Fe-V中间合金中σ相形成机理及其工业化技术应用研究

发布时间：2018-02-21 21:04

  本文关键词： σ相 拓扑密堆相 钒铁 原子半径比 电子因素　出处：《上海大学》2016年博士论文　论文类型：学位论文

【摘要】：通常情况下结构材料,特别是含有过渡金属元素的钴基或镍基高温合金以及高铬铁素体钢等材料中,拓扑密堆σ相的出现将严重破坏其性能,研究σ相的形成机理具有重要的科学意义及工程实用价值。深入认识该相的形成机理还有助于更好理解过渡金属的合金化行为,实现对其析出进行调控,可以有效规避该相对材料性能可能造成的致命危害。迄今为止,对σ相的形成规律及机理认识尚不清晰,相关研究主要集中在电子浓度及电负性等因素,较少涉及原子尺寸。单纯从电子因素角度出发的相关研究并不能解释σ相的形成机理且欠缺物理科学意义。本论文提出二元过渡金属σ相的形成同时受制于电子因素和原子尺寸因素,其化学键合为共存的金属键和非饱和共价键,后者居主导地位,正是由于共价键的存在并配合以恰当的原子尺寸才会导致拓扑密堆σ相的生成。本论文提出采用价电子总数(VET)概念描述过渡金属σ相中的化学键合,基于金属玻璃、二十面体准晶和拓扑密堆相在短程有序范围内局域结构非常相似的特点,引入金属玻璃高效堆积模型,提出原子尺寸参数R=rs/rl和1/R=rl/rs(rs和rl分别为较小原子和较大原子的半径)用以表征Frank-Kasper配位多面体形成的几何要求以及对σ相形成的影响。结果表明:在限定过渡金属范围内,12≤VET≤15能够涵盖目前所有存在σ相的二元合金体系,在此范围内满足0.896R0.955、1.0471/R1.116或0.976R1与11/R1.025条件时将有利于σ相的形成。在12≤VET≤15的范围内,上述几何条件还可以有效区分σ相,Laves和μ相。将该方法拓展至过渡金属二元系中的Laves相,我们进一步提出了d电子总数(DET)参数,发现1/R1.116可以作为Laves相液相析出的必要条件之一,满足该条件且处于5DET10范围内的过渡金属二元系倾向于形成Laves相。基于σ相形成对应着特定的原子尺寸参数范围这一特性,我们提出通过引入原子尺寸与σ相二元系组元差异较大的第三元素,通过造成原子尺寸参数的显著改变进而影响σ相的稳定性,最终实现抑制σ相析出的目的。在Fe-V合金体系验证实验结果表明,较大原子半径Al元素引入后可以有效抑制σ相的形成,且Al含量的临界成分与理论计算值吻合较好。相关研究成果为二元、三元甚至多元合金中σ相的析出控制提供了一种新的思路。针对现有直筒炉电铝热法冶炼钒铁出现的合金强度高,难破碎及细粉率高的难题,本论文基于这一思路提出了一种新的梯度式电铝热冶炼钒铁的工业化生产技术,该技术在工业化实际生产实践中显著改善了电铝热法冶炼FeV50的破碎性能。
[Abstract]:In general, structural materials, especially cobalt-based or nickel-base superalloys containing transition metal elements and high-chromium ferrite steels, the appearance of topological dense 蟽 phase will seriously damage their properties. It is of great scientific significance and practical value to study the formation mechanism of 蟽 phase. It is also helpful to understand the alloying behavior of transition metals and to regulate the precipitation of transition metals. So far, the formation law and mechanism of 蟽 phase are not clear, and the related studies mainly focus on the factors such as electron concentration and electronegativity, etc. Atomic size is less involved. The related studies from the angle of electronic factors alone can not explain the formation mechanism of 蟽 phase and lack of physical scientific significance. In this paper, it is proposed that the formation of 蟽 phase in binary transition metals is constrained by electrons at the same time. Factor and atomic size factor, Their chemical bonds are coexisting metal bonds and unsaturated covalent bonds, the latter being dominant. It is due to the existence of covalent bonds and the proper atomic size that the topological dense stack 蟽 phase is formed. In this paper, the concept of valence electron sum (VET) is used to describe the chemical bonding in the transition metal 蟽 phase, which is based on metallic glass. The local structure of 20 hedron quasicrystal and topological dense phase is very similar in the short range order range, so the metal glass high efficiency stacking model is introduced. It is proposed that the atomic dimension parameters Rnrsrl and Rnrrrrr _ s and r _ l are smaller atoms and larger atomic radii respectively) to characterize the geometric requirements of the formation of Frank-Kasper coordination polyhedrons and their effects on the formation of 蟽 -phase. The results show that the transition metal norm is limited to the transition metal norm. Weinai 12 鈮，

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