Hexagonal boron nitride ceramic（h-BN） based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resu...Hexagonal boron nitride ceramic（h-BN） based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resultant products were investigated and the reaction mechanism was discussed. Results showed that the reaction between B and N2 occurred vigorously at temperatures ranging from 1 000 ℃ to 1 300 ℃, which resulted in the generation of t-BN. When the temperature exceeded 1 450 ℃, transformation from t-BN to h-BN began to occur. As the sintering temperature increased, the spherical particles of t-BN gradually transformed into fine sheet particles of h-BN. These particles subsequently displayed a compact arrangement to achieve a more uniform microstructure, thereby increasing the strength.展开更多
Plasma cladding was used to prepare a CoCrFeMnNi high-entropy alloy(HEA)coating under different conditions.The process parameters were optimized using an orthogonal experiment design based on surface morphology qualit...Plasma cladding was used to prepare a CoCrFeMnNi high-entropy alloy(HEA)coating under different conditions.The process parameters were optimized using an orthogonal experiment design based on surface morphology quality characteristics,dilution rate,and hardness.The optimal process parameters were determined through range and variance analysis to be a cladding current of 70 A,a cladding speed of 7 cm·min^(-1),and a powder gas flow rate of 8 L·s^(-1).During the optimized experiments,both the cladded and annealed CoCrFeMnNi HEA coatings exhibit some pores,micro-voids,and a small amount of aggregation.However,the aggregation in the annealed coating is more dispersed than that in the cladded coating.The cladded CoCrFeMnNi HEA coating consists of simple FCC phases,while a new Cr-rich phase precipitates from the FCC matrix after annealing the coating at a temperature range of 550°C-950°C.After annealing at 850°C,the proportion of the FCC phase decreases compared to the cladded coating,and the number of large-angle grain boundaries is significantly reduced.However,the proportion of grains with sizes below 50μm increases from 61.7%to 74.3%.The micro-hardness and wear resistance of the cladded coating initially increases but then decreases with an increase in annealing temperature,indicating that appropriate annealing can significantly improve the mechanical properties of the CoCrFeMnNi HEA coatings by plasma cladding.The micro-hardness of the CoCrFeMnNi HEA coatings after annealing at 650°C increases to 274.82 HV_(0.2),while the friction coefficient decreases to below 0.595.展开更多
In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and ...In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and time） on microstructure and mechanical properties of LZQT500-7 ductile iron dense bars with 172 mm in diameter which were produced by horizontal continuous casting （HCC）. The results show that the major factors influencing the hardness of austempered ductile iron （ADI） are austenitizing temperature and austempering temperature. The fraction of retained austenite increases as the austenitizing and austempering temperatures increase. When austenitizing temperature is low, acicular ferrite and retained austenite can be efifciently obtained by appropriately extending the austenitizing time. The proper austmepering time could ensure enough stability of retained austenite and prevent high carbon austenite decomposition. The optimal mechanical properties of ADI can be achieved with the fol owing process parameters： austenitizing temperature and time are 866 ＆#176;C and 135 min, and austempering temperature and time are 279 ＆#176;C and 135 min, respectively. The microstructure of ADI under the optimal austempering process consists of ifne acicular ferrite and a smal amount of retained austenite, and the hardness, tensile strength, yield strength, elongation and impact toughness of the bars are HBW 476, 1670 MPa, 1428 MPa, 2.93%and 25.7 J, respectively.展开更多
Thermal stabilities of microstructure and mechanical property have been investigated on superalloy U720Li, which is of great interest of application for jet engine and land-based turbine disc. The results showed that,...Thermal stabilities of microstructure and mechanical property have been investigated on superalloy U720Li, which is of great interest of application for jet engine and land-based turbine disc. The results showed that, the primary and secondary gamma' particles maintain good thermal stability at 650 and 700 degreesC with aging time up to 3000 h, while the tertiary gamma' is apparently dependent on aging temperature and time. The tertiary gamma' particles undergo a procedure of coarsening, dissolution and eventually complete disappearance with the increasing of aging time and temperature. They exhibit unusual high sensibility upon aging temperature, which is attributed to the lattice misfit between the gamma' precipitates and the matrix in the alloy. The grain boundary phase M23C6 remains stable without forming of sigma phase even with aging time up to 3000 h at 700 degreesC. Microhardness decreases apparently with increasing aging time and aging temperature. Theoretical analysis based on dislocation mechanism indicates that the change of microhardness should be attributed to the evolution of the tertiary gamma' during aging.展开更多
