高能球磨锐钛矿型TiO2晶型转变的研究

应用机械力化学原理，研究高能行星磨粉磨锐钛矿型TiO2引起晶型转变的过程，采用XRD、SEM、TEM、FT－IR技术对粉体进行表征，探讨了机械力化学引起晶型转变的机制。研究发现：在一定操作参数（行星磨公转转速300r/min)条件下，粉磨初期（5h)为无定形形成期，颗粒出现团聚现象，晶粒尺寸减小，晶格畸变，转变为无定形，并形成金红石型TiO2晶核；粉磨中期（5－15h)为晶粒长大期，金红石型TiO2晶粒长大；粉磨后期（15h以后）为动态平衡期，晶粒长大与粉磨引起的晶粒减小处于动态平衡，研究表明；行星磨粉磨锐钛矿型TiO2可使晶型转变为金红石型TiO2，团聚的二次颗粒尺寸为1μm左右，并由颗粒尺寸为20－40nm团聚组成。     

The nanostructure evolution of Ag powder synthesized by high energy ball milling

In this paper, nanostructured silver with an average crystallite size of 28 nm and internal strain of 0.44% was synthesized by mechanochemical reduction of Ag₂O using graphite in a high energy planetary ball mill. XRD, SEM and TEM techniques were used to characterize the structural evolution and morphological changes of products. The results showed that the reaction is progressed by a nucleation and growth mechanism process. Although the changes of crystallite size and internal strain in Ag₂O were regular during the milling, there was an irregularity in the aforementioned parameters of Ag particles. This irregularity was probably owing to the progressive generation of silver during the milling.     

Microstructural evolution during high energy ball milling of Fe2O3-SiO2 powders

The reaction of a 25 mol% Fe₂O₃-SiO₂ (hematite-amorphous silica) powder mixture during high energy ball milling in both closed and open containers has been studied by x-ray diffraction and Mössbauer spectroscopy. After around 21 h of milling, the α-Fe₂O₃ powders with an average particle size of 15 nm have formed and no reaction between α-Fe₂O₃ and SiO₂ is found in the two types of milling containers. This demonstrates that the high energy mechanical milling technique is able to prepare a dispersion of ultrafine α-Fe₂O₃ particles. After extended milling in the open container all iron atoms are found in a hematite phase. In the closed container the hematite phase transforms into an iron-rich spinel phase and some of the iron atoms react with the amorphous SiO₂, forming a new Fe(II)-containing silicate compound.     

Nanocrystals by high energy ball milling

It has been shown that nanometer-size grains can be induced in even brittl e intermetallic compounds by high energy ball milling. The large grain boundary area provided by these nanocrystallites can help provide, along with the disordering energy, the driving free energy for the crystalline-to-amorphous transformation. Examples were given for Nb₃Sn (complete amorphization), Ni₃Al (partial amorphization), and Ni₃Si (no amorphization).     

高能球磨时间和退火温度对制备TiNi合金粉的影响

为获得高能球磨时间和退火温度对TiNi机械合金粉特性的影响机制,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱仪(EDS)、差示扫描量热法(DSC)等分析方法对TiNi合金粉进行了研究。结果表明,机械合金的相成分随着在氩气保护气氛中的球磨时间和退火温度的不同而发生变化。球磨22h的产物是非晶态TiNi合金、Ti的固溶体、Ni的固溶体,球磨27h的产物是非晶态TiNi合金粉和Ni固溶体相,球磨30h发生了明显的固相反应,生成了TiNi、Ni3Ti、Ti3Ni4等物相;在650℃/5h和1000℃/5h下的退火产物都是Ni3Ti、Ti2Ni、TiNi2、TiNi和TiC,但在上述2个退火温度下TiNi并不是主要物相,其中在650℃退火时TiNi的含量明显更低。     

Study on the milling-induced transformation in TiO2 powder with different grain sizes

Mechanical alloying can trigger the transformations from anatase to srilankite and rutile phases in TiO₂. The grain size of the powder has a significant effect on the kinetics of the milling-induced phase transformations. In the TiO₂ powder with smaller grain size, the rate of the phase transformations is faster and that of the grain refinement is slower.     

