Ni3Al合金的滑移特征及形变过程的晶界行为

通过SEM动态拉伸形变试验,研究了具有各种化学成分和不同热处理态Ni_3Al合金的形变滑移特征,并用TEM观察了晶界区域的位错组态。研究结果表明,在含硼Ni_3Al合金的晶界附近存在一个过渡滑移区,该区域中滑移线重新取向或其它滑移系开动,从而产生了局部应变调节并使晶界应力集中松弛。硼降低了开动晶界位错源所需的应力并可能同时增加了位错源本身的数目。硼对Ni_3Al的韧化作用强烈受到基体Al含量、合金元素及热处理等因素的影响。     

硼对快凝Ni3Al组织结构及力学性能的影响

本文通过快凝及加硼合金化的方法改善金属间化合物Ni_3Al的韧性。实验表明:加入0.5-1.4at.-％的硼对Ni_3Al的塑性提高最有利。结构分析表明:在含1.37at.-％硼的Ni_3Al中,硼以Ni_(23)B_6弥散相及晶界偏聚方式存在;当硼量增至2.22at.-％时,硼以粗大的Ni_(23)B_6及NiB_(12)相在晶界处析出。无硼的Ni_3Al晶界为大角度晶界;当硼加至1.37at.-％时,Ni_3Al晶界以位错排列成亚晶界,以小角晶界形式存在。     

Ni3Al晶界结构的计算机模拟

本文运用嵌入原子法势函数和静态弛豫最陡梯度的计算方法,模拟[100],[110]和[111]轴一系列具有不同晶界几何参量及化学成分的Ni_3Al对称倾侧晶界原子结构、晶界能和晶界的内聚能、电荷密度分布及应力场等内容,并着重研究和讨论了它们与硼偏聚,Ni_3Al的晶界韧脆行为,特别是硼韧化的化学计量效应之间的关系。     

Ni3Al中Re诱导缺陷对螺位错交滑移的影响

Ni3Al的高温异常流变行为与超级部分位错的交滑移密切相关,本文利用第一性原理计算探究Re在Ni3Al晶体中的占位倾向及Re效应对Ni3Al中位错形核与运动的影响。由Re占据Ni3Al不同晶格点位所对应的点缺陷形成焓及能量因子,可知单个Re原子在Ni3Al中优先占据Al位,两个Re原子优先占据Al-Al位。通过对Ni3Al晶体和滑移系广义堆垛层错能的计算,发现Re原子占据Al位能促进超级部分位错的交滑移。两个Re原子垂直滑移方向排列比沿着滑移方向排列能有效阻碍位错形核与运动;两个Re原子排布在相邻原子面上比排列在同一个原子面上时会进一步促进螺位错的交滑移。分析缺陷和间的关联能对Ni3Al晶体超级部分位错交滑移的影响,结果表明缺陷和间较弱的交互作用有利于改善高温时Ni3Al的异常流变行为。Re原子优先占据Al位置提高Ni3Al的屈服强度能够归功于间的弱交互作用。     

Ni/Ni3Al拉伸力学性能的分子动力学模拟

采用分子动力学方法研究了Ni/Ni_3Al的拉伸力学性能。首先模拟了在室温、恒定应变速率环境下γ′强化相的含量对Ni/Ni_3Al拉伸力学性能的影响,重点研究了具有3种典型特征的γ′强化相含量的Ni/Ni_3Al微观组织演化。研究结果表明:相比于单晶Ni,γ′强化相可以提高Ni/Ni_3Al的抗拉强度。这是因为在塑性变形过程中,随着位错的不断增殖,位错密度逐渐增大,导致位错塞积,增大了位错运动的阻力,提高了抗拉强度。接着研究了温度对Ni/Ni_3Al拉伸力学性能的影响,发现Ni/10%Ni3Al(体积分数,下同)的抗拉强度随着温度的升高呈下降趋势。这是因为随着温度的升高,原子动能增大,导致原子热运动更剧烈,原子间的结合力更弱,脱离平衡位置的原子来不及回到平衡位置,fcc结构转变为大量的hcp结构和其他无序原子排列结构,导致晶格畸变,降低了抗拉强度。最后研究了应变速率对Ni/Ni_3Al的拉伸力学性能的影响,结果表明,抗拉强度对低应变速率不敏感,对高应变速率敏感。     