A low-alloyed Mg-2Zn-0.8Sr-0.2Ca matrix composite reinforced by TiC nano-particles was successfully prepared by semi-solid stirring under the assistance of ultrasonic,and then the as-cast composite was hot extruded.Th...A low-alloyed Mg-2Zn-0.8Sr-0.2Ca matrix composite reinforced by TiC nano-particles was successfully prepared by semi-solid stirring under the assistance of ultrasonic,and then the as-cast composite was hot extruded.The results indicated that the volume fraction of dynamical recrystallization and the recrystallized grain size have a certain decline at lower extrusion temperature or rate.The finest grain size of~0.30μm is obtained in the sample extruded at 200℃ and 0.1 mm/s.The as-extruded sample displays a strong basal texture intensity,and the basal texture intensity increases to 5.937 mud while the extrusion temperature increases from 200 to 240℃.The ultra-high mechanical properties(ultimate tensile strength of 480.2 MPa,yield strength of 462 MPa)are obtained after extrusion at 200℃ with a rate of 0.1 mm/s.Among all strengthening mechanisms for the present composite,the grain refinement contributes the most to the increase in strength.A mixture of cleavage facets and dimples were observed in the fracture surfaces of three as-extruded nanocomposites,which explain a mix of brittle-ductile fracture way of the samples.展开更多
The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure a...The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of Al Si Ti phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.展开更多
The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-...The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.展开更多
Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the ...Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the composites were increased by the addition of SiC platelet until the content up to 20 vol pct. A slight decrease in flexural Strength was measured at room temperature with increasing SiC platelet content. The high temperature flexural strength tests at 1150, 1250, and 1350℃ were conducted. It was found that the flexural strength at elevated temperature was degraded with the rising temperature, and the downward trend of flexural strength for the composite containing 10 vol. pct SiC platelet was less. The results indicate that SiC platelet had a positive influence on the high temperature strength. Effects of SiC platelet reinforcement were presented展开更多
The feasibility of using coral reef sand（CRS） in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are a...The feasibility of using coral reef sand（CRS） in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are analyzed. Mechanical properties and microstructure of concrete with CRS are studied and compared to concrete with natural river sand. The relationship between the microstructure and performance of CRS concrete is established. The CRS has a porous surface with high water intake capacity, which contributes to the mechanical properties of concrete. The interfacial transition zone between the cement paste and CRS is densified compared to normal concrete with river sand. Hydration products form in the pore space of CRS and interlock with the matrix of cement paste, which increases the strength. The total porosity of concrete prepared with CRS is higher than that with natural sand. The main difference in pore size distribution is the fraction of fine pores in the range of 100 nm.展开更多
Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characteri...Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation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
The effects of sphere size on the microstructural and mechanical properties of ductile iron–steel hollow sphere（DI–SHS） syntactic foams were investigated in this study. The SHSs were manufactured by fluidized-bed ...The effects of sphere size on the microstructural and mechanical properties of ductile iron–steel hollow sphere（DI–SHS） syntactic foams were investigated in this study. The SHSs were manufactured by fluidized-bed coating via the Fe-based commercial powder–binder suspension onto expanded polystyrene spheres（EPSs）. Afterwards, the DI–SHS syntactic foams were produced via a sand-mold casting process. The microstructures of specimens were investigated by optical microscopy, scanning electron microscopy（SEM）, and energy-dispersive X-ray spectroscopy（EDS）. The microscopic evaluations of specimens reveal distinct regions composed of the DI matrix, SHS shells, and compatible interface. As a result, the microstructures and graphite morphologies of the DI matrix depend on sphere size. When the sphere size decreases, the area fractions of cementite and graphite phases are observed to increase and decrease, respectively. Compression tests were subsequently conducted at ambient temperature on the DI–SHS syntactic foams. The results reveal that the compression behavior of the syntactic foams is enhanced with increasing sphere size. Furthermore, the compressed specimens demonstrate that microcracks start and grow from the interface region.展开更多
