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
By introducing Cu, AlCoCrFeNiCux （x values in molar ratio, x = 0, 0.1, 0.5, 1.0, 1.5, 2.0, and 2.5） alloys were designed and prepared. The effects of Cu on microstructure and properties of Al Co Cr Fe Ni alloy were ...By introducing Cu, AlCoCrFeNiCux （x values in molar ratio, x = 0, 0.1, 0.5, 1.0, 1.5, 2.0, and 2.5） alloys were designed and prepared. The effects of Cu on microstructure and properties of Al Co Cr Fe Ni alloy were investigated. The introduction of Cu results in the formation of Cu-rich FCC solid solution phase when Cu content is low.There are two FCC solid solution phases, i.e., Cu-rich FCC solid solution phase and phase transformation-induced FCC solid solution phase, when the Cu content is more than 1.0. Both the yield stress and plastic strain of alloy show a turning point when the Cu content is 0.5. Among the seven alloys, Cu0.5 alloy exhibits the largest yield stress of 1187 MPa and the lowest plastic strain of 16.01 %.展开更多
In the present study, Cu-modified pipeline steels were fabricated to mitigate MIC by the antimicrobial ability of Cu element. The microstructure, mechanical properties and the antimircobial performance of the Cu-modif...In the present study, Cu-modified pipeline steels were fabricated to mitigate MIC by the antimicrobial ability of Cu element. The microstructure, mechanical properties and the antimircobial performance of the Cu-modified steel were systematically investigated. The Cu-modified steels showed good antimicrobial performance with remarkable strength enhancement by nanoscale Cu-rich precipitates and good impact toughness without changing the original base microstructures after the optimal aging treatment of 500 °C/1 h.展开更多
Friction stir welding is a new and innovative welding method used to fuse materials. In this welding method, the heat generated by friction and plastic flow causes significant changes in the microstructure of the mate...Friction stir welding is a new and innovative welding method used to fuse materials. In this welding method, the heat generated by friction and plastic flow causes significant changes in the microstructure of the material, which leads to local changes in the mechanical properties of the weld. In this study, the effects of various welding parameters such as the rotational and traverse speeds of the tool on the microstructural and mechanical properties of copper plates were investigated; additionally, Charpy tests were performed on copper plates for the first time. Also, the effect of the number of welding passes on the aforementioned properties has not been investigated in previous studies. The results indicated that better welds with superior properties are produced when less heat is transferred to the workpiece during the welding process. It was also found that although the properties of the stir zone improved with an increasing number of weld passes, the properties of its weakest zone, the heat-affected zone, deteriorated.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
Electron beam welding （EBW） was applied to a 10-mm-thick plate cut from Ti-6246 compressor disk. The microstructural characteristics, microhardness and room temperature tensile properties were investigated. Microstr...Electron beam welding （EBW） was applied to a 10-mm-thick plate cut from Ti-6246 compressor disk. The microstructural characteristics, microhardness and room temperature tensile properties were investigated. Microstructure observations indicated that there existed plenty of thin needle-like α platelets studding in the matrix of the columnar β grains in the as-welded fusion zone （FZ）. Post-weld heat treat- ment （PWHT） led to the precipitation of small secondary α platelets in the β matrix in heat affected zone and FZ. The thickness and the density of α platelets increased as the temperature of PWHT increased from 545 to 645 C. The microhardness across the Ti-6246 EBWjoint exhibited a nonuniform distribution. The hardness increased with the decrease of distance to the weld center, and reached the maximum of 467 HV in FZ when PWHT was carried out at 595 C. All the weldments tested with tension were fractured at the base material （BM） and exhibited a ductile fracture mode. The major deformation barrier in BM was the platelet α/β interfaces, however, the major deformation barrier in FZ was found to be β grain boundaries and secondary α/β interfaces. The BM with thicker platelet α phases had lower strength than the other two zones in the joint, and the BM deformed first and led to fracture in this zone.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
