SiO2–BN ceramic and Ti plate were joined by active brazing in vacuum with Ag–Cu–Ti＋BN composite filler.The effect of BN content,brazing temperature and time on the microstructure and mechanical properties of the b...SiO2–BN ceramic and Ti plate were joined by active brazing in vacuum with Ag–Cu–Ti＋BN composite filler.The effect of BN content,brazing temperature and time on the microstructure and mechanical properties of the brazed joints was investigated.The results showed that a continuous Ti N–Ti B2reaction layer formed adjacent to the SiO2–BN ceramic,whose thickness played a key role in the bonding properties.Four Ti–Cu compound layers,Ti2Cu,Ti3Cu4,Ti Cu2and Ti Cu4,were observed to border Ti substrate due to the strong affinity of Ti and Cu compared with Ag.The central part of the joint was composed of Ag matrix,over which some fine-grains distributed.The added BN particles reacted with Ti in the liquid filler to form fine Ti B whiskers and Ti N particles with low coefficients of thermal expansion（CTE）,leading to the reduction of detrimental residual stress in the joint,and thus improving the joint strength.The maximum shear strength of 31 MPa was obtained when 3 wt%BN was added in the composite filler,which was 158%higher than that brazed with single Ag–Cu–Ti filler metal.The morphology and thickness of the reaction layer adjacent to the parent materials changed correspondingly with the increase of BN content,brazing temperature and holding time.Based on the correlation between the microstructural evolution and brazing parameters,the bonding mechanism of SiO2–BN and Ti was discussed.展开更多
Vacuum brazing of SiO2 glass ceramic and TC4 alloy using a commercially available TiZrNiCu foil was investigated. The interfacial microstructure and the fractures were examined with an optical microscope （OM） and an...Vacuum brazing of SiO2 glass ceramic and TC4 alloy using a commercially available TiZrNiCu foil was investigated. The interfacial microstructure and the fractures were examined with an optical microscope （OM） and an S-4700 scanning electron microscope （SEM） equipped with an energy dispersive spectrometer （EDS） and an electron probe X-ray microanalyzer （EPMA）. The structure of joint interface was identified by XRD （JDX-3530M）. Meanwhile, the fracture paths of the joints were comprehensively studied. The results show that processing parameters, especially the brazing temperature, have a significant effect on the microstructure and mechanical properties of joints. The typical interface structure is SiO2/Ti2O＋Zr3Si2＋Ti5Si3/（Ti,Zr）＋Ti2O＋ TiZrNiCu/Ti（s.s）/TiZrNiCu＋Ti（s.s）＋Ti2（Cu,Ni）/TC4 from SiO2 glass ceramic to TC4 alloy side. Based on the mechanical property tests, the joints brazed at 880 ℃ for 5 rain has the maximum shear strength of 23 MPa.展开更多
Porous Y 2SiO 5 ceramic is a promising high-temperature thermal insulator in harsh environment.However,all the published relevant works faced serious problems,such as severe linear shrinkage,low porosity and low stren...Porous Y 2SiO 5 ceramic is a promising high-temperature thermal insulator in harsh environment.However,all the published relevant works faced serious problems,such as severe linear shrinkage,low porosity and low strength.In this study,porous Y 2SiO 5 ceramic with low sintering shrinkage and high porosity was successfully prepared by foam-gelcasting method using gelatin as the gelling agent.The effects of sintering methods,including in situ reaction sintering and direct sintering,and sintering temperatures on the phase composition,microstructure,shrinkage,porosity,and compressive strength of porous Y 2SiO 5were investigated.Compared with samples fabricated by direct sintering,porous Y 2SiO 5 ceramic prepared via in situ reaction sintering method has the merits of the low linear shrinkage of 1.0%-4.7%,low bulk density of 0.79-0.88 g/cm^3,high porosity of 82.1%-80.1%,and high strength of 3.54-8.03 MPa,when the sintering temperatures increase from 1350 to 1550 ℃.Porous Y 2SiO 5 has unique multiple pore structures,especially containing the interconnected small pores in skeleton.The thermal conductivity of porous Y 2SiO 5 is very low,which is 0.228 W/（m·K） for the sample with a porosity of 79.6%.This work reports an optimal processing method of highly porous Y 2SiO 5 with the potential application as high-temperature thermal insulation material.展开更多
