机械合金化制备纳米晶铁-铜合金粉体

利用机械合金化方法制备了纳米晶铁-铜合金粉体,采用XRD、SEM和粒度分析仪对粉体在球磨过程中的固态相变、微观形貌和粒径变化进行了分析。结果表明:球磨20 h后,粉体的衍射峰宽化并形成固溶体,随球磨时间延长,粉体的晶粒尺寸逐渐减小,微观应变和晶格常数逐渐增大;粉体颗粒首先被碾压成扁平状并相互焊合使颗粒尺寸粗化,然后随球磨的继续进行变成球状的小颗粒,使颗粒尺寸逐渐减小;球磨65 h后,颗粒形貌和组织趋于稳定,获得了平均粒径为5.80～7.76μm的纳米晶粉体,粉体平均晶粒尺寸达到8 nm左右。     

不同Al2O3含量ZrO2(3Y)/Al2O3纳米复合粉体的制备与表征

采用化学共沉淀法制备了Al2O3数量分数为0%～30%的ZrO2(3Y)/Al2O3纳米复合粉体,研究了Al2O3含量和煅烧温度对粉体相结构、晶粒尺寸和晶格畸变的影响.结果表明800℃×2 h煅烧的复合粉体只出现t-ZrO2相,不出现Al2O3的任何晶相;Al2O3的添加抑制了ZrO2(3Y)晶粒的增长和四方相向单斜相的结构相变,使相变温度显著提高,晶格畸变增大.     

高能球磨制备纳米级Al_2O_3/Al复合粉体过程中铝相晶粒尺寸和结构的变化

利用X射线衍射仪分析了在高能球磨制备纳米Al_2O_3/Al混合粉体过程中,球磨时间和纳米Al_2O_3含量对铝相晶粒尺寸和晶格应变的影响。结果表明:在初期短时间的球磨中,微米铝粉的晶粒尺寸迅速细化到纳米级,但随着球磨时间的进一步延长,高能球磨为晶粒融合和再生长提供了能量,使铝晶粒沿着某些晶向有长大的趋势;当Al_2O_3体积分数较低(5%)时可促进铝粉的破碎,但高含量的Al_O_3则对铝粉的球磨破碎不利。     

超临界流体干燥法制备纳米ZrO2粉体及其煅烧行为研究

用超临界流体干燥法制备了纳米ZrO2粉体,并用不同热处理工艺进行处理,之后对样品进行TEM和XRD分析。结果表明,煅烧温度和煅烧时间对纳米ZrO2粉体性能的影响是显著的。随着煅烧温度的提高和时间的延长,粉体由t相转变为m相,晶粒尺寸逐渐增大,但是煅烧温度对ZrO2相组成和晶粒尺寸的影响比时间的影响更大。     

机械合金化法制备超细Al-Ti粉及其反应活性研究

采用机械球磨法,通过控制球磨时间和硬脂酸添加量,制备了具有纳米晶粒度的Al-Ti合金粉Al0.9Ti0.1和Al0.7Ti0.3,用该样品与Fe2O3混合制备Al-Ti/Fe2O3复合铝热剂样品。结构表征表明,机械合金化后得到的Al-Ti粉程粒状,其表面存在1-10μm的超细微观结构,Al、Ti之间相互扩散,形成薄片状的Al-Ti二元复合结构;且元素含量与合金粉的原配比相一致。热分析结果表明Al-Ti合金粉就有很高的反应活性。在空气中,在熔化前发生了明显的氧化还原反应,这种固-气相反应在原料Al粉的DSC图谱中却没有出现,且Al Ti-O2体系的高温反应放热峰较Al-O2体系提前。此外对Al-Ti与Fe2O3铝热体系,其在合金融化前也发生了显著的固-固反应,并且Al粉融化前出现了明显的固-固相反应反应,这表明由Al-Ti合金组成的铝热剂具有优异的点火性能。     