The microstructure and mechanical properties of pulse metal inert-gas （MIG） welded dissimilar joints between 4 mm thick wrought 6061-T6 and cast A356-T6 aluminum alloy plates were investigated. The tensile strength ...The microstructure and mechanical properties of pulse metal inert-gas （MIG） welded dissimilar joints between 4 mm thick wrought 6061-T6 and cast A356-T6 aluminum alloy plates were investigated. The tensile strength of the joints reached 235 MPa, which is 83% of that of 6061 aluminum alloy, and then decreased with the increase of travel speed while keeping other welding parameters constant. The microstructure, composition and fractography of joints were examined by the optical microscopy （OM）, scanning electron microscopy （SEM） and electron probe microanalysis （EPMA）. Grain boundary liquation and segregation occurred in the partially melted zone （PMZ） on 6061 aluminum alloy side, and brittle Fe-rich phases were observed in partially melted zone on A356 aluminum alloy side. The minimum microhardness appeared in heat-affected zone （HAZ） near A356 aluminum alloy substrate. The samples during tensile test failed mainly in PMZ and HAZ on A356 aluminum alloy side through mixed fracture mode with quasi cleavage and dimples on fracture surface.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
Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated...Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated. Results show that, during ARB process, the evolution of deformation mechanism oft Mg-5Li-1Al alloy is as follows： twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization （DRX）. The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.展开更多
Martensitic stainless steel containing Cr of 12% to 18%（mass percent） are common utilized in quenching and tempering processes for knife and cutlery steel. The properties obtained in these materials are significantl...Martensitic stainless steel containing Cr of 12% to 18%（mass percent） are common utilized in quenching and tempering processes for knife and cutlery steel. The properties obtained in these materials are significantly influ- enced by matrix composition after heat treatment, especially as Cr and C content. Comprehensive considered the hardness and corrosion resistance, a new type martensitic stainless steel 6Crl5MoV has been developed. The effect of heat treatment processes on microstructure and mechanical properties of 6Crl5MoV martensitic stainless steel is emphatically researched. Thermo-Calc software has been carried out to thermodynamic calculation; OM, SEM and TEM have been carried out to microstructure observation; hardness and impact toughness test have been carried out to evaluate the mechanical properties. Results show that the equilibrium carbide in 6Cr15MoV steel is M23 C6 car- bide, and the M23 C6 carbides finely distributed in annealed microstructure. 6Crl5MoV martensitic stainless steel has a wider quenching temperature range, the hardness value of steel 6Cr15MoV can reach to HRC 60.8 to HRC 61.6 when quenched at 1 060 to 1 100 ℃. Finely distributed carbides will exist in quenched microstructure, and effectively inhabit the growth of austenite grain. With the increasing of quenching temperature, the volume fraction of undis- solved carbides will decrease. The excellent comprehensive mechanical properties can be obtained by quenched at 1 060 to 1 100℃ with tempered at 100 to 150 ℃, and it is mainly due to the high carbon martensite and fine grain size. At these temperature ranges, the hardness will retain about HRC 59.2 to HRC 61.6 and the Charpy U-notch impact toughness will retain about 17.3 to 20 J. A lot of M23C6 carbides precipitated from martensite matrix, at the same time along the boundaries of martensite lathes which leading to the decrease of impact toughness when tempered at 500 to 540 ℃. The MaC precipitants also existed in the martensite matrix of test steel after tempered at 500 ℃, and the mean size of M3 C precipitates is bigger than that of M23 C6 precipitates.展开更多
To investigate the effect of high temperature ageing on the microstructure and mechanical properties of S31042steel,solid solution treatment at 700℃ was carried out for various time from 10to 6 000h.Experimental resu...To investigate the effect of high temperature ageing on the microstructure and mechanical properties of S31042steel,solid solution treatment at 700℃ was carried out for various time from 10to 6 000h.Experimental results showed that the change of mechanical properties is closely related to the amount of precipitated phases.During ageing from 10to 300h,precipitation in the tested steel increases rapidly,and correspondingly,the high temperature yield strength and room temperature hardness of tested steel increase rapidly.Meanwhile,the thickness of the secondary phase on grain boundaries widens sharply and the room temperature Charpy impact absorb energy decreases.Ageing beyond 300h,the precipitation in the steel increases gradually and the precipitates coarsen to a certain extent.The high temperature yield strength of the steel keeps stable,and the room temperature Charpy impact energy and hardness decrease slowly.Ageing beyond 3 000h,the mechanical properties of the steel tend to be stable.The main precipitates are M23C6,NbCrN and NbC in the tested steel.展开更多
