Mechanical alloys in the Ti-B-H system: Influence of dispersion and alloying by boron upon thermal stability of hydride phases

Influence of dispersion and alloying by boron upon thermal stability and decomposition temperature of hydride phases of mechanical alloys of the Ti-B-H system that were derived in the conditions of high-energy ball milling either of (TiH_1.9 + 9 wt.% B + 13 wt.% Ti) and (TiH_1.9 + 50 wt.% TiB₂) mixtures (50 h milling, rotation speed 1000 rpm) or of (TiH_1.9 + 40 wt.% B) and (TiH_1.9 + 50 wt.% TiB₂) mixtures (20 milling, rotational speed 1630 rpm) has been studied employing scanning electron microscopy, X-ray diffraction analysis, and thermal desorption spectroscopy. It has been established that, dispersion and boron additives to the TiH_1.9 powder followed by mechanical treatment influence thermal stability of the hydride. Mechanical milling the (TiH_1.9 + 9 wt.% B + 13 wt.% Ti) mixture for 50 h in argon causes decreasing the decomposition temperature of a Ti(B,H)_x hydride phase by more than 300° compared with that of the initial TiH_1.9 hydride. Mechanisms of influence of both dispersion and boron alloying upon thermal stability of the TiH_1.9 hydride have been studied.     

Novel Al-matrix nanocomposites reinforced with multi-walled carbon nanotubes

Novel Al-based nanocomposites reinforced with multi-walled carbon nanotubes were produced by mechanical milling followed by pressure-less sintering at 823 K under vacuum. The interface between Al matrix and the multi-walled carbon nanotubes was examined using transmission electron microscopy. These observation showed that the multi-walled carbon nanotubes were not damaged during the preparation of the nanocomposite and that no reaction products were detected after sintering. The mechanical properties of sintered nanocomposites specimens were evaluated by a compression test. The yield stress (σ_y) and the maximum strength (σ_max) obtained were considerably higher than those reported in the literature for pure Al prepared by the same route. The values for σ_y and σ_max increase as the volume fraction of multi-walled carbon nanotubes increases. The milling time and the concentration of multi-walled carbon nanotubes have an important effect on the mechanical properties of the nanocomposite.     

Modification to the composition of nanocrystalline RuO2 through reactive milling under O2

Crystalline ruthenium dioxide (RuO₂) has been ball-milled in an O₂ atmosphere and the changes in the physico-chemical properties induced by different milling atmospheres (Ar and O₂) or milling sequences have been established. Cyclic voltammetry and BET measurements were used to evaluate the electrochemically active surface charge (, expressed in C g⁻¹) and the specific surface area (expressed in m² g⁻¹), respectively. The extent of oxygen uptake in the processed samples was determined by X-ray photoelectron spectroscopy (XPS). The value of RuO₂ milled under O₂ for 30 h (sample S4) is 120.7 C g⁻¹, a factor of two higher than the value of RuO₂ milled under Ar for the same period of time (sample S1, 60.3 C g⁻¹). A still higher value is obtained when the O₂ atmosphere of the crucible is frequently replenished (sample S5, 138.7 C g⁻¹) or when the milling operation is prolonged up to 81 h (sample S6, 160.5 C g⁻¹). These changes are paralleled by a variation of the BET surface area, which increases from 24 m² g⁻¹ for sample S1 to 51.5 m² g⁻¹ for sample S5. The concentration ratio [O_{bound to Ru}]/[Ru] determined by XPS increases steadily from sample S1 to sample S6, indicating that the amount [O_{bound to Ru}] increases with the exposure of RuO₂ to oxygen during the milling process. All these changes are explained by the fact that freshly exposed RuO₂ surfaces created during the milling process react with O₂ molecules, thereby lowering the surface energies and the tendency of the milled material to cluster into larger aggregates.     

机械合金化法制备金锡合金

采用高能球磨机械合金化法制备了Au-20%Sn合金,分析了合金物相、组织和硬度随球磨时间的变化规律,探讨了合金塑性与合金组织及制备工艺的关系。结果表明:采用高能球磨机械合金化法可以制备Au-20%Sn合金;随球磨时间的增加,Au-20%Sn的合金化程度增加,组织中的金属间化合物逐渐增多,最终基本上为δ相和ζ′相;合金的硬度随球磨时间的延长逐渐升高,并在球磨60min后获得最高硬度104.2HV,然后开始下降;球磨后的合金粉末在190℃×2h的烧结过程中发生了不同程度的再结晶和晶粒长大,再结晶程度随球磨时间的延长而增加,导致烧结后合金硬度在球磨时间超过60min后反而下降。     

Preparation of TiAl alloy powder by high-energy ball milling and diffusion reaction at low temperature

