晶粒尺寸对304奥氏体不锈钢组织演变和性能的影响

研究了初始织构相近而晶粒尺寸不同的304奥氏体不锈钢在后续10%压缩变形和热处理过程中微观组织、力学和耐蚀性的变化。结果表明,具有相似织构而晶粒尺寸不同的样品变形热处理后其织构不同,粗晶在变形中织构的变化更大;织构相近时抗拉强度对晶粒尺寸的依赖较大;织构不同时,织构对硬度和抗拉强度的影响大于晶粒尺寸和微应变的影响;变形热处理后普通大角度晶界和晶内微应变的增大降低了试样的耐腐蚀性能;初始晶粒尺寸较小的试样在变形热处理后出现四种密排面平行于外表面的织构,其耐点蚀的性能更优。     

稀土铈与磷相互作用对纯铜晶粒尺寸和导电性能的影响

在纯铜铸锭中添加不同含量的稀土铈和磷元素,借助电导率测试和微观组织结构分析,研究了稀土铈与磷元素相互作用对纯铜晶粒尺寸和导电性能的影响,阐明了铈、磷元素相互作用影响含磷纯铜晶粒尺寸与导电性能的有关机理.结果表明:纯铜中稀土铈与磷元素相互作用可显著细化铸锭晶粒尺寸,并提高其电导率.含0.016％磷纯铜中添加稀土铈后,晶粒尺寸可由963.67μm减小至198.75μm,晶粒形态由柱状晶转变为等轴晶;电导率随稀土铈含量的增加呈先提高后降低的趋势,铈含量增加至0.014％时,电导率可由81.16％lACS提高至96.14％lACS.这主要与稀土铈可以和磷相互作用形成铈磷化合物有关;一方面,铈磷化合物的形成可抑制磷元素凝固偏析而导致的柱状晶长大,并起到钉扎阻碍晶粒长大的作用;另一方面,可降低铜中固溶磷含量而提高导电性能,但铈过量时将会导致晶界和第二相数量过多、铜材纯度降低,进而影响电子散射而降低其导电性能.     

基于EBSD技术的超低碳IF钢中铁素体晶粒尺寸表征

借助电子背散射衍射(EBSD)技术对超低碳IF钢铁素体晶粒尺寸的表征方法进行了研究与探讨。结果显示,对于具有较强织构的IF钢来讲,铁素体晶粒显示以5°为晶内最大取向差进行晶粒尺寸的测量与统计更为准确,与金相法显示的晶界轮廓基本吻合。利用该表征方法测量晶粒尺寸,不仅可以给出晶粒尺寸的平均值、最大值和最小值,还可以给出晶粒尺寸分布图。     

AZ91D镁合金的晶粒细化

AZ91D镁合金属于密排六方结构，它在塑性变形性能和力学性能上呈现较低的特征。采用晶粒细化的方法可在很大程度上改善镁合金的力学性能。选用MgCO3，La2(CO3)3及两者的混和物分别作为AZ91D镁合金的细化剂。实验结果表明，MgCO3和La2(CO3)3作为镁合金的细化剂各有特点，而用MgCO3与La2(CO3)3的混和物细化效果更好。     

电磁-悬浮铸造对变形镁合金晶粒细化的影响

在悬浮铸造的基础上引入了电磁搅拌,并将其与悬浮铸造的优点有机结合,通过不同电磁搅拌时间对悬浮铸造AZ61变形镁合金进行了试验,悬浮剂的加入使合金液中形成了大的能量起伏和成分起伏,有助于形成细晶组织,电磁搅拌的引入加速了悬浮剂和合金母液的均匀混合,有效避免了悬浮剂在合金液中的聚集"搭桥"现象和悬浮剂在铸件中的夹生,结果表明在悬浮剂为2%(质量分数)时进行2 min搅拌时效果最佳,组织的平均晶粒度最小,达到57.5 μm,是悬浮铸造时的三分之一,是金属型铸造的四分之一.析出相Mg17Al12明显减少和细化,并且在基体上的分布更加弥散.电磁悬浮铸造(2min,2%)对比金属型铸造,抗拉强度提高了约20%,屈服强度提高了约30%,延伸率提高了近50%.     

镁合金晶粒细化的研究进展

综述了变质剂处理法、熔体搅拌法、快速凝固、过热处理等液态工艺和热挤压、等通道角挤压、大比率挤压等固态成型工艺对镁合金晶粒细化的研究进展,系统地讨论了细化剂细化机理、工艺的研究现状和存在的问题,为镁合金晶粒细化的发展和研究提供一些思路和参考。     

Mg-Al基镁合金晶粒细化的研究进展

综述了添加含碳变质剂,含钛、硼细化剂,碱金属,碳族元素,氮族元素,稀土元素和准晶合金对Mg-Al基镁合金晶粒细化的研究进展,系统讨论了各种细化剂对Mg-Al基镁合金的晶粒细化效果,以及对各种细化剂细化机理的研究,旨在为镁合金晶粒细化研究提供一个参考.     

