increasing reduction temperature and time, the grain size of metallic iron obviously increases. According to the classical grain growth equation, the growth kinetic parameters, i.e., time exponent, growth activation energy, and pre-exponential constant, are estimated to be 1.3759 ± 0.0374, 103.18 kJ·mol^-1, and 922.05, respec- tively. Using these calculated parameters, a growth model is established to describe the growth behavior of metallic iron grains.展开更多
The nickel-based superalloy Inconel 718 is treated with Coupled Ultrasonic and Electric Pulse Treatment(CUEPT),and the surface grain is refined from the average size of 9550.0 nm to287.9,216.3,150.5,126.3,25.8 nm by d...The nickel-based superalloy Inconel 718 is treated with Coupled Ultrasonic and Electric Pulse Treatment(CUEPT),and the surface grain is refined from the average size of 9550.0 nm to287.9,216.3,150.5,126.3,25.8 nm by different effective treatment currents,respectively.The ultraprecision turning experiments are carried out on the processed workpiece after CUEPT.The experimental results show that the average cutting force increases with the decrease of surface grain size.Moreover,a mathematical model that can describe the relationship between grain size and cutting force is established,and the calculated results match the experimental results well.The calculated results also indicate that the variation of cutting force caused by the same variation of grain size decreases as the degree of grain refinement increases.Finally,the influence mechanism of grain refinement on cutting force is analyzed.The improvement of stability of grain boundaries and the increase of number of grain boundaries cause the increase of cutting force after grain refinement.展开更多
Increasing mechanical flexibility without sacrificing electrochemical performance of the electrode material is highly desired in the design of flexible electrochemical energy storage devices.In metal-related materials...Increasing mechanical flexibility without sacrificing electrochemical performance of the electrode material is highly desired in the design of flexible electrochemical energy storage devices.In metal-related materials science,decreasing the grain size introduces more grain boundaries;this stops dislocations and crack propagation under deformation,and results in increased strength and toughness.However,such a size refinement effect has not been considered in the mechanical properties,particle stacking,wetting,and electrochemical performances of flexible supercapacitor electrodes.In this paper,MXene was used as an electrode material to study the size refinement effect of flexible supercapacitors.Size refinement improved the strength and toughness of the MXene electrodes,and this resulted in increased flexibility.Finite elemental analysis provided a theoretical understanding of size refinement-increased flexibility.Moreover,the size refinement also improved the specific surface area,electric conductance,ion transportation,and water wetting properties of the electrode,and the size refinement provided highly increased energy density and power density of the MXene supercapacitors.A highly flexible,water-proof supercapacitor was fabricated using size-refined MXene.The current study provides a new viewpoint for designing tough and flexible energy storage electrodes.The size refinement effect may also be applicable for metal ion batteries and electronic and photo devices composed of MXene and other nanoparticles.展开更多
Magnesium is the lightest constructional metal,which makes it an important material for different applications like automotive,transportation,aviation and aerospace.There are several studies about developing propertie...Magnesium is the lightest constructional metal,which makes it an important material for different applications like automotive,transportation,aviation and aerospace.There are several studies about developing properties of existing Mg alloys and introducing new alloy systems to industrial producers.An important way to improve properties of metallic materials is to decrease grain size that results almost in increasing all kind of properties of the material.This review paper aims to summarize the literature about grain refining of magnesium alloys.The text is consisting of three sections,which focused on the(1)grain refining methods used in the past,which are not used today,(2)grain refining methods currently being used in the industry and(3)novel and newly developed methods that may find usage in the industry in future.Before explaining grain refining methods of magnesium alloys a general summary about grain refinement of metals is also provided.展开更多
The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1...The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1. The activation energy（Q） for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization（DRX） behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides（〈1 μm） act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction（EBSD） observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.展开更多
