| Titanium matrix composites exhibiting more excllent fatigue and creep resistence in high temperature are attractive materials for tubes applied in aerospace hydraulic pipeline, marine power plant and automotive engine oil pipeline. However, there are few researches on titanium matrix composites tubes, especially on the thin tubes with large aspect ratio.3.5vol%TiBw/TC4composite was used as intial billet to explore the extrusion-rotary forging process and microstructure evolution, for the purpose to find a technical feasible process in this study. Meanwhile, Deform-2D was used to study the effects of filler material and blank size on the deformed TiBw/TC4composite tube during extrusion. Besides, the effects of solid soiution and aging treatment on the microstructure and mechanical propertities of TiBw/TC4composite tube were also studied.The simulation result of extrusion showed that: the shape of the extruded tubes was unaffected by the different filler materials; the friction between filling materials and composite materials was conducive to the coordination deformation; the increased thickness at the bottom of the extrusion billet was needed to make the filler material to avoid uneven deformation zone, and thereasionable thickness was7mm. Result of the experimental testings proved that the shape of deformed tubes was little affected by the filling materials, and this was well whith the simulation result. Compared to the metallic filling materials, the nonmetallic powders were more easily removed after deformation. Finally, BN powers were selected as filling material due to the smooth inner wall surface and uniform wall thickness of the deformed tubes.The TiBw/TC4composite tubes with outer diameter of8mm and wall thickness of2mm were successfully fabricated by extrusion-rotary forging process. After the extrusion at1100℃, the matrix microstructure was significantly refined and the average width of lamellar α phase decreased from10μm to1.8μm. Additionally, the initial network microstructure of TiB whiskers was broken and the TiB whiskers tended to align along the extruding direction simultaneously. The ultimate tensile strength of the composite was elevated from1051MPa to1272MPa and the elongation from6.5%to9.1%. After further rotary forging deformation, the matrix became equiaxed and the TiB whiskers were more discreted but still kept the orientational distribution. The final tubes exhibited an ultimate tensile strength of about1221MPa and an elongation of about11.8%.The solution treatment of900~990℃for40minutes and the aging treatment of500~650℃for6h were systemically studied. The result showed that the matrix microstructure was composed of primary α and a small amount of martensite after900℃solution. With the solution temperature increased, the content of primary α was decreased but the martensite was increased, and the hardness of composites was also improved gradually. There was a lot of martensite in the matrix microstructure and the hardness reach to HV480.8after960℃. The metastable phase such as martensite was decomposed into fine α+β, but the decomposition was not completed. When the aging temperature was over600℃, decomposed microstructure became coarse. With the aging temperature increased, the hardness was increasd firstly then decreased latter. The hardness reached to HV532after aging treatment at550℃. After the solution treatment of960℃for40minutes and the aging treatment of550℃for6hours, the ultimate tensile strength of the TiBw/TC4composite tubes was about1388MPa at roomtempreture, which was increased by13.7%, and the ultimate tensile strength at600℃could still reach to635MPa. |
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