Industrial wastes such as steel slag and coal gangue etc.were chosen as raw materials for preparing ceramic via the conventional solid-state reaction method.With steel slag and coal gangue mixed in various mass ratios...Industrial wastes such as steel slag and coal gangue etc.were chosen as raw materials for preparing ceramic via the conventional solid-state reaction method.With steel slag and coal gangue mixed in various mass ratios,from 100%steel slag to 100%coal gangue at 10%intervals,microstructure and possible phase evolution of the coal gangue-steel slag ceramics were investigated using X-ray powder diffraction,scanning electron microscopy,mercury intrusion porosimetry and Archimedes boiling method.The experimental results suggest that the phase compositions of the as-prepared ceramics could be altered with the increased amount of coal gangue in the ceramics.The anorthite-diopside eutectic can be formed in the ceramics with the mass ratios of steel slag to coal gangue arranged from 8:2 to 2:8,which was responsible for the melting of the steel slag-coal gangue ceramics at relatively high temperature.Further investigations on the microstructure suggested that the addition of the proper amount of steel slag in ceramic compositions was conducive to the pore formation and further contributed to an increment in porosity.展开更多
A multilayer tungsten carbide particle(WCp)-reinforced Ni-based alloy coating was fabricated on a steel substrate using vacuum cladding technology.The morphology,microstructure,and formation mechanism of the coating...A multilayer tungsten carbide particle(WCp)-reinforced Ni-based alloy coating was fabricated on a steel substrate using vacuum cladding technology.The morphology,microstructure,and formation mechanism of the coating were studied and discussed in different zones.The microstructure morphology and phase composition were investigated by scanning electron microscopy,optical microscopy,X-ray diffraction,and energy-dispersive X-ray spectroscopy.In the results,the coating presents a dense and homogeneous microstructure with few pores and is free from cracks.The whole coating shows a multilayer structure,including composite,transition,fusion,and diffusion-affected layers.Metallurgical bonding was achieved between the coating and substrate because of the formation of the fusion and diffusion-affected layers.The Ni-based alloy is mainly composed of y-Ni solid solution with finely dispersed Cr7C3/Cr(23)C6,CrB,and Ni+Ni3Si.WC particles in the composite layer distribute evenly in areas among initial Ni-based alloying particles,forming a special three-dimensional reticular microstructure.The macrohardness of the coating is HRC 55,which is remarkably improved compared to that of the substrate.The microhardness increases gradually from the substrate to the composite zone,whereas the microhardness remains almost unchanged in the transition and composite zones.展开更多
TiC reinforced titanium composites has been produced with different Al content and C content by XDTM. The results have shown that TiC particles are of two different morphologies f coarse dendritical primary TiC and sh...TiC reinforced titanium composites has been produced with different Al content and C content by XDTM. The results have shown that TiC particles are of two different morphologies f coarse dendritical primary TiC and short bar-shape eutectic TiC. Al content has great effects on the morphology of TiC. With the increasing of Al content, the morphology of primary TiC changes from coarse developed dendrite into short bar-shape or plate--shape TiC with 35%Al. Meanwhile, the structure of the matrix changes from single Ti to Ti and Ti3Al, and to Ti3Al and TiAl. However, the C content has no influence on the microstructure of matrix. When the C content is less than 1.2%, the dendrite TiC disappears and only short bar-shape or plate-shape TiC exists in the composites. In addition, the effect of he3t treatment on the morphology of TiC has also Studied.展开更多
Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the ...Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the microstructure has also been studied.展开更多
To further investigate the microstructure characteristic and solidification mechanism, so as to provide knowledge for the microstructure control of a NiTi-AI based high-temperature structural material, the microstruct...To further investigate the microstructure characteristic and solidification mechanism, so as to provide knowledge for the microstructure control of a NiTi-AI based high-temperature structural material, the microstructure of Ni-43Ti-4AI-2Nb-2Hf (at.%) alloy ingots prepared by conventional casting (arc-melting) and directional solidification (DS) at various drawing velocities (2 mm.min-', 18 mm.min-1, 30 mm-min-' and 60 mmmin~, respectively) was investigated by means of electron probe microanalyses. Experimental results reveal that the microstructures are composed of NiTi matrix phase,/3-Nb phase and Ti2Ni phase for samples obtained by both conventional casting and DS. Conventional casting has an equiaxial structure, while DS has a slender and acicular cellular structure which grows along the [001] orientation preferentially. Small amounts of white/3-Nb phase and black Ti2Ni phase co-exist at the grain boundaries or intercellular regions. With an increase in drawing velocity, the NiTi matrix phase is inclined to grow along (100) and (200) crystallographic planes, and the cellular arm spacing reduce gradually, but the directionality of the solidified structure weakens significantly. The homogeneous dispersion of,8-Nb phase and the decrease of Ti2Ni phase in DS samples are beneficial to improving the mechanical properties. Solidification mechanism analysis indicates that the dark grey NiTi matrix phase initially precipitates from the liquid phase, and then the divorced eutectic reaction takes place, which produces the light gray matrix phase and/^-Nb phase. Finally, the peritectic reaction happens, which generates the black Ti2Ni phase.展开更多
