The main factors limiting the mass production of TiAl-based components are the high reactivity of TiAl-based alloys with the crucible or mould at high temperature.In this work,various crucibles (e.g.CaO,Y2O3 ceramic c...The main factors limiting the mass production of TiAl-based components are the high reactivity of TiAl-based alloys with the crucible or mould at high temperature.In this work,various crucibles (e.g.CaO,Y2O3 ceramic crucibles and water-cooled copper crucible) were used to fabricate the Ti-47Al-2Cr-2Nb alloy in a vacuum induction furnace.The effects of crucible materials and melting parameters on the microstructure and mechanical properties of the alloy were analyzed by means of microstructure observation,chemical analysis,tensile test and fracture surface observation.The possibilities of melting TiAl alloys in crucibles made of CaO and Y2O3 refractory materials were also discussed.展开更多
To further investigate the microstructure characteristic and solidification mechanism,so as to provide knowledge for the microstructure control of a NiTi-Al based high-temperature structural material,the microstructur...To further investigate the microstructure characteristic and solidification mechanism,so as to provide knowledge for the microstructure control of a NiTi-Al based high-temperature structural material,the microstructure of Ni-43Ti-4Al-2Nb-2Hf(at.%)alloy ingots prepared by conventional casting(arc-melting)and directional solidification (DS)at various drawing velocities(2 mm·min -1 ,18 mm·min -1 ,30 mm·min -1 and 60 mm·min -1 ,respectively)was investigated by means of electron probe microanalyses.Experimental results reveal that the microstructures are composed of NiTi matrix phase,β-Nb phase and Ti 2 Ni phase for samples obtained by both conventional casting and DS.Conventional casting has an equiaxial structure,while DS has a slender and acicular cellular structure which grows along the[001]orientation preferentially.Small amounts of whiteβ-Nb phase and black Ti 2 Ni phase co-exist at the grain boundaries or intercellular regions.With an increase in drawing velocity,the NiTi matrix phase is inclined to grow along(100)and(200)crystallographic planes,and the cellular arm spacing reduce gradually, but the directionality of the solidified structure weakens significantly.The homogeneous dispersion ofβ-Nb phase and the decrease of Ti2Ni phase in DS samples are beneficial to improving the mechanical properties.Solidification mechanism analysis indicates that the dark grey NiTi matrix phase initially precipitates from the liquid phase,and then the divorced eutectic reaction takes place,which produces the light gray matrix phase andβ-Nb phase.Finally, the peritectic reaction happens,which generates the black Ti2Ni phase.The complete solidified path of the alloy is L→NiTi+L→NiTi+β-Nb+L→NiTi+β-Nb+Ti 2 Ni.展开更多
文摘The main factors limiting the mass production of TiAl-based components are the high reactivity of TiAl-based alloys with the crucible or mould at high temperature.In this work,various crucibles (e.g.CaO,Y2O3 ceramic crucibles and water-cooled copper crucible) were used to fabricate the Ti-47Al-2Cr-2Nb alloy in a vacuum induction furnace.The effects of crucible materials and melting parameters on the microstructure and mechanical properties of the alloy were analyzed by means of microstructure observation,chemical analysis,tensile test and fracture surface observation.The possibilities of melting TiAl alloys in crucibles made of CaO and Y2O3 refractory materials were also discussed.
基金supported by the Natural Science Foundation of China(Grant No.51101003)
文摘To further investigate the microstructure characteristic and solidification mechanism,so as to provide knowledge for the microstructure control of a NiTi-Al based high-temperature structural material,the microstructure of Ni-43Ti-4Al-2Nb-2Hf(at.%)alloy ingots prepared by conventional casting(arc-melting)and directional solidification (DS)at various drawing velocities(2 mm·min -1 ,18 mm·min -1 ,30 mm·min -1 and 60 mm·min -1 ,respectively)was investigated by means of electron probe microanalyses.Experimental results reveal that the microstructures are composed of NiTi matrix phase,β-Nb phase and Ti 2 Ni phase for samples obtained by both conventional casting and DS.Conventional casting has an equiaxial structure,while DS has a slender and acicular cellular structure which grows along the[001]orientation preferentially.Small amounts of whiteβ-Nb phase and black Ti 2 Ni phase co-exist at the grain boundaries or intercellular regions.With an increase in drawing velocity,the NiTi matrix phase is inclined to grow along(100)and(200)crystallographic planes,and the cellular arm spacing reduce gradually, but the directionality of the solidified structure weakens significantly.The homogeneous dispersion ofβ-Nb phase and the decrease of Ti2Ni phase in DS samples are beneficial to improving the mechanical properties.Solidification mechanism analysis indicates that the dark grey NiTi matrix phase initially precipitates from the liquid phase,and then the divorced eutectic reaction takes place,which produces the light gray matrix phase andβ-Nb phase.Finally, the peritectic reaction happens,which generates the black Ti2Ni phase.The complete solidified path of the alloy is L→NiTi+L→NiTi+β-Nb+L→NiTi+β-Nb+Ti 2 Ni.