The effects of different aging processes on the microstructure and mechanical properties of a novel Al-Cu-Li alloy have been investigated by X-ray diffraction, scanning electron microscopy and transmission electron mi...The effects of different aging processes on the microstructure and mechanical properties of a novel Al-Cu-Li alloy have been investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the tensile properties of a novel Al-Cu-Li alloy are sensitive to aging processes, which correspond to different microstructures. σ（Al_5Cu_6Mg_2） and T_1（Al_2CuLi） phases are the major precipitates for the alloy in T6 aging condition（165 ℃/60 h）. After duplex aging condition（150 ℃/24 h ＋ 180 ℃/12 h）, σ, θ＇（Al_2Cu） and T_1 phases are detected. Only the T_1 phases can be found in the T8 state alloy（6% pre-strain＋135 ℃/60 h）. The failure modes of alloy in T6 and duplex aging conditions are dimple-intergranular fracture, while typical quasi-cleavage fracture in T8 condition.展开更多
Microstructure evolution and the changes in mechanical properties of HR3 Csteel during long-term aging at650,700 and 750℃ were investigated.The precipitated phases of the aging steel included M23C6 carbides,Z-phase a...Microstructure evolution and the changes in mechanical properties of HR3 Csteel during long-term aging at650,700 and 750℃ were investigated.The precipitated phases of the aging steel included M23C6 carbides,Z-phase and a trace amount of Nb（C,N）.The M23C6 carbides were distributed mainly at the grain boundary,while Z-phase was mainly inside the grains.Amounts of both M23C6 carbides and Z-phase during the aging process increased with increasing aging period and temperature.Coarsening of M23C6 carbides was influenced significantly by aging time and temperature,while the size of the Z-phase was relatively less affected by the aging time and temperature,which had a steady strengthening effect.Coarsening of the M23C6 carbides was the main reason for the decline in high temperature yield strength during long-term aging at 750℃.The M23C6 carbides were linked into a continuous chain along the grain boundary which accounted for the decrease of toughness during aging.展开更多
Vacuum brazing was successfully used to join Ti-22Al-25Nb alloy using Ti-Ni-Nb brazing alloys prepared by arc-melting. The influence of Nb content in the Ti-Ni-Nb brazing alloys on the interfacial microstructure and m...Vacuum brazing was successfully used to join Ti-22Al-25Nb alloy using Ti-Ni-Nb brazing alloys prepared by arc-melting. The influence of Nb content in the Ti-Ni-Nb brazing alloys on the interfacial microstructure and mechanical properties of the brazed joints was investigated. The results showed that the interfacial microstructure of brazed joint consisted of B2, O, ？3, and Ti2 Ni phase, while the width of brazing seams varied at different Nb contents. The room temperature shear strength reached359 MPa when the joints were brazed with eutectic Ti40Ni40Nb20 alloy at 1180？C for 20 min, and it was321, 308 and 256 MPa at 500, 650 and 800？C, respectively. Cracks primarily initiated and propagated in ？3compounds, and partially traversed B2＋O region. Moreover, the fracture surface displayed typical ductile dimples when cracks propagated through B2＋O region, which was favorable for the mechanical properties of the brazed joint.展开更多
In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was inve...In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was investigated. The results showed that the microstructure including the grain size, the degree of dynamic recrystallization, the misorientation angle distribution and the precipitation phase containing its size, type and content exhibited a gradient distribution along the thickness direction. The testing results of mechanical properties of the slices showed that the nugget was gradually weakened along the depth from the top to the bottom. The maximum ultimate tensile strength, yield strength and elongation of the slice in the nugget top-middle are obtained, which are 415 MPa, 255 MPa and 8.1%, respectively.展开更多
Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM,X-ray diffraction（XRD）,EPMA,scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）...Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM,X-ray diffraction（XRD）,EPMA,scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）.The results showed that the dendrites sizes of α phase were decreased by the Nd addition.When the amount of addition Nd was 1.6 wt.%,the alloy with the smallest α phase was obtained.The refining mechanism mainly owed to the increasing constitutional supercooling at the solidification front.Furthermore,the compound Al 2 Nd generated by the reaction of Al and Nd,which distributed at the phase boundary and inside β phase,could also restrain the growth of α phase.Nd could improve the tensile strength and elongation of Mg-8Li-3Al alloy,however,excessive Al 2 Nd might also become crack source and decrease the elongation.展开更多
Effect of the addition of trace HA particles into Mg-2Zn-0.5Sr on microstructure, mechanical properties, and bio-corrosion behavior was investigated in comparison with pure Mg. Microstructures of the Mg-2Zn-0.5Sr-xHA ...Effect of the addition of trace HA particles into Mg-2Zn-0.5Sr on microstructure, mechanical properties, and bio-corrosion behavior was investigated in comparison with pure Mg. Microstructures of the Mg-2Zn-0.5Sr-xHA composites （x= 0, 0.1 and 0.3 wt%） were characterized by optical microscopy （OM）, scanning electron microscopy （SEM） equipped with energy dispersion spectroscopy （EDS） and X-ray diffraction （XRD）. Results of tensile tests at room temperature show that yield strength （YS） of Mg- 2Zn-0.5Sr/HA composites increases significantly, but the ultimate tensile strength （UTS） and elongation decrease with the addition of HA particles from 0 up to 0.3 wt%. Bio-corrosion behavior was investigated by immersion tests and electrochemical tests. Electrochemical tests show that corrosion potential （Ecorr） of Mg-2Zn-0.5Sr/HA composites significantly shifts toward nobler direction from -1724 to -1660 mVscE and the corrosion current density decreases from 479.8 to 280.8 p.Acm^-2 with the addition of HA particles. Immersion tests show that average corrosion rate of Mg-2Zn-0.BSr/HA composites decreases from 11.7 to 9.1 mm/year with the addition of HA particles from 0 wt% up to 0.3 wt%. Both microstructure and mechanical properties can be attributed to grain refinement and mechanical bonding of HA particles with second phases and α-Mg matrix. Bio-corrosion behavior can be attributed to grain refinement and the formation of a stable and dense CaHPO4 protective film due to the adsorption of Ca^2＋ on HA particles. Our analysis shows that the Mg-2Zn-0.5Sr/0.3HA with good strength and corrosion resistance can be a good material candidate for biomedical applications.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
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
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.
基金financially supported by the National Natural Science Foundation of China (No. 50825402)the National Basic Research Program of China (No. 2011CB610405)+2 种基金Guangxi Natural Science Foundation (No. 2013GXNSFBA019251)Guangxi University of Science and Technology Research Projects (No. 2013YB071)Guangxi University for Nationalities Research Projects (No. 2011QD021)
文摘By introducing Cu, AlCoCrFeNiCux （x values in molar ratio, x = 0, 0.1, 0.5, 1.0, 1.5, 2.0, and 2.5） alloys were designed and prepared. The effects of Cu on microstructure and properties of Al Co Cr Fe Ni alloy were investigated. The introduction of Cu results in the formation of Cu-rich FCC solid solution phase when Cu content is low.There are two FCC solid solution phases, i.e., Cu-rich FCC solid solution phase and phase transformation-induced FCC solid solution phase, when the Cu content is more than 1.0. Both the yield stress and plastic strain of alloy show a turning point when the Cu content is 0.5. Among the seven alloys, Cu0.5 alloy exhibits the largest yield stress of 1187 MPa and the lowest plastic strain of 16.01 %.
基金financial support by the National Key Technologies R&D Program of China (No. 2011BAE25B03)
文摘In the present study, Cu-modified pipeline steels were fabricated to mitigate MIC by the antimicrobial ability of Cu element. The microstructure, mechanical properties and the antimircobial performance of the Cu-modified steel were systematically investigated. The Cu-modified steels showed good antimicrobial performance with remarkable strength enhancement by nanoscale Cu-rich precipitates and good impact toughness without changing the original base microstructures after the optimal aging treatment of 500 °C/1 h.