In this paper, TiAl alloy powders were prepared successfully by high-energy ball milling and diffusion reaction in vacuum at low temperature. The titanium powder, aluminum powder, and titanium hydride powder were used as raw materials. The samples were characterized by scanning electron microscopy(SEM), X-ray diffraction(XRD), field-emission scanning electron microscopy(FESEM), and differential thermal analysis(DTA). The results show that the alloy powders with the main intermetallic compounds of TiAl are obtained using Ti-Al powders and TiH_2-Al powders after heated for 2 h at 500 ℃,3 h at 600 ℃,and 3 h at 750 ℃,respectively.The average grain sizes of alloy powder are about 45 and20 μm with irregular shape, respectively. The prepared TiAl alloy powders are relatively pure, and the average quality content of oxygen in the alloy powders is0.33 wt%. The forming process of alloy powder contains both the diffusion reaction of Ti and Al,which gives priority to the diffusion reaction of aluminum.     

In situ nanocrystalline Fe–Si coating by mechanical alloying

A new approach for deposition of in situ nanocrystalline Fe–Si alloy coating on mild steel substrate by mechanical milling has been proposed. The thickness of nanocrystalline coating was a function of milling time and speed. Milling speed of 200 rpm was the optimum condition for development of uniform, hard, adherent and dense 200–300 μm thick nanocrystalline coating. A possible mechanism, consisting of three steps like repeated impact, cold welding and delamination, has been proposed for the formation of coating. These coatings have resulted in the increase of the hardness to almost double the value before coating.     

3种分散剂对ITO浆料稳定性能的影响

选用3种分散剂(聚乙烯吡咯烷酮、柠檬酸三铵、β-丙氨酸),通过球磨分散法制备ITO浆料,通过考察球磨分散时间和分散剂量对ITO浆料稳定性能的影响,分析比较不同分散剂对浆料稳定性作用,并探究其分散机理。结果表明:3种分散剂分散机制均为静电和空间位阻稳定作用;在相对ITO粉体质量比为5%、最佳球磨分散时间为48 h时,在15 d内ITO浆料的RSH可维持在10%以内;3种分散剂对ITO浆料稳定性的影响由强至弱的顺序为:聚乙烯吡咯烷酮>β-丙氨酸>柠檬酸三铵,与其在溶液中酸碱性强弱顺序一致,其中聚乙烯吡咯烷酮的分散效果最好。     

Consolidation and mechanical properties of ball milled Zr50Cu50 glassy ribbons

Bulk Zr₅₀Cu₅₀ partially crystallized glassy specimens have been produced by powder metallurgy methods. Zr₅₀Cu₅₀ powder has been prepared by controlled milling of melt spun glassy ribbons and subsequently consolidated by hot pressing into bulk cylindrical samples of 10 mm diameter and 10 mm length. The consolidated material exhibits interesting mechanical properties, namely, a perfect elastic regime of 1.5%, high strength of about 1350 MPa and hardness of 4.80 GPa. However, no macroscopic ductility is visible, most likely due to the residual porosity of the consolidated specimens. These results indicate that powder metallurgy methods may become a valid alternative to casting techniques for the production of glassy and partially crystallized Zr-based alloys.     

Synthesis of Nd0.7Sr0.3MnO3 ceramics by high-energy ball milling

Strontium doped perovskite-type manganite Nd_0.7Sr_0.3MnO₃ is synthesized by high-energy ball milling. Nd_0.7Sr_0.3MnO₃ single phase with perovskite structure is formed completely after milling 4 h and the perovskite phase decreases gradually and changes into amorphous state with increasing ball milling time up to 12 h. The interesting point in this work is that the Nd_0.7Sr_0.3MnO₃ perovskite can be formed again from the amorphous with subsequent 6 h ball milling. In addition, the re-obtained perovskite seems to be more stable than Nd_0.7Sr_0.3MnO₃ compound prepared using solid-state reaction method.     

Al-V合金预磨状态对Al-Fe-V-Si-Nd机械合金化过程中显微组织演化的影响

采用高能球磨法制备Al89.5Fe6 .4V0 .7Si2 .4Nd合金粉末 ,并用X射线衍射技术研究了球磨过程中的组成。发现经 60h高能球磨 ,合金粉末的微观组织由Al非晶和Al3V相组成 ;Al V合金的预磨状态影响Al89.5Fe6 .4 V0 .7Si2 .4Nd合金机械合金化过程中显微组织演化。     

Manufacturing a TiAl alloy by high-energy ball milling and subsequent reactive sintering

A TiAl alloy was fabricated by high-energy ball milling and subsequent reactive sintering from the mixed powders of Ti and Al. High-energy ball milling produced a kind of particular composite powders with an extremely fine altemative Ti and Al lamella structure. The composite powders not only possessed good consolidation and densification characteristics, but also resulted in the augment of nucleation rate of α and γ titanium aluminides during solid-phase reactive sintering After a series of processing, pressing, degassing, extrusion, and sintering, the resultant TiAl alloy presented high relative density and refined grain sizes of （α2 ＋ γ） lamella and γ phases. The compressive yield strength of the sintered TiAl reached 600 MPa at 800℃.     

