B4C-TiB2-Al composites were fabricated by infiltrating aluminum into porous B4C-TiB2 preforms in vacuum. The microstucture and mechanical properties of the B4C-TiB2-Al composites were investigated. The hardness decrea...B4C-TiB2-Al composites were fabricated by infiltrating aluminum into porous B4C-TiB2 preforms in vacuum. The microstucture and mechanical properties of the B4C-TiB2-Al composites were investigated. The hardness decreased, the flexural strength increased, and the fracture toughness first increased and then decreased slightly with an increase in TiB2 content. The BaC-TiB2-Al composite with 40wt.% TiB2 showed the optimized properties. The infiltrated aluminum addition was the leading reason for the fracture toughness improvement of the composites. The tear ridges and dimples on the fracture surface of the composites increased gradually with the increase of infdtrated alu- minum content showing inter/transgranular fracture mode. The relationships between the microstructures and the mechanical properties of the composites were discussed.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
ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-syn...ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-synthesized composites was studied.Mechanical properties of the composites were reported.A partial displacement of Nb atoms in NbC by Zr atoms from Zr-Cu melt occurs during the reaction between Zr-Cu melt and porous NbC preform.The formation of a core-shell structure suggests the reaction is mainly a dissolutionprecipitation type.NbC dissolves into Zr-Cu melt,from which the(Nb,Zr)C_(z)phase precipitates and grows.With increasing Zr content in the Zr-Cu infiltrator,the reaction is enhanced and the infiltration is easily chocked.ZrC_(x)-NbC_(y)-Cu composite is synthesized using Zr_(14)Cu_(51)infiltrator.The flexural strength and fracture toughness of ZrC_(x)-NbC_(y)-Cu composite reach 637 MPa and 12.7 MPa·m^(1/2),respectively.And the improved toughness is probably attributed to residual Cu phase and plate-like Nb_(x)C_(y)phases.展开更多
Cu47Ti33Zr11Ni6Sn2Si1-based bulk metallic glass matrix composites reinforced with tungsten wires were fabricated by infiltration process at different temperatures （850, 900, 950 and 1000 °C） and time （10, 20 a...Cu47Ti33Zr11Ni6Sn2Si1-based bulk metallic glass matrix composites reinforced with tungsten wires were fabricated by infiltration process at different temperatures （850, 900, 950 and 1000 °C） and time （10, 20 and 30 min） in a quartz or a steel tube. The mechanical tests were carried out by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The results show that the maximum strength and total strain of the composite are 1778 MPa and 2.8% fabricated in steel tube at 900 °C for 10 min, and 1582 MPa and 3.6% fabricated in quartz tube at 850 °C for 10 min, respectively.展开更多
A novel two step mixing method including injection of particles into the melt by inert gas and stirring was used to prepare aluminum matrix composites （AMCs） reinforced with Al2O3 particles. Different mass fractions...A novel two step mixing method including injection of particles into the melt by inert gas and stirring was used to prepare aluminum matrix composites （AMCs） reinforced with Al2O3 particles. Different mass fractions of micro alumina particles were injected into the melt under stirring speed of 300 r/min. Then the samples were extruded with ratios of 1.77 or 1.56. The microstructure observation showed that application of the injection and extrusion processes led to a uniform distribution of particles in the matrix. The density measurements showed that the porosity in the composites increased with increasing the mass fraction of Al2O3 and stirring speed and decreased by extrusion process. Hardness, yield and ultimate tensile strengths of the extruded composites increased with increasing the particle mass fraction to 7%, while for the composites without extrusion they increased with particle mass fraction to 5%.展开更多
Silicon oxycarbide composites reinforced by three-dimensional braided carbon fiber （3D-B Cf/Si-O-C） were fabricated via precursor infiltration and pyrolysis of polysiloxane, and the effects of processing variables o...Silicon oxycarbide composites reinforced by three-dimensional braided carbon fiber （3D-B Cf/Si-O-C） were fabricated via precursor infiltration and pyrolysis of polysiloxane, and the effects of processing variables on mechanical properties and microstructures of 3D-B Cf/Si-O-C composites were investigated. It is found that the mechanical properties and densities of 3D-B Cf/Si-O-C composites can be increased if the first pyrolysis cycle is assisted by hot-pressing. Pyrolysis temperature has great effects on mechanical properties and microstructures of 3D-B Cf/Si-O-C composites. The composite, which is hot-pressed at 1 600 ℃ for 5 min with pressure of 10 MPa in the first pyrolysis cycle, exhibits high mechanical properties: bending strength 502 MPa and fracture toughness 23.7 MPa·m1/2. The high mechanical properties are mainly attributed to desirable interfacial structure and high density.展开更多
