钛合金中合金元素与位错交互作用与高温强化

通过计算机编程建立钛的→b=-1/3〈1 1 -2 0〉刃位错模型,用实空间的连分数方法计算合金元素以及稀土元素在完整晶体及位错区引起的总结构能、环境敏感镶嵌能以及各合金元素与钛的键级积分,讨论合金元素在位错区的偏聚及交互作用.计算结果表明,Al和Sn在位错扩张区偏聚,Mo,W等合金元素以及稀土元素易于在位错芯区偏聚,这些偏聚为第二相粒子析出提供了条件,从而阻碍位错运动,提高了Ti合金蠕变性能.Al与Ti的作用最强,固溶强化效果最好.稀土主要是通过细化晶粒,提高钛合金蠕变性能的.     

Fe中掺Ti刃型位错体系的电子结构研究

能量计算结果表明,在铁基刃型位错芯处掺入合金化元素Ti后,掺杂体系的结合能比纯刃型位错体系的结合能降低,这意味着置换型掺杂刃型位错体系具有相对的稳定性.杂质形成能计算预期Ti在位错芯区的偏聚倾向,反映了位错芯对杂质Ti的捕获效应.从原子间相互作用能计算和Mulliken轨道占据数的分析中发现掺杂体系中Ti原子与其近邻基体Fe原子间具有强相互作用及电荷转移,形成较强的电荷关联区.原子间键合力增强,将影响刃型位错在基体中的力学行为.考虑到掺Ti对位错芯区电子结构及能量的影响可得出结论:Fe中掺Ti的量子力学计算发现微量合金化元素Ti具有固溶强化效应,影响过渡金属的力学性质.     

高纯Fe-0.2%P-2%Cr-C合金晶界的高分辨俄歇能谱分析

利用高分辨俄歇能谱仪研究了高纯Fe 0 2 %P 2 %Cr C合金的晶界·结果表明 ,沿晶断面上有大量尺寸约 0 3 μm的颗粒状碳化物·碳化物处碳的PHR值分别为 3 4 9%和 3 3 3 % ,铬的PHR值为 1 4 6%和 7 3 % ,碳化物为富铬碳化物 ;晶界上无碳化物处存在显著的磷偏聚和碳偏聚 ,磷的平均偏聚量分别为 2 0 2 %和 1 9 6% (PHR) ,晶界富集系数为 5 6和 5 4,碳的PHR值分别为 8 6%和 1 2 6% ,晶界富集系数为 3 0 8和 45 0 ;随合金碳量增加 ,碳在晶界偏聚量增加 ,磷的偏聚量稍有降低     

耐热钢12Cr1MoV高温时效中的耗散结构

介绍了非平衡系统的自组织现象和耗散结构,概述了珠光体耐热钢12Cr1MoV原始组织结构非平衡状态的特征、高温时效后成分和组织结构变化的主要结果,并对材料发生自组织行为的条件作了具体分析.指出12Cr1MoV钢在高温长时时效中产生的3类耗散结构特征是:合金元素、碳的晶界偏聚及脱溶沉淀;碳化物由晶内无序分布状态到晶界上的有序分布;位错数量减少及有序的特征形态.     

回火次数对P91焊管接头力学性能的影响

采用光学显微镜、X射线衍射分析、透射电镜、选区电子衍射及常温与高温拉伸试验等检测手段,基于不同回火次数下P91焊接接头显微组织的演化过程研究其对力学性能的影响.结果表明,随着回火次数的增多,接头显微组织主要保留了板条马氏体位向的回火索氏体,主要相为α-Fe相和Fe-Cr相,热影响区的室温及高温强度先增大后减小.在回火一次时,弥散析出的MX(M=V/Nb,X=C/N)型碳氮化物、位错缠结及亚稳态的位错网对接头有一定的析出强化及位错强化作用,其力学性能较佳,高温抗拉强度达最大值232.66MPa;随着回火次数进一步增多,离散分布的碳化物Cr23C6逐渐偏聚并在晶界处演化为串链状分布,使晶界脆化,强度降低,但韧性有所改善.     

粉末高温合金平衡相析出行为的热力学对比

利用热力学平衡相计算方法及相应的高温合金数据库对René95,Rene88DT和эп741нп三种合金在平衡相析出温度范围和析出量以及之间的关联性进行了系统的热力学计算对比分析.结果表明:三种粉末高温合金的平衡相种类基本相同,主要平衡相为γ,γ'和碳化物M23C6,MC,M6C.René95合金中的碳化物含量要高于其他两种合金.3п741нп有着较高的γ'相析出温度和较大的析出量.随温度降低,Co和Nb从γ'相中析出,在其周围富集,其中3п741нп合金中尤为明显.合金元素的偏聚度也和合金的初熔点与终熔点之差的大小有关,其熔解区间越大即初熔点和终熔点之差越大,合金元素的偏聚度越大.     

