化学法制备ODS钢的新工艺技术

氧化物弥散强化(Oxide Dispersion Strengthened,ODS)铁素体钢,由于其优异的高温力学性能和良好的抗辐照能力被认为是快堆与超临界水堆燃料包壳管候选材料之一。传统ODS钢的制备方法是采用机械合金化法向铁素体钢中添加高熔点弥散细小的氧化物Y2O3而具有优良的高温强度,但合金的塑性和冲击韧性较差,热加工中存在严重的组织和性能各向异性,给合金制备或薄壁管带来极大的困难。     

14CrODS铁素体钢的制备及其拉伸性能

通过机械合金化制备了成分(质量分数/%)为Fe-14Cr-0.5Ti-0.35Y2O3的氧化物弥散强化合金粉末,机械合金化后粉末内部各合金元素分布均匀。采用热等静压的方法制得14CrODS铁素体钢,并对其进行锻造和热处理。与未添加氧化物弥散颗粒的14CrNA相比,14CrODS钢的强度有明显提高,但是与MA957有一定差距,抗拉强度有待改进;与MA957相比,14CrODS表现出良好的塑性,锻造可进一步提高14CrODS的高温塑性,但是锻造过程中的残余应力使材料低温拉伸时呈脆性,退火可去除残余应力,极大地提高14CrODS的塑性,使其远优于MA957。     

机械合金化制备纳米Cu-Zn-Al2O3复合粉末的研究

采用X射线衍射仪、电子扫描电镜和透射电镜等研究了Ar气氛保护下Cu-Zn-Al2O3复合粉末在高能球磨过程中发生的机械合金化反应,分析了不同球磨时间对a-Cu(Zn)的晶格常数、晶粒尺寸以及复合粉末粉体形貌、颗粒尺寸的影响.结果表明,球磨初期,Cu的晶格常数增大,但75h后由于γ相的析出,a-Cu(Zn)晶格常数减小;高能球磨120h后,可获得氧化铝颗粒弥散分布的纳米级Cu(Zn)复合粉末.     

球磨参数对ODS奥氏体不锈钢机械合金化效果的影响

为了研究球磨参数对ODS奥氏体不锈钢机械合金化效果的影响,以Fe、Cr、Ni、W、Ti纯金属元素粉末和纳米Y2O3为原料进行混合(配比为Fe-18Cr-8Ni-2W-1Ti-0.35Y2O3,质量分数),通过高能球磨的方式实现混合粉末的机械合金化.研究球磨时间、转速的变化对粉末粒度、成分均匀度和固溶程度的影响.结果表明,在真空环境下,球料比为10∶1、转速为380r/min、球磨时间60h时,粉末达到了很好的机械合金化效果,成分分布均匀;当球磨时间延长到100h时,粉末颗粒达到最细,继续球磨,粉末将出现明显的团聚.对最优机械合金化工艺参数获得的粉末进行热压致密化研究表明,随着温度的升高,试样的密度随之升高,维氏硬度随之降低.     

粉末冶金法制备Al-Pb合金微观组织分析EI

采用机械合金化与真空热压烧结制备Al-Pb合金,并通过热挤压变形细化显微组织。XRD检测分析表明:Al,Pb衍射峰随机械合金化的进行不断宽化,晶粒尺寸减小。SEM分析表明:球磨15h后可以得到合金粉末,其具有Pb粒子弥散分布于Al基体的复相结构。再通过550℃/20MPa真空热压烧结1h,可制备出Al-Pb合金块体。适当的热挤压工艺能够细化组织,减小Pb颗粒的尺寸。其抗拉强度可达231.6MPa,延伸率为17.6%。     

机械合金化制备纳米级超细晶不锈钢的研究

用机械合金化的方法制备了纳米级超细晶不锈钢粉末,用X射线衍射仪及扫描电镜技术研究了机械合金化过程中粉末颗粒尺寸及晶粒度的变化.结果表明,随着球磨时间的延长,粉末颗粒的尺寸先略微增大,而后一直减小到约几个微米后保持不变;而粉末的晶粒一直减小,球磨时间达到1 844min左右就达到纳米级.     