Fe3A1金属间化合物的机械合金化

利用X射线衍射(XRD)、示差扫描量热计(DSC)以及透射电镜(TEM)研究了Fe-Al元素混合粉末球磨过程中的结构演变。结合Fe3Al各种相衍射规律的分析,阐述了合成的B2-Fe3Al在XRD中未出现超点阵衍射峰的原因。球磨中,加工硬化和回复这一相互矛盾的过程,决定球磨粉末具有极限晶粒度。     

机械合金化制备各向同性NdFeB纳米晶磁粉的研究

在高纯氩气气氛保护下,通过机械合金化技术制备出了纳米晶NdFeB各向同性磁粉.采用X射线衍射分析(XRD)对原料粉的合金化过程及其晶粒尺寸和微观应变进行研究,利用扫描电子显微镜(SEM)和振动样品磁强计(VSM)对制得的纳米晶NdFeB各向同性磁粉的微观形貌及磁学性能进行了研究.结果表明:球磨初始时的冷焊阶段Nd、B原子就已经进入Fe的晶格形成间隙固溶体,随着球磨时间的增加合金粉微观应变增加、平均晶粒度迅速降低,球磨40 h后获得的合金粉平均晶粒度达到8 nm左右.     

Al/Fe3Al网状结构复合材料的制备

采用机械合金化及退火工艺制备纳米级Fe3Al金属间化合物粉体;利用有机前驱体烧蚀技术,氩气保护下在真空热处理炉中经过1460℃热处理,制备具有高气孔率、高尺寸稳定性、耐高温的Fe3Al金属间化合物网状结构;采用负压浸渗法制备Al/Fe3Al网状结构复合材料,材料的耐磨性能明显优于基体材料,在100N载荷、400r/min转速的试验条件下,摩擦时间为20min时,Al/Fe3Al复合材料的磨损量较纯Al试样降低66%.     

机械合金化制备TiC/W纳米晶复合粉体的烧结特性

利用高能机械球磨制备出W-10%TiC复合粉体并进行烧结,分析了粉体特性和烧结体的组织形貌.结果表明:球磨使引入的镍铁和钨形成固溶体,并且产生大量缺陷,从而促进烧结致密化.随着球磨时间的延长,粉体晶粒尺寸下降,点阵畸变逐渐增大,经过球磨后粉体具有较高的烧结活性,并且随着球磨时间的延长,复合粉体烧结后密度逐渐增加.烧结体显微组织均匀致密,没有间隙和空洞出现,其中钨颗粒近似呈球状,粒径为20～30 μm,碳化钛颗粒基本保持原始颗粒大小(1～2 μm)弥散分布在相邻的钨颗粒边界处;钨镍铁相呈网状组织包围着部分钨和碳化钛颗粒,其体积随着球磨时间延长而增加.     

纳米Fe2O3-环氧树脂/胺复合材料的制备及其溶解性探讨

用溶胶-凝胶法制备纳米Fe2O3粉体并与环氧树脂／胺复合，通过XRD、TEM测定了纳米Fe2O3粉体的物相和粒径。结果表明，粉体均为α-Fe2O3的刚玉结构，平均晶粒度为27．7nm。分析了复合过程中引发剂乙二胺用量对Fe2O3-环氧树脂／胺复合材料的影响，并探讨了该纳米复合材料的磁性以及在水和生理盐水中的溶解情况及温度对它的影响。     

Preparation and characterization of nanocrystalline ZrO2-7%Y2O3 powders for thermal barrier coatings by high-energy ball milling

High-energy ball milling is an effective method to produce nanocrystalline oxides. In this study, a conventional ZrO₂-7%Y₂O₃ spray powder was ball-milled to produce nanocrystalline powders with high levels of crystalline disorders for deposition of thermal barrier coatings. The powder was milled both with 100Cr6 steel balls and with ZrO₂-3%Y₂O₃ ceramic balls as grinding media. The milling time was varied in order to investigate the effect of the milling time on the crystallite size. The powders were investigated in terms of their crystallite sizes and morphologies by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that under given milling conditions the powder was already nanostructured after 40 min milling. The crystallite size decreased significantly with increasing milling time within first 120 min. After that, a further increase of milling time did not lead to a significant reduction of the crystallite size. Ball-milling led to lattice microstrains. Milling with the steel balls resulted in finer nano-sized crystal grains, but caused the contamination of the powder. The nano-sized crystal grains coarsened during the heat-treatment at 1250°C.     