Butt joints between Mg alloy AZ31 B and pure Al 1 060 sheets were produced via metal inert gas welding process with Zn-Cd alloy foil. Crack-free Al/Mg butt joints between AZ31 B Mg alloy and pure Al 1060 sheets were o...Butt joints between Mg alloy AZ31 B and pure Al 1 060 sheets were produced via metal inert gas welding process with Zn-Cd alloy foil. Crack-free Al/Mg butt joints between AZ31 B Mg alloy and pure Al 1060 sheets were obtained. Intermetallic compound layer 1 and layer 2 had formed in fusion zone/Mg alloy and the average thickness of the layer 1 was about 50 μm. The intermetallic compound layer 1 consisted of Al12Mg17 and Mg2Si phases while layer 2 consisted of Al12Mg17, Mg2Si and Mg Zn2 phases. The crack started from the IMC layer at the bottom of the joint and propagated along the brittle IMC layer, then expanded into weld metal during the SEM in situ tensile test. The highest tensile strength of the dissimilar metal butt joints could reach 46.8 MPa and the effect ofinterfacial IMC layer on mechanical property of the joint was discussed in detail in the present study.展开更多
In the present research, microstructure of akind of limnetic shell （Hyriopsis cumingii） is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are ...In the present research, microstructure of akind of limnetic shell （Hyriopsis cumingii） is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are carried out by using bending and tensile tests. The dependence of mechanical properties of the shell nacre on its microstructure is analyzed by using a modified shear-lag model, and the overall stress-strain relation is obtained. The experimental results reveal that the mechanical properties of shell nacre strongly depend on the water contents of the limnetic shell. Dry nacre shows a brittle behavior, whereas wetting nacre displays a strong ductility. Compared to the tensile test, the bending test overestimates the strength and underestimates the Young＇s modulus. The modified shear-lag model can characterize the deformation features of nacre effectively.展开更多
The low carbon Nb-Ti mieroalloyed tested steel was prepared by the process of vacuum induction furnace smelting, forging and hot rolling. The new steel aims to meet the demand of high strength, high toughness and high...The low carbon Nb-Ti mieroalloyed tested steel was prepared by the process of vacuum induction furnace smelting, forging and hot rolling. The new steel aims to meet the demand of high strength, high toughness and high plasticity for building facilities. The effects of quenching process on microstructure and mechanical properties of tested steel were investigated. The results showed that prior austenite grain size, phase type and precipitation behavior of （ Nb, Ti） （ C, N） play important roles in mechanical properties of the steel. Through modified appropriately, the model of austenite grain growth during heating and holding is d^5.7778 = 5. 6478^5.7778 ＋ 7.04 × 10^22t^1.6136 exp（- 427. 15 ×10^3 /（RT））. The grain growth activation energy is Qg = 427. 15 kJ. During quenching, the microscopic structures are mainly martensite and lath bainite which contains lots of lath substructure and dislocations. The content of phases, fine and coarsening （ Nb, Ti ） （ C, N ） precipitated changes during different quenching temperatures and holding time. Finally compared with the hardness value, the best quenching process can be obtained that heating temperature and holding time are 900 ℃ and 50 mins, respectively.展开更多
C–Mn steels prepared by annealing at 800°C for 120 s and overaging at 250–400°C were subjected to pre-straining（2%） and baking treatments（170°C for 20 min） to measure their bake-hardening（BH_2） ...C–Mn steels prepared by annealing at 800°C for 120 s and overaging at 250–400°C were subjected to pre-straining（2%） and baking treatments（170°C for 20 min） to measure their bake-hardening（BH_2） values. The effects of overaging temperature on the microstructure, mechanical properties, and BH_2 behavior of 600 MPa cold-rolled dual-phase（DP） steel were investigated by optical microscopy, scanning electron microscopy, and tensile tests. The results indicated that the martensite morphology exhibited less variation when the DP steel was overaged at 250–350°C. However, when the DP steel was overaged at 400°C, numerous non-martensite and carbide particles formed and yield-point elongation was observed in the tensile curve. When the overaging temperature was increased from 250 to 400°C, the yield strength increased from 272 to 317 MPa, the tensile strength decreased from 643 to 574 MPa, and the elongation increased from 27.8% to 30.6%. Furthermore, with an increase in overaging temperature from 250 to 400°C, the BH_2 value initially increases and then decreases. The maximum BH_2 value of 83 MPa was observed for the specimen overaged at 350°C.展开更多