Optimisation of high energy ball milling parameters to synthesize oxide dispersion strengthened Alloy 617 powder and its characterization

In the present work, ultra-fine powder of oxide dispersion strengthened Alloy 617 was synthesized by high energy ball milling. Milling parameters such as rpm and milling time were varied in the range of 500–2000 and 5–360 min, respectively. Energy applied to the powder in the milling process (Energy per unit mass per hit, E_c) was estimated using the collision model. Effect of milling parameters on the microstructure of powder and refinement of oxides was investigated using X-ray Diffraction (XRD), Scanning electron Microscopy (SEM), conventional Transmission Electron Microscopy (TEM) and High resolution Transmission Electron Microscopy (HRTEM). Desired convoluted lamellar structure with average particle size ∼33 μm was observed during milling at 1000 rpm (E_c ∼ 0.4 kJ/g.hit) for 6 h. TEM analysis of the powder showed the presence of fine oxide dispersoids in the size range 4–16 nm. HRTEM analysis substantiated the presence of fine dispersoids of size ∼4 nm and showed the presence of deformation twins in the matrix. The fine dispersoids in a nanocrystalline matrix is expected to provide superior creep strength to the material at high temperatures.     

Structural changes in iron powder during ball milling

X-ray diffraction line profile analysis is a powerful and convenient method to investigate the microstructural characteristics of plastically deformed materials. The selection of a suitable and reliable analysis method is critical to derive correct microstructural/material property values. Different techniques of the X-ray peak profile analysis have been used to study the microstructural parameters of ball milled iron powders viz., coherent domain size, dislocation density and nature of dislocations. The classical and modified Williamson–Hall technique and momentum method are used to derive microstructural information. The stored energy estimates were obtained using differential scanning calorimetry while the morphological details are studied with a scanning electron microscope. The domain size decreases to about 270 nm and dislocation density increases to 3.6 × 10¹⁵ m⁻² after 20 h of milling. SEM results supplements the XRD results. Stored energy of deformation also increases to 171 J/g after 20 h of milling.     

Development of high performance powder metallurgy steels by high-energy milling

High-energy milling is considered to be one of the most efficient techniques for producing materials that have a well-controlled chemical composition and microstructural features that are difficult to obtain using other synthesis routes. In this study, the mechanical alloying technique (MA) was used to develop special powder metallurgy (PM) steels with two different types of properties. The use of this technique is essential for obtaining the target microstructure, which ensures the desired performance of the resulting material. Oxide dispersion strengthened (ODS) ferritic steels were produced using MA based on the prealloyed grade Fe–20Cr–5Al and Fe–14Cr–5Al–3 W steels with the addition of Ti and Y₂O₃ as reinforcements. The incorporation of Y₂O₃ enables a homogeneous dispersion of nano-oxides and nano-clusters in a submicron-grained structure that should enhance the mechanical properties up to 600 °C. In addition, the base alloying system, Fe–Cr–Al (Ti), should enable the development of protective oxide layers through high-temperature treatments, which improves the compatibility with the environment, avoids liquid–metal embrittlement and contributes to the increase of the mechanical response up to 600 °C. Furthermore, microalloyed powders can be obtained using MA and consolidated with a pressure-assisted sintering process in an attempt to control the final grain size, to achieve microalloyed steels, and to achieve an extraordinary balance of properties.     

Microstructural evolution during combustion reaction between CuO and Al induced by high energy ball milling

The product of the combustion reaction between CuO and Al induced by high energy ball milling has been characterised by using X-ray diffractometry and scanning electron microscopy. It has been observed that the combustion reaction can be ignited very easily by the ball milling. The reaction product consists of polycrystalline Cu in bulk and particle forms and a large number of nanometer sized spherical Al2O3 particles attached to the surface of the Cu. It has been demonstrated that this microstructure is evolved through rapid solidification of Cu and Al2O3 melts and rapid condensation of Cu vapour. Cu and Al2O3 phases are separated in the reaction product. The reason for this is mainly attributed to the large difference in their density and the shaking force of the ball mill.     

氧化铝高能球磨时机构力化学效应研究

研究了氧化铝在高能球磨过程中机械力化学效应的变化,机械力化学效应因子随球磨时间的变化可分为三个阶段;第一阶段主要是晶粒尺寸减小和显微应变增加同时进行;第二阶段主要是有效温度系数的增加;第三阶段主要是点阵膨胀至饱和。用溶解法比较了球磨前后氧化铝的活性,发现经球磨后,氧化铝在盐酸中的溶解活化能由１８ｋＪ／ｍｏｌ降至４ｋＪ／ｍｏｌ,表面活化层增厚。     

Mo-Cu高能球磨过程实验研究及固溶度数值模拟

采用高能球磨方法对Mo-3%(质量分数)Cu、Mo-10%(质量分数)Cu复合粉末进行机械合金化加工,球磨时间为0～50h。通过扫描电镜及X射线衍射等对复合粉末的形貌、X射线衍射特征进行了分析,并对Cu在Mo中的固溶度用热力学方法进行了研究。结果表明,通过机械合金化方法可以得到超细小且均匀的纳米晶复合粉末,平均晶粒尺寸在60nm左右;从热力学平衡角度出发,通过细化晶粒来提高Cu在Mo中的固溶度极限可以用数值模拟来表达。     