钛屑再生制备Al-Ti-B细化剂及其晶粒细化行为的研究

钛及钛合金属于难切削加工材料,生产过程中易产生大量废屑,再生利用钛屑已成为急需解决的问题.本文利用钛屑和氟硼酸钾在铝熔体中反应制备了Al-5Ti-1B细化剂,通过金相显微镜、扫描电子显微镜和X射线衍射仪对细化剂进行分析,研究了细化剂加入量和保温时间对工业纯铝细化效果的影响.研究表明,Al-5Ti-1B细化剂主要由α-Al、TiAl3和TiB2相组成,TiAl3相主要为块状,尺寸为10~30μm;TiB2相均匀分布在合金中,平均尺寸小于2μm。随着细化剂加入量的增加,晶粒尺寸不断减小;当加入量达到0.3%时,晶粒细化效果最好,进一步增大细化剂添加量,晶粒尺寸下降不明显。细化剂保温60 min时,晶粒细化效果良好;保温120 min时,出现了严重的细化衰退现象,晶粒尺寸达到953μm;商业杆状细化剂保温120 min时未出现明显的细化衰退。     

K4169高温合金化学法晶粒细化工艺及机理的研究

(1)本研究工作针对K4169高温合金的结构和物性特点,筛选并制备了适合K4169高温合金的二元和三元金属间化合物型细化剂。微量细化剂的加入不形成夹杂,不改变合金的相组成。(2)在通常的浇注温度1400℃下,对合金熔体进行和不进行均匀化处理的前提下,加入复合细化剂可使圆柱锭的晶粒分别细化至ASTM 1.7级和ASTM 3.2级;断面等轴晶的比例分别达96％和99％以上。当浇注温度为1420℃并对合金熔体进行了均匀化处理时,加入复合细化剂可使晶粒细化至ASTM M10.5级,断面等轴晶的比例达9％以上。成功利用化学法浇注获得细晶叶片样件,该叶片组织比较均匀、成型性好且无铸造缺陷。发现晶粒细化后,细晶试样中的元素枝晶偏析得以减轻,这有利于提高铸件的机械性能;另外,晶粒的形态也改变了,由普通铸造组织中的几乎全部是树枝晶向细晶组织中的粒状晶转变。(3)提出了细晶枝晶粒状化是由球形界面失稳与否、失稳的程度以及晶粒生长的外部环境决定的。建立了失稳判据,指出现有球形界面失稳理论还应考虑元素枝晶偏析、粗化作用以及对流等的影响,比较合理地解释了晶粒细化后变为球状的原因。     

钢铁晶粒超细化方法及其研究进展

综述了目前钢铁材料的各种晶粒细化方法、原理及其研究动态,展望了钢铁材料晶粒细化技术的研究前景,以期对新一代钢铁材料的研究和开发提供理论指导。分析认为今后钢铁晶粒超细化技术的研究方向主要有2个方面:一是继续深入讨论和探索晶粒超细化机理以及超细晶粒材料结构与性能的关系;二是开发适宜于工业化生产的钢铁晶粒超细化技术。     

Strengthening mechanisms of pure tungsten subjected to high pressure torsion: Deviation from classic Hall-Petch relation

In this work, the ultrafine grained (UFG) tungsten has been fabricated via high pressure torsion (HPT) of various turning numbers at a temperature of 823 K and a pressure of 1.5 GPa. The microstructure characteristics and mechanical properties of initial and high pressure torsion processed tungsten have been comparatively investigated by means of x-ray diffraction (XRD), electron backscatter diffraction (EBSD), transmission electron microscope (TEM) and microhardness tests. It is shown that high pressure torsion leads to microstructure refinement with an average grain size of ∼0.92 μm and the fraction of high angle grain boundaries (HAGB) increasing to 62.9 %. Moreover, the dislocation density increases from initial 1.17×10¹⁴ m⁻² to 3.89×10¹⁴ m⁻². The microhardness tests revealed that hardness increased gradually and its distribution became more homogeneous with torsion strain increasing. The strengthening model was established considering the grain boundary strengthening and dislocation strengthening mechanisms. Resultantly, deviation of Hall-Petch slope was found from the classic values, which is attributed to the easy movement of the extrinsic dislocations in the high angle grain boundaries with high distortion energy and high density of defects.     

表面机械研磨处理的纯铜拉伸形变机制

采用扫描电镜电子通道衬度技术(SEM-ECC)研究了表面机械研磨处理(SMAT)铜表面在室温拉伸的形变特征.结果表明:剪切带是纳米晶层、亚微晶层以及由位错胞组成的过渡层的共同形变特征,在不同的结构表层,剪切带的形貌略有差别.纳米晶层和亚微晶层内的剪切带主要为沿平面界面剪切滑动的结果,而过渡层的形变主要是以SMAT处理前的初始晶粒为单元发生的,剪切带的形成基本符合晶体学规律.     