A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity...A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples＇ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness（Hv = 122 MPa）, compressive yield strength（382 MPa）, tensile yield strength（332 MPa）, ultimate tensile strength（370 MPa）, and elongation（9%）. This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.展开更多
An experimental 2618(Al-Cu-Mg-Fe-Ni) alloy added with trace Sc and Zr was prepared by ingot metallurgy (IM) method. The aging behavior of the alloy was studied by Vickers hardness measurement at 200℃ and 300℃. and ...An experimental 2618(Al-Cu-Mg-Fe-Ni) alloy added with trace Sc and Zr was prepared by ingot metallurgy (IM) method. The aging behavior of the alloy was studied by Vickers hardness measurement at 200℃ and 300℃. and the tensile properties of alloy specimens were measured at 20℃, 200℃, 250℃ and 300℃. The microstructure was observed by using optical microscope, SEM and TEM. It was found that the addition of Sc and Zr to 2618 alloy resulted in a primary Al_3(Sc,Zr) phase which could refine the grain because it acts as nuclei of heterogeneous crystallization in the melt during solidification. The secondary Al_3(Sc,Zr) particles were full coherent with matrix and had obvious precipitation hardening effect. They also made the S' phase precipitate more homogeneous. So the strength of alloy increases at both ambient and elevated temperatures without a decrease of ductility. The ductile fracture of alloy occurs by microvoid nucleation, growth and coalescence, so the microvoid coalescence is the dominant fracture mechanism.展开更多
A novel micro fused-casting for metal（MFCM） process for producing A356 aluminum alloy slurry was proposed. MFCM means that the refined metal slurry is pressed out from the outlet of bottom of crucible to the horizon...A novel micro fused-casting for metal（MFCM） process for producing A356 aluminum alloy slurry was proposed. MFCM means that the refined metal slurry is pressed out from the outlet of bottom of crucible to the horizontal movable plate. With the aid of 3D manufacturing software, the melt is solidified and formed layer by layer. The stirring could keep the ingredients and the heat diffusion of metal slurry uniform in the crucible due to the shear force breaking down the dendrite arms. The solidus and liquidus temperatures of A356 alloy were 559.2 and 626.3 ℃, respectively, which were measured by differential scanning calorimetry（DSC）. Effect of different stirring velocities of MFCM on the microstructure and mechanical properties of A356 slurry was investigated with the pouring temperature controlled at 620 ℃. The microstructure and mechanical performance were the best when the stirring velocity was 1 200 r/min in MFCM. The microstructures of the A356 aluminum alloy slurry were mainly composed of fine spherical or rose grains. The average roundness and average grain size reached 2.2 and 41 μm and the tensile strength of A356 alloy slurry reached 207.8 MPa, while the average vickers hardness was 81.1 HV.展开更多
The present work focused on the Ni_3Al-based alloy with a high melting point. The aim of the research is to study the effect of withdrawal rate on the microstructures and mechanical properties of directionally solidif...The present work focused on the Ni_3Al-based alloy with a high melting point. The aim of the research is to study the effect of withdrawal rate on the microstructures and mechanical properties of directionally solidified Ni-25 Al alloy. Ni_3 Al intermetallics were prepared at different withdrawal rates by directional solidification(DS) in an electromagnetic cold crucible directional solidification furnace. The DS samples contain Ni_3 Al and Ni Al phases. The primary dendritic spacing(λ) decreases with the increasing of withdrawal rate(V), and the volume fraction of Ni Al phase increases as the withdrawal rate increases. Results of tensile tests show that ductility of DS samples is enhanced with a decrease in the withdrawal rate.展开更多
基金Funded by the Scientific and Technological Development Project of Yantai(2013JH020)
文摘Hexagonal boron nitride ceramic（h-BN） based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resultant products were investigated and the reaction mechanism was discussed. Results showed that the reaction between B and N2 occurred vigorously at temperatures ranging from 1 000 ℃ to 1 300 ℃, which resulted in the generation of t-BN. When the temperature exceeded 1 450 ℃, transformation from t-BN to h-BN began to occur. As the sintering temperature increased, the spherical particles of t-BN gradually transformed into fine sheet particles of h-BN. These particles subsequently displayed a compact arrangement to achieve a more uniform microstructure, thereby increasing the strength.
