摘要：钛及钛合金具有优异的力学性能，主要用于航空航天、汽车制造等行业，但是由于其加工困难，使得其无法再工业中大量应用。在钛及钛合金上采用梯度结构组织不但可以提高材料的综合性能，扩大材料的使用范围，而且对低成本钛合金的梯度结构处理实现综合性能的提升，达到甚至超过高成本材料的使用性能。62161

本文以工业纯钛TA2为研究对象，采用弯曲轧制和异步轧制期望获得晶粒梯度组织，其中在弯曲轧制中为了研究弯曲轧制的方式以及轧制道次对工业纯钛TA2的延伸率的影响，在四辊轧机开展了反复弯曲轧制实验和弯曲轧制+平轧的轧制实验，异步轧制中为了研究轧制方向以及异步轧制这种轧制方式对工业纯钛TA2的延伸率的影响，在四辊轧机上开展了不同轧制方向的异步轧制。并且在不同工艺中，取其中的一个试样进行了680℃×1h的再结晶退火的热处理，最后对所有的试样进行显微组织分析。

拉伸试验结果以及金相显微组织分析表明，14道次的反复弯曲轧制有效提高了TA2的塑性，延伸率达到了54.2%，相比原始试样提高了16%左右，试样内部形成了上、下近表面等轴细晶、内部粗晶的双对称梯度组织，近表面的细晶层大约70μm。而弯轧+平轧的的轧制方式得到的晶粒组织大小分布更加均匀，其中经过12道次的弯轧+平轧的试样延伸率达到了54.8%。经过680℃×1h的热处理可以消除孪晶以及内应力，延伸率达到了59.2%,相比原始试样提高了21%左右。异步轧制中没有发现梯度晶粒层，晶粒变形严重，塑性明显下降，强度大幅上升。由于异步轧制是大塑形变形，如果道次见压下量过大，会导致整个材料的晶粒会严重变形，从而影响获得梯度晶粒层的效果。所以异步轧制过程中尽量采取多道次、少压下的轧制工艺，使其塑形变形发生在材料表面，这样在外力反复作用下，随着表面位错密度的升高，使得表面晶粒尺寸不断减小。

毕业论文关键词：钛合金； 梯度纳米结构；剧烈塑形变形； 制备加工

Effect of gradient grain structure on elongation rate of titanium alloy sheet

Abstract:Titanium and titanium alloy has excellent mechanical properties,mainly used in aerospace, automobile manufacturing and other industries.But due to its processing difficulties,it can not be a large number of industrial applications.Titanium and titanium alloy on the gradient structure can not only improve the material of comprehensive performance, expand the scope of use of materials,but also the gradient structure of low cost titanium alloy processing improve the comprehensive performance in order to meet or exceed the performance of the high cost of materials.

The industrial pure titanium TA2 are expected to gain grain gradient structure through bending roll and asynchronous rolling.To study bending roll and rolling of industrial pure titanium TA2 extension rate, the experiment of repeated bending and rolling and rolling of flat rolling were carried out on the four roll rolling mill.In order to study the influence of the rolling direction and the rolling process on the elongation of industrial pure titanium TA2,asynchronous rolling with different rolling directions was carried out on the four roll mill.And in different processes, one of the samples was 680℃×1h recrystallization annealing heat treatment, and finally to all of the samples for the analysis of the microstructure.

The results of tensile test and microstructure analysis show that the plastic properties of the double symmetric gradient structure, the upper and lower surface of the thin crystal and the internal coarse grain, are effectively improved after 14 times of repeated bending.Elongation rate reached 54.2%, compared to the original sample increased by about 16%.The size distribution of grain size distribution was more uniform, and the elongation of the specimen reached 54.8% after 12 pass rolling and flat rolling.The heat treatment of 680℃×1h can eliminate the twin and internal stress. At the same time, the elongation reached 54.2% and is increased by about 21% compared to the original sample.n the asynchronous rolling, there is no gradient grain layer,  the deformation of the grain is serious,the plasticity is obviously decreased, and the strength is greatly increased.Asynchronous rolling is a large plastic deformation. If the reduction of each time of deformation is too large, it will affect the gradient grain layer leading to severe deformation of the material grains. Thus, the asynchronous rolling process is supposed to take multiple times, less pressure in the rolling process as far as possible, so that the plastic deformation occurs in the material surface. And with the increase of the surface dislocation density, the surface grain size decreases under the action of external force.