A self designed Split Hopkinson tensile bar setup with a rotating disk was used to investigate room temperature tensile properties of a γ TiAl alloy in duplex (DP) and fully lamellar (FL) microstructural forms under ...A self designed Split Hopkinson tensile bar setup with a rotating disk was used to investigate room temperature tensile properties of a γ TiAl alloy in duplex (DP) and fully lamellar (FL) microstructural forms under the dynamic strain rates between 70 and 800 s -1 . It was found that for both forms the alloy is brittle at these strain rates, exhibiting near zero ductility. The σ b at dynamic strain rate is greater than that at the static strain rate of 5×10 -1 s -1 , and the σ b of the DP material is higher than that of the FL material. Fractography analysis indicated that both materials at dynamic strain rates fracture in a mixed mode of predominant transgranular cleavage and minor intergranular cracking, which is similar to that at the static strain rate. The room temperature brittleness of the alloy is not environmentally related. : A self designed Split Hopkinson tensile bar setup with a rotating disk was used to investigate room temperature tensile properties of a γ TiAl alloy in duplex (DP) and fully lamellar (FL) microstructural forms under the dynamic strain rates between 70 and 800 s -1 . It was found that for both forms the alloy is brittle at these strain rates, exhibiting near zero ductility. The σ b at dynamic strain rate is greater than that at the static strain rate of 5×10 -1 s -1 , and the σ b of the DP material is higher than that of the FL material. Fractography analysis indicated that both materials at dynamic strain rates fracture in a mixed mode of predominant transgranular cleavage and minor intergranular cracking, which is similar to that at the static strain rate. The room temperature brittleness of the alloy is not environmentally related.展开更多
Activation volume V , activation enthalpy Δ H , activation free enthalpy Δ G and activation entropy Δ S of tensile deformation of Ti 47Al 2Mn 2Nb alloy with near lamellar microstructure were measured at yield point...Activation volume V , activation enthalpy Δ H , activation free enthalpy Δ G and activation entropy Δ S of tensile deformation of Ti 47Al 2Mn 2Nb alloy with near lamellar microstructure were measured at yield point using strain rate jumping method in a temperature range from 77 K to 1 373 K. Based on the measured values of activation parameters and temperature dependence of tensile properties, different thermally activated dislocation motion mechanisms were speculated to control tensile deformation of the alloy in three temperature regions: in low temperature region (77～398 K), the mechanism is mainly characterized by the overcoming of Peierls Nabarro friction; in intermediate temperature region (398～1 073 K), the mechanism is an abnormally weak thermal activated motion; in high temperature region (1 073～1 373 K), dislocation climbing is the controlling mechanism.展开更多
Gamma titanium aluminide (γ-TiAl)intermetallic compounds are spotlighted as lightweight heat-resistant materials, and have been investigated extensively to aiming commercial use.Fundamental approaches in which phase...Gamma titanium aluminide (γ-TiAl)intermetallic compounds are spotlighted as lightweight heat-resistant materials, and have been investigated extensively to aiming commercial use.Fundamental approaches in which phase diagrams of Ti -Al -Cr and TiAl -Nb have been studied based on the experimental data and calculations , have been performed in the national project For industrial approach, ingot process and direct casting process have been developed to provide sheet form of TiAl. By these approaches, γ-TiAl base ,intermetallic compounds show a great possibility to apply in the variety of fields .However, a more detailed understanding of phase equilibrium in Ti-Al -X and the relationship between the mechanical properties and microstructure will be necessary展开更多
Two TiAl alloys,Ti^47.5Al-3.7(Cr,V,Zr)and Ti77.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were melted and cast with the same process,respectively.Microstructures with strongly oriented lamellae were both observed in these two alloys...Two TiAl alloys,Ti^47.5Al-3.7(Cr,V,Zr)and Ti77.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were melted and cast with the same process,respectively.Microstructures with strongly oriented lamellae were both observed in these two alloys followed by hot isostatic pressing and heat treatment.Ti2AlC carbides were identified in the alloy with C addition.Stress rupture tests were carried out at 800 and 850°C,with tensile stress from 220 to 400 MPa,respectively.It was shown that the alloy with C experienced much longer lives than the other,especially under the condition of 800°C/260 MPa,800°C/300 MPa,850°C/220 MPa,850°C/240 MPa and 850°C/260 MPa.Observation of ruptured specimens revealed that the microstructure stability was improved significantly in the alloy with C addition which is attributed to the strengthening effect of Ti-Al-C carbides.The Ti2AlC carbides mainly increased the resistance of dislocation passing through the interfaces and kept the integrity of the interfaces.And Ti3AlC carbide was formed during stress rupture process,which could not only effectively act as the barrier of dislocation movement inside the lamellae,but also strengthen the lamellae itself.展开更多