基金This work was financially supported by the National Natural Science Foundation of China(No.51861025)the Jiangxi Provincial Department of Science and Technology(No.20203BDH80W008).
文摘Plasma cladding was used to prepare a CoCrFeMnNi high-entropy alloy(HEA)coating under different conditions.The process parameters were optimized using an orthogonal experiment design based on surface morphology quality characteristics,dilution rate,and hardness.The optimal process parameters were determined through range and variance analysis to be a cladding current of 70 A,a cladding speed of 7 cm·min^(-1),and a powder gas flow rate of 8 L·s^(-1).During the optimized experiments,both the cladded and annealed CoCrFeMnNi HEA coatings exhibit some pores,micro-voids,and a small amount of aggregation.However,the aggregation in the annealed coating is more dispersed than that in the cladded coating.The cladded CoCrFeMnNi HEA coating consists of simple FCC phases,while a new Cr-rich phase precipitates from the FCC matrix after annealing the coating at a temperature range of 550°C-950°C.After annealing at 850°C,the proportion of the FCC phase decreases compared to the cladded coating,and the number of large-angle grain boundaries is significantly reduced.However,the proportion of grains with sizes below 50μm increases from 61.7%to 74.3%.The micro-hardness and wear resistance of the cladded coating initially increases but then decreases with an increase in annealing temperature,indicating that appropriate annealing can significantly improve the mechanical properties of the CoCrFeMnNi HEA coatings by plasma cladding.The micro-hardness of the CoCrFeMnNi HEA coatings after annealing at 650°C increases to 274.82 HV_(0.2),while the friction coefficient decreases to below 0.595.
基金financially supported by the fund of the Key Projects of Shaanxi Provincial International Technology Cooperation Plan(2013KW16)the Scientific Research Program funded by Shaanxi Provincial Education Department(2013JK0914)+2 种基金the State Key Laboratory of Solidifi cation Processing in NWPU(SKLSP201115)the Scientific Research Project of Xi'an University of Technology(2013CX004)the fund of the Key Laboratory of Electrical Materials and Infi ltration Technology of Shaanxi Province,China(2014)
文摘In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and time） on microstructure and mechanical properties of LZQT500-7 ductile iron dense bars with 172 mm in diameter which were produced by horizontal continuous casting （HCC）. The results show that the major factors influencing the hardness of austempered ductile iron （ADI） are austenitizing temperature and austempering temperature. The fraction of retained austenite increases as the austenitizing and austempering temperatures increase. When austenitizing temperature is low, acicular ferrite and retained austenite can be efifciently obtained by appropriately extending the austenitizing time. The proper austmepering time could ensure enough stability of retained austenite and prevent high carbon austenite decomposition. The optimal mechanical properties of ADI can be achieved with the fol owing process parameters： austenitizing temperature and time are 866 ＆#176;C and 135 min, and austempering temperature and time are 279 ＆#176;C and 135 min, respectively. The microstructure of ADI under the optimal austempering process consists of ifne acicular ferrite and a smal amount of retained austenite, and the hardness, tensile strength, yield strength, elongation and impact toughness of the bars are HBW 476, 1670 MPa, 1428 MPa, 2.93%and 25.7 J, respectively.