冷喷涂制备cBN-NiCrAl金属陶瓷涂层EI北大核心

采用机械合金化制备40vol%cBN-NiCrAl金属陶瓷复合结构粉末,采用冷喷涂制备了40%cBN-NiCrAl(体积分数)金属陶瓷复合结构涂层。研究了机械合金化过程对粉末的相组成、晶粒尺寸以及显微组织的影响。采用扫描电子显微镜和X射线衍射分别表征不同球磨时间下粉末以及冷喷涂涂层的显微组织和相结构。采用Scherrer公式估算不同球磨时间下粉末以及冷喷涂涂层中合金基体相的晶粒尺寸。结果表明,40vol%cBN-NiCrAl金属陶瓷粉末球磨40h后,基体的平均晶粒尺寸达到~50nm;复合结构涂层组织致密,硬质颗粒在合金基体中分布均匀。喷涂过程中,粉末相结构未发生变化,晶粒尺寸也未发生明显的长大。测试表明涂层的显微硬度约为1170HV0.3。     

机械合金化和放电等离子烧结制备Y3Al5O12陶瓷

采用机械合金化和放电等离子烧结制备YAG陶瓷,研究了球磨时间对原料颗粒大小和烧结合成YAG纯度的影响,并利用x射线衍射(XRD)、扫描电镜(SEM)等手段对反应过程及产物形貌和物相进行了分析.研究结果表明,机械合金化Y2O3和Al2O3粉体,可明显细化氧化物颗粒,球磨20h后,Y2O3和Al2O3晶粒大小约为34nm和32nm.球磨处理的Y2O3和Al2O3粉体具有很高的活性,促进放电等离子烧结低温反应合成和获得致密的YAG.对球磨20h的粉体在不同温度进行放电等离子烧结,在1200℃即可获得纯YAG陶瓷,在1500℃烧结,可得到相对密度为99.5%的YAG陶瓷.1500℃烧结的块体在可见光范围内透过率为13.8%.     

MGH956合金TIG焊原位合金化对其组织性能的影响

采用TIG焊对氧化物弥散强化(ODS)高温合金MGH956进行原位合金化焊接.在相同的焊接条件下,填加两种不同的填充材料:与母材化学成分相似的基体填充材料,以及在基体填充材料基础上加入了合金元素Al和Fe2O3的Al-Fe2O3填充材料.通过对比分析两组试样在焊接过程中发生的原位合金化反应机理,及其对焊缝微观组织和力学性能的影响,研究原位合金化反应对ODS合金TIG焊接头组织与性能的影响.结果表明:在填充材料中加入Al和Fe2O3合金元素时,焊缝处的气孔数量明显减少,气孔尺寸也较为减小;焊缝中原位生成了新的增强相颗粒Al2O3、TiC以及YAlO3,同时,基体中的纳米级增强相Al-Y复合氧化物团聚倾向降低.力学性能试验结果表明,填加Al-Fe2O3填充材料时焊缝显微硬度值明显提高,接头抗拉强度达到了578 MPa,为母材强度的80.3%.     

氧化物弥散强化高温合金及其在航空上的应用

氧化物弥散强化高温合金,简称ODS高温合金(Oxide Dispersion Strengthened Su-peralloys )是粉末高温合金的一大分枝,也是高温合金的一个重要发展方向。 高温合金的氧化物弥散强化是指在高温合金中加入一定量的热力学稳定的氧化物,使其弥散分布于基体中,形成不溶于基体的氧化物弥散相,从而使合金得以进一步强化的一种新的强化途径。     

高能球磨对Mg-Zn-Zr合金微观组织与力学性能的影响

在氩气条件下以400r/min高能球磨镁合金粉末,并将球磨后的粉末经过冷压—热压烧结—热挤压成型。研究了不同球磨时间的粉末以及挤压态样品的微观组织和力学性能。结果表明:随着球磨时间的延长,粉末颗粒尺寸可以细化到8μm,晶粒尺寸有效细化到34nm,在整个球磨过程中粉末有一定程度的氧化,并伴随有MgO纳米颗粒产生。粉末经过热压烧结—热挤压成型后,材料内部有MgZn2相颗粒析出,且均匀分布于Mg基体中。随着粉末颗粒的细化,材料性能得到改善,当球磨至10h时,粉末挤压态样品的极限拉伸强度为365 MPa,压缩屈服强度高达325 MPa,极限压缩强度保持在466 MPa。球磨至25h,颗粒平均尺寸细化至8μm左右,使得颗粒表面能大幅度增大,颗粒表面的氧化膜增厚,在热压烧结过程中阻碍了颗粒之间的结合,进而使得材料的力学性能恶化。     

