Preparation of W–15 wt%Ti prealloyed powders

W–15 wt%Ti prealloyed powders were prepared by high-energy milling W and TiH₂ powders, and the prealloyed powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The size of W and TiH₂ grains was estimated by Williamson–Hall formula from width of XRD peaks. The results show that the grain size decreases with increasing milling time, while the lattice parameter increases. After milling for 40 h, nanocrystalline β-W_xTi_1−x solid solution with the form of thin laminar exists in the W–TiH₂ prealloyed powders.     

Synthesis process of Mg–Ti BCC alloys by means of ball milling

The synthesis process of Mg–Ti alloys with a BCC (body centered cubic) structure by means of ball milling was studied by X-ray diffraction and various microscopic techniques. The morphology and crystal structure of Mg–Ti alloys changed with increase of milling time. During ball milling of Mg and Ti powders in molar ratio of 1:1, firstly, plate-like particles stuck on the surface of the milling pot and balls. After these plate-like particles fell off from the surface of the milling pot and balls, spherical particles with the mean diameter of 1 mm, in which concentric layers of Mg and Ti were disposed, were formed. These spherical particles were crushed into spherical particles with the diameter of around 10 μm by introduction of cracks along the boundaries between Mg and Ti layers. Finally, the Mg₅₀Ti₅₀ BCC phase with the lattice parameter of a = 0.342(1) nm and the grain size of 3 nm was formed. During milling of Mg and Ti to synthesize the BCC alloy, Mg and Ti were deformed mainly by the basal plane slip and the twinning deformation, respectively. Ti acted as abrasives for Mg which had stuck on the surface of the milling pot and balls. The BCC phase was found after Mg dissolved in Ti.     

Nanocrystalline τ2 phase obtained by mechanical alloying of Al60Fe15Si15Ti10 powder mixture followed by consolidation

In the present work an elemental powder mixture of Al60Fe15Si15Ti10 (at.%) was mechanically alloyed in a high-energy ball mill. A part of the milling product was examined in a calorimeter, while another portion was subjected to consolidation by hot-pressing at 1000 °C for 180 s under a pressure of 7.7 GPa. The results obtained show that a nanocrystalline cubic phase with the lattice parameter a₀ = 11.645 Å, isomorphous with the τ₂ (Al₂FeTi) phase, is formed during mechanical alloying process. Heating of the milling product in the calorimeter up to 720 °C causes limited growth of grains, however the τ₂ phase remains nanocrystalline with the mean crystallite size of 28 nm. Grain growth takes place during consolidation of the milling product as well, although the τ₂ phase remains nanocrystalline with the mean crystallite size of 34 nm. The microhardness of the bulk nanocrystalline sample is 1013 HV0.2 and its open porosity is 0.3%. The results obtained show that the quality of compaction with preserving nanometric grain size of the τ₂ phase is satisfactory and its microhardness is relatively high.     

The wide band gap of highly oriented nanocrystalline Al doped ZnO thin films from sol–gel dip coating

Undoped and Al doped ZnO thin films were prepared on glass substrate by sol–gel dip coating from PVP-modified zinc acetate dihydrate and aluminium chloride hexahydrate solutions. The XRD patterns of all thin films indexed a highly preferential orientation along c-axis. The AFM images showed the average grain size of undoped ZnO thin film was about 101 nm whereas the smallest average grain size at 8 mol% Al was about 49 nm. The values of direct optical band gap of thin films varied in the range of 3.70–3.87 eV.     

机械合金化过程中Fe50Als50二元系的结构演变

利用高能球磨和后续热处理技术制备纳米晶Fe5A150（摩尔分数，％）合金粉体。采用X射线衍射、透射电镜和扫描电镜对元素混合粉在机械合金化过程中的结构演变及热处理对合金化粉体结构的影响等进行分析，讨论其机械合金化合成机制。结果表明：球磨过程中Al向Fe中扩散，形成Fe（A1）固溶体。机械合金化合成Fe（Al）遵循连续扩散混合机制；球磨30h后，粉体主要由纳米晶Fe（A1）构成，晶粒尺寸5．65nm；热处理导致Fe（A1）纳米晶粉体有序度提高，转变为有序的B2型FeAl金属间化合物，粉体的晶粒尺寸增大，但仍在纳米尺度范围。     

Effect of composition and milling parameters on the critical ball milling of Ti–Si–B powders