文摘Friction stir welding is a new and innovative welding method used to fuse materials. In this welding method, the heat generated by friction and plastic flow causes significant changes in the microstructure of the material, which leads to local changes in the mechanical properties of the weld. In this study, the effects of various welding parameters such as the rotational and traverse speeds of the tool on the microstructural and mechanical properties of copper plates were investigated; additionally, Charpy tests were performed on copper plates for the first time. Also, the effect of the number of welding passes on the aforementioned properties has not been investigated in previous studies. The results indicated that better welds with superior properties are produced when less heat is transferred to the workpiece during the welding process. It was also found that although the properties of the stir zone improved with an increasing number of weld passes, the properties of its weakest zone, the heat-affected zone, deteriorated.
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.
文摘Electron beam welding （EBW） was applied to a 10-mm-thick plate cut from Ti-6246 compressor disk. The microstructural characteristics, microhardness and room temperature tensile properties were investigated. Microstructure observations indicated that there existed plenty of thin needle-like α platelets studding in the matrix of the columnar β grains in the as-welded fusion zone （FZ）. Post-weld heat treat- ment （PWHT） led to the precipitation of small secondary α platelets in the β matrix in heat affected zone and FZ. The thickness and the density of α platelets increased as the temperature of PWHT increased from 545 to 645 C. The microhardness across the Ti-6246 EBWjoint exhibited a nonuniform distribution. The hardness increased with the decrease of distance to the weld center, and reached the maximum of 467 HV in FZ when PWHT was carried out at 595 C. All the weldments tested with tension were fractured at the base material （BM） and exhibited a ductile fracture mode. The major deformation barrier in BM was the platelet α/β interfaces, however, the major deformation barrier in FZ was found to be β grain boundaries and secondary α/β interfaces. The BM with thicker platelet α phases had lower strength than the other two zones in the joint, and the BM deformed first and led to fracture in this zone.
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.
基金financially supported by the National Natural Science Foundation of China(No.51374048)the Fundamental Research Funds for the Central Universities(No.DUT16RC(3)009)
文摘The microstructure and mechanical properties of pulse metal inert-gas （MIG） welded dissimilar joints between 4 mm thick wrought 6061-T6 and cast A356-T6 aluminum alloy plates were investigated. The tensile strength of the joints reached 235 MPa, which is 83% of that of 6061 aluminum alloy, and then decreased with the increase of travel speed while keeping other welding parameters constant. The microstructure, composition and fractography of joints were examined by the optical microscopy （OM）, scanning electron microscopy （SEM） and electron probe microanalysis （EPMA）. Grain boundary liquation and segregation occurred in the partially melted zone （PMZ） on 6061 aluminum alloy side, and brittle Fe-rich phases were observed in partially melted zone on A356 aluminum alloy side. The minimum microhardness appeared in heat-affected zone （HAZ） near A356 aluminum alloy substrate. The samples during tensile test failed mainly in PMZ and HAZ on A356 aluminum alloy side through mixed fracture mode with quasi cleavage and dimples on fracture surface.
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.201703D421039)
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 Natural Science Foundation of China (51671063)Research Fund for the Doctoral Program of Higher Education (20132304110006)+1 种基金the Fundamental Research Funds for the Central Universities (HEUCF20161016)Harbin City Application Technology Research and Development Project (2015AE4AE005, 2015RQXXJ001, 2016AB2AG013)
文摘Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated. Results show that, during ARB process, the evolution of deformation mechanism oft Mg-5Li-1Al alloy is as follows： twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization （DRX）. The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.
文摘Martensitic stainless steel containing Cr of 12% to 18%（mass percent） are common utilized in quenching and tempering processes for knife and cutlery steel. The properties obtained in these materials are significantly influ- enced by matrix composition after heat treatment, especially as Cr and C content. Comprehensive considered the hardness and corrosion resistance, a new type martensitic stainless steel 6Crl5MoV has been developed. The effect of heat treatment processes on microstructure and mechanical properties of 6Crl5MoV martensitic stainless steel is emphatically researched. Thermo-Calc software has been carried out to thermodynamic calculation; OM, SEM and TEM have been carried out to microstructure observation; hardness and impact toughness test have been carried out to evaluate the mechanical properties. Results show that the equilibrium carbide in 6Cr15MoV steel is M23 C6 car- bide, and the M23 C6 carbides finely distributed in annealed microstructure. 6Crl5MoV martensitic stainless steel has a wider quenching temperature range, the hardness value of steel 6Cr15MoV can reach to HRC 60.8 to HRC 61.6 when quenched at 1 060 to 1 100 ℃. Finely distributed carbides will exist in quenched microstructure, and effectively inhabit the growth of austenite grain. With the increasing of quenching temperature, the volume fraction of undis- solved carbides will decrease. The excellent comprehensive mechanical properties can be obtained by quenched at 1 060 to 1 100℃ with tempered at 100 to 150 ℃, and it is mainly due to the high carbon martensite and fine grain size. At these temperature ranges, the hardness will retain about HRC 59.2 to HRC 61.6 and the Charpy U-notch impact toughness will retain about 17.3 to 20 J. A lot of M23C6 carbides precipitated from martensite matrix, at the same time along the boundaries of martensite lathes which leading to the decrease of impact toughness when tempered at 500 to 540 ℃. The MaC precipitants also existed in the martensite matrix of test steel after tempered at 500 ℃, and the mean size of M3 C precipitates is bigger than that of M23 C6 precipitates.