Mechanical alloying of biocompatible Co–28Cr–6Mo alloy

We report on an alternative route for the synthesis of crystalline Co–28Cr–6Mo alloy, which could be used for surgical implants. Co, Cr and Mo elemental powders, mixed in an adequate weight relation according to ISO Standard 58342-4 (ISO, 1996), were used for the mechanical alloying (MA) of nano-structured Co-alloy. The process was carried out at room temperature in a shaker mixer mill using hardened steel balls and vials as milling media, with a 1:8 ball:powder weight ratio. Crystalline structure characterization of milled powders was carried out by X-ray diffraction in order to analyze the phase transformations as a function of milling time. The aim of this work was to evaluate the alloying mechanism involved in the mechanical alloying of Co–28Cr–6Mo alloy. The evolution of the phase transformations with milling time is reported for each mixture. Results showed that the resultant alloy is a Co-alpha solid solution, successfully obtained by mechanical alloying after a total of 10 h of milling time: first Cr and Mo are mechanically prealloyed for 7 h, and then Co is mixed in for 3 h. In addition, different methods of premixing were studied. The particle size of the powders is reduced with increasing milling time, reaching about 5 μm at 10 h; a longer time promotes the formation of aggregates. The morphology and crystal structure of milled powders as a function of milling time were analyzed by scanning electron microscopy and XR diffraction.     

Preparation and structural investigation of nanostructured oxide dispersed strengthened steels

Although capability of steels has been improved in the past by thermomechanical treatment, utilization of powder metallurgy provides more controlled microstructure, a homogeneous dispersion of nanosized oxide particles in the metal matrix and tailored properties in terms of strength and radiation resistance. This article is summarizing recent results on preparation, structural, and mechanical investigation of oxide dispersed strengthened steel (ODS). Two commercial steel powders, austenitic 17Cr12Ni2.5Mo2.3Si0.1C and martensitic Fe16Cr2Ni0.2C powders have been used as starting materials. Nanosized yttria dispersed martensitic and austenitic sintered steel samples have been realized by powder metallurgical methods. An efficient dispersion of nano-oxides in ODS steels was achieved by employing high efficient attrition milling. A combined wet and dry milling process of fine ceramic and steel particles is proposed. Spark Plasma Sintering (SPS) was applied to realize nanostructured steel compacts. Grains with 100 nm mean size have been observed by SEM in sintered austenitic ODS. In comparison, the sintered martensitic dry milled and martensitic dry and combined milled ODS microstructure consisted of grain size with 100–300 nm in each case. A brittle behavior is shown in all of the cases. The martensitic ODS is two times harder than the austenitic ODS. The bending strength high as 1806.7 MPa was found for the martensitic ODS, whereas 1210.8 MPa was determined for the austenitic ODS. The combined milling assured higher strength and hardness compared to dry milling.     

Microstructural studies on nanocrystalline oxide dispersion strengthened austenitic (Fe–18Cr–8Ni–2W–0.25Y<Subscript>2</Subscript>O<Subscript>3</Subscript>) alloy synthesized by high energy ball milling and vacuum hot pressing

In the present work, nanostructured (Fe–18Cr–8Ni–2W) austenitic base and oxide dispersion strengthened (ODS) alloy powders were produced through mechanical alloying and these nano powders were consolidated by vacuum hot pressing. The results showed that initially bcc solid solution formed in both the alloys and this transformed to fcc with continued milling. The bcc solid solution formation and the subsequent transformation to fcc were significantly faster in the ODS alloys when compared to the base alloy. In the ODS alloy, a grain size of ~25 nm is achieved within 5 h of milling. Study of variation of microhardness of mechanically alloyed powder particles with grain size showed linear Hall–Petch kind of behavior. Following vacuum hot pressing of mechanically alloyed powders, nearly fully dense (>99% of theoretical density) compacts were obtained with a grain size of ~80 nm. The bulk hardness of base and ODS alloys are ~530 and ~900 HV, respectively. These are significantly higher than the values reported in the literature so far. The enhanced strength the ODS alloy is due to increased dislocation density and presence of fine dispersoids along with the nanocrystalline grains.     