Magnesium and its alloys,as a promising class of materials,is popular in lightweight application and biomedical implants due to their low density and good biocompatibility.Additive manufacturing(AM)of Mg and its alloy...Magnesium and its alloys,as a promising class of materials,is popular in lightweight application and biomedical implants due to their low density and good biocompatibility.Additive manufacturing(AM)of Mg and its alloys is of growing interest in academia and industry.The domain-by-domain localized forming characteristics of AM leads to unique microstructures and performances of AM-process Mg and its alloys,which are different from those of traditionally manufactured counterparts.However,the intrinsic mechanisms still remain unclear and need to be in-depth explored.Therefore,this work aims to discuss and analyze the possible underlying mechanisms regarding defect appearance and elimination,microstructure formation and evolution,and performance improvement,based on presenting a comprehensive and systematic review on the relationship between process parameters,forming quality,microstructure characteristics and resultant performances.Lastly,some key perspectives requiring focus for further progression are highlighted to promote development of AM-processed Mg and its alloys and accelerate their industrialization.展开更多
Thermodynamic analysis of refractory siderite ore during carbothermic reduction was conducted. Micro- structure characteristics and phase transformation of siderite ore during sodium-carbonate-added catalyzing carboth...Thermodynamic analysis of refractory siderite ore during carbothermic reduction was conducted. Micro- structure characteristics and phase transformation of siderite ore during sodium-carbonate-added catalyzing carboth- ermic reduction were investigated. X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive analysis of X rays were used to characterize the reduced samples. Results indicate that the solid reaction between FeO and SiO2 is inevitable during carbothermic reduction and the formation of fayalite is the main hindrance to the rapid reduction of siderite. The phase transformation of present siderite ore can be described as: siderite-magnetite-metallic iron, complying with the formation of abundant fayalite. Improving the reduction temperature (-1050 -C ) and duration is helpful for the formation and aggregation of metallic iron. The iron particle size in the reduced ore was below 20 l-m, and fayalite was abundant in the absence of sodium carbonate. With 5% Na2CO3 addition, the iron particle size in the reduced ore was generally above 50μm, and the diffraction intensity associated with metallic iron in the XRD pattern increased. The Na2O formed from the dissociation of Na2 CO3 can catalyze the carbothermie reduction of the siderite. This catalytic activity may be mainly caused by an increase in the reducing reaction activity of FeO.展开更多
A Li-B alloy has been prepared using a pretreated amorphous B powder and pure Li ingot as starting materials by continually slow addition of B powder and intensified stirring in the process of melting. The microstruct...A Li-B alloy has been prepared using a pretreated amorphous B powder and pure Li ingot as starting materials by continually slow addition of B powder and intensified stirring in the process of melting. The microstructure and the discharge characteristic of the materials have been investigated- Results show that the problem of temperature control in synthesis would be modified by means of continual addition of B powder, the Li7B6 would be more finely distributed in the metal Li by means of intensified stirring. The discharge characteristic of the Li-B alloy using amorphous B as starting materials is almost the same with that of using crystalline B.展开更多
A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the all...A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the alloy was very fine and its microstructure was mainly consisted of Si crystals plus intermetallic compound A19FeSi3, which were.very fine and uniformly distributed.展开更多
The creep properties, microstructural characteristics and creep mechanisms of as-cast Mg-5Bi-5Sn(BT55) alloy without and with Mn(BTM550) addition were investigated via creep at 423, 448, and 473 K as well as stresses ...The creep properties, microstructural characteristics and creep mechanisms of as-cast Mg-5Bi-5Sn(BT55) alloy without and with Mn(BTM550) addition were investigated via creep at 423, 448, and 473 K as well as stresses of 30, 50 and 75 MPa. The results indicate that adding Mn can result in the formation of primary and the dynamic precipitated α-Mn phases. In addition, the morphology of the precipitated Mg_(3)Bi_(2) phase and the orientation relationship between Mg_(2)Sn precipitates and α-Mg can be effectively modified. Tailoring the microstructural characteristics is responsible for the improved creep performance of BTM550 alloy. The dominant creep mechanisms in BT55 and BTM550 alloys are dislocation cross-slip and climb, respectively. Furthermore, twinning and pyramidal slip play an assisting part in both alloys during creep process.展开更多
The paper studied the relationship between microstructure and shape recovery characteristics by using colored microstructure analysis under polarized light on the thermomechanical cycled CuAlNi single crystals. The tw...The paper studied the relationship between microstructure and shape recovery characteristics by using colored microstructure analysis under polarized light on the thermomechanical cycled CuAlNi single crystals. The two-way shape memory effect in quenched thin bar resulted from the preferential formation/extinction of martensite variant due to the internal quench stress, and the variant was formed at an angle of about 45 deg. with the tension direction ([001] of the βphase). Initial thermomechanical cycling under relatively low stress single variant stress-induced martensite was formed at an angle of 45 deg. with the tension and its morphology was a lath of parallel twins. More than one group of variants were formed after several training cycles and such variants also caused tilting of some thermally formed accommodated martensite. By overheating the trained sample containing stabilized multi-variants of stress-induced martensite, very coarse martensite structure with a strong asymmetry was produced, which caused the reverse two-way shape memory effect.展开更多
