球磨纯铁中纳米铁素体的退火行为

通过形貌观察和硬度测试研究了球磨纯铁中纳米铁素体的退火行为，观察到球磨制备的纳米铁素具有相对较高的热稳定性，在高温退火的条件下，纳米铁素体区域内出现了一些具有不规则晶界结构的大晶粒，分析表明，纳米铁素体的晶粒长大是通过邻近晶粒的聚合而完成的。显微硬度测试表明，纳米铁素体的硬度随着退火温度的升高而降低，然而在相同的退火条件下，纳米铁素体区的硬度仍然明显高于加工硬化区的硬度，这主要是因为纳米铁素体区的晶粒尺寸比较小以及退火时晶粒长大速率相对缓慢所致。     

短时退火对纳米层片结构低碳钢加工硬化的影响

通过准静态拉伸测试、显微硬度测试研究短时退火对含碳量为0.10%(质量分数)的纳米层片结构低碳钢加工硬化的影响,利用扫描电镜观察微观结构和断口形貌。结果表明:短时退火处理使轧制态10号钢试样软硬微区组织不均匀性增加,增强了加工硬化能力。随着退火温度升高,晶粒长大,层片结构不明显,导致加工硬化能力减弱。     

片状粉末冶金法制备ODS铁素体不锈钢及其微观结构特征研究

采用片状粉末冶金方法制备了氧化物弥散增强(ODS)铁素体不锈钢。利用SEM研究了铁素体不锈粉末在低能球磨工艺中粉末形貌的演化规律以及烧结后样品的微观组织。结果表明:铁素体不锈粉末具有优异的塑性变形能力,在低速球磨过程中发生减薄和弯折等变形,随着球磨时间的增长,初始不规则粉末被研磨成薄片状粉末。当球磨时间达到20 h时,片状粉末厚度达到纳米尺寸(100～200 nm),径厚比达到最大值(约为110)。经冷压烧结后,铁素体基体呈现结状组织,Y2O3颗粒弥散分布在原纳米片状粉末界面处,这说明采用高径厚比的纳米片状粉末能实现Y2O3颗粒的弥散分布。     

高能球磨Ti55.5Cu18.5Ni17.5Al8.5合金非晶化研究

采用机械合金化(MA)制备出Ti_(55.5)Cu_(18.5)Ni_(17.5)Al_(8.5)非晶粉末。利用X射线衍射仪(XRD)、示差扫描量热分析仪、扫描电镜、透射电镜等研究了不同球磨时间粉末的微观形貌以及非晶化行为,探讨了非晶化对合金硬度的影响。结果表明,首先随着球磨时间的增加,微观组织的演变规律是合金晶粒逐渐变小,出现纳米晶化合物;随后纳米晶化合物内部发生局部结构长程无序化,纳米晶化合物分割成更为细小的纳米晶;最终纳米晶颗粒完全非晶化。从原子尺度证明了非晶化的主要原因是高能球磨过程中发生了剧烈塑性变形,形成了高密度位错以及严重的晶格畸变,最终导致原子长程无序化从而形成非晶。球磨引起加工硬化和非晶晶化,使得球磨后的合金粉末硬度显著增加。     

Ti-Nb-Mo微合金钢回火过程中纳米碳化物的析出行为及组织演变

通过SEM和TEM等方法对Ti-Nb-Mo微合金钢在两种不同冷却工艺下回火处理后的析出相分布、形貌和粒度进行了观察和分析,结合拉伸实验结果和硬度测试结果研究了回火过程中纳米析出颗粒的变化对试验钢强度变化的影响。结果表明,热轧淬火后试验钢基体组织为板条贝氏体,经650℃回火处理后并未形成纳米析出相,因此导致试验钢强度明显下降;而热轧空冷后试验钢基体组织主要为铁素体,部分铁素体中形成了大量的相间析出颗粒并具有良好的热稳定性,经650℃回火0.5 h后屈服强度提升明显,回火过程中铁素体基体和位错上形成了大量的纳米碳化物颗粒,这类碳化物的析出量大,尺度分布均匀,颗粒尺寸细小,是试验钢获得高强度最主要的原因。     