基金supported by the National Natural Science Foundation of China (No. 51405332)
文摘SiO2–BN ceramic and Ti plate were joined by active brazing in vacuum with Ag–Cu–Ti＋BN composite filler.The effect of BN content,brazing temperature and time on the microstructure and mechanical properties of the brazed joints was investigated.The results showed that a continuous Ti N–Ti B2reaction layer formed adjacent to the SiO2–BN ceramic,whose thickness played a key role in the bonding properties.Four Ti–Cu compound layers,Ti2Cu,Ti3Cu4,Ti Cu2and Ti Cu4,were observed to border Ti substrate due to the strong affinity of Ti and Cu compared with Ag.The central part of the joint was composed of Ag matrix,over which some fine-grains distributed.The added BN particles reacted with Ti in the liquid filler to form fine Ti B whiskers and Ti N particles with low coefficients of thermal expansion（CTE）,leading to the reduction of detrimental residual stress in the joint,and thus improving the joint strength.The maximum shear strength of 31 MPa was obtained when 3 wt%BN was added in the composite filler,which was 158%higher than that brazed with single Ag–Cu–Ti filler metal.The morphology and thickness of the reaction layer adjacent to the parent materials changed correspondingly with the increase of BN content,brazing temperature and holding time.Based on the correlation between the microstructural evolution and brazing parameters,the bonding mechanism of SiO2–BN and Ti was discussed.
基金Project(50705022) supported by the National Natural Science Foundation of ChinaProject(HIT0804) supported by the Foundation of the National Key Laboratory of Precision Hot Processing of Metals,ChinaProject supported by Program of Excellent Team in Harbin Institute of Technology,China
文摘Vacuum brazing of SiO2 glass ceramic and TC4 alloy using a commercially available TiZrNiCu foil was investigated. The interfacial microstructure and the fractures were examined with an optical microscope （OM） and an S-4700 scanning electron microscope （SEM） equipped with an energy dispersive spectrometer （EDS） and an electron probe X-ray microanalyzer （EPMA）. The structure of joint interface was identified by XRD （JDX-3530M）. Meanwhile, the fracture paths of the joints were comprehensively studied. The results show that processing parameters, especially the brazing temperature, have a significant effect on the microstructure and mechanical properties of joints. The typical interface structure is SiO2/Ti2O＋Zr3Si2＋Ti5Si3/（Ti,Zr）＋Ti2O＋ TiZrNiCu/Ti（s.s）/TiZrNiCu＋Ti（s.s）＋Ti2（Cu,Ni）/TC4 from SiO2 glass ceramic to TC4 alloy side. Based on the mechanical property tests, the joints brazed at 880 ℃ for 5 rain has the maximum shear strength of 23 MPa.
基金supported by the National Natural Science Foundation of China under Grant Nos.51032006 and 51372252
文摘Porous Y 2SiO 5 ceramic is a promising high-temperature thermal insulator in harsh environment.However,all the published relevant works faced serious problems,such as severe linear shrinkage,low porosity and low strength.In this study,porous Y 2SiO 5 ceramic with low sintering shrinkage and high porosity was successfully prepared by foam-gelcasting method using gelatin as the gelling agent.The effects of sintering methods,including in situ reaction sintering and direct sintering,and sintering temperatures on the phase composition,microstructure,shrinkage,porosity,and compressive strength of porous Y 2SiO 5were investigated.Compared with samples fabricated by direct sintering,porous Y 2SiO 5 ceramic prepared via in situ reaction sintering method has the merits of the low linear shrinkage of 1.0%-4.7%,low bulk density of 0.79-0.88 g/cm^3,high porosity of 82.1%-80.1%,and high strength of 3.54-8.03 MPa,when the sintering temperatures increase from 1350 to 1550 ℃.Porous Y 2SiO 5 has unique multiple pore structures,especially containing the interconnected small pores in skeleton.The thermal conductivity of porous Y 2SiO 5 is very low,which is 0.228 W/（m·K） for the sample with a porosity of 79.6%.This work reports an optimal processing method of highly porous Y 2SiO 5 with the potential application as high-temperature thermal insulation material.