Al-4. 5Cu-5Pb alloy was prepared by sand and chill casting. The same alloy was also spray deposited at a gas pressure of 1.6 MPa. The microstructural features exhibit a coarse to fine dendritic morphology for sand ...Al-4. 5Cu-5Pb alloy was prepared by sand and chill casting. The same alloy was also spray deposited at a gas pressure of 1.6 MPa. The microstructural features exhibit a coarse to fine dendritic morphology for sand and chill cast alloys. Equiaxed grains were observed for spray formed alloys. Wear testing employing a pin-on-disc type set-up, reveals considerably lower wear of spray deposited alloy compared to that of chill and sand cast alloys. The morphological features of wear track on specimen and debris indicated a mixed oxidative-cum-adhesive wear mechanisms for these alloys tested in the present investigation. (Edited author abstract) 36 Refs.展开更多
In the present work,the laminar plasma surface hardening method is employed to enhance the service life of metal components fabricated from 65 Mn steel.The mechanical and wear behaviors of the laminar plasma surface h...In the present work,the laminar plasma surface hardening method is employed to enhance the service life of metal components fabricated from 65 Mn steel.The mechanical and wear behaviors of the laminar plasma surface hardened 65 Mn steel were analyzed.The martensite transition transformation of the temperature of the laminar plasma-hardened 65 ferrite Mn steel was determined by a thermal-solid coupling model.Based on the orthogonal experimental results,the optimal hardening parameters were confirmed.The scanning velocity,quenching distance and arc current are 130 mm/min,50 mm and 120 A,respectively.The pearlites and ferrites are transformed into martensites in the hardened zone,while the ratio of martensite in the heataffected zone decreases with the increase in the hardening depth.Compared to the untreated 65Mn steel,the average hardness increases from 220 HV_(0.2)to 920 HV_(0.2)in the hardened zone and the corresponding absorbed power increases from 118.7 J to 175.5 J.At the same time,the average coefficient of friction(COF)decreases from 0.763 to 0.546,and the wear rate decreases from 5.39×10^(-6)mm^(3)/(N·m)to 2.95×10^(-6)mm^(3)/(N·m),indicating that the wear resistance of 65Mn steel could be significantly improved by using laminar surface hardening.With the same hardening parameters,the depth and width of the hardened zone predicted by the thermal-solid coupling model are 1.85 mm and 11.20 mm,respectively,which are in accordance with the experimental results;depth is 1.83 mm and width is 11.15 mm.In addition,the predicted hardness distributions of the simulation model are in accordance with the experimental results.These results indicate that the simulation model could effectively predict the microstructure characteristics of 65 Mn steel.展开更多
A novel joining method,double-stage diffusion-brazing of an AZ31 magnesium alloy and a 304L austenitic stainless steel,was carried out using a pure copper interlayer.The solid-state diffusion bonding of 304L to copper...A novel joining method,double-stage diffusion-brazing of an AZ31 magnesium alloy and a 304L austenitic stainless steel,was carried out using a pure copper interlayer.The solid-state diffusion bonding of 304L to copper was conducted at 850 ℃ for 20 min followed by brazing to AZ31 at 520 ℃ and 495 ℃ for various time.Microstructural characteristics of the diffusion-brazed joints were investigated in detail.A defect free interface of Fe-Cu diffusion area appeared between the Cu alloy and the 304L steel.Cu-Mg reaction products were formed between AZ31 and Cu alloys.A layered structure including AZ31/Cu-Mg compounds/Cu/Fe-Cu diffusion layer/304L was present in the joint.With time prolonging,the reduction in the width of Cu layer was balanced by the increase in the width of Cu-Mg compounds zone.Microhardness peaks in the zone between AZ31 and Cu layer were attributed to the formation of Mg-Cu compounds in this zone.展开更多
In the present study,the thermal,mechanical,and biological properties of xAg/Ti-30Ta(x=0,0.41,0.82 and 2.48 at%)shape memory alloys(SMAs)were investigated.The study was conducted using optical and scanning electron mi...In the present study,the thermal,mechanical,and biological properties of xAg/Ti-30Ta(x=0,0.41,0.82 and 2.48 at%)shape memory alloys(SMAs)were investigated.The study was conducted using optical and scanning electron microscopy(SEM),X-ray diffractometry(XRD),compression test,and shape memory testing.The xAg/Ti-Ta was made using a powder metallurgy technique and microwave-sintering process.The results revealed that the addition of Ag has a significant effect on the pore size and shape,whereas the smallest pore size of 11μm was found with the addition of 0.41 at%along with a relative density of 72%.The fracture stress and strain increased with the addition of Ag,reaching the minimum values around 0.41 at%Ag.Therefore,this composition showed the maximum stress and strain at fracture region.Moreover,0.82 Ag/Ti-Ta shows more excellent corrosion resistance and biocompatibility than other percentages,obtaining almost the same behaviour of the pure Ti and Ti-6Al-4V alloys,which can be recommended for their promising and potential response for biomaterial applications.展开更多
Recent research on microstructural characteristics and oxidation behavior of Ti(1-x)AlxN thin film were surveyed. The Ti(1-x)AlxN coatings have three different phase regions, Bl structure for lower x value, wurtzite s...Recent research on microstructural characteristics and oxidation behavior of Ti(1-x)AlxN thin film were surveyed. The Ti(1-x)AlxN coatings have three different phase regions, Bl structure for lower x value, wurtzite structure for higher x value and unidentified structure for medium x value. Based upon the selective oxidation mechanism the oxidation results of Ti(1-x)AlxN thin film with different Ti/Al ratio were predicated.展开更多