The mechanical behavior of VCoNi medium-entropy alloys with five different grain sizes at three different temperatures was investigated.The VCoNi alloys with different grain sizes exhibit a traditional strength–ducti...The mechanical behavior of VCoNi medium-entropy alloys with five different grain sizes at three different temperatures was investigated.The VCoNi alloys with different grain sizes exhibit a traditional strength–ductility trade-off at 77 K,194 K and 293 K.Both the yield strength and the uniform elongation of the VCoNi alloys with similar grain size increase with decreasing the deformation temperature from 293 to 77 K.Obvious strain hardening rate recovery characterized by an evident up-turn behavior at stage II is observed in VCoNi alloys with the grain size above 11.1μm.It is found that the extent of the strain hardening rate recovery increases with increasing grain size or decreasing deformation temperature.This may mainly result from the faster increase in the dislocation multiplication rate caused by the decrease in the dislocation mean free path,the decrease in the absorption of dislocations by grain boundaries and the dynamic recovery from the cross-slip with increasing grain size,as well as the suppressed dynamic recovery at cryogenic temperatures.The critical grain sizes for the occurrence of the recovery of strain hardening rate are determined to be around 9.5μm,8.3μm and 3μm for alloys deformed at 293 K,194 K and 77 K,respectively.The basic mechanism for the strain hardening behavior of the VCoNi alloys associated with grain size and deformation temperature is analyzed.展开更多
Mechanical properties and microstructures of AZ31 magnesium alloys containing different impurity levels but having the same alloying element content, were investigated at ambient temperature. These AZ31 alloys were pr...Mechanical properties and microstructures of AZ31 magnesium alloys containing different impurity levels but having the same alloying element content, were investigated at ambient temperature. These AZ31 alloys were produced by semi-continuous casting, wherein the content of impurity was varied systematically. Microstructure observation shows that finer grains are existent in the alloy with lower impurity level. Tensile testing reveals that a reduction of impurity content results in a noticeable increase of the strength and elongation in the alloys in the cast, homogenized and extruded states. As the impurity content decreases from 0.0462wt% to 0.0163wt%, the ultimate tensile strength is evidently enhanced by 62 MPa and the elongation is nearly doubled in the homogenized specimen. The observed property improvement was discussed in terms of the microstructure variation with impurity reduction.展开更多
The Al-2.5C master alloy is prepared to investigate the effect of the Al4C3 particle size distribution on the refining efficiency of the AZ31 alloy. The results indicate that the Al4C3 particles are potent nucleation ...The Al-2.5C master alloy is prepared to investigate the effect of the Al4C3 particle size distribution on the refining efficiency of the AZ31 alloy. The results indicate that the Al4C3 particles are potent nucleation substrates for primary α-Mg grains. With 1.0 wt% master alloy addition, the grain size is reduced from 204 to 70 μm. The grain refining efficiency of the Al4C3 particles on the AZ31 alloy is calculated to be 0.04%-0.75%. Such low refining efficiency is mainly attributed to the size distribution of the Al4C3 particles. The particle sizes are in the range from 0.18 to 7.08 μm, and their distribution is well fitted by a log-normal function. The optimum particle size range for significant grain refinement is proposed to be around 5.0-7.08 μm in the present conditions.展开更多
Grain refining process plays a significant role in preventing columnar and coarse grains and it encourages fine grain formation. Although Al-Ti-B master alloys use widely as aluminium grain refiners, there are several...Grain refining process plays a significant role in preventing columnar and coarse grains and it encourages fine grain formation. Although Al-Ti-B master alloys use widely as aluminium grain refiners, there are several problems in their applications. So, this kind of master alloys use less than last. Because of great properties of Al-Ti-C refiners, they can be considered as suitable candidates for use instead of Al-Ti-B master alloys. In recent years, Al-Ti-C refiners have attracted huge attention among researchers. In this paper, Al-3Ti-1C master alloy is prepared with a melting reaction method. This method involves adding graphite powder and fine titanium particles into superheated pure aluminium. Then microstructure of this master alloy is studied by scanning electron microscope (SEM) and its phases are distinguished by energy dispersive spectroscopy (EDS). In the next part, 200 ppm of Al-3Ti-1C master alloy is added to pure aluminium and its refining efficiency is compared with the condition in which TiC powders are added to aluminium melt directly. It is found that the fading time for both Al-3Ti-1C and TiC powder is about 15 minutes and in overall, grain refining efficiency of Al-3Ti-1C is more than TiC powders in 60 minutes.展开更多
The influence of processing temperature on grain size reduction in AA 6063 aluminum alloy subjected to repetitive corrugation and straightening (RCS) is investigated in this work. The aluminum alloy was processed by R...The influence of processing temperature on grain size reduction in AA 6063 aluminum alloy subjected to repetitive corrugation and straightening (RCS) is investigated in this work. The aluminum alloy was processed by RCS at different temperatures (room temperature, 100 ℃, 200 ℃ and 300 ℃) till the maximum number of passes possible before failure and the mechanical properties such as tensile strength and hardness were measured. The grain size and their misorientation of grains of the processed samples were analyzed using the electron backscattered diffraction. The results indicated that the transformation of low-angle grain boundaries to high-angle grain boundaries and dislocation tangles were highly dependent on the strain imparted, which could be controlled by selecting the proper processing temperature. As a result, the mechanical properties are affected. In particular, the room temperature tensile strength and hardness values of the processed material decrease with increasing processing temperature.展开更多