A novel method of screw extrusion was used for producing a bimetal composite Al/Mg from granules containing aluminium alloy 6063 （AA6063） and commercial pure magnesium. Up to 12.5%（mass fraction） pure magnesium wa...A novel method of screw extrusion was used for producing a bimetal composite Al/Mg from granules containing aluminium alloy 6063 （AA6063） and commercial pure magnesium. Up to 12.5%（mass fraction） pure magnesium was added to the aluminium alloy. In general, the material consisted of a fine grained microstructure. In addition to the phases originating from the input materials, intermetallic phases were observed as islands consisting of the Al2Mg3 phase surrounded byγ-Mg17Al12, throughout the microstructure. The mechanical properties of the extruded material showed a gradual increase in strength with increasing the addition of Mg. The highest registered UTS, well above 350 MPa, was observed for the material containing 10%Mg. Examinations of the fracture surfaces indicated that increasing the magnesium content led to a higher degree of brittle fracture and a gradual change of the fracture micro-mechanisms. The optimization of the post-extrusion processing conditions is still ongoing.展开更多
The effects of hot extrusion on the interfacial microstructures and tensile properties of 15 vol.SiCp/2009Al composites fabricated at different hot pressing temperatures were investigated.After hot extrusion,the relat...The effects of hot extrusion on the interfacial microstructures and tensile properties of 15 vol.SiCp/2009Al composites fabricated at different hot pressing temperatures were investigated.After hot extrusion,the relative density of the composites increased,the SiC particle distribution became more uniform,and the SiC particles tended to align along the extrusion direction.Furthermore,the interface bonding was improved after hot extrusion;however,the extrusion exerted no obvious effect on the interfacial reaction products formed during sintering process.Tensile tests indicated that the mechanical properties of the composites were improved significantly after extrusion.Fractography revealed that the fracture mechanism of the extruded composites fabricated at the hot pressing temperatures below 540℃ was mainly the interfacial debonding.For the extruded composites fabricated at 560-600℃,the fracture was the matrix ductile fracture and the SiC particle fracture.When the composites were hot pressed at or above 620℃,after extrusion,the fracture mechanism of the composites was the matrix ductile fracture,the interface cracking and the SiC particle fracture.展开更多
Tubes of 3.5 vol,% TiB whiskers reinforced Ti6Al4V matrix composites （TiBw/Ti6Al4V） were successfully fabricated by a two-step hot-hydrostatic extrusion process： （3 extrusion at 1100 ℃ and subsequent near-β extr...Tubes of 3.5 vol,% TiB whiskers reinforced Ti6Al4V matrix composites （TiBw/Ti6Al4V） were successfully fabricated by a two-step hot-hydrostatic extrusion process： （3 extrusion at 1100 ℃ and subsequent near-β extrusion at 950℃. The dimensions of tubes were about 7 mm in diameter and 2 mm in thickness. A refined basket-weave structure in Ti6Al4V matrix was achieved at ambient temperature after the extrusion process. Besides, the original network structure formed by TiB whiskers synthesized was broken, while the TiB whiskers were preferentially aligned in the extruding direction. Meanwhile, a fibrous texture was evolved finally, resulting from partial dynamic recrystallization during the β extrusion and the involvement of α phase during the near-β extrusion. The tensile and compressive tests results showed that both the strength and ductility of the tubes were significantly improved. In particular, the tubes exhibited good mechanical properties at elevated temperatures.展开更多