机械球磨Ti_(50)Al_(50)复合粉的压制特性

研究了机械球磨Ti50 Al50 复合粉的组织与压制特性。结果表明 ,球磨导致粉末硬度增加 ,压制特性变差 ,这是由于球磨使层片结构细化 ,Ti和Al组元晶体缺陷增加和晶粒细化造成的 ;但球磨 3h形成纳米晶复合粉后 ,尤其是在球磨 7.5h开始发生非晶转变后 ,进一步球磨 ,粉末压制特性变化并不明显     

7075铝合金表面HVOF喷涂WC-12Co颗粒的沉积行为（英文）

在抛光的7075铝基体上采用HVOF（超音速火焰喷涂）沉积了WC-12Co颗粒，用SEM、EDS和纳米压痕硬度仪对沉积物的显微组织、成分和硬度进行了分析。研究了未融颗粒、未完全熔融颗粒和熔融颗粒这3种不同熔融状态下6种颗粒的沉积行为，发现不同类型的颗粒均对基体有冲击，使其发生变形或有一定的撕裂。未熔融颗粒沉积时，高速冲击铝基体使其发生挤压变形，颗粒反弹后，基体遗留挤压坑。除了反弹的未熔融颗粒，未完全熔融颗粒和熔融颗粒的沉积物与原始粉末相比，沉积物的表面形貌和横截面形貌与原始粉末不同，沉积物表面有一定的熔化特征，这是颗粒在HVOF焰流中受热温度较高使其有一定的熔融；高温高速的颗粒冲撞基体后，沉积物横截面更为致密，它们与基体之间存在冶金结合，形成了一个互熔区，表明沉积物撞击基体时温度高于铝的熔点，将铝融化并挤压进颗粒中。颗粒沉积后，在基体表面上形成一层厚度约为5μm的硬化层，该层的硬度呈梯度变化，近表面处硬度为3420 MPa，是基体（2200 MPa）硬度的1.56倍。硬度的增加源于两个因素：高温高速颗粒的喷丸作用，及颗粒挤压基体塑形变形的加工硬化。     

Ti—46at%Al机械合金化过程中的显微组织演变

采用扫描电镜（SEM）、显微硬度分析、Ｘ－ray衍射和差热分析（ＤＴＡ）技术研究了Ｔi-46at%Al混合粉末机械合金化过程中的显微组织演变。结果表明：随着球磨过程的进行，Ｔi-46at%Al颗粒逐渐等轴化，粒度变小，粒度分布变窄；显微硬度增大，硬度分布和颗粒内成分逐渐均匀。经过６０h高能球磨，Ａl元素完全固溶入Ｔi晶格内，形成纳米Ｔi（Ａl）过饱和固溶体，同时，有非晶相形成；球磨至１００h，形成完全非晶相。非晶相的形成是界面处非平衡扩散的结果，在Ｔi-46at%Al合金中，机械合金化致非晶的晶粒条件是：晶粒尺寸≤１５nm。     

激光成形修复2Cr13不锈钢热影响区的组织研究

对激光成形修复2Cr13不锈钢热影响区分别进行了单道单层、多道单层、单道多层和多道多层4种形式的修复实验.通过金相观察和硬度测试确定了激光成形修复区域的组织特征,结合热影响区温度场模拟分析了组织形成机理.结果表明:热影响区内微观组织从基材到修复区底部呈现连续性变化,其中,主要相结构经历了α铁素体→α铁素体+少量马氏体→马氏体+少量α铁素体→马氏体的转变,马氏体的出现导致硬度快速上升;同时,原M23C6型碳化物逐渐溶解,直至消失,且晶内碳化物先于晶界碳化物发生溶解;伴随碳化物的溶解逐渐出现δ铁素体;随着趋近修复区底部,δ铁素体逐渐增多、长大并连成骨架;当沉积层数增加后,硬度峰值随之下降,在热影响区中部的部分区域会出现晶粒细化,且热影响区顶部的晶界逐渐开始析出碳化物,同时,δ铁素体骨架逐步被晶界打断.     