铸造Ni_3Al基合金疲劳裂纹扩展的电镜断口观察

本文研究了微量元素硼、锆和钛等对铸造Ni_3Al基合金疲劳行为的影响,并用S360扫描电镜观察其循环形变(滑移),疲劳裂纹萌生和扩展特征,以及研究γ′(Ni_3Al)相(包括γ′+γ共晶小大,分布)和γ′+γ/γ相界而,Ni_3Al多晶体晶界和缺陷淀对疲劳裂纹生长的影响。     

金属锆中螺位错与孪晶界反应的原子模拟（英文）

采用分子静力学模拟密排六方金属锆中孪晶界与螺位错之间的交互作用。在移动晶界模型中,研究一个移动的{1012}孪晶界与一个静止的1120螺位错之间的交互作用。在此类交互作用中孪晶位错的形核与移动起到了重要的作用。静止的螺位错穿过了孪晶界并转换为基面上的一个具有宽位错芯的缺陷。在移动位错模型中,一个移动的1120位错穿过孪晶界并转换为两个基面部分位错及它们之间的一段极短的层错。如果在同一个模型中将孪晶界置换为{1011}类型,这个移动的1120柱面螺位错将被完全吸收并分解为孪晶界上的两个孪晶位错。分析相应的应力-应变曲线与缺陷结构,揭示位错与孪晶界之间的复杂交互作用。     

两种高温合金渗Al防护层的退化过程

研究了两种镍基高温合金上的渗Al层的退化过程。两种合金用两种方法施加的涂层组织相似:外层以NiAl Ni_2Al_3为母体,上面弥散着Ti(C,N)和Al_3Ti;内层由NiAl,Ni_3Al,Ti(C,N),M_(23)C_6和M_6C等相组成。渗Al层高温氧化时的退化与外层相变紧密相关,其过程如下: Ni_2Al_3 NiAl(富Al)→NiAl(富Ni)→NiAl Ni_3Al→Ni_3Al→Ni_3Al γNi_2Al_3和NiAl(富Al)相极不稳定,而NiAl(富Ni)相十分稳定。Ni_3Al沿NiAl晶界生核标志着渗层退化的开始,渗层NiAl完全变成Ni_3Al γ是退化的终了。     

Zr对铸造Ni3Al合金塑性的影响

大量压缩和拉伸实验表明:在无硼Ni_3Al合金中加入适量的Zr可使其具有较好的室温塑性,Zr对Ni_3Al合金的韧化作用并不局限于富Ni的Ni_3Al合金,对Al含量略高于化学计量成分的Ni_3Al也有一定的韧化作用,而且Zr在晶界仅略有偏聚,因此,可以认为Zr对Ni_3Al合金的韧化机理与硼不同,Zr对改善中温脆性和提高高温塑性也都具有一定的效果     

DETERIORATION OF ALUMINIDE COATING ON NICKEL-BASE SUPERALLOYS

研究了两种镍基高温合金上的渗Al层的退化过程。两种合金用两种方法施加的涂层组织相似:外层以NiAl+Ni_2Al_3为母体,上面弥散着Ti(C,N)和Al_3Ti;内层由NiAl,Ni_3Al,Ti(C,N),M_(23)C_6和M_6C等相组成。渗Al层高温氧化时的退化与外层相变紧密相关,其过程如下: Ni_2Al_3+NiAl(富Al)→NiAl(富Ni)→NiAl+Ni_3Al→Ni_3Al→Ni_3Al+γ Ni_2Al_3和NiAl(富Al)相极不稳定,而NiAl(富Ni)相十分稳定。Ni_3Al沿NiAl晶界生核标志着渗层退化的开始,渗层NiAl完全变成Ni_3Al+γ是退化的终了。     