Transmission electron microscopy studies of microstructure of Ti–Nb and Ti–Ta alloys after ball milling and hot consolidation

Two Ti alloys with compositions Ti?10Ta and Ti?10Nb (at.%) were milled in a high‐energy mill for a maximum of 80 h in an argon atmosphere. A nanocrystalline structure of α‐Ti(X) (X = Ta or Nb) solid solution was formed in both investigated alloys after milling, as shown by X‐ray diffraction. Transmission electron microscopy observations of powders milled for 80 h revealed chemical inhomogeneity of particles in nanometre‐scale regions and an average crystallite size of about 10 nm. The pulse plasma sintering method was applied for hot consolidation of milled powders. The mean density of pulse plasma sintering compacts of Ti–Nb alloy was about 99.5% of the theoretical value, whereas the density of the Ti?10Ta sample was lower, close to 92% of the theoretical value. Transmission electron microscopy observation of compacted samples showed that the sintering process caused the formation of a two‐phase α + β structure in both investigated alloys, with a mean grain size of 220 nm. The chemical inhomogeneity and high degree of deformation in nanometre‐scale regions of milled powders led to a martensitic transformation, resulting in formation of a 9R martensite structure.     

HRTEM studies of NiNbZr + Ag amorphous-nanocrystalline composites

Amorphous powder of composition corresponding to Ni60Ti20Zr20 (in at%) was obtained by ball milling in a high-energy mills starting from pure elements. Formation of the amorphous structure was observed already after 20 h of milling, although complete amorphization occurred after 40 h. The microhardness of powders increased from about 30 HV for pure elements to above 400 HV (1290 MPa) after 40 h of milling. Transmission electron microscopy (TEM) allowed to identify nanocrystalline inclusions of intermetallic phases of size 2–10 nm. Uniaxial hot pressing was performed in vacuum at temperature below the crystallization T_x it is 510°C and pressure of 600 MPa, Mixed amorphous powders and nanocrystalline silver powders were used to form a composite, in which microhardness was near 970 MPa HV and 400 HV for the amorphous phase and nanocrystalline silver, respectively. The compression strength of the composite containing 20 wt% of nanocrystalline Ag powder was equal to 600 MPa and plastic strain was 2%. Microstructure studies showed low porosity of composites of less than 1%, uniform distribution of the silver phase and a transition zone between both components, about 150 nm thick, where diffusion of nickel, niobium and zirconium into silver was observed. High-resolution TEM allowed identifying the structure of nanocrystalline inclusions in the amorphous matrix after hot pressing as either Ni₃Zr or Ni₁₇Nb₃. The identification was performed basing on measurements of angles and interatomic distances using inverse Fourier transformed images with enhanced contrast using Digital Micrograph computer program.     

Scanning and transmission electron microscopy microstructure characterization of mechanically alloyed Nb–Ti–Al alloys

Results are presented of an investigation of the microstructure development during mechanical alloying and following consolidation of an Nb15Ti15Al alloy. The alloy was synthesized from elemental as well as pre‐alloyed powders. The microstructure of this material was examined by transmission electron microscopy, scanning electron microscopy and X‐ray diffraction. The use of pre‐alloyed TiAl powder for synthesis of the Nb15Ti15Al alloy meant that a much shorter time was required to complete the mechanical alloying process compared with the synthesis of elemental powders. The investigation indicates that three phases were present in the consolidated materials: the Nb solid solution, the Nb₃Al intermetallic phase and the dispersoid.     

Characterization of nanoscaled heterogeneities in mechanically alloyed and compacted CuFe.