文摘Thermal stabilities of microstructure and mechanical property have been investigated on superalloy U720Li, which is of great interest of application for jet engine and land-based turbine disc. The results showed that, the primary and secondary gamma' particles maintain good thermal stability at 650 and 700 degreesC with aging time up to 3000 h, while the tertiary gamma' is apparently dependent on aging temperature and time. The tertiary gamma' particles undergo a procedure of coarsening, dissolution and eventually complete disappearance with the increasing of aging time and temperature. They exhibit unusual high sensibility upon aging temperature, which is attributed to the lattice misfit between the gamma' precipitates and the matrix in the alloy. The grain boundary phase M23C6 remains stable without forming of sigma phase even with aging time up to 3000 h at 700 degreesC. Microhardness decreases apparently with increasing aging time and aging temperature. Theoretical analysis based on dislocation mechanism indicates that the change of microhardness should be attributed to the evolution of the tertiary gamma' during aging.
基金financially supported by the National Natural Science Foundation of China (Nos. 51771129, 51401144, and 51771128)the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi, China+1 种基金the Natural Science Foundation of Shanxi Province, China (Nos. 2015021067 and 201601D011034)the Projects of International Cooperation in Shanxi, China (No. 2017 03D421039)
文摘A low-alloyed Mg-2Zn-0.8Sr-0.2Ca matrix composite reinforced by TiC nano-particles was successfully prepared by semi-solid stirring under the assistance of ultrasonic,and then the as-cast composite was hot extruded.The results indicated that the volume fraction of dynamical recrystallization and the recrystallized grain size have a certain decline at lower extrusion temperature or rate.The finest grain size of~0.30μm is obtained in the sample extruded at 200℃ and 0.1 mm/s.The as-extruded sample displays a strong basal texture intensity,and the basal texture intensity increases to 5.937 mud while the extrusion temperature increases from 200 to 240℃.The ultra-high mechanical properties(ultimate tensile strength of 480.2 MPa,yield strength of 462 MPa)are obtained after extrusion at 200℃ with a rate of 0.1 mm/s.Among all strengthening mechanisms for the present composite,the grain refinement contributes the most to the increase in strength.A mixture of cleavage facets and dimples were observed in the fracture surfaces of three as-extruded nanocomposites,which explain a mix of brittle-ductile fracture way of the samples.
基金supported by the National Key Research Project(No.2016YFB0300901)
文摘The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of Al Si Ti phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.
基金Funded by the "11th Five" National Science and Technology Support Project(No.2006BAE03A13)
文摘The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.
文摘Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the composites were increased by the addition of SiC platelet until the content up to 20 vol pct. A slight decrease in flexural Strength was measured at room temperature with increasing SiC platelet content. The high temperature flexural strength tests at 1150, 1250, and 1350℃ were conducted. It was found that the flexural strength at elevated temperature was degraded with the rising temperature, and the downward trend of flexural strength for the composite containing 10 vol. pct SiC platelet was less. The results indicate that SiC platelet had a positive influence on the high temperature strength. Effects of SiC platelet reinforcement were presented
基金Funded by the Fundamental Research Funds for the Central Universities(WUT:142201001)
文摘The feasibility of using coral reef sand（CRS） in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are analyzed. Mechanical properties and microstructure of concrete with CRS are studied and compared to concrete with natural river sand. The relationship between the microstructure and performance of CRS concrete is established. The CRS has a porous surface with high water intake capacity, which contributes to the mechanical properties of concrete. The interfacial transition zone between the cement paste and CRS is densified compared to normal concrete with river sand. Hydration products form in the pore space of CRS and interlock with the matrix of cement paste, which increases the strength. The total porosity of concrete prepared with CRS is higher than that with natural sand. The main difference in pore size distribution is the fraction of fine pores in the range of 100 nm.