Al-Zn-Mg-Cu系铝合金中不同区域电子结构及应力腐蚀机理分析

利用计算机编程建立了Al--Zn--Mg--Cu合金 (7175铝合金) 中α--Al, η相及α--Al大角度晶界原子集团模型, 采用递归法计算 合金中Zn, Mg, Cu和H的环境敏感镶嵌能、原子间相互作用能、Fermi能级和态密度等电子结构参数, 分析了合金的应力腐蚀机理. 计算 结果表明: Mg, Cu和H容易在晶界偏析. Mg对H具有吸引作用, 促进H在晶界偏析, 引起晶界氢脆; Zn增大晶界与晶内的电位差, 降低合 金抗腐蚀性; Cu能减小晶界与晶内Fermi能级差, 降低晶界与晶内的电位差, 具有减缓合金腐蚀的作用. 计算结果还表明: η相的Fermi能 级最高, 腐蚀过程中作为阳极优先溶解. 由于η相俘获H, 当晶界析出断续η相时可减弱晶界H的偏析, 提高抗腐蚀性; 但晶界连续分布η相则形成腐蚀通道, 加速腐蚀进程.     

Phase field crystal model of solute drag

The atomic scale interaction of solute with a migrating grain boundary has been studied using a binary phase field crystal (PFC) model. This model bridges between atomistic and continuum simulation techniques as it operates on diffusive timescales but at atomistic length scales. For this study, a two-dimensional channel containing two grains separated by a flat grain boundary has been constructed that allows for a channel length on the order of one micrometer. A new formalism has been developed to allow for the application of an external driving pressure for the growth of one grain. These simulations account for solute/grain boundary interactions, resulting in a solute drag effect on the grain boundary motion. The PFC simulations show good agreement with classical solute drag theory, though deviations due to the atomic scale nature of the interface exist.     

Computation of Five-Dimensional Grain Boundary Energy

A broken-bond type computational method has been developed for the calculation of the five-dimensional grain boundary energy. The model allows quick quantification of the unrelaxed five-dimensionally specified grain boundary energy in arbitrary orientations. It has been validated on some face-centred cubic metals. The stereo projections of grain boundary energy of ∑3,∑5,∑7,∑9,∑11,∑17 b and ∑31a have been studied. The results of Ni closely resemble experimentally determined grain boundary energy distribution figures, suggesting that the overall anisotropy of grain boundary energy can be reasonably approximated by the present simple model. Owing to the overlooking of relaxation matter, the absolute values of energy calculated in present model are found to be higher than molecular dynamic-based results by a consistent magnitude, which is 1 J/m2 for Ni. The coverage of present method forms a bridge between atomistic and meso-scale simulations regarding polycrystalline microstructure.     

SIMULATIVE INVESTIGATION OF GRAIN BOUNDARIES IN NiAl ALLOY

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Calculation of Second Phase Particle-Grain Boundary Interaction Range

On the basis of the grain boundary equation by HeUman and corresponding analysis of Worner, this article deals with the interaction range between the second-phase particle （SPP） and grain boundary （GB） as viewed from the applicability of grain boundary equation. Also, a new expression describing the interaction range has been derived, which solves the problem in theory that the interaction range between SPP and GB can only be qualitatively analyzed previously. It is shown that given the interaction position between SPP and GB, the interaction range can be quantitatively determined by use of this expression.     

The influence of boron-doping on the effectiveness of grain boundary hardening in Ni3Al

The influence of boron-doping on the effectiveness of grain boundary hardening in Ni₃Al has been investigated by measuring microhardness profiles across grain boundaries of binary and boron-doped Ni₃Al bicrystals. It was found that although boron gives rise to significant solution strengthening in Ni₃Al, the effectiveness of grain boundary hardening in Ni₃Al is lessened by the addition of boron. Furthermore, the contribution of grain boundary hardening to the overall strength decreases as the segregation extent of boron at the grain boundary increases. A theoretical model of grain boundary hardening considering the various effects of boron-doping has been developed. Application of the model can deconvolute the individual effects of boron-doping on solution hardening, distribution of microcavities along grain boundaries and the interaction of dislocations on different slip systems. Analyzing the experimental results with the model suggests that boron-doping can (i) improve the transfer efficiency of shear stress across a grain boundary by reducing the amount of microcavities along the grain boundary; (ii) suppress the hardening effect from the interaction of dislocations moving on different slip systems and (iii) cause a significant solution hardening effect.     