球磨法制备纳米TiC及其生成机理

采用高能球磨法制备纳米TiC颗粒,通过对不同球磨时间试样进行X射线衍射分析、扫描电镜及透射电镜进行形貌观察,得出球磨过程中TiC的生成机理。结果表明,球磨过程中,首先石墨和钛粉细化,石墨形成片状而钛粉形成细小颗粒;随着球磨时间的延长,片状石墨包裹钛粉;当磨球碰撞时达到Ti和C反应温度,Ti和C发生反应产生TiC,反应放出的热量维持反应的进行。制备的TiC粒度为10～100nm。     

纳米晶W粉的制备及烧结性能

用高能球磨法制取纳米晶Ｗ粉,在真空炉内将此Ｗ粉分别进行无压和热压烧结成致密块体。利用扫描电镜,透射电镜,Ｘ－ｒａｙ衍射仪等观测球磨过程中粉末粒度,形貌和结构的经及烧结块体的质量密度随温度的变化,并与普通粉的烧结性能作了比较。结果表明：脆性材料在高能球磨过程中不出现片层状结构,一直保持颗粒状结构,纳米晶超细Ｗ粉与普通Ｗ粉相比,由于颗粒和晶粒小,扩散系数高,表面能高,比表面原子烤多,晶格畸变严重,熔点     

Formation of nanocrystalline structure in steels by ball drop test

Formation of nanocrystalline structure in a eutectoid steel by severe plastic deformation has been studied by a `ball drop test'. The microstructures and hardness similar to those of nanocrystalline structures produced by ball milling have been obtained near the surface of specimens. The high strain rate of around 10⁴ s⁻¹ is proposed to be an essential condition to produce nanostructure by deformation.     

Synthesis of TiC–Al2O3 nanocomposite powder from impure Ti chips, Al and carbon black by mechanical alloying

The possibility of providing TiC–Al₂O₃ nanocomposite as a useful composite from low-cost raw materials has been investigated. Impure Ti chips were placed in a high energy ball mill with carbon black and aluminum powder and sampled after different times. XRD analysis showed that TiC has been synthesized after 10 h of milling. It could be observed from the width of XRD patterns’ peaks that the size of produced TiC crystallites is in the order of nanometer. In order to forming of TiC–Al₂O₃ composite, heat treatment was performed in different temperatures. Investigations have revealed that formation temperature of TiC as the dominant phase decreased for the milled specimens during heat treatment, also nanocrystalline TiC–Al₂O₃ composite was formed in this situation. Furthermore milling led to increase of strain and decrease of TiC lattice parameter while during heat treatment nanocrystalline grains grow up and strain decreases.     

Structural and phase transformations during ball milling of titanium in medium of liquid hydrocarbons

It has been shown using X-ray diffraction, scanning electron microscopy, and chemical analysis that, upon ball milling of α-titanium in liquid organic media (toluene and n-heptane), a nanocrystalline fcc phase is formed that is a metastable carbohydride Ti(C,H) deficient in hydrogen and carbon compared to stable carbohydrides. The dimensions of powder particles after milling in toluene and n-heptane differ substantially (are 5–10 and 20–30 μm, respectively. It has been shown that the kinetics of the formation of Ti(C,H) is independent of the milling medium. The atomic ratios H/C in the products of mechanosynthesis agree well with those corresponding to the employed organic media, i.e., H/C = 1.1 for toluene and 2.3 for n-heptane. A solid-liquid mechanism of mechanosynthesis is suggested, which includes repeated processes of particle fracturing with the formation of fresh surfaces, adsorption of liquid hydrocarbons on these surfaces, and subsequent cold welding of the newly formed particles. It is assumed that the formation of the fcc phase in the process of milling is connected with the generation of stacking faults in α-Ti. Upon annealing at 550°C, the fcc phase decomposes with the formation of stable titanium carbide TiC (annealing in a vacuum) or stable titanium carbohydride and a β-Ti(H) solid solution (annealing in argon) with a partial reverse transformation Ti(C,H) → α-Ti in both cases.     

