大塑性变形工业纯钛变形机理及力学性能的研究

发布时间：2018-03-19 19:37

  本文选题：工业纯钛　切入点：表面机械研磨处理　出处：《昆明理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：钛元素在地壳中有着丰富的含量,并且钛及钛合金拥有着优异的耐蚀性、耐高低温性、生物相容性、和高于其他金属的比强度等优点,使其被普遍的应用于航空航天、船舶、生物医疗、汽车等行业及领域,有着“航空材料”、“海洋材料”等佳誉。而对于金属而言,高强度和高塑性一贯是困扰着材料领域科学家的一个难题。而使用大塑性变形工艺(Severe Plastic Deformation,SPD)对材料进行加工以提高材料的性能是近年来研究的热门之一。本论文以工业纯钛TA1为研究对象,研究不同塑性变形工艺如表面机械研磨处理(Surface Mechanical Attrition Treatment,SMAT)、轧制工艺(Rolling)以及低温轧制后退火处理工艺(Annealing)对试样的显微结构和力学性能的影响。并探讨了不同加工工艺下材料的强化原理和变形机制。使用SMAT工艺对试样进行处理,钢球以任意角度撞击试样表面,对试样产生一个从表及里的应变速率和应变量梯度,从而导致一个从表面纳米晶到心部粗晶晶粒尺寸梯度分布的梯度结构。这种梯度结构使材料优异的性能。本文通过在低温(77 K)和室温(293 K)环境下对工业纯钛进行SMAT处理,发现降低温度能有效的提高材料内部显微应变、位错密度和孪晶密度,进一步细化晶粒,从而提高材料的强硬度。处理时间选取30 min、60 min、90 min,实验结果表示,随处理时间的延长,试样的强硬度上升,塑性下降。并且具有最佳力学性能的为LNSMAT-60min试样。此外,还对仪器内钢球与试样间的距离进行调整,发现距离变短时,材料表层的应变量和应变速率增加并且表面梯度层的厚度更厚,这也使得材料的强度的得到大幅度的提升。本文对工业纯钛进行低温和室温环境下的轧制处理。发现在低温轧制(LNR)的情况下试样内部的位错密度、显微应变和孪晶密度有显著提高,晶粒更加细小。拉伸和硬度实验结果表明,低温轧制能在保持材料塑性的情况下显著提高材料的强度和硬度。而且,通过分析可知轧制时低温环境能促使变形机制由位错机制主导向孪晶机制主导的转变。采用LNR50%试样进行低温短时间退火。微观测试结果表明,试样经过低温短时间退火后得到了小晶粒包围大晶粒的结构。在进行拉伸实验时,因这种特殊结构结构的存在试样内部会产生一个非常复杂的应力状态,这种应力状态会促进更多的滑移系启动,从而提高材料的加工硬化。并且退火后能引进大量的大角度晶界,这对材料塑性的提高是十分明显的。拉伸实验结果表明,随着退火时间的延长或退火温度的升高,材料强度下降,塑性提高。其中具有最佳性能的为LNR1-450℃-10min试样(LNR50%试样450℃退火10min),其屈服强度为341 MPa,均匀延伸率为11.6%,屈服强度和均匀延伸率均比粗晶高。通过对比几种不同的大塑性变形工艺处理后试样的实验结果,发现轧制后退火工艺对工业纯钛力学性能的提高是最显著的。
[Abstract]:Titanium is abundant in the earth's crust, and titanium and titanium alloys have the advantages of excellent corrosion resistance, high and low temperature resistance, biocompatibility, and higher specific strength than other metals, which make them widely used in aerospace, ship, and so on. Biomedical, automotive and other industries and fields have a good reputation for "aeronautical materials", "marine materials" and so on. But for metals, High strength and high plasticity have always been a difficult problem for scientists in the field of materials. However, the use of large plastic deformation process to process materials to improve the properties of materials is one of the hot topics in recent years. The industrial pure titanium TA1 was used as the research object. The effects of different plastic deformation processes such as surface Mechanical Attrition treatment matting, rolling process rolling and annealing treatment after low temperature rolling on the microstructure and mechanical properties of the specimens were studied. The strengthening principle and deformation mechanism of the material. The SMAT process is used to treat the specimen. When the steel ball strikes the surface of the specimen at any angle, it produces a strain rate and strain gradient from the surface and inside the specimen. As a result, a gradient structure with size gradient distribution from nanocrystalline to coarse-grained grains at the center of the surface. This gradient structure makes the material excellent. In this paper, commercial pure titanium was treated with SMAT at low temperature (77K) and room temperature (293K). It is found that decreasing the temperature can effectively increase the internal microstrain, dislocation density and twin density, further refine the grain size and improve the toughness of the material. The treatment time is 30 min ~ 60 min ~ 90 min. The experimental results show that the treatment time increases with the increase of the treatment time. In addition, the distance between the steel ball and the specimen in the instrument is adjusted to find that the distance becomes shorter, while the toughness of the specimen increases and the plasticity decreases, and the best mechanical properties of the specimen are obtained by adjusting the distance between the steel ball and the specimen in the instrument. The strain and strain rate of the surface layer of the material are increased and the thickness of the gradient layer of the surface is thicker. In this paper, the rolling treatment of commercial pure titanium at low temperature and room temperature is carried out. It is found that the dislocation density of the sample is obtained under the condition of low temperature rolling (LNR) and low temperature rolling (LNR). The results of tensile and hardness experiments show that low temperature rolling can significantly increase the strength and hardness of the material while keeping the plasticity of the material. The analysis shows that low temperature environment can promote the transformation of deformation mechanism from dislocation mechanism to twinning mechanism. LNR50% samples are annealed at low temperature for a short time. The results of microcosmic test show that the deformation mechanism is changed from dislocation mechanism to twinning mechanism. After annealing for a short time at low temperature, the structure surrounded by small grain is obtained. In the tensile experiment, a very complex stress state can be produced in the sample due to the existence of this special structure. This stress state will promote the initiation of more slip systems and thus improve the work hardening of the materials. After annealing, a large number of large angle grain boundaries can be introduced, which is very significant for the improvement of the plasticity of the materials. The tensile test results show that a large number of large angle grain boundaries can be introduced after annealing. With the prolongation of annealing time or the increase of annealing temperature, the strength of the material decreases. The plasticity was improved. The best properties were obtained by annealing at 450 鈩，

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