合金化对FeCoNiCr系高熵合金组织及力学性能的影响

发布时间：2018-02-16 22:08

本文关键词： 高熵合金合金化组织结构析出强化力学性能　出处：《北京科技大学》2017年博士论文　论文类型：学位论文

【摘要】：高熵合金是上世纪90年代提出的一种全新的合金设计理念,其每种组成元素比例接近,但一般不超过35%。由于高混合熵效应,高熵合金一般形成简单固溶体,其晶格中存在较大的畸变,并因此衍生出了一系列特点,比如微观结构热稳定性高,扩散缓慢等,因而具有许多独特的性能。目前高熵合金的研究仍然处于起步阶段,许多科学问题亟待解决。首先,现有的高熵合金力学性能的研究,过多地集中在了室温压缩以及硬度上,而关系到能否实际应用的拉伸性能,却较少报道；其次,缺乏对成分-组织-性能关联的系统研究；最后,由于高熵合金突出的高温相稳定性以及迟滞扩散等特点,其在高温材料领域,具有极大的应用潜力,但是相应的研究仍十分匮乏。本论文以塑性优异、结构简单的面心立方(fcc) FeCoNiCr(Mn)系高熵合金为基础展开研究。首先,系统探索了A1元素在FeCoNiCrMn高熵合金中的合金化作用,发现A1的添加导致了合金微观组织从fcc向bcc(体心立方)的转变,而B2相的形成是拉伸强度提高及塑性降低的主要原因；其次,研究了FeCoNiCrMn高熵合金在1023～1123 K高温下的流变行为,发现其变形过程为扩散所主导,而微观组织变化表明其固溶体结构在低应力下不够稳定需要引入其它强化机制：再次,在上述结果基础上,通过同时引入合金化元素Ti和A1,成功地在FeCoNiCr高熵基体中析出了均匀弥散的纳米Y’第二相,在保持塑性优良的前提下,由于析出强化的作用显著提高了室温拉伸强度；随后又研究了Ti和Al含量以及热处理工艺对其组织结构和力学性能的影响,发现了γ’和Heusler相的析出竞争关系,确定了最优合金成分(FeCoNiCr)94Ti2A14;最后,研究了优化后合金的高温流变及蠕变性能,发现其稳态应变速率降低了约2个数量级,但是其硬脆的Heusler相及软弱的界面区域导致蠕变寿命略显不足。此外,本研究还初步探索了FeCoNiCrMn在不同模式(拉伸、压缩及扭转)下的动态变形行为。结果表明,晶粒细化(36μm)极大地促进了形变孪晶的发生,从而获得了优异的综合力学性能。
[Abstract]:High entropy alloy is a new design concept of alloy put forward in -10s. The proportion of each component element is close, but generally does not exceed 35.As a result of high mixing entropy effect, high entropy alloy generally forms simple solid solution. There is a large distortion in the lattice, and a series of characteristics have been derived, such as high thermal stability of microstructure, slow diffusion and so on, so it has many unique properties. At present, the study of high-entropy alloys is still in its infancy. Many scientific problems need to be solved. First, the existing research on mechanical properties of high-entropy alloys is focused on room temperature compression and hardness, but the tensile properties related to their practical application are seldom reported. There is no systematic study on the relationship between composition, microstructure and properties. Finally, high entropy alloys have great potential for application in the field of high temperature materials due to their outstanding high temperature phase stability and hysteresis diffusion. However, the corresponding research is still very scarce. This thesis is based on the high entropy alloy FeCoNiCr-Mn-based, which has excellent plasticity and simple structure. Firstly, the alloying effect of A1 element in FeCoNiCrMn high entropy alloy is systematically explored. It is found that the addition of A1 leads to the transformation of microstructure from fcc to BCC, while the formation of B2 phase is the main reason for the increase of tensile strength and the decrease of plasticity. Secondly, the rheological behavior of FeCoNiCrMn high entropy alloy at 1023 ~ 1123K is studied. It is found that the deformation process is dominated by diffusion, while the microstructure changes indicate that the instability of the solid solution structure under low stress requires the introduction of other strengthening mechanisms: thirdly, on the basis of the above results, By introducing alloying elements Ti and A1 at the same time, the uniformly dispersed second phase of nanometer Y 'was successfully precipitated in the high entropy matrix of FeCoNiCr. The tensile strength at room temperature was obviously increased because of the effect of precipitation strengthening on the premise of keeping good plasticity. Then the effects of Ti and Al contents and heat treatment on the microstructure and mechanical properties of the alloy were studied. The precipitated competition relationship between 纬 'and Heusler phase was found, and the optimum alloy composition, FeCoNiCrTi94Ti2A14, was determined. The rheological and creep properties of the optimized alloy at high temperature are studied. It is found that the steady strain rate of the alloy decreases by about two orders of magnitude, but the creep life of the alloy is slightly inadequate due to the hard and brittle Heusler phase and the weak interface region. The dynamic deformation behavior of FeCoNiCrMn in different modes (tensile, compression and torsion) was also preliminarily investigated. The results show that the grain refinement (36 渭 m) greatly promotes the occurrence of deformation twins, and the excellent comprehensive mechanical properties are obtained.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG139

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