Deformation mechanisms of a modified 316L austenitic steel subjected to high pressure torsion

The present work is assigned to the microstructural evolution of a modified 316L stainless steel during high pressure torsion (HPT) in a temperature range between −196 °C and 720 °C. The aspect of microstructural evolution is similar to that of materials with low stacking fault energy: at high deformation temperatures (T_def > 450 °C) the dominant deformation mechanism is dislocation glide whereas for medium temperatures (450 °C > T_def > 20 °C) mechanical twinning is observed. At very low deformation temperatures (20 °C > T_def > −196 °C) mechanical twinning is replaced by the deformation induced martensite transformation γ(fcc) → ?(hcp). Based on the present results, the formation mechanisms of nanocrystalline austenite are discussed.     

两种通电快速烧结方法制备超细晶粒纯钨

采用在超高压力下通电快速烧结新方法在不添加任何烧结助剂的条件下制备出相对密度为97.9%、晶粒尺寸小于1 μm的超细晶粒纯钨块体材料,研究了细钨粉块体的致密化行为.在超高压力下通电烧结过程中,超高压力使烧结样品具有高密度,而样品的力学性能则主要得益于通电烧结.与"放电等离子体烧结"方法相比,超高压力下通电烧结不但能更好的保持材料的原始晶粒尺寸,还能进一步细化晶粒.     

Microstructure development and hardening during high pressure torsion of commercially pure aluminium: Strain reversal experiments and a dislocation based model

The effect of strain reversal on hardening due to high pressure torsion (HPT) was investigated using commercially pure aluminium. Hardening is lower for cyclic HPT (c-HPT) as compared to monotonic HPT (m-HPT). When using a cycle consisting of a rotation of 90° per half cycle, there is only a small increase in hardness if the total amount of turns is increased from 1 to 16. Single reversal HPT (sr-HPT) processing involves torsion in one direction followed by a (smaller) torsion in the opposite direction. It is shown that a small reversal of 0.25 turn (90°) reduces hardness drastically, and that decrease is most marked for the centre region. These behaviours and other effects are interpreted in terms of the average density of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs). A model is presented that describes the experimental results well. A key element of the model is the assumption that at the very high strains developed in severe plastic deformation processes such as HPT, the dislocation density reaches a saturation value. The model indicates that the strength/hardness is predominantly due to GNDs and SSDs.     

Synthesis and purification of long copper nanowires. Application to high performance flexible transparent electrodes with and without PEDOT:PSS

We demonstrate the hydrothermal synthesis of long copper nanowires based on a simple protocol. We show that the purification of the nanowires is very important and can be achieved easily by wet treatment with glacial acetic acid. Fabrication of random networks of purified copper nanowires leads to flexible transparent electrodes with excellent optoelectronic performances （e.g., 55 Ω/sq. at 94% transparency）. The process is carried out at room temperature and no post-treatment is necessary. Hybrid materials with the conductive polymer PEDOT：PSS show similar properties （e.g., 46 Ω/sq, at 93% transparency）, with improved mechanical properties. Both electrodes were integrated in capacitive touch sensors.     

Improve stress corrosion cracking resistance and mechanical properties of Al‐Zn‐Mg‐Cu‐Zr alloy with heterogeneous lamellae structure produced by high pressure torsion

High pressure torsion experiment followed with heat treatment were carried out on as‐cast Al‐Zn‐Mg‐Cu‐Zr alloy at 400 °C under the pressure of 1 GPa. The microstructure, mechanical property and stress corrosion resistance properties for the as‐cast and high pressure torsion processed samples were studied. The results show that high pressure torsion processing can improve the mechanical property by the refinement of grains and grain boundary precipitates, as well as the homogeneous distribution of fine matrix precipitates. On the other side, the grain refinement, broken of coarse grain boundary precipitates and narrowed precipitates free zone caused by the high pressure torsion result in the improvement of stress corrosion cracking resistance. And due to the influence of heterogeneous lamellae structure, the sample after 0.5 high pressure torsion turn shows preferable mechanical property and stress corrosion cracking resistance than the sample after 2 high pressure torsion turns.     

Advances in metals and alloys for joint replacement

Metals, ceramics, polymers, and composites have been employed in joint arthroplasty with ever increasing success since the 1960s. New materials to repair or replace human skeletal joints (e.g. hip, knee, shoulder, ankle, fingers) are being introduced as materials scientists and engineers develop better understanding of the limitations of current joint replacement technologies. Advances in the processing and properties of all classes of materials are providing superior solutions for human health. However, as the average age of patients for joint replacement surgery decreases and the average lifespans of men and women increases worldwide, the demands upon the joint materials are growing. This article focuses solely on advances in metals, highlighting the current and emerging technologies in metals processing, metal surface treatment, and integration of metals into hybrid materials systems. The needed improvements in key properties such as wear, corrosion, and fatigue resistance are discussed in terms of the enhanced microstructures that can be achieved through advanced surface and bulk metal treatments. Finally, far reaching horizons in metals science that may further increase the effectiveness of total joint replacement solutions are outlined.