The absence of brittle phases and elevated temperature during ball milling of a powder mixture containing a large amount of ductile component can contribute to reach an excessive agglomeration denoting a critical ball milling (CBM) behavior. This work reports in the effect of composition and milling parameters on the CBM behavior of Ti–Si–B powders. High-purity elemental Ti–Si–B powder mixtures were processed in a planetary ball mill in order to prepare the Ti₆Si₂B compound and two-phase Ti + Ti₆Si₂B alloys. TiH₂ chips instead of titanium powder were used as a starting material. To avoid elevated temperature in the vials during ball milling of Ti–Si–B powders the process was interrupted after each 10 min followed by air-cooling. Following, the milled powders were hot-pressed at 900 °C for 1 h. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). Short milling times followed by air-cooling contributed to obtain a large amount of powders higher than 75% in the vials. Only Ti and TiH₂ peaks were observed in XRD patterns of Ti–Si–B and TiH₂–Si–B, respectively, suggesting that extended solid solutions were achieved. The large amount of Ti₆Si₂B and Ti + Ti₆Si₂B structures were formed during hot pressing from the mechanically alloyed Ti–Si–B and TiH₂–Si–B powders.     

Characterization and Formation Mechanism of Ni3Si–Al2O3 Nanocomposite Prepared by Mechanochemical Reduction Method

In this present work, Ni₃Si–Al₂O₃ nanocomposite powders were synthesized by mechanical milling using NiO, Si and Al as raw materials. The phase transformation, formation mechanism and microstructure evolution of the powders during mechanical milling were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), transition electron microscopy (TEM) and microhardness measurements. Results showed that the Ni₃Si, Al₂O₃ and Ni₃₁Si₁₂ phases formed after 5 h of milling with a rapid mechanically induced self-propagating synthesis mode. The average grain size and internal strain of Ni₃Si and Al₂O₃ after 30 h of milling were (16.8 nm, 1.27%) and (19.6 nm, 0.94%), respectively. The maximum microhardness value of 813 HV was obtained in the 30 h milled powder. The relationship between the hardness and grain size of the powders satisfies the Hall–Petch relationship. Ni₃Si–Al₂O₃ nanocomposite powders are very stable during heating at 950 °C. By annealing of the milled powders leads to grain growth, internal strain and microhardness of Ni₃Si powder decrease and transformation of disordered structure to an ordered state. A long-range ordering parameter (LRO) of 0.97 for the ordered Ni₃Si can be achieved after annealing at 950 °C for 2 h.

     

高能球磨制备Al-Pb-Si-Sn-Cu纳米晶粉末的特性

通过机械合金化制备了Al-15％Pb-4％Si-1％Sn-1．5％Cu(质量分数)纳米晶粉末。采用X射线衍射(XRD)，扫描电镜(SEM)和透射电镜(TEM)对不同球磨时间的混合粉末的组织结构、晶粒大小、微观形貌以及颗粒中化学成分分布情况进行了研究。结果表明混合粉末经过球磨后形成了纳米晶，其组织非常均匀。球磨对Pb的作用效果明显大于对Al的作用效果，经过40h球磨后Pb粒子达到40nm，而Al在球磨60h后晶粒为65nm；经球磨后，Cu和Si固溶于Al的晶格中，而Sn则固溶于Pb晶格中，并且Al和Pb发生了互溶，形成了Pb(Al）超饱和固溶体；在球磨过程中硬度高的脆性粒子Si难于完全实现合金化。     

Effects of ball milling time on the synthesis and consolidation of nanostructured WC–Co composites

The effects of ball milling time on the synthesis and consolidation of WC–10 wt%Co powder were investigated by high energy milling in a horizontal ball mill. Nanostructured powder was mechanically alloyed after 60 min cyclic milling with a WC average domain size of 21 nm. The number of nanosize (<0.2 μm) particles increased with milling time. Contamination by Fe increased with milling time, reaching almost 3 wt% after 300 min milling. The onset of the WC–Co eutectic was lowered to 1312 °C through an increase in milling time. The density of the compacted powders increased with the compaction pressure but decreased with milling time achieving 61.7% after 300 min milling compared to 64.4% for 30 min. The compressibility behaviour of the milled powders was determined using a compaction equation. Densification and hardness reached optimum levels for the 60 min milled powder after both pressureless sintering and sinter-HIP.     

Structural evolution and grain growth kinetics of the Fe–28Al elemental powder during mechanical alloying and annealing

The structural evolution and grain growth kinetics of the Fe–28Al (28 at.%) elemental powder during mechanical alloying and annealing were studied. Moreover, the alloying mechanism during milling the powder was also discussed. During mechanical alloying the Fe–28Al elemental powder, the solid state solution named Fe(Al) was formed. The lattice parameter of Fe(Al) increases and the grain size of Fe(Al) decreases with increasing milling time. The Fe and Al particles were first deformed, and then, the composite particles of the concentric circle-like layers were generated. Finally, the composite particles were substituted by the homogeneous Fe(Al) particles. The continuous diffusion mixing mechanism is followed, mainly by the diffusion of Al atoms into Fe. During annealing the milled Fe–28Al powder, the order transformation from Fe(Al) to DO₃-Fe₃Al and the grain growth of DO₃-Fe₃Al occurred. The grain growth kinetic constant, K = 1.58 × 10⁻⁹ exp(−540.48 × 10³/RT) m²/s.     