Transparent hydroxyapatite(HAp) ceramics with the grain size ranging 86-1 300 nm were successfully synthesized by spark plasma sintering(SPS) at 925-1 200 ℃. All the sample achieved final density higher than 99.7%. T...Transparent hydroxyapatite(HAp) ceramics with the grain size ranging 86-1 300 nm were successfully synthesized by spark plasma sintering(SPS) at 925-1 200 ℃. All the sample achieved final density higher than 99.7%. The phase stability was identified by X-ray diffraction(XRD) and Fourier transform infrared spectroscopy(FTIR). The experimental results indicate that there is no decomposition or dehydroxylation during the SPS processes. The influences of microstructure refinement on the hardness were investigated using HallPetch(H-P) relationship, and the hardness of transparent HAp ceramic increases with the decrease of grain size. It is demonstrated that the grain boundaries and defects play important roles on the hardness.展开更多
The reduction pretreatment process has been proposed to improve the center quality of large billet and reduce the rolling ratio.The microstructure evolution during the reduction pretreatment was further understood.The...The reduction pretreatment process has been proposed to improve the center quality of large billet and reduce the rolling ratio.The microstructure evolution during the reduction pretreatment was further understood.The austenite grains were refined after the reduction pretreatment experiment,especially those at the center of the billet.The effects of strain and strain rate on the average grain size were dependent on the deformation temperature.At a strain rate of 0.01 s-1 and 1200°C,the newly formed strain-free austenite grains grew very fast as the strain continued to increase,which resulted in the coarsening of austenite grains.The calculation results of the microstructure evolution model showed that at the same deformation temperature,the evolution curves of average grain size with different strain rates had the intersection points.With the increase in temperature,the position of intersection point moved to the downward direction of strain.The simulation results showed that when the reduction amount increased to 20%,the average grain size at the center was smaller than that near the surface.It could be inferred that when the reduction amount greatly exceeded 20%,the dynamic recrystallization at the center was mostly completed,and the austenite grain growth would become the main mechanism.展开更多
The growing characteristics of metallic iron particles during reductive roasting of boron-bearing magnetite concentrate under different conditions were investigated.The size of the metallic iron particles was quantita...The growing characteristics of metallic iron particles during reductive roasting of boron-bearing magnetite concentrate under different conditions were investigated.The size of the metallic iron particles was quantitatively measured via optical image analysis with consideration of size calibration and weighted ratio of image numbers in the core,middle and periphery zones of cross-section of pellets.In order to guarantee the measurement accuracy,54 images were captured in total for each specimen,with a weighted ratio of 1:7:19 with respect to the core,middle and periphery section of the cross-section of pellets.Increasing reduction temperature and time is favorable to the growth of metallic iron particles.Based on the modification of particle size measurement,in terms of time(t)and temperature(T)a predicting model of metallic iron particle size(D),was established as:D=125−0.112t−0.2352T−5.355×10^−4t^2+2.032×10^−4t∙T+1.134×10^−4T^2.展开更多
Ceria-stabilized tetragonal zirconia polycrystal(Ce-TZP)has exceptional fracture toughness and flaw tolerance due to facile t‒m phase transformation toughening.However,its wider-range applications are limited by its r...Ceria-stabilized tetragonal zirconia polycrystal(Ce-TZP)has exceptional fracture toughness and flaw tolerance due to facile t‒m phase transformation toughening.However,its wider-range applications are limited by its relatively low strength due to its large grain size and low transformation stress,which results in yield-like failure.Here,we combined additive manufacturing(AM),pressureless two-step sintering,and hot isostatic pressing(HIP),and addressed the challenging grain size refinement problem in Ce-TZPs.We successfully produced dense ultrafine-grained Ce-TZP ceramics with an average grain size below 500 nm,a three-point bending strength above 800 MPa,and a single-edge-notch-beam fracture toughness in the range of 11‒12 MPa·m^(1/2).The critical roles of processing design,mixed Ce valences,and under-vs.over-stabilization of tetragonal polymorphs were noted.Our work offers insights and strategies for the future development of stronger and tougher Ce-TZP ceramics that can compete with tetragonal yttria-stabilized zirconia in various applications,including additive manufacturing.展开更多
