The TiAl-based alloys sheet with 150 mm×100 mm×0.4 mm and the TiAl/Nb laminated composites with 150 mm×100 mm×0.2 mm were fabricated by using electron beam-physical vapor deposition(EB-PVD) method,...The TiAl-based alloys sheet with 150 mm×100 mm×0.4 mm and the TiAl/Nb laminated composites with 150 mm×100 mm×0.2 mm were fabricated by using electron beam-physical vapor deposition(EB-PVD) method, respectively. The microstructure and properties of the sheet were investigated by AFM, SEM and EDS. The results show that the TiAl based alloys sheet has a good surface quality, and its microstructure is columnar crystal. The component of the alloys indicates a regular and periodical gradient change which leads to the spontaneous delamination along the normal direction of substrate. In the TiAl/Nb laminated composites alternating overlaid by TiAl of 24 layers and Nb of 23 layers, the interface of each layer evenly distributed throughout the cross-section is transparent, and the interlayer spacing is about 8μm. The component of TiAl layers also changes regularly along the normal direction of substrate, but no delamination phenomenon is found. The TiAl/Nb laminated composites have better ductility than the TiAl-based alloys sheet.展开更多
High Al content inhibits the formation of B2 phase,which improves creep resistance in high Al/Nb-containing TiAl alloys.In this work,the microstructure evolution and creep behavior of TiAl based alloy Ti-46Al-8Nb(at.%...High Al content inhibits the formation of B2 phase,which improves creep resistance in high Al/Nb-containing TiAl alloys.In this work,the microstructure evolution and creep behavior of TiAl based alloy Ti-46Al-8Nb(at.%)with a high Al/Nb content,produced by the vacuum consumable electrode melting technology and the electromagnetic cold crucible melting technology,were studied.The microstructure of the Ti-46Al-8Nb alloy is composed ofα_(2)/ηphases arranged in layers with different orientations,which possesses smooth grain boundaries due to small-blocky segregation and irregular serrated grain boundaries caused by large-blocky segregation.Under conditions of 780-820℃and 125-175 MPa for 200 h,it exhibits typical power-law creep characteristics.The apparent activation energy of creep(Q)and apparent stress exponent(n)of the Ti-46Al-8Nb alloy are Q=274 kJ·mol^(-1)and n=1.97,respectively.The creep deformation mechanism is grain boundary sliding.Cracks easily form at the smooth boundary.The irregular serrated boundaries with small specific surface area hinder the dislocation movement,thereby improving the boundary creep resistance.When the stress concentration reaches a certain degree,the cracks will initiate between the lamellar structures within the grain.The crack usually propagates along the boundary perpendicular to or at an angle of 45 with the stress axis until creep failure occurs.展开更多
The elimination of the B2 phase in aβ-solidifying high Nb-containing TiAl alloy withβ/B2 andγphases was investigated using different heat treatments,with a focus on understanding the phase transformations and lamel...The elimination of the B2 phase in aβ-solidifying high Nb-containing TiAl alloy withβ/B2 andγphases was investigated using different heat treatments,with a focus on understanding the phase transformations and lamellae formation during the process.The phase transformation and lamellae formation during B2 phase elimination differs from that observed in conventional TiAl alloys.During the holding stage of heat treatment,theβ/B2 phase is replaced by theαphase through primary phase transformations ofβ→αandγ→α.Lamellae formation occurs within bothαandγgrains during cooling,initiating 30-40℃below the annealing temperature.This lamellar structure was formed via two main mechanisms:nucleation at grain boundaries followed by growth into the grain,and direct precipitation and growth within the grain.The orientation relationship between theγphase and its adjacentαphase is(111)_(γ)//(0001)_(α)and[011]_(γ)//[1120]_(α),with a coherency between the phases characterized by a misfit of approximately 1.7%.展开更多
A TiAl-Nb composite was prepared by spark plasma sintering （SPS） at 1250 °C and 50 MPa for 5 min from prealloyed TiAl powder and elemental Nb powder in a molar ratio of 9：1 for improving the fracture toughness...A TiAl-Nb composite was prepared by spark plasma sintering （SPS） at 1250 °C and 50 MPa for 5 min from prealloyed TiAl powder and elemental Nb powder in a molar ratio of 9：1 for improving the fracture toughness of TiAl alloy at room temperature. The microstructure, phase constitute, fracture surface and fracture toughness were determined by X-ray diffractometry, electron probe micro-analysis, scanning and transmission electron microscopy and mechanical testing. The results show that the sintered samples mainly consist of γ phase, O phase, niobium solid solution （Nbss） phase and B2 phase. The fracture toughness is as high as 28.7 MPa？m1/2 at room temperature. The ductile Nbss phase plays an important role in absorbing the fracture energy in front of the cracks. Moreover, B2 phase can branch the propagation of the cracks. The microhardness of each phase of the composite was also tested.展开更多
基金Projects(90205034, 90405016) supported by the National Natural Science Foundation of China
文摘The TiAl-based alloys sheet with 150 mm×100 mm×0.4 mm and the TiAl/Nb laminated composites with 150 mm×100 mm×0.2 mm were fabricated by using electron beam-physical vapor deposition(EB-PVD) method, respectively. The microstructure and properties of the sheet were investigated by AFM, SEM and EDS. The results show that the TiAl based alloys sheet has a good surface quality, and its microstructure is columnar crystal. The component of the alloys indicates a regular and periodical gradient change which leads to the spontaneous delamination along the normal direction of substrate. In the TiAl/Nb laminated composites alternating overlaid by TiAl of 24 layers and Nb of 23 layers, the interface of each layer evenly distributed throughout the cross-section is transparent, and the interlayer spacing is about 8μm. The component of TiAl layers also changes regularly along the normal direction of substrate, but no delamination phenomenon is found. The TiAl/Nb laminated composites have better ductility than the TiAl-based alloys sheet.