Magnetic properties and thermal ordering of mechanically alloyed Fe–40 at% Al

A metastable, nanostructured, disordered bcc Fe–40 at% Al solid solution was produced from elemental powders using a high-energy ball mill. The effects of milling and subsequent annealing on (1) the formation of disordered nanocrystals, (2) changes in the lattice parameter and grain size, and (3) the disorder-to-order, ferromagnetic-to-paramagnetic transformations were studied by examination of both the microstructure and magnetic measurements. Oxidation and contamination of the powder during processing may play a significant role in the thermal ordering.     

A study on mechanochemical behavior of B2O3–Al system to produce alumina-based nanocomposite

One possible route for producing the fine and homogenous distribution of hard particles in composite microstructure is the mechanochemical processing in which high-energy ball milling promotes the reaction in a mixture of reactive powders. In this study mechanochemical reaction of B₂O₃ and Al powder during ball milling was studied. The phase transformation and microstructure of powder particles during ball milling were investigated by X-ray diffractometry and scanning electron microscopy. The results showed that during ball milling the B₂O₃–Al reacted with a combustion mode producing Al₂O₃–AlB₁₂ nanocomposite. The crystallite size of Al₂O₃ and AlB₁₂ was 40 and 25 nm, respectively. This structure appeared to be stable upon annealing.     

Nanophase intermetallic FeAl obtained by sintering after mechanical alloying

The preparation of bulk nanophase materials from nanocrystalline powders has been carried out by the application of sintering at high pressure. Fe–50 at.%Al system has been prepared by mechanical alloying for different milling periods from 1 to 50 h, using vials and balls of stainless steel and a ball-to-powder weight ratio (BPR) of 8:1 in a SPEX 8000 mill. Sintering of the 5 and 50 h milled powders was performed under high uniaxial pressure at 700 °C. The characterization of powders from each interval of milling was performed by X-ray diffraction, Mössbauer spectroscopy, scanning and transmission electron microscopy. After 5 h of milling formation of a nanocrystalline α-Fe(Al) solid solution that remains stable up to 50 h occurs. The grain size decreases to 7 nm after 50 h of milling. The sintering of the milled powders resulted in a nanophase-ordered FeAl alloys with a grain size of 16 nm. Grain growth during sintering was very small due to the effect of the high pressure applied.     

Microstructures of mechanically activated Ti-46at.%Al powders and spark plasma sintered ultrafine TiAl alloy

Powder of Ti-46at.%Al was synthesized through mechanical activation (MA) for different milling times, and the 16 h MAed powder was sintered by using a spark plasma sintering (SPS) process at different sintering temperatures. The XRD profiles showed that the MAed Ti-46at%Al powder for 12,16, and 20 h contained initial α-Ti and Al phases, and that the SPSed TiAl alloys contained the gamma TiAl and α2-Ti3Al phases. The TEM showed two different types of regions in the 16 h MAed Ti-46at.%Al powder. One type consisted of only Al with a grain size about 80 nm, and the other type a mixture of Al and Ti with a grain size of 30 nm. According to the optical micrographs of MA-SPSed samples, the alloys sintered at higher temperatures showed a coarser microstructure. In the case of the 1473 K sintering, typical duplex structures ((α2 γ) lamella and γ phases) with interlamellar spacings of 50-400 nm and the grain size either less man 100 nm, or 1000 nm were observed.     

Substitution of Cu and/or Al in η phase (MgZn2) and the implications for precipitation in Al–Zn–Mg–(Cu) alloys

The effects of Cu and Al substituting for Zn within bulk samples of η phase (nominally MgZn₂) have been studied by laboratory X-ray powder diffraction and nuclear magnetic resonance. Increasing Al concentration causes both of the η phase lattice parameters to increase linearly, while increasing Cu concentration causes both parameters to decrease linearly. These effects also appear to combine in a linear fashion if both Al and Cu are substituted into the MgZn₂ structure, particularly in the case of the a lattice parameter. Al was found to substitute evenly onto both Zn sites, while Cu substitutes preferentially onto the 6(h) site at low Cu concentrations, before causing significant disruptions to the structure at concentrations above 1.1 at.%, leading to the transition to long period stacking phases at the expense of η. High-resolution synchrotron powder diffraction from a commercial Al–Zn–Mg–(Cu) alloy revealed that the η phase precipitates with lattice parameters that are substantially smaller than for pure MgZn₂, indicating Cu concentrations of at least 8.9 at.% and probably higher. It is likely that the Al matrix provides a mechanical constraint on the formation of any long period stacking phases and allows the η phase to exist in these alloys with such high Cu concentrations.     