Mineral deformation and rock flow mechanism in the lithosphere are related to the rheological behavior and weakening mechanism of the continent. Natural deformation behaviors of feldspars are not well understood due t...Mineral deformation and rock flow mechanism in the lithosphere are related to the rheological behavior and weakening mechanism of the continent. Natural deformation behaviors of feldspars are not well understood due to the complexity of their mineral compositions, crystal structures, as well as changing deformation conditions. The refined microstructure,fabric and composition of major minerals in the deformed granitic rocks within the Gaoligong shear zone(GLGSZ), southwestern Yunnan, China, were studied. With increasing mylonitization, two fabric types of end-members have been distinguished(type-I banded granitic mylonite and type-II banded ultramylonite). The two types of deformed granitic rocks have the same mineral assemblage, but different mineral modes. The type-I banded granitic mylonite has a greater proportion of K-feldspar(mostly present as porphyroclasts)>plagioclase>quartz±biotite, however, the type-II banded ultramylonite has a greater proportion of fine-grained plagioclase>K-feldspar>quartz±biotite. The crystallographic preferred orientation(CPO) patterns of quartz combined with two-feldspar geothermometer, confirm that the quartz grains in the type-I and type-II granitic rock have undergone high-temperature dislocation creep deformation. The K-feldspar grains in the matrix of type-II banded ultramylonite show a dominant(100)[010] slip system with dislocation creep recrystallization, while the fine-grained plagioclase grains present a weak CPO pattern with superplastic flow. The K-feldspar porphyroclasts show grain-size reduction associated with mineral composition and fabric transformation. The myrmekite formation with the fine-grained neocrystallization of plagioclase and quartz significally replaced the K-feldspar porphyroclasts. Finally, the fine-grained neocrystallization plagioclases were formed further into the high strain localized ultramylonites with superplastic flow.展开更多
Hybrid aluminum matrix composite powders reinforced with bimodal-sized Al2O3 particles were synthesized by mechanical milling.Two different approaches were investigated for the addition of submicron-and nano-sized Al2...Hybrid aluminum matrix composite powders reinforced with bimodal-sized Al2O3 particles were synthesized by mechanical milling.Two different approaches were investigated for the addition of submicron-and nano-sized Al2O3 particles to the aluminum powders,It was observed that the simultaneous addition of bimodal-sized Al2O3 particles to the aluminum powders resulted in an equiaxed morphology of the composite powders and the average particle size stabilized after 5 h of milling,indicating that the presence of bimodal-sized particles has greater effect on accelerating milling process as compared to nano-sized particles;the grain size of the aluminum matrix in composite powders was reduced to under 40 nm,approximate to the value obtained in the separate addition case,while a lower rate of refining was observed due to hindrance of submicron-sized particles on the interactions between nano-sized particles and the aluminum matrix.展开更多
The microstructure-dependent corrosion resistance of dual structured fine-grained Mg-7.5 Li-3 Al-lZn has been investigated.The alloys were extruded using extrusion with a forward-backward rotating die(KoBo,a newly dev...The microstructure-dependent corrosion resistance of dual structured fine-grained Mg-7.5 Li-3 Al-lZn has been investigated.The alloys were extruded using extrusion with a forward-backward rotating die(KoBo,a newly developed SPD method)at two different extrusion ratios.The fine-grained microstructures formed in the alloys were characterized,and the influence of grain refinement on corrosion resistance was analyzed.For fine-grained(α+β)Mg-Li alloys,a higher extrusion ratio led to more intensive grain refinement;however,this relationship did not improve their corrosion resistance in a chloride-containing solution.The corrosion resistance of the alloys was mainly controlled by the refinement ofα(Mg)andβ(Li),along with the distribution of second phases.The presence of MgLi_(2) Al at grain boundaries facilitated their dissolution.展开更多
基金supported by the National Natural Science Foundation of China (Grant No 50572067)
文摘This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction （XRD）, respectively. Our results show that the average grain size of samples decreases from about 830 nm to 127 nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.
基金the Hundred Outstanding Creative Talents Projects in Hebei University,Chinathe Project Program of Heavy Machinery Collaborative Innovation CenterChina and the National Natural Science Foundation of China(No.51171182)。
文摘A low carbon hypoeutectoid steel(0.19 wt%C)with proeutectoid ferrite and pearlite dual-components was subjected to surface plastic deformation via pipe inner surface grinding(PISG)at room temperature.The deformation microstructures for each component were systematically characterized along depth,and the patterns of structural evolution toward nanometer regime as well as the governing parameters were addressed.Proeutectoid ferrite grains were refined down to 17 nm,and the pattern covering a length scale of 4–5 orders of magnitude from micron-to nanometer-scale follows:formation of cellular dislocation structure(CDS),elongated dislocation structure(EDS),ultrafine lamellar structure(UFL)and finally the nanolaminated structure(NL).The pearlite experiences the deformation and refinement,and finally the transforming the ultrafine pearlite(UFP)into nanolaminated pearlite(NLP)with the ferrite lamellae as thin as 20 nm.Refinement for both UFL(UFP)and NL(NLP)can be realized via forming novel extended boundaries within ferrite lamellae.A critical lattice curvature of~2.8°is required for forming such extended boundary,corresponding to a minimum strain gradient of 0.25μm^(-1)for a 100 nm-thick lamella.Refinement below size limit(expressed by lamellar thickness d_Tin nm)is correlated with the strain gradient(χ,inμm^(-1))by:d_T=12.5/x.Refinement contributions from strain gradient caused by PISG processing and material heterogeneity were discussed.