文摘A self designed Split Hopkinson tensile bar setup with a rotating disk was used to investigate room temperature tensile properties of a γ TiAl alloy in duplex (DP) and fully lamellar (FL) microstructural forms under the dynamic strain rates between 70 and 800 s -1 . It was found that for both forms the alloy is brittle at these strain rates, exhibiting near zero ductility. The σ b at dynamic strain rate is greater than that at the static strain rate of 5×10 -1 s -1 , and the σ b of the DP material is higher than that of the FL material. Fractography analysis indicated that both materials at dynamic strain rates fracture in a mixed mode of predominant transgranular cleavage and minor intergranular cracking, which is similar to that at the static strain rate. The room temperature brittleness of the alloy is not environmentally related. : A self designed Split Hopkinson tensile bar setup with a rotating disk was used to investigate room temperature tensile properties of a γ TiAl alloy in duplex (DP) and fully lamellar (FL) microstructural forms under the dynamic strain rates between 70 and 800 s -1 . It was found that for both forms the alloy is brittle at these strain rates, exhibiting near zero ductility. The σ b at dynamic strain rate is greater than that at the static strain rate of 5×10 -1 s -1 , and the σ b of the DP material is higher than that of the FL material. Fractography analysis indicated that both materials at dynamic strain rates fracture in a mixed mode of predominant transgranular cleavage and minor intergranular cracking, which is similar to that at the static strain rate. The room temperature brittleness of the alloy is not environmentally related.
文摘Activation volume V , activation enthalpy Δ H , activation free enthalpy Δ G and activation entropy Δ S of tensile deformation of Ti 47Al 2Mn 2Nb alloy with near lamellar microstructure were measured at yield point using strain rate jumping method in a temperature range from 77 K to 1 373 K. Based on the measured values of activation parameters and temperature dependence of tensile properties, different thermally activated dislocation motion mechanisms were speculated to control tensile deformation of the alloy in three temperature regions: in low temperature region (77～398 K), the mechanism is mainly characterized by the overcoming of Peierls Nabarro friction; in intermediate temperature region (398～1 073 K), the mechanism is an abnormally weak thermal activated motion; in high temperature region (1 073～1 373 K), dislocation climbing is the controlling mechanism.
文摘Gamma titanium aluminide (γ-TiAl)intermetallic compounds are spotlighted as lightweight heat-resistant materials, and have been investigated extensively to aiming commercial use.Fundamental approaches in which phase diagrams of Ti -Al -Cr and TiAl -Nb have been studied based on the experimental data and calculations , have been performed in the national project For industrial approach, ingot process and direct casting process have been developed to provide sheet form of TiAl. By these approaches, γ-TiAl base ,intermetallic compounds show a great possibility to apply in the variety of fields .However, a more detailed understanding of phase equilibrium in Ti-Al -X and the relationship between the mechanical properties and microstructure will be necessary
基金National 973 Project of China(2015CB654902)Chinese National Natural Science Foundation(11374174,51390471 and 51527803).
文摘Two TiAl alloys,Ti^47.5Al-3.7(Cr,V,Zr)and Ti77.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were melted and cast with the same process,respectively.Microstructures with strongly oriented lamellae were both observed in these two alloys followed by hot isostatic pressing and heat treatment.Ti2AlC carbides were identified in the alloy with C addition.Stress rupture tests were carried out at 800 and 850°C,with tensile stress from 220 to 400 MPa,respectively.It was shown that the alloy with C experienced much longer lives than the other,especially under the condition of 800°C/260 MPa,800°C/300 MPa,850°C/220 MPa,850°C/240 MPa and 850°C/260 MPa.Observation of ruptured specimens revealed that the microstructure stability was improved significantly in the alloy with C addition which is attributed to the strengthening effect of Ti-Al-C carbides.The Ti2AlC carbides mainly increased the resistance of dislocation passing through the interfaces and kept the integrity of the interfaces.And Ti3AlC carbide was formed during stress rupture process,which could not only effectively act as the barrier of dislocation movement inside the lamellae,but also strengthen the lamellae itself.
