| TiAl based alloys are regarded as one of the most promising high-temperature Structure Materials due to their attractive properties,such as low density,high strength,excellent creep resistance and anti-oxidation properties.However,the low room-temperature ductility and intrinsic brittleness limit their engineering applications.Studies have shown that hot processing is an effective method to refine microstructure and improve mechanical properties of TiAl alloys.In this paper,we focused on Ti-43Al-(Cr,Mn,Y)alloy,Ti-43Al-2Cr-1.5Mn-Y and Ti-43Al-1.5Cr-1Mn-Y alloy sheet were prepared by ingot metallurgy method,their microstructure and mechanical properties of forging and rolling TiAl alloys were investigated systematically.The effects of different additions of Cr and Mn on the hot-deformation and mechanical properties were studied.The evolution of microstructure was analyzed in the heat treatment process.The Ti-43Al-(Cr,Mn,Y)alloy ingot was prepared by induction shell melting,the appearance of the ingot was intact and did not have big defect.Ti-43Al-(Cr,Mn,Y)pancake was obtained by canned forging in two kinds of processes with uniform contours,Completed shape and good quality surface.The forged Ti-43Al-2Cr-1.5Mn-Y alloy consists of about 79.5% of γ and 14.2% B2 fine DRX grains by one-step forming process,the mean grain size is about 8.6μm.Precipitation of striped β/B2 phase formingβ/B2+γ lamellar structure in as forged TiAl alloy by two-step forming process,the mean grain size is about 9.6μm.The forged Ti-43Al-1.5Cr-1Mn-Y alloy comprises a large number of dynamicly recrystallized γ grains and extended lamellar colonies by one-step forming process,while the forged TiAl alloy by two-step forming process contains more remnant lamellar colonies.the content of B2 and α2 phase is about 4%and 17.5% in forged Ti-43Al-1.5Cr-1Mn-Y alloy.The ultimate tensile strength is about616 MPa with an elongation value of 0.32% at room temperature of forged Ti-43Al-2Cr-1.5Mn-Y alloy,while the forged Ti-43Al-1.5Cr-1Mn-Y alloy exhibits strength of about 840 MPa with an elongation of 0.92% at room temperature.Ti-43Al-2Cr-1.5Mn-Y alloy sheets were prepared by hot pack rolling with the initial rolling temperatures at 1170℃ and 1200℃,respectively.The as rolled TiAl alloyconsists of about 80% of γ and 10% B2 fine DRX grains,the mean grain size is about7-8μm.Ti-43Al-1.5Cr-1Mn-Y alloy sheets were prepared by hot pack rolling with the initial rolling temperatures at 1235℃ and 1250℃,which comprises about of 60%-70%lamellar colonies with mean size of 10μm and dynamicly recrystallized γ grains with mean size of 1-5μm,the content of B2 phase less than 5%.Both of the two alloy rolling sheets exhibits good tensile properties at room temperature,the UTS is about 696 MPa with an elongation value of 1.22% at room temperature of as rolled Ti-43Al-2Cr-1.5Mn-Y alloy,while the as rolled Ti-43Al-1.5Cr-1Mn-Y alloy exhibits strength of about 864 MPa with an elongation of 2.03% at room temperature.It can be seen that Duplex structure exhibits better tensile properties,and the increase of B2 phase will lead to the decrease of room-temperature ductility.The heat treatment of Ti-43Al-(Cr,Mn,Y)alloy and its effect on tensile properties were also studied.As to Ti-43Al-2Cr-1.5Mn-Y alloy,fully lamellar microstructure with dimensions of about 100-200 μ m can be obtained after heat treatment at 1300 ℃/30min/FC,the UTS and elongation at room temperature reduced to 589 MP and 0.6%,respectively.Duplex microstructure with equiaxed γ grains with mean size of 10-20μm and lamellaes with mean size of 20-40μm can be produced after heat treatment at1250°C/4h/FC,the UTS reduced to 589 MP and the elongation increased to 0.5%.As to Ti-43Al-1.5Cr-1Mn-Y alloy,the original structure of TiAl alloy sheets is Duplex microstructure,so just analyze their FL and NL heat treatment.Near lamellar microstructure with dimensions of about 50-80μm can be obtained after heat treatment at 1300 ℃ /10min/FC,the ultimate tensile strength(UTS)reduced to 491 MPa.Fully lamellar microstructure with dimensions of about 60 μ m can be produced after heat treatment at 1320℃/10min/FC,after heat treatment,the TiAl alloy exhibits strength of about 680 MPa with an elongation of 1.02% at room temperature. |
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