In this study,the recycled short carbon fiber(CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion.The objective was to investigate the impact of CF content(...In this study,the recycled short carbon fiber(CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion.The objective was to investigate the impact of CF content(2.5 and 5.0 wt.%)and fiber length(100 and 500μm)on the microstructure,mechanical properties,and creep behavior of AZ91 alloy matrix.The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy.In comparison to the unreinforced AZ91 alloy,the composites with 2.5 wt.%CF exhibited an increase in hardness by 16-20%and yield strength by 5-15%,depending on the fiber length,while experiencing a reduction in ductility.When the reinforcement content was increased from 2.5 to 5.0 wt.%,strength values exhibited fluctuations and decline,accompanied by decreased ductility.These divergent outcomes were discussed in relation to fiber length,clustering tendency due to higher reinforcement content,and the presence of interfacial products with micro-cracks at the CF-matrix interface.Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy,suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 50372010 and 50902018)the Research Fund for the Doctoral Program of Higher Education (No. 20060145028)the Program for Changjiang Scholars and Innovative Research Team in Universities of China (IRT0713)
文摘B4C-TiB2-Al composites were fabricated by infiltrating aluminum into porous B4C-TiB2 preforms in vacuum. The microstucture and mechanical properties of the B4C-TiB2-Al composites were investigated. The hardness decreased, the flexural strength increased, and the fracture toughness first increased and then decreased slightly with an increase in TiB2 content. The BaC-TiB2-Al composite with 40wt.% TiB2 showed the optimized properties. The infiltrated aluminum addition was the leading reason for the fracture toughness improvement of the composites. The tear ridges and dimples on the fracture surface of the composites increased gradually with the increase of infdtrated alu- minum content showing inter/transgranular fracture mode. The relationships between the microstructures and the mechanical properties of the composites were discussed.
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Funded by the National Natural Science Foundation of China(Nos.52002003 and 52002098)Natural Science Foundation of Anhui Province,China(No.2008085QE196)Open Fund of Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials(Anhui University of Technology),Ministry of Education(No.GFST2020KF09)。
文摘ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-synthesized composites was studied.Mechanical properties of the composites were reported.A partial displacement of Nb atoms in NbC by Zr atoms from Zr-Cu melt occurs during the reaction between Zr-Cu melt and porous NbC preform.The formation of a core-shell structure suggests the reaction is mainly a dissolutionprecipitation type.NbC dissolves into Zr-Cu melt,from which the(Nb,Zr)C_(z)phase precipitates and grows.With increasing Zr content in the Zr-Cu infiltrator,the reaction is enhanced and the infiltration is easily chocked.ZrC_(x)-NbC_(y)-Cu composite is synthesized using Zr_(14)Cu_(51)infiltrator.The flexural strength and fracture toughness of ZrC_(x)-NbC_(y)-Cu composite reach 637 MPa and 12.7 MPa·m^(1/2),respectively.And the improved toughness is probably attributed to residual Cu phase and plate-like Nb_(x)C_(y)phases.
文摘Cu47Ti33Zr11Ni6Sn2Si1-based bulk metallic glass matrix composites reinforced with tungsten wires were fabricated by infiltration process at different temperatures （850, 900, 950 and 1000 °C） and time （10, 20 and 30 min） in a quartz or a steel tube. The mechanical tests were carried out by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The results show that the maximum strength and total strain of the composite are 1778 MPa and 2.8% fabricated in steel tube at 900 °C for 10 min, and 1582 MPa and 3.6% fabricated in quartz tube at 850 °C for 10 min, respectively.
基金Research Deputy of Ferdowsi University of Mashhad for supporting this project
文摘A novel two step mixing method including injection of particles into the melt by inert gas and stirring was used to prepare aluminum matrix composites （AMCs） reinforced with Al2O3 particles. Different mass fractions of micro alumina particles were injected into the melt under stirring speed of 300 r/min. Then the samples were extruded with ratios of 1.77 or 1.56. The microstructure observation showed that application of the injection and extrusion processes led to a uniform distribution of particles in the matrix. The density measurements showed that the porosity in the composites increased with increasing the mass fraction of Al2O3 and stirring speed and decreased by extrusion process. Hardness, yield and ultimate tensile strengths of the extruded composites increased with increasing the particle mass fraction to 7%, while for the composites without extrusion they increased with particle mass fraction to 5%.