Structure and hydrogen storage properties of MgH2 catalysed with La2O3

The catalytic effect of the addition of lanthanum oxide (La₂O₃), in the range 0.5–2.0 mol%, on the hydrogen storage properties of MgH₂ prepared by ball milling has been studied. The addition of La₂O₃ reduces the formation during milling of the metastable orthorhombic γ-MgH₂ phase. The desorption rate of samples with 1 and 2 mol% La₂O₃ comes out to be about 0.010 wt% per second at 573 K under an hydrogen pressure of 0.3 bar, better than for sample with 0.5 mol% La₂O₃. The presence of LaH₃ after hydrogenation/dehydrogenation cycles has been observed in all samples. The sample with 1 mol% of La₂O₃ gives a lower hysteresis factor compared with sample with 2 mol%.     

粉末加工工艺对银钯合金靶材制备的影响

粉末冶金法制备的银钯合金靶材存在孔隙率较高和相对密度较低的缺点。采用不同的粉末工艺制备了银钯合金粉末样品,使用氢氧含量分析、表面形貌分析、XRD线形分析等方法,探究使用各组样品经真空热压烧结制备的靶材的差异及其机理。结果表明,球磨后的合金粉末在烧结前有必要真空煅烧除氧;随着球磨时间和球磨转速的增加,粉末先细化后形成薄片,烧结体的相对密度先上升后下降;100 r/min球磨2 h所得粉末制备的烧结体具有最高的相对密度,为99.264%。     

Ni合金化对Finemet合金热稳定性及软磁性能的影响

通过铜辊甩带法制备了成分为Fe_73.5-xSi_13.5B₉Cu₁Nb₃Ni_x(x=0、1、2、3)的非晶带材,并对其进行退火处理。利用XRD、DSC、VSM和软磁直流测试仪等对带材的相结构、热稳定性以及软磁性能进行测试分析。结果表明,所制备合金带材淬火态下均为完全非晶结构,经560 ℃保温60 min退火处理后,合金中形成了非晶和α-Fe(Si)纳米晶双相共存结构。随着Ni含量的增加,整体上非晶带材的一级起始晶化温度T_s1和二级起始晶化温度T_s2先减小后增大,两级起始晶化温度之差ΔT_s整体呈下降的趋势,由166.0 ℃下降至132.8 ℃,热稳定性降低。淬火态下,Ni元素的添加使得非晶带材的软磁性能有所恶化。经退火处理后,带材的软磁性能明显提升,当Ni含量x=1时,具有较好的软磁性能,其饱和磁化强度为157.7 emu/g,矫顽力为6.8 Oe。     

球磨条件对Sn-0.7Cu合金形成的影响

通过对Sn、Cu混合粉末的机械球磨,利用X射线衍射仪、差热热分析仪和扫描电镜对粉末进行了检测与分析,研究了不同球磨条件对Sn-0．7Cu合金形成的影响。结果表明,电压、球料比及球磨时间对Sn-0．7Cu合金的形成有很大影响。对于Sn-Cu二元系,其机械合金化反应机制是通过机械诱发原子扩散,使原子间发生置换固溶和晶界溶解,而逐渐形成Cu4Sn5等合金相的。     

纳米晶镍块体的制备及烧结致密度研究

以高能球磨法和直流氢电弧等离子蒸发法两种不同工艺制备纳米晶镍粉体,并结合预压烧结工艺制备了纳米晶镍块体试样,研究了纳米晶镍块体结构、形貌的变化.运用TEM技术观察了两种粉体的形貌,并给出了选区电子衍射图;运用XRD、Archimedes法等分析手段对纳米晶镍块体的致密度及晶粒尺寸进行测定,并对两种试样进行了对比分析,表征结果显示,随着烧结温度的升高,纳米晶镍块体试样的晶体尺寸增大,晶格应变减小,同时致密度增加;高能球磨试样晶粒生长速率和致密度升高速率比等离子蒸发试样的快.     

铟对MgH2脱氢性能的影响

将MgH2和In的混合粉末在行星式球磨机上进行球磨,制备了一种Mg H2-In的复合物。利用XRD分析了复合物的相组成以及吸放氢过程中的相转变;用气相色谱仪和差示扫描量热仪测定了复合物的脱氢性能和相转变温度,并用基于Sievert原理的全自动气体吸附仪测定了复合物的吸放氢热力学和动力学性能。结果表明,脱氢过程中Mg3In和Mg(In)固溶体的形成使Mg H2的脱氢反应焓和激活能显著降低,从而降低了Mg H2的脱氢温度,并显著改善了动力学性能。