Cr25Ni35Nb和Cr35Ni45Nb裂解炉管的抗高温渗碳能力

以Cr25Ni35Nb和Cr35Ni45Nb合金为炉管材料对象,通过渗碳试验研究了高温(1 000和1 100 °C)下2种合金的渗碳动力学规律,采用金相和扫描电子显微镜观察分析其中Fe、Cr、Ni与Nb元素含量和渗碳层变化、组织结构及微区成分转变的情况,并对其抗渗碳能力进行分析.结果表明：Cr35Ni45Nb的抗渗碳能力比Cr25Ni35Nb更强;经2次渗碳后,2种合金试样出现了表面渗碳层剥落的现象,且Cr25Ni35Nb较为严重,并使得裂解炉管结焦而管壁变薄,从而降低了炉管的承载能力和服役寿命;合金的非渗碳层区域析出了大量弥散的碳化物,碳化物的密度随渗碳层与试样表面距离的增加而降低;在1 100 °C下,2种合金的骨架状组织形态消失,且晶界处碳化物出现了剥离.     

无钴高强高韧钢中奥氏体相价的电子结构

利用固体与分子经验电子理论(EET)对无钴高强高韧钢奥氏体中含碳与不含碳晶胞的价电子结构进行了计算和分析·得到含碳晶胞的nA值大于不含碳晶胞的nA值,故在相的转变中主要考虑含碳晶胞的影响·在含碳晶胞中合金元素Ni,Si,Cr,Mo与碳原子形成偏聚区,且Ni,Si与C的结合力比Cr,Mo的大,偏聚区能降低C的扩散能力,阻碍位错运动,推迟马氏体相变;使基体中保持高度的位错,也会导致材料中有一定数量的残余奥氏体,并细化奥氏体晶粒,使转变的马氏体尺寸减小,这对材料的韧性有利·     

锌铝合金中稀土及杂质的晶界行为

用分子动力学方法获得了液态ZA27合金的原子集团,构造出ZA27合金α相与液相界面原子模型及α相大角度晶界模型.采用递归法计算了稀土及杂质元素在晶粒内、固液相界面及α相晶界处的环境敏感镶嵌能,分析了这些元素对晶界处铝、锌之间电子转移量的影响.从理论角度说明稀土、杂质元素在结晶时富集于固液相界前沿液体中,合金凝固后偏聚于晶界,并在晶界产生复杂的交互作用,进而影响合金的使用性能.     

热时效和辐照环境下Fe-Cr-Mn奥氏体钢晶界溶质元素偏聚和相析出

研究了含2％W和V的Fe-Cr-Mn合金经热时效处理和电子辐照条件下,溶质元素晶界偏聚和析出相的行为。实验结果表明:在含W、V合金中热时效引起Cr、Mn晶界贫化,它决定于富Cr碳化物M_(23)C_6中组元组成。辐照条件下,两种合金中Cr、Mn都发生晶界贫化,它决定于辐照产生空位浓度和空洞体胀量,辐照诱起晶界元素偏聚影响析出相成分。     

热作模具钢淬火回火态的内耗谱分析

对热作模具钢淬火后回火态试样的内耗谱进行了分析.研究表明，淬火态试样的内耗谱由3部分构成.其中：157.2 °C处的内耗峰是由于体心立方结构的马氏体晶格畸变引起应力感生碳原子微扩散的结果；225.5 °C处为溶质原子与位错交互作用产生的SKK峰及其背景内耗峰.随着回火温度升高，SKK峰的弛豫强度逐渐减小，此时，碳原子与部分合金元素以碳化物形式结合而从基体中析出，使得其晶格畸变减弱，157.2 °C处的内耗峰消失；部分碳化物在位错处形核并使位错段增长、弛豫时间增大；内耗峰位置的移动主要归因于合金元素与碳原子的作用.     

9SiCr工具钢表面激光熔覆合金的组织与性能

使用CO2激光器对9SiCr工具钢表面进行Co基和Ni基合金熔覆处理,X射线衍射仪、扫描电子显微镜分析了激光合金熔覆层的相组成和显微组织;显微硬度计对合金熔覆区的显微硬度进行测量·结果表明,合金熔覆层在微观结构上存在熔覆区、结合区和基体热影响3个区域·Co基合金熔覆区相组成为奥氏体+铁素体+碳化物,Ni基合金熔覆区相组成为奥氏体+铁素体+碳化物+金属间化合物·Ni基合金熔覆层的显微硬度约为Co基的2倍     

Precipitation behaviors of X80 acicular ferrite pipeline steel

The precipitation behaviors of X80 acicular ferrite pipeline steel were investigated by using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The results show that dendritic precipitates in the as-cast steel slabs precipitate mainly in grain boundaries, and these dendritic precipitates dissolve and re-precipitate to two kinds of carbonitrides: Ti- and Nb-rich (Ti, Nb)(C, N) carbonitrides during reheating. Four types of precipitates mainly exist in the hot rolled plate: Ti-rich carbonitrides resulted from the dendritic carbonitrides undissolved during the reheating process; Ti-rich carbonitrides re-precipitated along austenite grain boundaries during the reheating process; NbC carbides mainly heterogeneously nucleated on the small pre-existing Nb-rich carbonitrides in the hot rolling process; and NbC carbides precipitated on dislocations during hot rolling.     