Structure and stability of nanocrystalline TiC-powders obtained by reactive high energy milling

Nanostructured TiC can be obtained by reactive high energy ball milling of titanium and carbon powders. Milling rates of 250 or 320 r.p.m. lead to TiC grains with 0.1–2 μm diameter. The TiC grains consist of a nanosubstructure with the extent of 7 nm. The nanocrystals possess a high degree of lattice strains (0.8%). Neighboring nanocrystals in one grain are similar in their crystallographic orientation and are distinguished by small angle boundaries. High temperature treatment of the nanostructured TiC lead to continuous reduction of the lattice defects with increasing temperature. The nanocrystals starts to grow at about 600°C.     

Microstructural characterization of Mg-SiC nanocomposite synthesized by high energy ball milling

High-energy ball milling is successfully used to produce magnesium matrix nanocomposites reinforced with SiC nanoparticles. Changes in morphology and microstructural features of the milled powders were characterized in order to highlight advantages of the mechanical milling process and evaluate the role of the SiC nanoparticles. It was observed that with increasing volume fraction of SiC nanoparticles, a finer nanocomposite powder with more uniform particle size distribution is obtained. A homogeneous distribution of SiC nanoparticles, even up to 10% volume fraction, in magnesium matrix after 25?h milling was confirmed by elemental mapping and TEM results. The analysis of the XRD patterns accompanied by dark-field TEM images revealed that magnesium crystallites refine to fine nanocrystalline sizes after the mechanical milling. The results showed that the crystallite size of the magnesium matrix reduced with increasing SiC nanoparticle content in addition to the induced lattice strain.     

Synthesis and microstructure of layered-ternary Ti2AlC ceramic by high energy milling and hot pressing

Fully dense and single-phase Ti₂AlC ceramic was successfully synthesized by a high energy milling and hot pressing using Ti, C and Al as starting materials. The effects of composition of the initial elemental powders and sintering temperatures on the purity and formation of Ti₂AlC were examined. The formation mechanism for the single-phase Ti₂AlC ceramics was investigated by XRD in details, which could be described as follows: the most of initial elements reacted to form TiC and Ti–Al intermetallics; the intermetallics and the residual Ti and Al transformed to TiAl phase; and finally the TiAl intermetallics and the TiC reacted to yield Ti₂AlC.     

高能球磨对碱式碳酸锌热分解活化能的影响

采用行星式球磨机对碱式碳酸锌进行湿法研磨,研究不同球磨工艺条件下,碱式碳酸锌颗粒形态、大小及分解活化能的变化;产物采用SEM、XRD、TG和DSC等进行分析表征。结果表明:球磨时间对碱式碳酸锌的颗粒大小形态及热分解活化能影响显著,球料比为10∶1(质量比),转速为200r/min,占物料质量64%的乙醇控制剂作用下,高能球磨6 h后,颗粒形态大小由粒径为50μm的片状变为粒径为50nm的等轴状,球磨至24h时,颗粒形态大小并没有进一步缩小;热分解活化能在球磨24h后由138.0 kJ·mol-1减少到112.4 kJ·mol-1,热分解的温度前推了14.8℃。     

Microstructure,grain growth,and hardness during annealing of nanocrystalline Cu powders synthesized via high energy mechanical milling

In this paper, the microstructure and hardness evolutions of commercially pure Cu subjected to high energy mechanical milling and subsequent annealing treatments in the temperature range of 400–700 °C are investigated. The results demonstrated the simultaneous occurrence of recovery, recrystallization, and grain growth during annealing of the nanocrystalline Cu. The volume fraction of the recrystallized grains estimated using the grain orientation spread exhibits lower values as a result of its dynamic recovery at higher temperatures. The normal grain growth in the range of 400–600 °C and significant abnormal grain growth at higher temperatures are observed during annealing. As a result of the abnormal grain growth, the microhardness value rapidly decreases for the sample annealed at 700 °C. An analysis of the grain growth kinetics using the parabolic equation in the temperature range of 400–600 °C reveals a time exponent of n ≈ 2.7 and an activation energy of 72.93 kJ/mol. The calculated activation energy for the grain growth in the nanocrystalline Cu is slightly less than the activation energy required for the lattice diffusion. This low activation energy results from the high microstrain as well as the Zener-pinning mechanism that arises from the finely dispersed impurities drag effect.