文摘The high performance magnesium alloy was investigated by adding B2O3 in magnesium and magnesium alloys. Experiments include adding B2O3 in Mg, Mg-Al and Mg-RE alloys, respectively, studying the effects of B2O3 on the microstructure, were studied measuring the change of grain size and microhardness of the materials, discussing the change of grain size, morphology and distribution. The results show that adding 3% or 6%(mass fraction) B2O3 in Mg can bring twinning in Mg, adding B2O3 in Mg-Al alloys and Mg-RE alloys can refine the alloy grain size. Adding 3%B2O3 in Mg-6Al alloys can refine the average grain size by about 5μm, with the average hardness increased by 13.3% (53.3-60.4 HV0.03); adding 6%B2O3 in Mg-6Al alloys can refine the average grain size by about 13μm, with the average hardness increased by 15.8% (53.3-61.73 HV0.03); adding 3% and 6%B2O3 into Mg-6RE alloys can refine the grain size by about 5 and 9μm, respectively, with the average hardness decreased to HV0.03 64.66 and HV0.03 57.86, respectively from HV0.03 88.57. In the Mg-6Al alloy the content of aluminum is increased, while in the Mg-6RE alloy the content of oxygen is decreased. It can be concluded that it is beneficial to develop Mg-Al-B-O particle reinforce composite alloys, and it is feasible to develop nanometer crystallization of block material by Mg-B-O-RE.
基金financially supported by the National Natural Science Foundation of China(Nos.51134002 and 51604063)the Fundamental Research Funds for the Central Universities(No.N140108001)
文摘To reveal the formation and characteristics of metallic iron grains in coal-based reduction, oolitic iron ore was isothermally re- duced in various reduction times at various reduction temperatures. The microstructure and size of the metallic iron phase were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and a Bgrimm process mineralogy analyzer. In the results, the re- duced Fe separates from the ore and forms metallic iron protuberances, and then the subsequent reduced Fe diffuses to the protuberances and grows into metallic iron grains. Most of the metallic iron grains exist in the quasi-spherical shape and inlaid in the slag matrix. The cumula- tive frequency of metallic iron grain size is markedly influenced by both reduction time and temperature. With increasing reduction temperature and time, the grain size of metallic iron obviously increases. According to the classical grain growth equation, the growth kinetic parameters, i.e., time exponent, growth activation energy, and pre-exponential constant, are estimated to be 1.3759 ± 0.0374, 103.18 kJ·mol^-1, and 922.05, respec- tively. Using these calculated parameters, a growth model is established to describe the growth behavior of metallic iron grains.
基金supported by National Natural Science Foundation of China(No.51875579)the Fundamental Research Fund for the Central Universities,China(No.19CX02023A)+2 种基金the Major Research Project of Shandong Province,China(No.2019GGX104068)the Science and Technology Support Plan for Youth Innovation of Universities in Shandong Province,China(No.2019KJB016)Source Innovation Project of Qingdao West Coast New Area,China(No.2020-82)。
文摘The nickel-based superalloy Inconel 718 is treated with Coupled Ultrasonic and Electric Pulse Treatment(CUEPT),and the surface grain is refined from the average size of 9550.0 nm to287.9,216.3,150.5,126.3,25.8 nm by different effective treatment currents,respectively.The ultraprecision turning experiments are carried out on the processed workpiece after CUEPT.The experimental results show that the average cutting force increases with the decrease of surface grain size.Moreover,a mathematical model that can describe the relationship between grain size and cutting force is established,and the calculated results match the experimental results well.The calculated results also indicate that the variation of cutting force caused by the same variation of grain size decreases as the degree of grain refinement increases.Finally,the influence mechanism of grain refinement on cutting force is analyzed.The improvement of stability of grain boundaries and the increase of number of grain boundaries cause the increase of cutting force after grain refinement.
基金supported by the National Key Research and Development Program of China(grant SQ2019YFE012189,grant2017YFB0307001)the National Natural Science Foundation of China(grants 51973093,U1533122,and 51773094)+5 种基金the Natural Science Foundation of Tianjin(grant number 18JCZDJC36800)the National Special Support Plan for High-level Talents people(grant number C041800902)the Science Foundation for Distinguished Young Scholars of Tianjin(grant number 18JCJQJC46600)the Frontiers Science Center for New Organic Matter(Grant Number 63181206)the Fundamental Research Funds for the Central Universities(grant 63171219)the State Key Laboratory for Modification of Chemical Fibers and Polymer Materials,Donghua University(grant LK1704)。
文摘Increasing mechanical flexibility without sacrificing electrochemical performance of the electrode material is highly desired in the design of flexible electrochemical energy storage devices.In metal-related materials science,decreasing the grain size introduces more grain boundaries;this stops dislocations and crack propagation under deformation,and results in increased strength and toughness.However,such a size refinement effect has not been considered in the mechanical properties,particle stacking,wetting,and electrochemical performances of flexible supercapacitor electrodes.In this paper,MXene was used as an electrode material to study the size refinement effect of flexible supercapacitors.Size refinement improved the strength and toughness of the MXene electrodes,and this resulted in increased flexibility.Finite elemental analysis provided a theoretical understanding of size refinement-increased flexibility.Moreover,the size refinement also improved the specific surface area,electric conductance,ion transportation,and water wetting properties of the electrode,and the size refinement provided highly increased energy density and power density of the MXene supercapacitors.A highly flexible,water-proof supercapacitor was fabricated using size-refined MXene.The current study provides a new viewpoint for designing tough and flexible energy storage electrodes.The size refinement effect may also be applicable for metal ion batteries and electronic and photo devices composed of MXene and other nanoparticles.