文摘Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation
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The effects of sphere size on the microstructural and mechanical properties of ductile iron–steel hollow sphere（DI–SHS） syntactic foams were investigated in this study. The SHSs were manufactured by fluidized-bed coating via the Fe-based commercial powder–binder suspension onto expanded polystyrene spheres（EPSs）. Afterwards, the DI–SHS syntactic foams were produced via a sand-mold casting process. The microstructures of specimens were investigated by optical microscopy, scanning electron microscopy（SEM）, and energy-dispersive X-ray spectroscopy（EDS）. The microscopic evaluations of specimens reveal distinct regions composed of the DI matrix, SHS shells, and compatible interface. As a result, the microstructures and graphite morphologies of the DI matrix depend on sphere size. When the sphere size decreases, the area fractions of cementite and graphite phases are observed to increase and decrease, respectively. Compression tests were subsequently conducted at ambient temperature on the DI–SHS syntactic foams. The results reveal that the compression behavior of the syntactic foams is enhanced with increasing sphere size. Furthermore, the compressed specimens demonstrate that microcracks start and grow from the interface region.
文摘Butt joints between Mg alloy AZ31 B and pure Al 1 060 sheets were produced via metal inert gas welding process with Zn-Cd alloy foil. Crack-free Al/Mg butt joints between AZ31 B Mg alloy and pure Al 1060 sheets were obtained. Intermetallic compound layer 1 and layer 2 had formed in fusion zone/Mg alloy and the average thickness of the layer 1 was about 50 μm. The intermetallic compound layer 1 consisted of Al12Mg17 and Mg2Si phases while layer 2 consisted of Al12Mg17, Mg2Si and Mg Zn2 phases. The crack started from the IMC layer at the bottom of the joint and propagated along the brittle IMC layer, then expanded into weld metal during the SEM in situ tensile test. The highest tensile strength of the dissimilar metal butt joints could reach 46.8 MPa and the effect ofinterfacial IMC layer on mechanical property of the joint was discussed in detail in the present study.
基金the National Natural Science Foundation of China (10432050,10428207 and 10672163)the Chinese Academy of Sciences (KJCX2-YW-M04)the Institute of Mechanics through Innovation Project
文摘In the present research, microstructure of akind of limnetic shell （Hyriopsis cumingii） is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are carried out by using bending and tensile tests. The dependence of mechanical properties of the shell nacre on its microstructure is analyzed by using a modified shear-lag model, and the overall stress-strain relation is obtained. The experimental results reveal that the mechanical properties of shell nacre strongly depend on the water contents of the limnetic shell. Dry nacre shows a brittle behavior, whereas wetting nacre displays a strong ductility. Compared to the tensile test, the bending test overestimates the strength and underestimates the Young＇s modulus. The modified shear-lag model can characterize the deformation features of nacre effectively.
基金Sponsored by the Major State Basic Research Development Program of China(Grant No.2010CB630801)
文摘The low carbon Nb-Ti mieroalloyed tested steel was prepared by the process of vacuum induction furnace smelting, forging and hot rolling. The new steel aims to meet the demand of high strength, high toughness and high plasticity for building facilities. The effects of quenching process on microstructure and mechanical properties of tested steel were investigated. The results showed that prior austenite grain size, phase type and precipitation behavior of （ Nb, Ti） （ C, N） play important roles in mechanical properties of the steel. Through modified appropriately, the model of austenite grain growth during heating and holding is d^5.7778 = 5. 6478^5.7778 ＋ 7.04 × 10^22t^1.6136 exp（- 427. 15 ×10^3 /（RT））. The grain growth activation energy is Qg = 427. 15 kJ. During quenching, the microscopic structures are mainly martensite and lath bainite which contains lots of lath substructure and dislocations. The content of phases, fine and coarsening （ Nb, Ti ） （ C, N ） precipitated changes during different quenching temperatures and holding time. Finally compared with the hardness value, the best quenching process can be obtained that heating temperature and holding time are 900 ℃ and 50 mins, respectively.