The characteristics of reactive magnesia(MgO)-carbonated silt in respect to long-term stability have not been well understood in severely cold climate despite the usage of reactive MgO in enhancing the engineering per...The characteristics of reactive magnesia(MgO)-carbonated silt in respect to long-term stability have not been well understood in severely cold climate despite the usage of reactive MgO in enhancing the engineering performances.Under the binder content of 15%and initial water content of 25%,MgO-admixed silt specimens were carbonized for 3 h and 6 h and then subjected to different numbers of freezingthawing(F-T)cycles.After different F-T cycles,the physico-mechanical properties of MgO-carbonated silt were analyzed in comparison with Portland cement(PC)-stabilized silt through physical and unconfined compression tests.Besides,a series of micro tests on MgO-carbonated specimens was performed including X-ray diffraction(XRD),scanning electron microscopy(SEM)and mercury intrusion porosimetry(MIP)tests.The results demonstrate that both mass change ratio and moisture content of carbonated/stabilized silt decrease,and these values of MgO-carbonated silt are significantly lower while the density is higher compared to PC-stabilized silt.The strengths and moduli of MgO-carbonated silt are still two times higher than those of PC-stabilized specimens and the strength change ratio of keeps above0.8 after F-T cycles.There is no visible transformation between nesquehonite and dypingite/hydromagnesite,although the XRD peaks of nesquehonite decrease and the bonding and filling effects weaken slightly.After 6 and 10 F-T cycles,the pore-size characteristics changed from a unimodal distribution to a three-peak and bimodal distribution,respectively.The total,macro and large pore volumes increase obviously while the medium and small pore volumes decrease except for intra-aggregate pore.The findings show better F-T durability of MgO-carbonated silt,which would be helpful for facilitating the application of MgO carbonation in the soil treatment.展开更多
In the present research,aluminum metal matrix composites were processed by the stir casting technique.The effects of TiB2 reinforcement particles,severe plastic deformation through accumulative roll bonding(ARB),and a...In the present research,aluminum metal matrix composites were processed by the stir casting technique.The effects of TiB2 reinforcement particles,severe plastic deformation through accumulative roll bonding(ARB),and aging treatment on the microstructural characteristics and mechanical properties were also evaluated.Uniaxial tensile tests and microhardness measurements were conducted,and the microstructural characteristics were investigated.Notably,the important problems associated with cast samples,including nonuniformity of the reinforcement particles and high porosity content,were solved through the ARB process.At the initial stage,particle-free zones,as well as particle clusters,were observed on the microstructure of the composite.However,after the ARB process,fracturing phenomena occurred in brittle ceramic particles,followed by breaking down of the fragments into fine particles as the number of rolling cycles increased.Subsequently,composites with a uniform distribution of particles were produced.Moreover,the tensile strength and microhardness of the ARB-processed composites increased with the increase in the reinforcement mass fraction.However,their ductility exhibited a different trend.With post-deformation aging treatment(T6),the mechanical properties of composites were improved because of the formation of fine Mg2Si precipitates.展开更多
The microstructure, hydriding performance, and electrochemical properties of LaNi4.0Ai0.2Fe0.4Cu0.4-x Snx(x = 0- 0.4) hydrogen storage alloys prepared by casting were investigated using XRD, SEM, pressure-compositio...The microstructure, hydriding performance, and electrochemical properties of LaNi4.0Ai0.2Fe0.4Cu0.4-x Snx(x = 0- 0.4) hydrogen storage alloys prepared by casting were investigated using XRD, SEM, pressure-composition isotherms, and electrochemical measurements. Substitution of Sn for Cu leads to the precipitation of LaNiSn phase. With increasing amount of tin substitution, cell volume, plateau pressures, and discharge capacities of the alloys decrease, whereas the cycle life of the alloys improves.展开更多
A method was developed to make a quantitative analysis of the microstructure of asphalt modified with styrene-butadiene-styrene block(SBS) copolymer. Moreover, both mixed and branched SBS were employed in the prepar...A method was developed to make a quantitative analysis of the microstructure of asphalt modified with styrene-butadiene-styrene block(SBS) copolymer. Moreover, both mixed and branched SBS were employed in the preparation of modified asphalt. By sampling specimens from the top, middle, and bottom, a number of microscope slides were made and 400 times micro images were gained. Binarized with the software of MATLAB, the images then went to the process of distribution test, when four typical distributions were employed to investigate the distribution of modifi er spread in asphalt. The distribution characteristic and its parameter were both found. The results show that asphalt phase clearly obeys Poisson distribution, and its parameter, λ, is bond up with the condition SBS performs in. Based on this parameter, indexes can be set up to evaluate the structure of the mixture and its performance as well. Compared with that modifi ed with mixed SBS, the asphalt modifi ed with branched SBS has better performance but worse stability, for it is easier to segregate.展开更多
基金Funded by the Scientific and Technological Innovation Project of Carbon Emission Peak and Carbon Neutrality of Jiangsu Province(No.BE2022028-4)。
文摘Industrial wastes such as steel slag and coal gangue etc.were chosen as raw materials for preparing ceramic via the conventional solid-state reaction method.With steel slag and coal gangue mixed in various mass ratios,from 100%steel slag to 100%coal gangue at 10%intervals,microstructure and possible phase evolution of the coal gangue-steel slag ceramics were investigated using X-ray powder diffraction,scanning electron microscopy,mercury intrusion porosimetry and Archimedes boiling method.The experimental results suggest that the phase compositions of the as-prepared ceramics could be altered with the increased amount of coal gangue in the ceramics.The anorthite-diopside eutectic can be formed in the ceramics with the mass ratios of steel slag to coal gangue arranged from 8:2 to 2:8,which was responsible for the melting of the steel slag-coal gangue ceramics at relatively high temperature.Further investigations on the microstructure suggested that the addition of the proper amount of steel slag in ceramic compositions was conducive to the pore formation and further contributed to an increment in porosity.