文摘Magnesium is the lightest constructional metal,which makes it an important material for different applications like automotive,transportation,aviation and aerospace.There are several studies about developing properties of existing Mg alloys and introducing new alloy systems to industrial producers.An important way to improve properties of metallic materials is to decrease grain size that results almost in increasing all kind of properties of the material.This review paper aims to summarize the literature about grain refining of magnesium alloys.The text is consisting of three sections,which focused on the(1)grain refining methods used in the past,which are not used today,(2)grain refining methods currently being used in the industry and(3)novel and newly developed methods that may find usage in the industry in future.Before explaining grain refining methods of magnesium alloys a general summary about grain refinement of metals is also provided.
基金Project(2012AA03A503) supported by the National High Technology Research and Development Program of China
文摘The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1. The activation energy（Q） for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization（DRX） behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides（〈1 μm） act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction（EBSD） observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.
基金This work was supported by the National Natural Science Foundation of China(NSFC,Grant No.52071319)the Fundamental Research Project of Shenyang National Laboratory for Materials Science(No.L2019F23).
文摘The mechanical behavior of VCoNi medium-entropy alloys with five different grain sizes at three different temperatures was investigated.The VCoNi alloys with different grain sizes exhibit a traditional strength–ductility trade-off at 77 K,194 K and 293 K.Both the yield strength and the uniform elongation of the VCoNi alloys with similar grain size increase with decreasing the deformation temperature from 293 to 77 K.Obvious strain hardening rate recovery characterized by an evident up-turn behavior at stage II is observed in VCoNi alloys with the grain size above 11.1μm.It is found that the extent of the strain hardening rate recovery increases with increasing grain size or decreasing deformation temperature.This may mainly result from the faster increase in the dislocation multiplication rate caused by the decrease in the dislocation mean free path,the decrease in the absorption of dislocations by grain boundaries and the dynamic recovery from the cross-slip with increasing grain size,as well as the suppressed dynamic recovery at cryogenic temperatures.The critical grain sizes for the occurrence of the recovery of strain hardening rate are determined to be around 9.5μm,8.3μm and 3μm for alloys deformed at 293 K,194 K and 77 K,respectively.The basic mechanism for the strain hardening behavior of the VCoNi alloys associated with grain size and deformation temperature is analyzed.
基金Funded by the National Natural Science Foundation of China(Nos.51101173,50725413 and 51271152)the National Key Technologies R&D Program(No.2011BAE22B04)
文摘Mechanical properties and microstructures of AZ31 magnesium alloys containing different impurity levels but having the same alloying element content, were investigated at ambient temperature. These AZ31 alloys were produced by semi-continuous casting, wherein the content of impurity was varied systematically. Microstructure observation shows that finer grains are existent in the alloy with lower impurity level. Tensile testing reveals that a reduction of impurity content results in a noticeable increase of the strength and elongation in the alloys in the cast, homogenized and extruded states. As the impurity content decreases from 0.0462wt% to 0.0163wt%, the ultimate tensile strength is evidently enhanced by 62 MPa and the elongation is nearly doubled in the homogenized specimen. The observed property improvement was discussed in terms of the microstructure variation with impurity reduction.
基金supported by the National Key Research and Development Program of China(No.2016YFB0701204)the project(DUT15JJ(G)01)supported by the Fundamental Research Funds for the Central Universities
文摘The Al-2.5C master alloy is prepared to investigate the effect of the Al4C3 particle size distribution on the refining efficiency of the AZ31 alloy. The results indicate that the Al4C3 particles are potent nucleation substrates for primary α-Mg grains. With 1.0 wt% master alloy addition, the grain size is reduced from 204 to 70 μm. The grain refining efficiency of the Al4C3 particles on the AZ31 alloy is calculated to be 0.04%-0.75%. Such low refining efficiency is mainly attributed to the size distribution of the Al4C3 particles. The particle sizes are in the range from 0.18 to 7.08 μm, and their distribution is well fitted by a log-normal function. The optimum particle size range for significant grain refinement is proposed to be around 5.0-7.08 μm in the present conditions.