基金financially supported by the National Natural Science Foundation of China(Nos.U1360202,51472030,and 51502014)
文摘C–Mn steels prepared by annealing at 800°C for 120 s and overaging at 250–400°C were subjected to pre-straining（2%） and baking treatments（170°C for 20 min） to measure their bake-hardening（BH_2） values. The effects of overaging temperature on the microstructure, mechanical properties, and BH_2 behavior of 600 MPa cold-rolled dual-phase（DP） steel were investigated by optical microscopy, scanning electron microscopy, and tensile tests. The results indicated that the martensite morphology exhibited less variation when the DP steel was overaged at 250–350°C. However, when the DP steel was overaged at 400°C, numerous non-martensite and carbide particles formed and yield-point elongation was observed in the tensile curve. When the overaging temperature was increased from 250 to 400°C, the yield strength increased from 272 to 317 MPa, the tensile strength decreased from 643 to 574 MPa, and the elongation increased from 27.8% to 30.6%. Furthermore, with an increase in overaging temperature from 250 to 400°C, the BH_2 value initially increases and then decreases. The maximum BH_2 value of 83 MPa was observed for the specimen overaged at 350°C.
基金financially supported by the Czech Science Foundation(No.P108/12/G043)
文摘A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples＇ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness（Hv = 122 MPa）, compressive yield strength（382 MPa）, tensile yield strength（332 MPa）, ultimate tensile strength（370 MPa）, and elongation（9%）. This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.
文摘An experimental 2618(Al-Cu-Mg-Fe-Ni) alloy added with trace Sc and Zr was prepared by ingot metallurgy (IM) method. The aging behavior of the alloy was studied by Vickers hardness measurement at 200℃ and 300℃. and the tensile properties of alloy specimens were measured at 20℃, 200℃, 250℃ and 300℃. The microstructure was observed by using optical microscope, SEM and TEM. It was found that the addition of Sc and Zr to 2618 alloy resulted in a primary Al_3(Sc,Zr) phase which could refine the grain because it acts as nuclei of heterogeneous crystallization in the melt during solidification. The secondary Al_3(Sc,Zr) particles were full coherent with matrix and had obvious precipitation hardening effect. They also made the S' phase precipitate more homogeneous. So the strength of alloy increases at both ambient and elevated temperatures without a decrease of ductility. The ductile fracture of alloy occurs by microvoid nucleation, growth and coalescence, so the microvoid coalescence is the dominant fracture mechanism.
基金Funded by the National Natural Science Foundation of China(No.51341009)
文摘A novel micro fused-casting for metal（MFCM） process for producing A356 aluminum alloy slurry was proposed. MFCM means that the refined metal slurry is pressed out from the outlet of bottom of crucible to the horizontal movable plate. With the aid of 3D manufacturing software, the melt is solidified and formed layer by layer. The stirring could keep the ingredients and the heat diffusion of metal slurry uniform in the crucible due to the shear force breaking down the dendrite arms. The solidus and liquidus temperatures of A356 alloy were 559.2 and 626.3 ℃, respectively, which were measured by differential scanning calorimetry（DSC）. Effect of different stirring velocities of MFCM on the microstructure and mechanical properties of A356 slurry was investigated with the pouring temperature controlled at 620 ℃. The microstructure and mechanical performance were the best when the stirring velocity was 1 200 r/min in MFCM. The microstructures of the A356 aluminum alloy slurry were mainly composed of fine spherical or rose grains. The average roundness and average grain size reached 2.2 and 41 μm and the tensile strength of A356 alloy slurry reached 207.8 MPa, while the average vickers hardness was 81.1 HV.
基金financially supported by the National Natural Science Foundation of China(Grant No.51471062)
文摘The present work focused on the Ni_3Al-based alloy with a high melting point. The aim of the research is to study the effect of withdrawal rate on the microstructures and mechanical properties of directionally solidified Ni-25 Al alloy. Ni_3 Al intermetallics were prepared at different withdrawal rates by directional solidification(DS) in an electromagnetic cold crucible directional solidification furnace. The DS samples contain Ni_3 Al and Ni Al phases. The primary dendritic spacing(λ) decreases with the increasing of withdrawal rate(V), and the volume fraction of Ni Al phase increases as the withdrawal rate increases. Results of tensile tests show that ductility of DS samples is enhanced with a decrease in the withdrawal rate.