基金supported by the National Natural Science Foundation of China(No.52425401)the Foundation of National Key Laboratory for Precision Hot Processing of Metals(No.JCKYS2021603C001)+1 种基金the Fundamental Research Funds for the Central Universities(No.2023FRFK06014)the Major Science and Technology Achievement Transformation Project of Heilongjiang Province(No.ZC2023SH0075)。
文摘High Al content inhibits the formation of B2 phase,which improves creep resistance in high Al/Nb-containing TiAl alloys.In this work,the microstructure evolution and creep behavior of TiAl based alloy Ti-46Al-8Nb(at.%)with a high Al/Nb content,produced by the vacuum consumable electrode melting technology and the electromagnetic cold crucible melting technology,were studied.The microstructure of the Ti-46Al-8Nb alloy is composed ofα_(2)/ηphases arranged in layers with different orientations,which possesses smooth grain boundaries due to small-blocky segregation and irregular serrated grain boundaries caused by large-blocky segregation.Under conditions of 780-820℃and 125-175 MPa for 200 h,it exhibits typical power-law creep characteristics.The apparent activation energy of creep(Q)and apparent stress exponent(n)of the Ti-46Al-8Nb alloy are Q=274 kJ·mol^(-1)and n=1.97,respectively.The creep deformation mechanism is grain boundary sliding.Cracks easily form at the smooth boundary.The irregular serrated boundaries with small specific surface area hinder the dislocation movement,thereby improving the boundary creep resistance.When the stress concentration reaches a certain degree,the cracks will initiate between the lamellar structures within the grain.The crack usually propagates along the boundary perpendicular to or at an angle of 45 with the stress axis until creep failure occurs.
基金supported by the National Natural Science Foundation of China(Nos.51871012,52071021)Beijing Natural Science Foundation,China(No.2162024)+1 种基金Fundamental Research Funds for the Central Universities,China(No.FRF-GF-20-20B)the National Program on Key Basic Research Project of China(No.2011CB605502)。
文摘The elimination of the B2 phase in aβ-solidifying high Nb-containing TiAl alloy withβ/B2 andγphases was investigated using different heat treatments,with a focus on understanding the phase transformations and lamellae formation during the process.The phase transformation and lamellae formation during B2 phase elimination differs from that observed in conventional TiAl alloys.During the holding stage of heat treatment,theβ/B2 phase is replaced by theαphase through primary phase transformations ofβ→αandγ→α.Lamellae formation occurs within bothαandγgrains during cooling,initiating 30-40℃below the annealing temperature.This lamellar structure was formed via two main mechanisms:nucleation at grain boundaries followed by growth into the grain,and direct precipitation and growth within the grain.The orientation relationship between theγphase and its adjacentαphase is(111)_(γ)//(0001)_(α)and[011]_(γ)//[1120]_(α),with a coherency between the phases characterized by a misfit of approximately 1.7%.
基金Project (2011CB605505) supported by the National Basic Research Program of ChinaProject (2008AA03A233) supported by the Hi-tech Research and Development Program of China
文摘A TiAl-Nb composite was prepared by spark plasma sintering （SPS） at 1250 °C and 50 MPa for 5 min from prealloyed TiAl powder and elemental Nb powder in a molar ratio of 9：1 for improving the fracture toughness of TiAl alloy at room temperature. The microstructure, phase constitute, fracture surface and fracture toughness were determined by X-ray diffractometry, electron probe micro-analysis, scanning and transmission electron microscopy and mechanical testing. The results show that the sintered samples mainly consist of γ phase, O phase, niobium solid solution （Nbss） phase and B2 phase. The fracture toughness is as high as 28.7 MPa？m1/2 at room temperature. The ductile Nbss phase plays an important role in absorbing the fracture energy in front of the cracks. Moreover, B2 phase can branch the propagation of the cracks. The microhardness of each phase of the composite was also tested.