文摘Grain refining process plays a significant role in preventing columnar and coarse grains and it encourages fine grain formation. Although Al-Ti-B master alloys use widely as aluminium grain refiners, there are several problems in their applications. So, this kind of master alloys use less than last. Because of great properties of Al-Ti-C refiners, they can be considered as suitable candidates for use instead of Al-Ti-B master alloys. In recent years, Al-Ti-C refiners have attracted huge attention among researchers. In this paper, Al-3Ti-1C master alloy is prepared with a melting reaction method. This method involves adding graphite powder and fine titanium particles into superheated pure aluminium. Then microstructure of this master alloy is studied by scanning electron microscope (SEM) and its phases are distinguished by energy dispersive spectroscopy (EDS). In the next part, 200 ppm of Al-3Ti-1C master alloy is added to pure aluminium and its refining efficiency is compared with the condition in which TiC powders are added to aluminium melt directly. It is found that the fading time for both Al-3Ti-1C and TiC powder is about 15 minutes and in overall, grain refining efficiency of Al-3Ti-1C is more than TiC powders in 60 minutes.
基金supported financially by the Department of Science and Technology, Government of India (No. SB/FTP/ETA-104/2012)
文摘The influence of processing temperature on grain size reduction in AA 6063 aluminum alloy subjected to repetitive corrugation and straightening (RCS) is investigated in this work. The aluminum alloy was processed by RCS at different temperatures (room temperature, 100 ℃, 200 ℃ and 300 ℃) till the maximum number of passes possible before failure and the mechanical properties such as tensile strength and hardness were measured. The grain size and their misorientation of grains of the processed samples were analyzed using the electron backscattered diffraction. The results indicated that the transformation of low-angle grain boundaries to high-angle grain boundaries and dislocation tangles were highly dependent on the strain imparted, which could be controlled by selecting the proper processing temperature. As a result, the mechanical properties are affected. In particular, the room temperature tensile strength and hardness values of the processed material decrease with increasing processing temperature.
基金financially supported by the State Key Laboratory of Advanced Technology for Material Synthesis and Processing (Wuhan University of Technology) (2017-KF-11)
文摘Transparent hydroxyapatite(HAp) ceramics with the grain size ranging 86-1 300 nm were successfully synthesized by spark plasma sintering(SPS) at 925-1 200 ℃. All the sample achieved final density higher than 99.7%. The phase stability was identified by X-ray diffraction(XRD) and Fourier transform infrared spectroscopy(FTIR). The experimental results indicate that there is no decomposition or dehydroxylation during the SPS processes. The influences of microstructure refinement on the hardness were investigated using HallPetch(H-P) relationship, and the hardness of transparent HAp ceramic increases with the decrease of grain size. It is demonstrated that the grain boundaries and defects play important roles on the hardness.
基金funded by the National Key Research and Development Program of China(2021YFE0113200)the Fundamental Research Funds for the Central Universities(FRF-TP-20-104A1).
文摘The reduction pretreatment process has been proposed to improve the center quality of large billet and reduce the rolling ratio.The microstructure evolution during the reduction pretreatment was further understood.The austenite grains were refined after the reduction pretreatment experiment,especially those at the center of the billet.The effects of strain and strain rate on the average grain size were dependent on the deformation temperature.At a strain rate of 0.01 s-1 and 1200°C,the newly formed strain-free austenite grains grew very fast as the strain continued to increase,which resulted in the coarsening of austenite grains.The calculation results of the microstructure evolution model showed that at the same deformation temperature,the evolution curves of average grain size with different strain rates had the intersection points.With the increase in temperature,the position of intersection point moved to the downward direction of strain.The simulation results showed that when the reduction amount increased to 20%,the average grain size at the center was smaller than that near the surface.It could be inferred that when the reduction amount greatly exceeded 20%,the dynamic recrystallization at the center was mostly completed,and the austenite grain growth would become the main mechanism.
基金Project(51804346)supported by the National Natural Science Foundation of ChinaProject(2019JJ50767)supported by the Natural Science Foundation of Hunan Province,ChinaProject(KY[2017]125)supported by Youth Foundation of Guizhou Education Department,China。
文摘The growing characteristics of metallic iron particles during reductive roasting of boron-bearing magnetite concentrate under different conditions were investigated.The size of the metallic iron particles was quantitatively measured via optical image analysis with consideration of size calibration and weighted ratio of image numbers in the core,middle and periphery zones of cross-section of pellets.In order to guarantee the measurement accuracy,54 images were captured in total for each specimen,with a weighted ratio of 1:7:19 with respect to the core,middle and periphery section of the cross-section of pellets.Increasing reduction temperature and time is favorable to the growth of metallic iron particles.Based on the modification of particle size measurement,in terms of time(t)and temperature(T)a predicting model of metallic iron particle size(D),was established as:D=125−0.112t−0.2352T−5.355×10^−4t^2+2.032×10^−4t∙T+1.134×10^−4T^2.