基金Sponsored by National Science and Technology Support Plan of China(2007BAE51B02)
文摘To investigate the effect of high temperature ageing on the microstructure and mechanical properties of S31042steel,solid solution treatment at 700℃ was carried out for various time from 10to 6 000h.Experimental results showed that the change of mechanical properties is closely related to the amount of precipitated phases.During ageing from 10to 300h,precipitation in the tested steel increases rapidly,and correspondingly,the high temperature yield strength and room temperature hardness of tested steel increase rapidly.Meanwhile,the thickness of the secondary phase on grain boundaries widens sharply and the room temperature Charpy impact absorb energy decreases.Ageing beyond 300h,the precipitation in the steel increases gradually and the precipitates coarsen to a certain extent.The high temperature yield strength of the steel keeps stable,and the room temperature Charpy impact energy and hardness decrease slowly.Ageing beyond 3 000h,the mechanical properties of the steel tend to be stable.The main precipitates are M23C6,NbCrN and NbC in the tested steel.
基金the National High Technology Research and Development Program of China (Grant No.2013AA032401)
文摘The effects of different aging processes on the microstructure and mechanical properties of a novel Al-Cu-Li alloy have been investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the tensile properties of a novel Al-Cu-Li alloy are sensitive to aging processes, which correspond to different microstructures. σ（Al_5Cu_6Mg_2） and T_1（Al_2CuLi） phases are the major precipitates for the alloy in T6 aging condition（165 ℃/60 h）. After duplex aging condition（150 ℃/24 h ＋ 180 ℃/12 h）, σ, θ＇（Al_2Cu） and T_1 phases are detected. Only the T_1 phases can be found in the T8 state alloy（6% pre-strain＋135 ℃/60 h）. The failure modes of alloy in T6 and duplex aging conditions are dimple-intergranular fracture, while typical quasi-cleavage fracture in T8 condition.
基金Item Sponsored by National High-Tech Research and Development Program(863Program)of China(2012AA03A501)International Science and Technology Cooperation Program of China(2012DFG51670)
文摘Microstructure evolution and the changes in mechanical properties of HR3 Csteel during long-term aging at650,700 and 750℃ were investigated.The precipitated phases of the aging steel included M23C6 carbides,Z-phase and a trace amount of Nb（C,N）.The M23C6 carbides were distributed mainly at the grain boundary,while Z-phase was mainly inside the grains.Amounts of both M23C6 carbides and Z-phase during the aging process increased with increasing aging period and temperature.Coarsening of M23C6 carbides was influenced significantly by aging time and temperature,while the size of the Z-phase was relatively less affected by the aging time and temperature,which had a steady strengthening effect.Coarsening of the M23C6 carbides was the main reason for the decline in high temperature yield strength during long-term aging at 750℃.The M23C6 carbides were linked into a continuous chain along the grain boundary which accounted for the decrease of toughness during aging.