Structural evolution of the Ti–Al coatings produced by mechanical alloying technique

By means of the mechanical alloying (MA) method, the Ti + Al coatings were deposited on Ti alloy substrates. The structural formation of the Ti–Al coatings as a function of the milling time was studied. The thickness of coatings and their structure depended on the milling duration. At initial stage Al covered the Ti substrate. Then Ti particles were embedded in the Al matrix. Gradually the composite coating was formed. Greater plastic deformation led to the formation of the layered coating structure. Prolonged milling resulted in refinement of the particles into the nanometer scale near surface region of the Ti–Al coating.     

Study of ac impedance spectroscopy of Al doped MnFe2−2xAl2xO4

We have reported electrical properties of Al doped MnFe₂O₄ ferrite using ac impedance spectroscopy as a function of frequency (42 Hz to 5 MHz) at different temperatures (300–473 K). XRD analysis shows that all the compositions are single phase cubic spinel in structure. The complex impedance analysis has been used to separate the grain and grain boundary resistance of MnFe_2−2xAl_2xO₄. From the analysis of impedance spectra it is found that the real (Z′), and imaginary (Z″) part of the impedance decrease with increasing frequency and both are found to decrease with Al doping up to 20%, and thereafter, these increase with further increasing the Al concentration. Experimental results have been fitted with two parallel RC equivalent circuits in series.     

纳米晶W粉和W-Ni-Fe预合金粉的制备

采用高能球磨法制备纳米晶W粉和W-Ni-Fe预合金粉，研究了不同的球磨材质包括硬质合金球(CCB)、钨球(TAB)和球磨转速、球料比及球磨时间等条件对球磨后粉末性能的影响。利用XRD，TEM和EDX分析球磨后粉末的晶粒尺寸、晶格畸变、形貌、结构变化及颗粒成分变化。结果表明：高能球磨法可制得10nm～80nm的W粉和W-Ni-Fe预合金粉，纳米级颗粒含量达80％以上。相同材质的钨球制得的纳米粉末综合性能较好。球磨过程中，粉末保持颗粒状结构，纳米级粉末颗粒形状最终趋于等轴化。     

机械合金化制备纳米晶C/Cu复合粉末的研究

将粗铜粉和石墨粉按不同配比混合后进行机械合金化,并对机械合金化粉末的物相、合金化特征、晶粒尺寸进行了分析研究。结果表明,在球磨过程中,随球磨时间延长有越来越多的C原子溶入Cu的晶格,点阵常数随球磨时间和粉末中石墨含量的增加而增加,球磨24h时达到最大值,继续球磨,点阵常数略有降低。机械合金化可以使晶粒细化并产生大量孪晶位错和纳米晶界面,有利于原子扩散形成过饱和固溶体和非晶,C/Cu复合粉末球磨30h后晶粒尺寸可达到22nm。     

The effect of zirconium addition on microstructure and properties of ball milled and hot compacted powder of Al–12 wt% Zn–3 wt% Mg–1.5 wt% Cu alloy

Elemental powders of the composition Al–12 wt% Zn–3 wt% Mg–1.5 wt% Cu with addition of 1 and 2 wt% Zr were ball milled in a planetary high-energy ball mill and then hot pressed in vacuum under 600 MPa pressure at 380 °C. The effect of ball milling and hot pressing on the microstructure was investigated by means of X-ray diffraction measurements (XRD), light microscopy, analytical and scanning transmission electron microscopy (TEM). Ball milling for 80 h leads to homogenous, highly deformed microstructure of aluminium solid solution with grain size below 100 nm. In the powder with zirconium addition, some part of the Zr atoms diffused in aluminium up to 0.3 wt% Zr. The remaining was found to form Zr-rich particles identified as face centered cubic (fcc) phase. Good quality samples without pores and cracks obtained by hot pressing composed of grains and subgrains of size below 200 nm. The particles of MgZn₂ phase were identified which were located mainly between compacted particles of milled powder. Hot pressed powder showed Vickers microhardness of about 195 HV (0.2 N) and ultimate compression strength in the range 611–658 MPa in the compression test. Addition of zirconium had no influence on the strength of the compacted powders.