In this paper, an approach to synthesizing carbon nanotubes （ CNTs ） reinforced A1-Si-Cu brazing powder was studied, which was accomplished by in-situ growth of the CNTs on the Al-Si-Cu powder at a relatively low te...In this paper, an approach to synthesizing carbon nanotubes （ CNTs ） reinforced A1-Si-Cu brazing powder was studied, which was accomplished by in-situ growth of the CNTs on the Al-Si-Cu powder at a relatively low temperature by plasma enhanced chemical vapor deposition （ PECVD ）. The synthesis parameters were optimized. The component of brazing powder was analyzed by X-ray diffraction （ XRD ）. The microstracture and dispersity of as-grown CNTs were investigated by scanning electron microscopy （SEM）. The graphitization and defects were characterized by Raman spectroscopy. The asgrown CNTs on Al-Si-Cu powder disperse uniformly and have moderate length and density, meanwhile its sp2 structure dominates minor quantity of amorphous carbons and defected carbon structures.展开更多
CNTs/TiH2 composite powders were prepared by plasma enhanced chemical vapor deposition （PECVD）. CNTs dispersed uniformly on the surface of Till2 particles and few defects were found in the tubular structure of the C...CNTs/TiH2 composite powders were prepared by plasma enhanced chemical vapor deposition （PECVD）. CNTs dispersed uniformly on the surface of Till2 particles and few defects were found in the tubular structure of the CNTs. According to DTA analysis, CNTs do not react with the base material Ti under 1 200 ~C. In order to investigate the application of CNTs/ Till2 powders in brazing, CNTs/TiH2 powders were mechanically mixed with Ni powders to develop a new type of brazing powder, and wetting experiments at 1 100 ~C showed a good wettability of CNTs/TiNi brazing powder.展开更多
Brazing of a Ni-based single crystal superalloy has been investigated with the additive Ni-based superalloy and filler Ni–Cr–W–B alloy at 1260℃, and attentions were paid to the microstructure evolution during braz...Brazing of a Ni-based single crystal superalloy has been investigated with the additive Ni-based superalloy and filler Ni–Cr–W–B alloy at 1260℃, and attentions were paid to the microstructure evolution during brazing and the stress-rupture behavior at 980℃ of such brazed joints after homogenization. Microstructure in the brazed joint generally includes brazing alloy zone（BAZ）, isothermally solidified zone（ISZ） and diffusion affected zone（DAZ）. Microstructure evolution during this brazing process is discussed at the heating stage, the holding stage and the cooling stage respectively, according to the diffusion path of B atoms. Initially well-distributed γ’/γ’ microstructure in the homogenized bonded zone after heat treatment and substantial γ’ rafts enhance the post-brazed joint to obtain a stress-rupture lifetime of more than 120 h at 980℃/250 MPa. On the other hand, the decreased stress-rupture behavior of post-brazed joint, compared with parenting material, is ascribed to the presence of inside brazing porosity and stray grain boundary, which not only reduces the effective loading-carrying area but also offers preferential sites for creep vacancy aggregation to further soften stray grain boundary. And finally an early fracture of these post-brazed joints through the intergranular microholes aggregation and growth mode under this testing condition was observed.展开更多
基金This work was supported by the National Natural Science Foundation of China （Grant No. 51105108 ） and the Fundamental Research Funds for the Central Universities （Grant No. HIT. NSRIF. 2010113）.
文摘In this paper, an approach to synthesizing carbon nanotubes （ CNTs ） reinforced A1-Si-Cu brazing powder was studied, which was accomplished by in-situ growth of the CNTs on the Al-Si-Cu powder at a relatively low temperature by plasma enhanced chemical vapor deposition （ PECVD ）. The synthesis parameters were optimized. The component of brazing powder was analyzed by X-ray diffraction （ XRD ）. The microstracture and dispersity of as-grown CNTs were investigated by scanning electron microscopy （SEM）. The graphitization and defects were characterized by Raman spectroscopy. The asgrown CNTs on Al-Si-Cu powder disperse uniformly and have moderate length and density, meanwhile its sp2 structure dominates minor quantity of amorphous carbons and defected carbon structures.
基金This work was supported by the National Natural Science Foundation of China （Grant No. 51105108 ） and the Fundamental Research Funds for the Central Universities （Grant No. HIT. NSRIF. 2010113）.
文摘CNTs/TiH2 composite powders were prepared by plasma enhanced chemical vapor deposition （PECVD）. CNTs dispersed uniformly on the surface of Till2 particles and few defects were found in the tubular structure of the CNTs. According to DTA analysis, CNTs do not react with the base material Ti under 1 200 ~C. In order to investigate the application of CNTs/ Till2 powders in brazing, CNTs/TiH2 powders were mechanically mixed with Ni powders to develop a new type of brazing powder, and wetting experiments at 1 100 ~C showed a good wettability of CNTs/TiNi brazing powder.
基金financial supports from the National High Technology Research and Development Program of China (“863 Program”, No. 20102014AA041701)the National Natural Science Foundation of China (No. 11332010, No. U1508213, No. 51331005, No. 51401210, No. 51601192, No. 51671188 and No. 51571196)
文摘Brazing of a Ni-based single crystal superalloy has been investigated with the additive Ni-based superalloy and filler Ni–Cr–W–B alloy at 1260℃, and attentions were paid to the microstructure evolution during brazing and the stress-rupture behavior at 980℃ of such brazed joints after homogenization. Microstructure in the brazed joint generally includes brazing alloy zone（BAZ）, isothermally solidified zone（ISZ） and diffusion affected zone（DAZ）. Microstructure evolution during this brazing process is discussed at the heating stage, the holding stage and the cooling stage respectively, according to the diffusion path of B atoms. Initially well-distributed γ’/γ’ microstructure in the homogenized bonded zone after heat treatment and substantial γ’ rafts enhance the post-brazed joint to obtain a stress-rupture lifetime of more than 120 h at 980℃/250 MPa. On the other hand, the decreased stress-rupture behavior of post-brazed joint, compared with parenting material, is ascribed to the presence of inside brazing porosity and stray grain boundary, which not only reduces the effective loading-carrying area but also offers preferential sites for creep vacancy aggregation to further soften stray grain boundary. And finally an early fracture of these post-brazed joints through the intergranular microholes aggregation and growth mode under this testing condition was observed.