Cu80Fe20 and Cu50Fe50 were mechanically alloyed from the pure elements by ball milling for 36 h. The alloy powder was compacted into tablets at room temperature by applying a pressure of 5 GPa. Characterization of the Cu80Fe20) and Cu50Fe50 alloys was carried out by high-resolution transmission electron microscopy (HREM), atom probe field ion microscopy and three-dimensional atom probe (3DAP). The grain size of the nanocrystalline microstructure of the ball-milled alloys observed with HREM varies between 3 and 50 nm.Atom probe and 3DAP measurements indicate that the as-prepared state is a highly supersaturated alloy, in which the individual nanocrystals have largely varying composition. Fe concentration in Cu was found to range from about 8 to 50 at%. It is concluded that by ball milling and compacting an alloy is produced which on a nanometer scale is heterogeneous with respect to morphology and composition.     

Synthesis and characterization of permalloy-reinforced Al2O3 nanocomposite powders by mechanical alloying

Intermetallics of Fe and Ni, which are known as permalloy, are under attention due to their excellent magnetic performance. Besides, mechanical properties of the materials can be improved by decreasing crystallite size of FeNi intermetallics or by reinforcing them with hard secondary phases such as Al₂O₃. In this study, FeNi–Al₂O₃ nanocomposite powders with three different compositions were successfully synthesized through mechanical alloying of Fe₂O₃, Ni, and Al powders mixture. Characterization of the samples was accomplished by scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy and X-ray diffraction. Effects of various parameters such as chemical composition of received materials, milling time, and annealing on the phase evolution, morphology, and microhardness of samples were investigated. It was found that by the addition of Fe as diluent, the required milling time for formation of FeNi intermetallic increased. By increasing milling time, mean crystallite size of FeNi decreased and reach to about 28 nm for FeNi-30 wt% Al₂O₃ nanocomposite powder sample. TEM observations also showed that in situ-formed Al₂O₃ particles, with particle size of about 65 nm, were uniformly dispersed within FeNi matrix.     

Determining the effect of process parameters on particle size in mechanical milling using the Taguchi method: Measurement and analysis

Micro and nano-particles have been successfully and widely applied in many industrial applications. The mechanical milling process is a popular technique used to produce micro and nano-particles. Therefore, it is very important to improve milling process efficiency and quality by determining the optimal milling parameters. In this study, the effects of the main mechanical milling parameters: milling time, process control agent (PCA), ball to powder ratio (BPR) and milling speed in the planetary ball milling of nanocrystalline Al 2024 powder were optimized by the Taguchi method. Mean particle size (d₅₀) was used to evaluate the effect of process parameters on the mechanical milling process. The orthogonal array experiment is conducted to economically obtain the response measurements. Analysis of variance (ANOVA) and main effect plot are used to determine the significant parameters and set the optimal level for each parameter. The as-received and milled powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and a laser particle size analyzer, respectively. The results indicate that the process control agent significantly affects (84% contribution) the mean particle size (d₅₀) while other parameters have a lower effect (16% contribution). The developed model can be used in the mechanical milling processes in order to determine the optimum milling parameters for minimum particle size.     

Structure studies of ball-milled ZrCuAl, NiTiZrCu and melt-spun ZrNiTiCuAl alloys

ZrNiTiCu and ZrNiTiCuAl alloys were amorphized using either a melt‐spinning or ball‐milling process in a high‐energy planetary mill. The elemental powders were initially blended to the desired composition (in at.%) of Zr, 65; Cu, 27.5; Al, 7.5 and of Ti, 25; Zr, 17; Cu, 29; Ni, 29, respectively. The composition of alloys was chosen to be the same as for the bulk amorphous ZrCuAl and easy glass‐forming ZrNiTiCu alloys. An almost fully amorphous structure was obtained after 80 h of milling in the case of both compositions. Transmission electron microscopy studies of ball‐milled powders revealed the presence of nano‐crystallites [2–5 nm for ZrCuAl and smaller (1–3 nm) for the ZrTiNiCu alloy]. High‐resolution transmission electron microscopy of melt‐spun ZrNiTiCuAl ribbons provided evidence of the amorphous structure.