Powder Metallurgy Tial Alloy Bag Set Of Rolling Technology And Its Heat Treatment

TiAl based alloys are very promising candidates as light-weight and high-temperature structural materials due to their low density, high specific strength, high specific stiffness and excellent oxidation and creep resistance, which possess wide capacities of engineering applications in aeronautics, space and automobile industries. With the development of TiAl based alloys application, it is urgent to fabricate TiAl sheets. This paper aims at systematically investigating the hot pack rolling process and heat treatment of PM Ti-47Al-2Cr-0.2Mo (at.%) alloy. Microstructural evolution and room temperature tensile properties of TiAl based alloys were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectrum (EDS) and room temperature tensile tests, to provide theoretical basis for optimization of the practical hot working parameter. A brief introduction to the study and main results are as follows:(1) By using appropriate hot-pack rolling processing, the PM Ti-47Al-2Cr-0.2Mo alloy sheets were prepared with a size of150mm (width)×1mm (thickness). The sheet which rolled at1280℃,1.4m/min,25%per pass reduction and total deformation to60%is enjoy the highest ultimate tensile strength of789MPa with the tensile elongation attaining2.5%, at room temperature.(2) Because processing temperature along with reduction per rolling step and deformation rate mainly governs the microstructure of the sheet, a stringent control of processing parameters is required. PM Ti-47Al-2Cr-0.2Mo billet should be rolling at1250℃～1300℃, and per pass reduction must be less than25%. The results indicate that mechanical properties of TiAl sheets improve with elevating of temperature and increasing per pass reduction. But the sheets with heavy deformation have lower strength and ductility. The appropriate rolling parameters of PM Ti-47Al-2Cr-0.2Mo alloy such as temperature is1280C, rolling speed is2.4m/min, per pass reduction less than25%and total deformation no more than70%. And the sheet has a good combination of strength and ductility.(3) After annealed at1150C and2h, the microstructure of as-rolled Ti-47Al-2Cr-0.2Mo alloy changes from duplex to near γ. The volume fraction and the grain size of lamella increase with solution treatment temperature and holding time. However, the spacing of lamella refined with solution treatment temperature elevation or time extension. The temperature of a phase transformation is between1300℃and1310℃. The optimum heat treatment process is at1150C for2h, then solution at1310℃for15min. finally, hold at900℃,2h. After this heat treatment process, the fine and uniform lamella can be obtained.