文摘Silicon oxycarbide composites reinforced by three-dimensional braided carbon fiber （3D-B Cf/Si-O-C） were fabricated via precursor infiltration and pyrolysis of polysiloxane, and the effects of processing variables on mechanical properties and microstructures of 3D-B Cf/Si-O-C composites were investigated. It is found that the mechanical properties and densities of 3D-B Cf/Si-O-C composites can be increased if the first pyrolysis cycle is assisted by hot-pressing. Pyrolysis temperature has great effects on mechanical properties and microstructures of 3D-B Cf/Si-O-C composites. The composite, which is hot-pressed at 1 600 ℃ for 5 min with pressure of 10 MPa in the first pyrolysis cycle, exhibits high mechanical properties: bending strength 502 MPa and fracture toughness 23.7 MPa·m1/2. The high mechanical properties are mainly attributed to desirable interfacial structure and high density.
文摘A novel method of screw extrusion was used for producing a bimetal composite Al/Mg from granules containing aluminium alloy 6063 （AA6063） and commercial pure magnesium. Up to 12.5%（mass fraction） pure magnesium was added to the aluminium alloy. In general, the material consisted of a fine grained microstructure. In addition to the phases originating from the input materials, intermetallic phases were observed as islands consisting of the Al2Mg3 phase surrounded byγ-Mg17Al12, throughout the microstructure. The mechanical properties of the extruded material showed a gradual increase in strength with increasing the addition of Mg. The highest registered UTS, well above 350 MPa, was observed for the material containing 10%Mg. Examinations of the fracture surfaces indicated that increasing the magnesium content led to a higher degree of brittle fracture and a gradual change of the fracture micro-mechanisms. The optimization of the post-extrusion processing conditions is still ongoing.
文摘The effects of hot extrusion on the interfacial microstructures and tensile properties of 15 vol.SiCp/2009Al composites fabricated at different hot pressing temperatures were investigated.After hot extrusion,the relative density of the composites increased,the SiC particle distribution became more uniform,and the SiC particles tended to align along the extrusion direction.Furthermore,the interface bonding was improved after hot extrusion;however,the extrusion exerted no obvious effect on the interfacial reaction products formed during sintering process.Tensile tests indicated that the mechanical properties of the composites were improved significantly after extrusion.Fractography revealed that the fracture mechanism of the extruded composites fabricated at the hot pressing temperatures below 540℃ was mainly the interfacial debonding.For the extruded composites fabricated at 560-600℃,the fracture was the matrix ductile fracture and the SiC particle fracture.When the composites were hot pressed at or above 620℃,after extrusion,the fracture mechanism of the composites was the matrix ductile fracture,the interface cracking and the SiC particle fracture.
基金financially supported by the National HighTech Research and Development Program of China("863 Program",No.2013AA031202)
文摘Tubes of 3.5 vol,% TiB whiskers reinforced Ti6Al4V matrix composites （TiBw/Ti6Al4V） were successfully fabricated by a two-step hot-hydrostatic extrusion process： （3 extrusion at 1100 ℃ and subsequent near-β extrusion at 950℃. The dimensions of tubes were about 7 mm in diameter and 2 mm in thickness. A refined basket-weave structure in Ti6Al4V matrix was achieved at ambient temperature after the extrusion process. Besides, the original network structure formed by TiB whiskers synthesized was broken, while the TiB whiskers were preferentially aligned in the extruding direction. Meanwhile, a fibrous texture was evolved finally, resulting from partial dynamic recrystallization during the β extrusion and the involvement of α phase during the near-β extrusion. The tensile and compressive tests results showed that both the strength and ductility of the tubes were significantly improved. In particular, the tubes exhibited good mechanical properties at elevated temperatures.
基金the German Academic Exchange Service (DAAD) for providing a scholarship to Dr. Sinan Kandemir during his tenure at Helmholtz-Zentrum Hereon (HZH)
文摘In this study,the recycled short carbon fiber(CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion.The objective was to investigate the impact of CF content(2.5 and 5.0 wt.%)and fiber length(100 and 500μm)on the microstructure,mechanical properties,and creep behavior of AZ91 alloy matrix.The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy.In comparison to the unreinforced AZ91 alloy,the composites with 2.5 wt.%CF exhibited an increase in hardness by 16-20%and yield strength by 5-15%,depending on the fiber length,while experiencing a reduction in ductility.When the reinforcement content was increased from 2.5 to 5.0 wt.%,strength values exhibited fluctuations and decline,accompanied by decreased ductility.These divergent outcomes were discussed in relation to fiber length,clustering tendency due to higher reinforcement content,and the presence of interfacial products with micro-cracks at the CF-matrix interface.Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy,suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep.