基金supported by the National Natural Science Foundation of China(No.51205178)the Natural Science Foundation of Gansu Province,China(No.1208RJZA189)the Doctor Fund Project of Lanzhou University of Technology
文摘A multilayer tungsten carbide particle(WCp)-reinforced Ni-based alloy coating was fabricated on a steel substrate using vacuum cladding technology.The morphology,microstructure,and formation mechanism of the coating were studied and discussed in different zones.The microstructure morphology and phase composition were investigated by scanning electron microscopy,optical microscopy,X-ray diffraction,and energy-dispersive X-ray spectroscopy.In the results,the coating presents a dense and homogeneous microstructure with few pores and is free from cracks.The whole coating shows a multilayer structure,including composite,transition,fusion,and diffusion-affected layers.Metallurgical bonding was achieved between the coating and substrate because of the formation of the fusion and diffusion-affected layers.The Ni-based alloy is mainly composed of y-Ni solid solution with finely dispersed Cr7C3/Cr(23)C6,CrB,and Ni+Ni3Si.WC particles in the composite layer distribute evenly in areas among initial Ni-based alloying particles,forming a special three-dimensional reticular microstructure.The macrohardness of the coating is HRC 55,which is remarkably improved compared to that of the substrate.The microhardness increases gradually from the substrate to the composite zone,whereas the microhardness remains almost unchanged in the transition and composite zones.
文摘TiC reinforced titanium composites has been produced with different Al content and C content by XDTM. The results have shown that TiC particles are of two different morphologies f coarse dendritical primary TiC and short bar-shape eutectic TiC. Al content has great effects on the morphology of TiC. With the increasing of Al content, the morphology of primary TiC changes from coarse developed dendrite into short bar-shape or plate--shape TiC with 35%Al. Meanwhile, the structure of the matrix changes from single Ti to Ti and Ti3Al, and to Ti3Al and TiAl. However, the C content has no influence on the microstructure of matrix. When the C content is less than 1.2%, the dendrite TiC disappears and only short bar-shape or plate-shape TiC exists in the composites. In addition, the effect of he3t treatment on the morphology of TiC has also Studied.
文摘Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the microstructure has also been studied.
基金supported by the Natural Science Foundation of China(Grant No.51101003)
文摘To further investigate the microstructure characteristic and solidification mechanism, so as to provide knowledge for the microstructure control of a NiTi-AI based high-temperature structural material, the microstructure of Ni-43Ti-4AI-2Nb-2Hf (at.%) alloy ingots prepared by conventional casting (arc-melting) and directional solidification (DS) at various drawing velocities (2 mm.min-', 18 mm.min-1, 30 mm-min-' and 60 mmmin~, respectively) was investigated by means of electron probe microanalyses. Experimental results reveal that the microstructures are composed of NiTi matrix phase,/3-Nb phase and Ti2Ni phase for samples obtained by both conventional casting and DS. Conventional casting has an equiaxial structure, while DS has a slender and acicular cellular structure which grows along the [001] orientation preferentially. Small amounts of white/3-Nb phase and black Ti2Ni phase co-exist at the grain boundaries or intercellular regions. With an increase in drawing velocity, the NiTi matrix phase is inclined to grow along (100) and (200) crystallographic planes, and the cellular arm spacing reduce gradually, but the directionality of the solidified structure weakens significantly. The homogeneous dispersion of,8-Nb phase and the decrease of Ti2Ni phase in DS samples are beneficial to improving the mechanical properties. Solidification mechanism analysis indicates that the dark grey NiTi matrix phase initially precipitates from the liquid phase, and then the divorced eutectic reaction takes place, which produces the light gray matrix phase and/^-Nb phase. Finally, the peritectic reaction happens, which generates the black Ti2Ni phase.
