Ti-43.5Al-4Nb-1Mo-0.1B合金的包套热挤压组织与拉伸性能

Microstructure and Tensile Properties of Ti-43.5Al-4Nb-1Mo-0.1B Alloy Processed by Hot Canned Extrusion

采用包套近等温热挤压工艺制备了Ti-43.5Al-4Nb-1Mo-0.1B合金方形棒材,通过OM、SEM、XRD、TEM和拉伸等实验方法研究了方棒不同状态和位置的组织及拉伸性能。结果表明,方棒材的挤压态组织较为均匀,不同位置的微观组织无明显差异;挤压变形使铸锭组织片层取向趋于一致,趋向平行于挤压方向;晶界处γ相存在颗粒状、块状和长条状3种形态;β相在挤压过程中碎化和被拉长呈平行挤压方向纤维状。在TEM下观察,棒材边部位置片层完全碎化,而心部位置片层断裂后呈长条状。β0相中生成大量ω0相,两者位相关系遵循:■。方棒材的室温拉伸强度达到1000 MPa以上,室温延伸率为0.5%左右;800℃拉伸屈服强度达到400 MPa以上,表现明显塑性。热挤压合金经时效热处理后在β0相中生成大量透镜状γ相,时效处理提高了合金的高温拉伸性能,但无法消除ω0相。

βsolidifyingγ-TiAl alloys are being considered for high-temperature application in the aerospace and automotive industries as high efficiency materials which can withstand temperatures up to 800℃and owns attractively thermal and mechanical properties.Through thermos-mechanical process can obtain excellent alloy properties,such as high strength and better elongation.But it will cause anisotropy.Ti-43.5Al-4Nb-1Mo-0.1B alloy rectangular bar was prepared by isothermal hot canned extrusion process.The OM,SEM,XRD,TEM and tensile methods were used to study the microstructure and tensile properties of the rectangular rods in different states and locations.The results show that the extruded structure of the rectangular rods is relatively uniform and there is no significant difference in the microstructure at different locations.The extrusion deformation makes the orientation of the lamellar uniform,tending to be parallel to the extrusion direction;γphase in the grain boundary exists in the three forms of graininess,bulk and strip;theβphase is shredded during extrusion and is elongated in a parallel extrusion direction.Under the TEM observation,lamellar at the edge of the bar was completely shredded,and lamellar at the core position was elongated after lamellar was broken.A large number ofω0 phases are generated in theβ0 phase,and the phase relationship of the two follows:[111¯111ˉ]β0β0//[0001]ω0ω0,{110}β0β0//{21¯1¯021ˉ1ˉ0}ω0ω0.The tensile strength reaches 1000 MPa or more and elongations are about 0.5%of the rectangular bar at room temperature;the yield strength is above 400 MPa at 800℃,which exhibits remarkable plasticity.After the ageing treatment of the hot extruded alloy,a large amount of lens-shapeγphase is formed in theβ0 phase,and the ageing treatment improves the high temperature tensile properties of the alloy,but theω0 phase can not be eliminated.