Investigation of microstructural characteristics of nanocrystalline 12YWT steel during milling and subsequent annealing by X-ray diffraction line profile analysis

The variations of dislocation density, character of dislocations, and crystallite size as a function of milling time and post-heat-treating temperature were investigated for 12YWT nanocomposite ODS ferritic steel using X-ray diffraction line profile analysis. The modified Williamson–Hall and the modified Warren–Averbach methods, which are based on the dislocation model of the strain anisotropy, were utilized to characterize the microstructural parameters of the nanocomposite material and the matrix alloy. The presence of nano-oxide particles in the ODS steel caused an initially sharp decrease in the average crystallite size; however, with increasing milling time, the crystallite size of the unreinforced alloy reached the comparable value of that of the reinforced material. The subsequent heat treating on the powders milled for 80 h showed that the presence of Y₂O₃ dispersoids increased the recrystallization temperature and suppressed the grain growth up to 800 °C in the 12YWT alloy as compared to the matrix alloy which occurred about 700 °C. The results of X-ray diffraction line profile analysis also showed that the contribution of edge components of the dislocations increased at the initial milling stages, while the screw components tended to increase after 40-h milling time.     

Synthesis, characterization and annealing of mechanically alloyed nanostructured FeAl powder

Elemental powders of Fe and Al were mechanically alloyed using a high energy rate ball mill. A nanostructure disordered Fe(Al) solid solution was formed at an early stage. After 28 h of milling, it was found that the Fe(Al) solid solution was transformed into an ordered FeAl phase. During the entire ball milling process, the elemental phase co-existed with the alloyed phase. Ball milling was performed under toluene to minimise atmospheric contamination. Ball milled powders were subsequently annealed to induce more ordering. Phase transformation and structural changes during mechanical alloying (MEA) and subsequent annealing were investigated by X-ray diffraction (XRD). Scanning electron microscope (SEM) was employed to examine the morphology of the powders and to measure the powder particle size. Energy dispersive spectroscopy (EDS) was utilised to examine the composition of mechanically alloyed powder particles. XRD and EDS were also employed to examine the atmospheric and milling media contamination. Phase transformation at elevated temperatures was examined by differential scanning calorimeter (DSC). The crystallite size obtained after 28 h of milling time was around 18 nm. Ordering was characterised by small reduction in crystallite size while large reduction was observed during disordering. Micro hardness was influenced by Crystallite size and structural transformation.     

Microstructure and hardness of nano-sized Fe-based self-fluxing alloy powder with SiC particles

The Fe-based self-fluxing alloy powders and SiC particles were mixed and milled by high energy ball-milling, and their microstructure and micro-hardness were investigated after subsequent compaction and sintering. The initial alloy powders with a mean size of approximately 80 microm were fined to 2.1 microm after milling at 800 rpm for 5 h. However, the powder mixture of alloy powder and SiC particle showed much larger powder size compared to the initial alloy powders. The bulk composites were obtained from the powder mixture by compaction under a pressure of 800 MPa for 10 min and sintering at 1073 K for 3 h. The composites had much higher micro-hardness of more than 700 Hv compared to alloy powder. The micro-hardness of composites slightly increased with the content of SiC particles.     

Microstructure and Mechanical Property of 2024 Aluminium Alloy Prepared by Rapid Solidification and Mechanical Milling

Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation     

Microstructural and morphological changes during ball milling of Copper-Silver-Graphite flake mixtures

The present study reports the microstructural and morphological changes during high energy ball milling of Cu with Ag and Graphite flakes. XRD patterns of ball milled Cu-Ag showed a reduction in the intensity of Ag peaks (1 1 1) and an increase in the lattice parameter of Cu. With an increase in milling time, the formation of metastable Cu-Ag solid solution was observed. Lattice parameter values for 40 h milled Cu (3.6169 Å) and Cu-GF composites (3.6166 Å) indicated that C does not dissolve in Cu. The lattice parameter of Cu in milled Cu-Ag-graphite flake was lower compared to milled Cu-Ag mixture indicating that graphite flakes inhibit solid solution formation. Raman spectra revealed that graphite flakes were converted into multilayer graphene after 10 h of milling. The crystallite size of Cu in the milled powders decreased with increase in milling time and reached a value of ∼25 nm after 35 h of milling. The lattice strain also increased with milling time. The D₁₀, D₅₀ and D₉₀ size reduced appreciably after 5 h of milling.