基金supported by Scientific Research Program Funded by Shaanxi Provincial Education Department(Program No.22JK0479)Research Start-up Project of Xi’an University of Technology(Grant No.101-256082204)+5 种基金International Science and Technology Cooperation Program of Shaanxi Province(No.2023-GHZD-50)Project of Science and Technology Shaanxi Province(No.2023-JC-YB-412)Project of Science and Technology Shaanxi Province(No.2023-JC-QN-0573)Projects of Major Innovation Platforms for Scientific and Technological and Local Transformation of Scientific and Technological Achievements of Xi’an(No.20GXSF0003)Projects of Major Scientific and Technological Achievements Local Transformation of Xi’an(No.2022JHZDZH-0039)Higher Education Institution Discipline Innovation and Intelligence Base of Shaanxi Provincial(No.S2021-ZC-GXYZ-0011).
文摘Magnesium and its alloys,as a promising class of materials,is popular in lightweight application and biomedical implants due to their low density and good biocompatibility.Additive manufacturing(AM)of Mg and its alloys is of growing interest in academia and industry.The domain-by-domain localized forming characteristics of AM leads to unique microstructures and performances of AM-process Mg and its alloys,which are different from those of traditionally manufactured counterparts.However,the intrinsic mechanisms still remain unclear and need to be in-depth explored.Therefore,this work aims to discuss and analyze the possible underlying mechanisms regarding defect appearance and elimination,microstructure formation and evolution,and performance improvement,based on presenting a comprehensive and systematic review on the relationship between process parameters,forming quality,microstructure characteristics and resultant performances.Lastly,some key perspectives requiring focus for further progression are highlighted to promote development of AM-processed Mg and its alloys and accelerate their industrialization.
基金Sponsored by National Science Foundation for Young Scientists of China(51404118)Yunnan Province Science Youth Experts Fund of China(2012FD012)Yunnan Province Department of Education Fund of China(2012Y530)
文摘Thermodynamic analysis of refractory siderite ore during carbothermic reduction was conducted. Micro- structure characteristics and phase transformation of siderite ore during sodium-carbonate-added catalyzing carboth- ermic reduction were investigated. X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive analysis of X rays were used to characterize the reduced samples. Results indicate that the solid reaction between FeO and SiO2 is inevitable during carbothermic reduction and the formation of fayalite is the main hindrance to the rapid reduction of siderite. The phase transformation of present siderite ore can be described as: siderite-magnetite-metallic iron, complying with the formation of abundant fayalite. Improving the reduction temperature (-1050 -C ) and duration is helpful for the formation and aggregation of metallic iron. The iron particle size in the reduced ore was below 20 l-m, and fayalite was abundant in the absence of sodium carbonate. With 5% Na2CO3 addition, the iron particle size in the reduced ore was generally above 50μm, and the diffraction intensity associated with metallic iron in the XRD pattern increased. The Na2O formed from the dissociation of Na2 CO3 can catalyze the carbothermie reduction of the siderite. This catalytic activity may be mainly caused by an increase in the reducing reaction activity of FeO.
基金State Ministry of Education Under contract No. 96053311.
文摘A Li-B alloy has been prepared using a pretreated amorphous B powder and pure Li ingot as starting materials by continually slow addition of B powder and intensified stirring in the process of melting. The microstructure and the discharge characteristic of the materials have been investigated- Results show that the problem of temperature control in synthesis would be modified by means of continual addition of B powder, the Li7B6 would be more finely distributed in the metal Li by means of intensified stirring. The discharge characteristic of the Li-B alloy using amorphous B as starting materials is almost the same with that of using crystalline B.
基金This work has been supported by the Flu,tda~ion Of harbin institute of Technology for Out standing YOungScientists (No. 1832).
文摘A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the alloy was very fine and its microstructure was mainly consisted of Si crystals plus intermetallic compound A19FeSi3, which were.very fine and uniformly distributed.
基金jointly supported by the National Natural Science Foundation of China (Grant Nos: 51704209,51701060,51901153)Natural Science Foundation of Shanxi province (Nos: 201801D121088,201901D211096)the Science and Technology Major Project of Shanxi province (Nos: 20191102007,20191102008)。
文摘The creep properties, microstructural characteristics and creep mechanisms of as-cast Mg-5Bi-5Sn(BT55) alloy without and with Mn(BTM550) addition were investigated via creep at 423, 448, and 473 K as well as stresses of 30, 50 and 75 MPa. The results indicate that adding Mn can result in the formation of primary and the dynamic precipitated α-Mn phases. In addition, the morphology of the precipitated Mg_(3)Bi_(2) phase and the orientation relationship between Mg_(2)Sn precipitates and α-Mg can be effectively modified. Tailoring the microstructural characteristics is responsible for the improved creep performance of BTM550 alloy. The dominant creep mechanisms in BT55 and BTM550 alloys are dislocation cross-slip and climb, respectively. Furthermore, twinning and pyramidal slip play an assisting part in both alloys during creep process.