Effect of rare earth and alloying elements on the thermal conductivity of austenitic medium manganese steel

The influence of different contents of Cr, Mo, and rare earth element (RE) additives on the thermal conductivity of austenitic medium manganese steel was studied and discussed. The results show that the addition of Cr in medium manganese steel can improved the ordering of C-Mn atomic clusters, so as to improve the steel's thermal conductivity. However, Cr will lead to precipitation of a great deal of carbides in medium manganese steel when its content is greater than 4wt%. These carbides would aggregate around the grain boundary, and as a result, the thermal conductivity is decreased. By the addition of Mo whose content is about 2wt%, spherical carbides will be formed, thus improving the thermal conductivity of the medium manganese steel. The interaction between rare earth elements and alloying elements will raise both the thermal conductivity and the wear-resisting property of medium manganese steel.     

Fe-∑M-C多元合金奥氏体中碳活度的估算

本文证明了在三元以上的合金钢中,当奥氏体与碳化物相平衡时,合金元素对奥氏体中碳活度的影响具有叠加性质。根据M.Hillert模型推导了在这种条件下多元合金钢奥氏体中的碳活度的关系式,认为合金元素、铁在碳化物-奥氏体间的分配系数是很重要的。据此可以计算合金奥氏体中的碳活度,根据上述方法求出的碳活度,预测了实用合金钢内氧化型渗碳时所需要的碳势,预测值与实验结果符合较好。     

共析钢经表面研磨处理后微观组织的演化

利用表面研磨处理(SMAT)在共析钢上制备出具有纳米晶体结构的表面层,并利用X射线衍射和透射电镜分析了纳米表面层的微观组织结构及其演变.结果表明:原始组织为层片状铁素体 渗碳体两相复合组织的共析钢经过SMAT后,铁素体晶粒由于位错产生、位错缠结形成位错胞,然后分割晶粒使铁素体细化至纳米尺度,而渗碳体在强烈塑性变形下,经历弯曲、断裂,最终分解成体心立方铁素体和底心正交的石墨.     

应用JMatPro软件对比研究两种抽油杆钢的合金化特点

采用JMatPro软件对比研究了两种抽油杆钢不同温度下的平衡相及其成分.结果表明,与7Mn2SiCr钢相比,12MnSi2Cr钢铁素体、奥氏体相中将固溶更多的Cr,Mo,Si元素,而碳化物总量减少了30％,微合金元素Nb的加入提高了钢中M(C,N)碳化物的稳定性.在此基础上,对12MnSi2Cr抽油杆钢的高韧性进行了探讨.     

First-principles investigation of the impurity-kink interaction in bcc iron

Using the first-principles self-consistent discrete variational method based on density functional theory, we investigated the effect of light impurities C and N on the electronic structure of kink on the [100]（010） edge dislocation （ED） in bcc iron. Our energetic calculations show that the light impurities have a strong segregation tendency to enter the kink. The results of the charge distribution and the local density of states indicate that the strong bonds between the impurity atoms and the neighboring Fe atoms are formed due to the hybridizations of impurity atoms 2p states and Fe 3d4s4p states. The introduction of light impurities can stabilize the kink system, and impedes the sideward motion of the kink in the [100]（010） ED. This is, the light impurities induce a strong pinning effect on the [100]（010） ED and may result in the solid solute hardening.     

Striped iron zoning of olivine induced by dislocation creep in deformed peridotites.

Deformation of solid materials affects not only their microstructures, but also their microchemistries. Although chemical unmixing of initially homogeneous multicomponent solids is known to occur during deformation by diffusion creep, there has been no report on their chemical zoning due to deformation by dislocation creep, in either natural samples or laboratory experiments. Here we report striped iron zoning of olivine ((Mg,Fe)2SiO4) in deformed peridotites, where the iron concentration increases at subgrain boundaries composed of edge dislocations. We infer that this zoning is probably formed by alignment of edge dislocations dragging a so-called Cottrell 'atmosphere' of solute atoms (iron in this case) into subgrain boundaries during deformation of the olivine by dislocation creep. We have found that the iron zoning does not develop in laboratory experiments of high strain rates where dislocations move too fast to drag the Cottrell atmosphere. This phenomenon might have important implications for the generation of deep-focus earthquakes, as transformation of olivine to high-pressure phases preferentially occurs in high-iron regions, and therefore along subgrain boundaries which would be preferentially aligned in plastically deformed mantle peridotites.     

Unique cyclic deformation behavior of a heavily alloyed Al–Si piston alloy at different temperatures

The cyclic deformation behavior of a near-eutectic Al–Si piston alloy with a variety of alloying elements is investigated. Due to the distinctive microstructure, the alloy exhibited various cyclic deformation characteristics at different temperatures. Unique double-stage cyclic hardening occurred at room temperature, while the first hardening was mainly caused by the interaction between the dislocations and the finely dispersive precipitates, and the dislocation/dislocation interaction resulted in the second hardening. At elevated temperatures (200 1C and 350 1C), the alloy mainly presented cyclic softening because of the fact that the thermally activated dislocations could bypass or shear the obstructive precipitates.