基金supported by the National Natural Science Foundation of China (Grant No. 51574177)the China Natural Founds for Distinguished Young Scientists (Grant No. 51325401)the National High Technology Research and Development Program of China (“863” Program, Granted No. 2015AA042504)
文摘Vacuum brazing was successfully used to join Ti-22Al-25Nb alloy using Ti-Ni-Nb brazing alloys prepared by arc-melting. The influence of Nb content in the Ti-Ni-Nb brazing alloys on the interfacial microstructure and mechanical properties of the brazed joints was investigated. The results showed that the interfacial microstructure of brazed joint consisted of B2, O, ？3, and Ti2 Ni phase, while the width of brazing seams varied at different Nb contents. The room temperature shear strength reached359 MPa when the joints were brazed with eutectic Ti40Ni40Nb20 alloy at 1180？C for 20 min, and it was321, 308 and 256 MPa at 500, 650 and 800？C, respectively. Cracks primarily initiated and propagated in ？3compounds, and partially traversed B2＋O region. Moreover, the fracture surface displayed typical ductile dimples when cracks propagated through B2＋O region, which was favorable for the mechanical properties of the brazed joint.
基金supported by the National Natural Science Foundation of China(NSFC)(No.51265043 and 51265042)the Special Construction Project of Advanced Science and Technology Innovation Team of Jiangxi Province(No.20171BCB24007)
文摘In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was investigated. The results showed that the microstructure including the grain size, the degree of dynamic recrystallization, the misorientation angle distribution and the precipitation phase containing its size, type and content exhibited a gradient distribution along the thickness direction. The testing results of mechanical properties of the slices showed that the nugget was gradually weakened along the depth from the top to the bottom. The maximum ultimate tensile strength, yield strength and elongation of the slice in the nugget top-middle are obtained, which are 415 MPa, 255 MPa and 8.1%, respectively.
基金supported by the National High Technology Research and Development Program ("863" Program) of China (2009AA03Z525)the Program of New Century Excellent Talents of the Ministry of Education of China (NCET-08-0080)+1 种基金the Science and Technology Fund of Dalian City (2009J21DW003)the Fundamental Research Funds for the Central Universities (DUT11ZD115)
文摘Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM,X-ray diffraction（XRD）,EPMA,scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）.The results showed that the dendrites sizes of α phase were decreased by the Nd addition.When the amount of addition Nd was 1.6 wt.%,the alloy with the smallest α phase was obtained.The refining mechanism mainly owed to the increasing constitutional supercooling at the solidification front.Furthermore,the compound Al 2 Nd generated by the reaction of Al and Nd,which distributed at the phase boundary and inside β phase,could also restrain the growth of α phase.Nd could improve the tensile strength and elongation of Mg-8Li-3Al alloy,however,excessive Al 2 Nd might also become crack source and decrease the elongation.
基金financial support by the National Key Project of Research and Development Plan (No. 2016YFB0700303)
文摘Effect of the addition of trace HA particles into Mg-2Zn-0.5Sr on microstructure, mechanical properties, and bio-corrosion behavior was investigated in comparison with pure Mg. Microstructures of the Mg-2Zn-0.5Sr-xHA composites （x= 0, 0.1 and 0.3 wt%） were characterized by optical microscopy （OM）, scanning electron microscopy （SEM） equipped with energy dispersion spectroscopy （EDS） and X-ray diffraction （XRD）. Results of tensile tests at room temperature show that yield strength （YS） of Mg- 2Zn-0.5Sr/HA composites increases significantly, but the ultimate tensile strength （UTS） and elongation decrease with the addition of HA particles from 0 up to 0.3 wt%. Bio-corrosion behavior was investigated by immersion tests and electrochemical tests. Electrochemical tests show that corrosion potential （Ecorr） of Mg-2Zn-0.5Sr/HA composites significantly shifts toward nobler direction from -1724 to -1660 mVscE and the corrosion current density decreases from 479.8 to 280.8 p.Acm^-2 with the addition of HA particles. Immersion tests show that average corrosion rate of Mg-2Zn-0.BSr/HA composites decreases from 11.7 to 9.1 mm/year with the addition of HA particles from 0 wt% up to 0.3 wt%. Both microstructure and mechanical properties can be attributed to grain refinement and mechanical bonding of HA particles with second phases and α-Mg matrix. Bio-corrosion behavior can be attributed to grain refinement and the formation of a stable and dense CaHPO4 protective film due to the adsorption of Ca^2＋ on HA particles. Our analysis shows that the Mg-2Zn-0.5Sr/0.3HA with good strength and corrosion resistance can be a good material candidate for biomedical applications.
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.
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