文摘The paper studied the relationship between microstructure and shape recovery characteristics by using colored microstructure analysis under polarized light on the thermomechanical cycled CuAlNi single crystals. The two-way shape memory effect in quenched thin bar resulted from the preferential formation/extinction of martensite variant due to the internal quench stress, and the variant was formed at an angle of about 45 deg. with the tension direction ([001] of the βphase). Initial thermomechanical cycling under relatively low stress single variant stress-induced martensite was formed at an angle of 45 deg. with the tension and its morphology was a lath of parallel twins. More than one group of variants were formed after several training cycles and such variants also caused tilting of some thermally formed accommodated martensite. By overheating the trained sample containing stabilized multi-variants of stress-induced martensite, very coarse martensite structure with a strong asymmetry was produced, which caused the reverse two-way shape memory effect.
文摘Al-4. 5Cu-5Pb alloy was prepared by sand and chill casting. The same alloy was also spray deposited at a gas pressure of 1.6 MPa. The microstructural features exhibit a coarse to fine dendritic morphology for sand and chill cast alloys. Equiaxed grains were observed for spray formed alloys. Wear testing employing a pin-on-disc type set-up, reveals considerably lower wear of spray deposited alloy compared to that of chill and sand cast alloys. The morphological features of wear track on specimen and debris indicated a mixed oxidative-cum-adhesive wear mechanisms for these alloys tested in the present investigation. (Edited author abstract) 36 Refs.
基金appreciate the support of the Key Laboratory of Mechanical Structure Optimization&Material Application Technology of Luzhou(No.SCHYZSA-2022-02)the Scientific Research and Innovation Team Program of Sichuan University of Science and Technology(No.SUSE652A004)+1 种基金the Key Laboratory of Intelligent Manufacturing of Construction Machinery Project(No.IMCM202103)the Panzhihua Key Laboratory of Advanced Manufacturing Technology Open Fund Project(No.2022XJZD01)。
文摘In the present work,the laminar plasma surface hardening method is employed to enhance the service life of metal components fabricated from 65 Mn steel.The mechanical and wear behaviors of the laminar plasma surface hardened 65 Mn steel were analyzed.The martensite transition transformation of the temperature of the laminar plasma-hardened 65 ferrite Mn steel was determined by a thermal-solid coupling model.Based on the orthogonal experimental results,the optimal hardening parameters were confirmed.The scanning velocity,quenching distance and arc current are 130 mm/min,50 mm and 120 A,respectively.The pearlites and ferrites are transformed into martensites in the hardened zone,while the ratio of martensite in the heataffected zone decreases with the increase in the hardening depth.Compared to the untreated 65Mn steel,the average hardness increases from 220 HV_(0.2)to 920 HV_(0.2)in the hardened zone and the corresponding absorbed power increases from 118.7 J to 175.5 J.At the same time,the average coefficient of friction(COF)decreases from 0.763 to 0.546,and the wear rate decreases from 5.39×10^(-6)mm^(3)/(N·m)to 2.95×10^(-6)mm^(3)/(N·m),indicating that the wear resistance of 65Mn steel could be significantly improved by using laminar surface hardening.With the same hardening parameters,the depth and width of the hardened zone predicted by the thermal-solid coupling model are 1.85 mm and 11.20 mm,respectively,which are in accordance with the experimental results;depth is 1.83 mm and width is 11.15 mm.In addition,the predicted hardness distributions of the simulation model are in accordance with the experimental results.These results indicate that the simulation model could effectively predict the microstructure characteristics of 65 Mn steel.
基金Project(51205428) supported by the National Natural Science Foundation of ChinaProject(CDJRC10130011) supported by the Fundamental Research Funds for the Central Universities,China
文摘A novel joining method,double-stage diffusion-brazing of an AZ31 magnesium alloy and a 304L austenitic stainless steel,was carried out using a pure copper interlayer.The solid-state diffusion bonding of 304L to copper was conducted at 850 ℃ for 20 min followed by brazing to AZ31 at 520 ℃ and 495 ℃ for various time.Microstructural characteristics of the diffusion-brazed joints were investigated in detail.A defect free interface of Fe-Cu diffusion area appeared between the Cu alloy and the 304L steel.Cu-Mg reaction products were formed between AZ31 and Cu alloys.A layered structure including AZ31/Cu-Mg compounds/Cu/Fe-Cu diffusion layer/304L was present in the joint.With time prolonging,the reduction in the width of Cu layer was balanced by the increase in the width of Cu-Mg compounds zone.Microhardness peaks in the zone between AZ31 and Cu layer were attributed to the formation of Mg-Cu compounds in this zone.
基金Project(Q.J130000.2524.12H60)supported by the Ministry of Higher Education of Malaysia and Universiti Teknologi Malaysia。
文摘In the present study,the thermal,mechanical,and biological properties of xAg/Ti-30Ta(x=0,0.41,0.82 and 2.48 at%)shape memory alloys(SMAs)were investigated.The study was conducted using optical and scanning electron microscopy(SEM),X-ray diffractometry(XRD),compression test,and shape memory testing.The xAg/Ti-Ta was made using a powder metallurgy technique and microwave-sintering process.The results revealed that the addition of Ag has a significant effect on the pore size and shape,whereas the smallest pore size of 11μm was found with the addition of 0.41 at%along with a relative density of 72%.The fracture stress and strain increased with the addition of Ag,reaching the minimum values around 0.41 at%Ag.Therefore,this composition showed the maximum stress and strain at fracture region.Moreover,0.82 Ag/Ti-Ta shows more excellent corrosion resistance and biocompatibility than other percentages,obtaining almost the same behaviour of the pure Ti and Ti-6Al-4V alloys,which can be recommended for their promising and potential response for biomaterial applications.