Phase Evolution and Thermal Analysis of Nanocrystalline AlCrCuFeNiZn High Entropy Alloy Produced by Mechanical Alloying

A multi-component nanocrystalline AlCrCuFeNiZn high entropy alloy with 12 nm crystallite size was successfully synthesized using high energy ball milling. The progress of solid solution formation during milling was analyzed using XRD. A major portion of the HEA is observed to be BCC in crystal structure after 30 h of milling. Thermal analysis showed that HEA powders exhibited exponential oxidation characteristics. Thermal analysis showed that low activation energy was sufficient to start recrystallization because of high energy stored in the milled powders. The crystallite size after consolidation is in nanocrystalline range due to the sluggish diffusion of atoms and nanotwinning. After consolidation, the crystallite size is around 79 nm. Samples sintered at 850 °C for 2 h exhibited high hardness values of 700 ± 15 HV_1.0, major volume fraction of the phases are having FCC crystal structure along with a minor phase having BCC crystal structure. Due to positive enthalpy mixing of Cu with other elements, decomposition of BCC to new FCC phases occurs.     

Structure and properties of a steel-based multilayer material produced by hot pack rolling

The structure of a multilayer metal material (MMM) produced from the U8 and 08Kh18N10 steels by the pack-rolling method has been studied using metallography and transmission electron microscopy. It has been found that two process cycles end in the formation of a laminated structure, which is characterized by structural and chemical inhomogeneity due to diffusion and relaxation processes. It is shown that, during pack rolling, an ultradispersed structure is formed in the layers; this structure is a mixture of ferrite, martensite, and austenite that consist of elements of submicrocrystalline, nanocrystalline, and microtwinned structures.     

球磨纳米TiO2的结构转变

采用X射线衍射研究锐钛矿型纳米TiO2在高能球磨过程中及球磨后的纳米TiO2在退火过程中的结构变化。结果表现在室温常压下高能球磨诱发锐钛矿相转变为金红石相和S相。随着退火温度升高，球磨纳米TiO2粉末的晶粒逐渐长大，锐钛矿相逐渐转变为金红石相，而S相并不直接转变为金红石相而是先转变为锐钛矿相，然后由锐钛矿相转变为金红石相。与未球磨的纳米TiO2相比，高能球磨导致的晶粒细化，显微畸变以及晶格缺陷密度的增加而引起的额外储能使球磨后纳米TiO2的锐钛矿相-金红石相转变温度明显降低。     

Partial martensitic transformation of nanocrystalline NiAl intermetallic during mechanical alloying

Nanocrystalline NiAl intermetallic powders were synthesized by mechanical alloying (MA) in a planetary ball mill. Microstructural characterization was accomplished using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The nanocrystalline NiAl powders were formed by a gradual exothermic reaction mechanism during MA. Prolonged milling resulted in partial martensitic transformation of B2-NiAl to tetragonal L1₀-NiAl structure. It is believed that the martensitic transformation is induced by mechanical stress during MA.     

Fabrication of nanostructured Mo coatings on Al and Ti substrates by ball impact cladding

Nanostructured multicomponent Mo coatings were fabricated on Ti and Al substrates by ball impact cladding at room temperature in an ambient atmosphere. The process involved subjecting the substrate and Mo foil fixed at the top of a vibration chamber to high-energy collisions with balls. The coating formation was the result of a simultaneous process of mechanically induced plastic flow, nanocrystallization, and interdiffusion caused by the ball collisions. Plastic deformation refined the grains at the Mo foil/substrate interface to the nanometre scale. The size of nanocrystalline grains in the Mo coatings ranged between 2 nm and 10 nm. The ball collisions caused atomic level intermixing of different elements, introduced into the surface from the steel balls used for milling, and solid solubility improved remarkably. The hardness of the Mo coatings on the Al and Ti substrates was 552 and 1010 HV, respectively. The initial hardness of the Mo foil was 287 HV. The high hardness of the Mo claddings was attributed to the fine grain structure, formation of supersaturated solid solutions, and high residual compressive stresses.