高阻尼镁合金Mg-0.6%Zr和Mg-Ni中内耗峰分析

在高阻尼镁合金研究中,发现了与合金室温下高阻尼性能有关的宽的弛豫内耗峰,该峰为位错内耗峰;该峰是基面位错在热激活作用下运动与点缺陷（空位与溶质原子）相互作用产生。同时在高阻尼合金Mg-Ni和Mg-0.6%Zr中发现了晶界内耗峰。有必要指出的是合金的显微组织会影响晶界弛豫：随着Ni的质量分数增加,晶粒细化同时晶界内耗峰向低温处迁移;同Mg-0.6%Zr合金相比,加入少量的Y后,Mg-0.6%Zr-Y合金晶界弛豫峰向高温处推进。     

Grain boundary segregation of phosphorus in iron-vanadium alloys

Grain boundary segregation of phosphorus has been studied in Fe---V---P and Fe---V---P---C alloys through fracture experiments in a scanning Auger microprobe with the objective of examining the effects of vanadium on the interaction processes operative under circumstances when the structure in the interior of the grain (in the present case carbide formation) and grain boundary segregation occur simultaneously. It is understood that to predict and analyse the behaviour of an alloy, it is pertinent to consider the atomic interactions both at the grain boundaries and in the grain interior and that between the constituents and the grain boundaries. The study suggests that the determining factor for suppression or decrease in the migration of phosphorus to the grain boundaries is whether vanadium is present in the combined form (say, carbide) or is available in solid solution form. When vanadium is present in solid solution form, grain boundary segregation of phosphorus is low because of the chemical interaction of vanadium and phosphorus. However, as carbon is increasingly introduced in the alloy, vanadium now preferentially interacts with carbon in view of a higher interaction for carbon as compared to that of phosphorus. A consequence of this is an increase in the grain boundary concentration of phosphorus. In such a situation, the presence of excess carbon in addition to what is stoichiometrically required to precipitate the entire vanadium as vanadium carbides serves as a palliative with regard to the reduction in the intergranular concentration of phosphorus. This palliative behaviour is explained in terms of the site-competition model. An effort is also made to examine the behaviour of segregating elements in terms of a whole range of probable interactions (both at the grain boundaries and in the grain interior) and chemical interaction energies.     

THE MECHANISM OF NON-EQUILIBRIUM SEGREGATION OF BORON TO AUSTENITE GRAIN BOUNDARIES

业已证实,淬火硼钢中硼向奥氏体晶界的偏聚,是在冷却过程中发生的一种非平衡的晶界偏聚。本文通过解变温扩散方程,导出了非平衡晶界偏聚的理论公式,建立了晶界贫硼区宽度与淬火加热温度、冷却速度以及非平衡晶界偏聚扩散激活能与扩散常数之间的关系,理论预言与实验结果较好地吻合。 根据实验结果和理论分析,提出这种非平衡晶界偏聚的机制,是在冷却过程中,过饱和空位或双空位带着硼原子向晶界(空位阱)迁移的结果。 基于这种非平衡晶界偏聚的新概念,可以较完满地说明影响硼钢淬透性的众多复杂因素。     

The effect of grain boundary microstructure on Barkhausen noise in ferromagnetic materials

The Barkhausen noise (BHN) was measured in ferromagnetic materials to investigate the interaction between the grain boundary microstructure and magnetic domain walls. The grain-size effect of the BHN was studied for pure iron specimens. The Hall–Petch type relationship between the grain-size and the BHN power was found. The effect of the grain-boundary misorientation on the BHN was also studied for silicon steel specimens. The BHN power increased with increasing the grain boundary misorientation angle. It has been suggested that the arrangement of magnetic domains along a grain boundary can be affected by the grain boundary character and that hysteresis of magnetization can be optimized by controlling the grain boundary microstructure in ferromagnetic materials. The importance of understanding the behavior of magnetic domains was discussed in terms of the control of magnetic properties in ferromagnetic materials.