文摘Recent research on microstructural characteristics and oxidation behavior of Ti(1-x)AlxN thin film were surveyed. The Ti(1-x)AlxN coatings have three different phase regions, Bl structure for lower x value, wurtzite structure for higher x value and unidentified structure for medium x value. Based upon the selective oxidation mechanism the oxidation results of Ti(1-x)AlxN thin film with different Ti/Al ratio were predicated.
基金the support of the National Natural Science Foundation of China(Grant Nos.41902286 and 41972269)Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(Grant No.Z019026)。
文摘The characteristics of reactive magnesia(MgO)-carbonated silt in respect to long-term stability have not been well understood in severely cold climate despite the usage of reactive MgO in enhancing the engineering performances.Under the binder content of 15%and initial water content of 25%,MgO-admixed silt specimens were carbonized for 3 h and 6 h and then subjected to different numbers of freezingthawing(F-T)cycles.After different F-T cycles,the physico-mechanical properties of MgO-carbonated silt were analyzed in comparison with Portland cement(PC)-stabilized silt through physical and unconfined compression tests.Besides,a series of micro tests on MgO-carbonated specimens was performed including X-ray diffraction(XRD),scanning electron microscopy(SEM)and mercury intrusion porosimetry(MIP)tests.The results demonstrate that both mass change ratio and moisture content of carbonated/stabilized silt decrease,and these values of MgO-carbonated silt are significantly lower while the density is higher compared to PC-stabilized silt.The strengths and moduli of MgO-carbonated silt are still two times higher than those of PC-stabilized specimens and the strength change ratio of keeps above0.8 after F-T cycles.There is no visible transformation between nesquehonite and dypingite/hydromagnesite,although the XRD peaks of nesquehonite decrease and the bonding and filling effects weaken slightly.After 6 and 10 F-T cycles,the pore-size characteristics changed from a unimodal distribution to a three-peak and bimodal distribution,respectively.The total,macro and large pore volumes increase obviously while the medium and small pore volumes decrease except for intra-aggregate pore.The findings show better F-T durability of MgO-carbonated silt,which would be helpful for facilitating the application of MgO carbonation in the soil treatment.
文摘In the present research,aluminum metal matrix composites were processed by the stir casting technique.The effects of TiB2 reinforcement particles,severe plastic deformation through accumulative roll bonding(ARB),and aging treatment on the microstructural characteristics and mechanical properties were also evaluated.Uniaxial tensile tests and microhardness measurements were conducted,and the microstructural characteristics were investigated.Notably,the important problems associated with cast samples,including nonuniformity of the reinforcement particles and high porosity content,were solved through the ARB process.At the initial stage,particle-free zones,as well as particle clusters,were observed on the microstructure of the composite.However,after the ARB process,fracturing phenomena occurred in brittle ceramic particles,followed by breaking down of the fragments into fine particles as the number of rolling cycles increased.Subsequently,composites with a uniform distribution of particles were produced.Moreover,the tensile strength and microhardness of the ARB-processed composites increased with the increase in the reinforcement mass fraction.However,their ductility exhibited a different trend.With post-deformation aging treatment(T6),the mechanical properties of composites were improved because of the formation of fine Mg2Si precipitates.
基金Project supported bythe Science and Technology Planned Project of Inner Mongolia , China (20050205) Higher EducationScience Research Project of Inner Mongolia ,China (NJ05064)
文摘The microstructure, hydriding performance, and electrochemical properties of LaNi4.0Ai0.2Fe0.4Cu0.4-x Snx(x = 0- 0.4) hydrogen storage alloys prepared by casting were investigated using XRD, SEM, pressure-composition isotherms, and electrochemical measurements. Substitution of Sn for Cu leads to the precipitation of LaNiSn phase. With increasing amount of tin substitution, cell volume, plateau pressures, and discharge capacities of the alloys decrease, whereas the cycle life of the alloys improves.
基金Funded by the National Natural Science Foundation of China(51178348)
文摘A method was developed to make a quantitative analysis of the microstructure of asphalt modified with styrene-butadiene-styrene block(SBS) copolymer. Moreover, both mixed and branched SBS were employed in the preparation of modified asphalt. By sampling specimens from the top, middle, and bottom, a number of microscope slides were made and 400 times micro images were gained. Binarized with the software of MATLAB, the images then went to the process of distribution test, when four typical distributions were employed to investigate the distribution of modifi er spread in asphalt. The distribution characteristic and its parameter were both found. The results show that asphalt phase clearly obeys Poisson distribution, and its parameter, λ, is bond up with the condition SBS performs in. Based on this parameter, indexes can be set up to evaluate the structure of the mixture and its performance as well. Compared with that modifi ed with mixed SBS, the asphalt modifi ed with branched SBS has better performance but worse stability, for it is easier to segregate.