【作者】 董明慧；

【导师】 韩培德；

【作者基本信息】 太原理工大学 ， 材料物理与化学， 2011， 硕士

【摘要】 层错能是材料塑性变形中的重要本征参数,对材料的脆性-韧性转变有着重要影响。常温下材料最常见的两种塑性变形方式是位错滑移和孪生,位错的滑移和孪生导致了滑移带和孪晶的产生。虽然滑移带和孪晶引起晶格的畸变量较小,但是层错能的高低,尤其是本征层错能(γisf)和非稳定层错能(γus),却影响着位错的形核、运动、束集、交滑移和分解。降低材料的层错能有利于进一步激发位错的滑移和孪生,从而改善材料的力学性能。N和Ni是奥氏体不锈钢中主要的合金化元素,对不锈钢的组织、性能有着重要影响。尽管实验上已有不锈钢γisf的值,但是测量过程对实验设备要求很高,并且只能获得γisf,且实验测得的γisf偏差较大。而计算材料科学的发展刚好弥补了实验上的不足,目前已经成功应用于Al、Fe、Cu、Ni等材料的层错能的研究。本论文采用基于密度泛函理论的第一性原理,从原子层次上研究了Ni、N对奥氏体不锈钢层错能的影响。主要研究内容如下：(1)研究了Ni、N对奥氏体不锈钢稳定性的影响。结果表明Ni、N固溶后都能够提高奥氏体不锈钢的稳定性,Ni、N的占位对于奥氏体不锈钢的稳定性影响不明显。(2)从电子层次上探索了Ni、N对于奥氏体不锈钢的影响：Ni固溶于奥氏体不锈钢后改善了Fe和Cr原子周围的电荷分布,加强了Cr原子和Fe原子之间的成键能力,N固溶于304不锈钢中能与Fe、Cr、Ni元素产生强烈的共价作用。(3)研究了Ni、N对奥氏体不锈钢γus、γisf的影响：Ni含量的增加,提高了位错滑移所需克服的势垒,增加了位错滑移的难度,而N的固溶却能够降低奥氏体不锈钢中位错滑移所需克服的势垒,有利于位错滑移。随着Ni含量的增加γus/γisf降低,有利于Frank全位错的形成,而γus/γisf却随着N含量的增加而增加,有利于Stockley部分位错和孪晶的形成。(4)综合分析对比了Ni、N对于奥氏体不锈钢的影响：Ni含量的增加使γus/γisf降低,但减缓的幅度很小,而微量的N含量即可使304奥氏体不锈钢的γus/γisf增加,且提高的幅度远高于镍。更多还原

【Abstract】 Stacking fault energies (SFE) is a crucial intrinsic parameter of materials plastic deformation, and has significient effect on brittle-to-ductile transition (BDT). At normal temperature, two of the most common and important plastic deformation modes of materials are dislocation slipping and deformation twinning, which will result in glide band (GB) and deformation twin (DT), respectively. GB and DT will not result in disorder of crystal obviously, however, the SFE, especially intrinsic stacking fault energies (γisf) and unstable stacking fault energies (γus), caused by crystal slipping, influence nucleation, movement, bundle, across glide, dissociation of dislocation. Reducing stacking fault energy of materials is conducive to further stimulate dislocation slipping and twinning, thus improving mechanical properties.Nitrogen and nickel belongs to key alloying elements in austenitic stainless steel, and has significient influence on texture and properties of austenitic stainless steel. Throughγisf had been got from experimental method, the criterion for experimental equipment is high, and cannot be measured the whole SFE curve except forγisf. In addition, the difference of results between various experimental methods is large. The development of calculational science remedy imperfection of experiment. At present, computational science has been successfully used to calculate SFE such as aluminium, iron, copper, nickel etc.Therefore, the first-principle, which based on density functional theory (DFT), is used to study the effect of nitrogen and nickel on SFE from atom and electron level. The main contents are as follows.(1) Effect of nickel and nitrogen on the stability of austenitic stainless steel was studied. The results show that nickel and nitrogen can stabilize austenitic stainless steel, and atomic position influence on stability is not obvious.(2) The effect of nitrogen and nickel on austenitic stainless steel was studied from electron level. Nickel doped in austenitic stainless steel can optimize density of electron around iron and chromium and imprive binding capacity of iron and chromium. Nitrogen doped in 304 austenitic stainless steel create covalence with iron, chromium and nickel.(3) The influence of nickel and nitrogen on yus,γisf of austenitic stainless steel was studied. With nickel content increase, the potential barrier which must be overcome for dislocation slipping increase. This will result whole dislocation dissociate partial dislocation difficulty. By contrast, nitrogen will decrease potential barrier, and result whole dislocation dissociate partial dislocation easy. For nickel content increase,γus/γisf will reduce which is beneficial for Frank whole dislocation formation. However, nitrogen will increaseγus/γisf and is beneficial for Shockley partial dislocation and twinning forming.(4) The comprehensive analyses of the effect of nickel and nitrogen on austenitic stainless steel indicate that nickel can reduceγus/γisf in small range. By contrast, a minute of nitrogen can increaseγus/γisf evidently compared with nickel.更多还原