基金the National Key R&D Program of China(No.2023YFB3812000),the National Natural Science Foundation of China(No.51972189)the Tsinghua University Initiative Scientific Research Program(No.20233080030).
文摘Ceria-stabilized tetragonal zirconia polycrystal(Ce-TZP)has exceptional fracture toughness and flaw tolerance due to facile t‒m phase transformation toughening.However,its wider-range applications are limited by its relatively low strength due to its large grain size and low transformation stress,which results in yield-like failure.Here,we combined additive manufacturing(AM),pressureless two-step sintering,and hot isostatic pressing(HIP),and addressed the challenging grain size refinement problem in Ce-TZPs.We successfully produced dense ultrafine-grained Ce-TZP ceramics with an average grain size below 500 nm,a three-point bending strength above 800 MPa,and a single-edge-notch-beam fracture toughness in the range of 11‒12 MPa·m^(1/2).The critical roles of processing design,mixed Ce valences,and under-vs.over-stabilization of tetragonal polymorphs were noted.Our work offers insights and strategies for the future development of stronger and tougher Ce-TZP ceramics that can compete with tetragonal yttria-stabilized zirconia in various applications,including additive manufacturing.
基金supported by the Excellent Youth Fund of National Natural Science Foundation of China (Grant No. 41722207)the National Key Research and Development Program (Grant No. 2017YFC0602401)the National Natural Science Foundation of China (Grant Nos. 41472188 & 41430211)
文摘Mineral deformation and rock flow mechanism in the lithosphere are related to the rheological behavior and weakening mechanism of the continent. Natural deformation behaviors of feldspars are not well understood due to the complexity of their mineral compositions, crystal structures, as well as changing deformation conditions. The refined microstructure,fabric and composition of major minerals in the deformed granitic rocks within the Gaoligong shear zone(GLGSZ), southwestern Yunnan, China, were studied. With increasing mylonitization, two fabric types of end-members have been distinguished(type-I banded granitic mylonite and type-II banded ultramylonite). The two types of deformed granitic rocks have the same mineral assemblage, but different mineral modes. The type-I banded granitic mylonite has a greater proportion of K-feldspar(mostly present as porphyroclasts)>plagioclase>quartz±biotite, however, the type-II banded ultramylonite has a greater proportion of fine-grained plagioclase>K-feldspar>quartz±biotite. The crystallographic preferred orientation(CPO) patterns of quartz combined with two-feldspar geothermometer, confirm that the quartz grains in the type-I and type-II granitic rock have undergone high-temperature dislocation creep deformation. The K-feldspar grains in the matrix of type-II banded ultramylonite show a dominant(100)[010] slip system with dislocation creep recrystallization, while the fine-grained plagioclase grains present a weak CPO pattern with superplastic flow. The K-feldspar porphyroclasts show grain-size reduction associated with mineral composition and fabric transformation. The myrmekite formation with the fine-grained neocrystallization of plagioclase and quartz significally replaced the K-feldspar porphyroclasts. Finally, the fine-grained neocrystallization plagioclases were formed further into the high strain localized ultramylonites with superplastic flow.
基金the financial support from the State Key Laboratory of Traction Power(Grant No.2015TPL_Z01)the State Key Laboratory of Solidification Processing(Grant Nos.82-TZ-2013 and SKLSP201609)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.2682017CX090)the‘‘111’’Project(B08040)
文摘Hybrid aluminum matrix composite powders reinforced with bimodal-sized Al2O3 particles were synthesized by mechanical milling.Two different approaches were investigated for the addition of submicron-and nano-sized Al2O3 particles to the aluminum powders,It was observed that the simultaneous addition of bimodal-sized Al2O3 particles to the aluminum powders resulted in an equiaxed morphology of the composite powders and the average particle size stabilized after 5 h of milling,indicating that the presence of bimodal-sized particles has greater effect on accelerating milling process as compared to nano-sized particles;the grain size of the aluminum matrix in composite powders was reduced to under 40 nm,approximate to the value obtained in the separate addition case,while a lower rate of refining was observed due to hindrance of submicron-sized particles on the interactions between nano-sized particles and the aluminum matrix.
文摘The microstructure-dependent corrosion resistance of dual structured fine-grained Mg-7.5 Li-3 Al-lZn has been investigated.The alloys were extruded using extrusion with a forward-backward rotating die(KoBo,a newly developed SPD method)at two different extrusion ratios.The fine-grained microstructures formed in the alloys were characterized,and the influence of grain refinement on corrosion resistance was analyzed.For fine-grained(α+β)Mg-Li alloys,a higher extrusion ratio led to more intensive grain refinement;however,this relationship did not improve their corrosion resistance in a chloride-containing solution.The corrosion resistance of the alloys was mainly controlled by the refinement ofα(Mg)andβ(Li),along with the distribution of second phases.The presence of MgLi_(2) Al at grain boundaries facilitated their dissolution.
