| Continuous variable cross-section recycled extrusion(CVCE) has been proved to be an effective method for the fabrication of various bulk ultrafine-grain materials. CVCE provides an procedure for obtaining the bulk micrometer scale materials by sever plastic deformation. Compared with other sever plastic deformations, CVCE mainly has the following advantages in simple operation and high efficiency. CVCE which can control the specimen uniform deformation is more advantageous to realize industrial production. Refining titanium alloy grain can effectively improve the material strength, toughness and corrosion resistance. Currently fine-grain titanium alloy by most SPD still exist many problems which included small size of the workpieces, the complex die structure, high cost and obvious tendency of texture. So it is difficult to widely applied in production..The effects of CVCE deformation process parameters and the heat treatment on the microstructure and properties of TC4 titanium alloy has been analyzed systematically.The temperature field and strain field have been simulated. In this paper, under the condition the main research contents and conclusions are as follows:(1) The microstructure of TC4 alloy which was deformed by CVCE has been investigated. The effects of different temperature, loop and speed on the microstructure of TC4 titanium alloy has been analyzed. The result shows that near the recrystallization temperature(700℃and750℃), the grain size of the alloy decreases rapidly with increasing deformation loop. However, at higher temperature(800℃~ 900℃), the refinement degree of the grain is increased firstly and then decreased with the increase of deformation loops.Moreover, with the increase of deformation temperature, the grain size decreases firstly and then increases due to recrystallization. When the specimen is deformed at 800℃with 2mm/s under 6 loops, the size of the primary α phase is reduced from 14 to 2 ~ 3μm and the microstructure is distributed homogeneously.(2)The effects of annealing temperature and annealing time on TC4 Titanium Alloy microstructure that deformed by CVCE has been studied. When the annealing temperature was raised to 800 ℃, the grain size that was deformed under 750 ℃, 6 loops, 2mm / s and 700 ℃, 6 loops, 2mm / s refined 10 ~ 13μm to 4 ~ 7μm. When the annealing time increased to 2h at 750 ℃, the deformation organization can achieve recrystallization refinement. The process parameters was 800 ℃, 6 loops, 2mm / s and 750 ℃, 12 loops, 2mm / s and 700 ℃, 12 loops, 2mm / s. Deformation process that was 800 ℃, 6 loops, 2mm / s optimum has been heat treated under 750 ℃,2hAC.The primary alpha size is 3 ~ 5μm, and the organizational boundaries was clearn. In addition secondary alpha axis increased greatly.(3). The microstructure of CVCE and heat treatment have been observed by transmission electron microscope. The mechanism of microstructure has been studied.When the deformation temperature is 750 ℃, the refining mechanism is the main deformation induced grain refinement. However, the dynamic recrystallization of deformation organization make contribution to grain refinement at 800℃.In the process of heat treatment,grain is mainly to refined by recrystallization.(4) The temperature field and strain field of a set of parameter(800℃,6loops,2mm/s)which is the better deformation effect has been simulated by Deform software. In the process of CVCE, the deformation energy turned to thermal. With the increase of deformation loop, the strain-effecive accumulates continuously.The strain-effecive of the middle sample which is deformed under 6 loops can reach 5.22 ~ 5.22,and is distributied more evenly. |
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