To determine the liquid-solid phase equilibria of the Nb-Si-Ti ternary system, Nb-Si-Ti alloys of different compositions are prepared. By means of scanning electron microscopy （SEM）, X-ray diffraction （XRD） and el...To determine the liquid-solid phase equilibria of the Nb-Si-Ti ternary system, Nb-Si-Ti alloys of different compositions are prepared. By means of scanning electron microscopy （SEM）, X-ray diffraction （XRD） and electron probe microanalysis （EPMA）, the phases in the alloys, such as Si-based solutions, Ti（Nb）Si, Ti（Nb）Si2, Nb（Ti）Si2, Ti（Nb）5Si4, Nb（Ti）5Si3, Ti（Nb）5Si3, Nb（Ti）3Si and Nb-based solutions are identified, and the phase evolution is analyzed. As a result, the microstmctural and microchemical evidence provides a clear definition of the Nb-Si-Ti liquidus surface projection and indicates that the ternary phase diagram has seven transition reactions.展开更多
Fabrication of ternary Nb-17Si-23Ti alloys was attempted by in situ reaction laser melting deposition（LMD）with dual powder feeding method from Nb-28 at.% Ti powder mixture and pure Si powder.The microstructures of t...Fabrication of ternary Nb-17Si-23Ti alloys was attempted by in situ reaction laser melting deposition（LMD）with dual powder feeding method from Nb-28 at.% Ti powder mixture and pure Si powder.The microstructures of the as-deposited alloys were examined with scanning electronic microscope,and the phase constituents were analyzed by X-ray energy-dispersive spectrometer and X-ray diffraction.Furthermore,the effect of laser power on microstructure charac-teristics,microhardness and indentation fracture toughness was also investigated.The in situ reaction LMD process resulted in remarkable refinement of the microstructure.The as-deposited samples mainly consisted of Nbss,metastable（NbTi）3Si and Ti-rich Nbss.With the increase in the laser power from 1000 to 2000 W,the Nbss morphology changed from discontinuous dendritic to near equiaxed,but the Ti-rich Nbss phase tended to vanish.Furthermore,with the increase in the laser power,the microhardness of as-deposited samples increased from 822 to 951 HV,while the indentation fracture toughness was improved from 12.3 to 14.1 MPa mt/2.The corresponding mechanism is also discussed.展开更多
Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied ...Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied at room temperature and 800 ℃ using SiC balls as the counterpart. The Zr-Y jointly modified silicide coating is mainly composed of a thick （Nb,X）Si2 outer layer and a thin （Ti,Nb）5Si4 inner layer. The coatings possess much higher microhardness than the base alloy. The wear rates of both the base alloy and coatings increase with increasing the sliding loads. However, the coatings have much lower wear rates than the base alloy under the same sliding conditions. The coatings have superior anti-friction property, and can provide effective protection for the base alloy at both room temperature and 800 ℃ in air.展开更多
基金National High-tech Research and Development Pro-gram(2006AA03Z102)Aeronautical Science Foundation of China(2006ZF51069)
文摘To determine the liquid-solid phase equilibria of the Nb-Si-Ti ternary system, Nb-Si-Ti alloys of different compositions are prepared. By means of scanning electron microscopy （SEM）, X-ray diffraction （XRD） and electron probe microanalysis （EPMA）, the phases in the alloys, such as Si-based solutions, Ti（Nb）Si, Ti（Nb）Si2, Nb（Ti）Si2, Ti（Nb）5Si4, Nb（Ti）5Si3, Ti（Nb）5Si3, Nb（Ti）3Si and Nb-based solutions are identified, and the phase evolution is analyzed. As a result, the microstmctural and microchemical evidence provides a clear definition of the Nb-Si-Ti liquidus surface projection and indicates that the ternary phase diagram has seven transition reactions.
基金the support by the National Natural Science Foundation of China(Grant No.51605456)
文摘Fabrication of ternary Nb-17Si-23Ti alloys was attempted by in situ reaction laser melting deposition（LMD）with dual powder feeding method from Nb-28 at.% Ti powder mixture and pure Si powder.The microstructures of the as-deposited alloys were examined with scanning electronic microscope,and the phase constituents were analyzed by X-ray energy-dispersive spectrometer and X-ray diffraction.Furthermore,the effect of laser power on microstructure charac-teristics,microhardness and indentation fracture toughness was also investigated.The in situ reaction LMD process resulted in remarkable refinement of the microstructure.The as-deposited samples mainly consisted of Nbss,metastable（NbTi）3Si and Ti-rich Nbss.With the increase in the laser power from 1000 to 2000 W,the Nbss morphology changed from discontinuous dendritic to near equiaxed,but the Ti-rich Nbss phase tended to vanish.Furthermore,with the increase in the laser power,the microhardness of as-deposited samples increased from 822 to 951 HV,while the indentation fracture toughness was improved from 12.3 to 14.1 MPa mt/2.The corresponding mechanism is also discussed.
基金Projects(51371145,51431003,U1435201,51401166)supported by the National Natural Science Foundation of ChinaProject(B080401)supported by the Programme of Introducing Talents of Discipline to Universities,China
文摘Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied at room temperature and 800 ℃ using SiC balls as the counterpart. The Zr-Y jointly modified silicide coating is mainly composed of a thick （Nb,X）Si2 outer layer and a thin （Ti,Nb）5Si4 inner layer. The coatings possess much higher microhardness than the base alloy. The wear rates of both the base alloy and coatings increase with increasing the sliding loads. However, the coatings have much lower wear rates than the base alloy under the same sliding conditions. The coatings have superior anti-friction property, and can provide effective protection for the base alloy at both room temperature and 800 ℃ in air.
