Microstructural and mechanical properties of Al-Mg/Al2O3 nanocomposite prepared by mechanical alloying

The effect of milling time on the microstructure and mechanical properties of Al and Al-10 wt.% Mg matrix nanocomposites reinforced with 5 wt.% Al₂O₃ during mechanical alloying was investigated. Steady-state situation was occurred in Al-10Mg/5Al₂O₃ nanocomposite after 20 h, due to solution of Mg into Al matrix, while the situation was not observed in Al/5Al₂O₃ nanocomposite at the same time. For the binary Al-Mg matrix, after 10 h, the predominant phase was an Al-Mg solid solution with an average crystallite size 34 nm. Up to 10 h, the lattice strain increased to about 0.4 and 0.66% for Al and Al-Mg matrix, respectively. The increasing of lattice parameter due to dissolution of Mg atom into Al lattice during milling was significant. By milling for 10 h the dramatic increase in microhardness (155 HV) for Al-Mg matrix nanocomposite was caused by grain refinement and solid solution formation. From 10 to 20 h, slower rate of increasing in microhardness may be attributed to the completion of alloying process, and dynamic and static recovery of powders.     

Microstructural characterization and amorphous phase formation in Co40Fe22Ta8B30 powders produced by mechanical alloying

In this work, microstructural evolution and amorphous phase formation in Co₄₀Fe₂₂Ta₈B₃₀ alloy produced by mechanical alloying (MA) of the elemental powder mixture under argon gas atmosphere was investigated. Milling time had a profound effect on the phase transformation, microstructure, morphological evolution and thermal behavior of the powders. These effects were studied by the X-ray powder diffraction (XRD) in reflection mode using Cu Kα and in transmission configuration using synchrotron radiation, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results showed that at the early stage of the milling, microstructure consisted of nanocrystalline bcc-(Fe, Co) phases and unreacted tantalum.Further milling, produced an amorphous phase, which became a dominant phase with a fraction of 96 wt% after 200 h milling. The DSC profile of 200 h milled powders demonstrated a huge and broad exothermic hump due to the structural relaxation, followed by a single exothermic peak, indicating the crystallization of the amorphous phase. Further XRD studies in transmission mode by synchrotron radiation revealed that the crystalline products were (Co, Fe)_20.82Ta_2.18B₆, (Co, Fe)₂₁ Ta₂ B₆, and (Co, Fe)₃B₂. The amorphization mechanisms were discussed in terms of severe grain refinement, atomic size effect, the concept of local topological instability and the heat of mixing of the reactants.     

Mechanical alloying and spark plasma sintering of the intermetallic compound Ti50Al50

This study investigates the microstructures and mechanical properties of Ti₅₀Al₅₀ alloys prepared via mechanical alloying (MA) starting from elemental powders. The process of the spark plasma sintering (SPS) has also been studied. It is found that the nanocrystallization process of the Ti–Al alloy proceeds and the sintering temperature can control the microstructure of alloy. The sintering of the compacts is carried out at the temperatures of 1100–1200 °C with a compaction pressure of 30 MPa and a heating rate of 30 °C min⁻¹. Specimens with high densities and approaching the equilibrium state can be obtained in short time by spark sintering than conventional sintering. Such shorter high temperature is important to prevent grain growth.     

Calorimetric and structural analysis of the new phase Al33Ni16Zr51 produced by direct synthesis and mechanical alloying

A new phase has been synthesized in the ternary phase diagram Al–Ni–Zr: its nominal composition is Al₃₃Ni₁₆Zr₅₁. For the Al₃₃Ni₁₆Zr₅₁ compound obtained by mixing the three components in suitable proportions, a study has been carried out by direct synthesis (calorimetry) and mechanical alloying in our laboratory. With the first method we know directly the enthalpy of formation of this alloy. For the amorphous alloys prepared by mechanical alloying we can determine the crystallisation enthalpy with the differential scanning calorimetry (DSC) method. So it is possible to determine a fundamental piece of information: the amorphous alloy formation enthalpy.     

Direct synthesis of MgCNi3 by mechanical alloying

MgCNi₃, an intermetallic compound with superconductivity, was synthesized from the Mg (or Mg₂Ni), Ni and graphite powders by mechanical alloying (MA). It is shown that the preliminary condition for the formation of MgCNi₃ is that Mg₂Ni must form in advance of MgCNi₃ in the MA process or be the starting component.     

ZrOCl2-Al体系熔体反应生成Al3Zr(p), Al2O3(p)/Al复合材料的反应机制

利用X射线衍射仪(XRD)和扫描电子显微镜(SEM),对ZrOCl     

Microstructural and mechanical evaluation of Al-TiB2 nanostructured composite fabricated by mechanical alloying

Production of bulk Al-TiB₂ nanocomposite from mechanically alloyed powder was studied. Al-20 wt.% TiB₂ metal matrix nanocomposite powder was obtained by mechanical alloying (MA) of pure Ti, B and Al powder mixture. A double step process was used to prevent the formation of undesirable phases like Al₃Ti intermetallic compound, which has been described in our previous papers. The resultant powder was consolidated by spark plasma sintering (SPS) followed up by hot extrusion. The structural characteristics of powder particles and sintered samples were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hardness measurements were conducted on the cross section of powder particles and sintered sample and the tensile behavior of extruded samples was evaluated. The results showed that the prepared Al-20 wt.% TiB₂ nanocomposite has good thermal stability against grain growth and particle coarsening. Extruded Al-20 wt.% TiB₂ showed a hardness value of 180 VHN and yield and tensile strength of 480 and 540 MPa, respectively, which are much higher than those reported for similar composites made by other processes.     

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 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.     

Al2O3/TiB2/Al复合材料的微观结构和高温力学性能

以细雾化铝粉和TiB₂颗粒为原料,通过粉末冶金和热轧制制备微米TiB₂和纳米Al₂O₃颗粒增强铝基复合材料。室温时,由于TiB₂和Al₂O₃的综合强化作用,Al₂O₃/TiB₂/Al复合材料的屈服强度和抗拉强度分别为258.7 MPa和279.3 MPa,测试温度升至350℃时,TiB₂颗粒的增强效果显著减弱,原位纳米Al₂O₃颗粒与位错的交互作用使得复合材料的屈服强度和抗拉强度达到98.2MPa和122.5 MPa。经350℃退火1000 h后,由于纳米Al₂O₃对晶界的钉扎作用抑制晶粒长大,强度和硬度未发生显著的降低。     

Al2O3/Ti生物相容连接接头微观组织及力学性能

文中对Al₂O₃陶瓷和金属Ti表面磁控溅射Mo和Ti金属层,以纯Au箔钎料,研究连接工艺及Ti金属化层厚度对连接接头微观组织和力学性能的影响.结果表明,焊缝主要由Au钎料和（Au,Mo） ss构成,（Au,Mo） ss中含有少量（Ti,Mo） ss和TixAuy金属间化合物.另外,在Al₂O₃/钎料界面处及焊缝中存在少量呈条状分布的TiO₂和Ti_xAl_y金属间化合物.连接工艺及Ti金属化层厚度主要影响各物相的数量及分布状态,通过影响焊缝中固溶体的分布均匀性及金属间化合物的数量而影响接头抗剪强度.当连接温度为1 080℃、保温时间为5 min、Ti金属化层厚度为0.2 μm时,接头的抗剪强度达到最大值138 MPa.     

MoSi_2含量对MoSi_2/Al_2O_3复合涂层介电与力学性能的影响(英文)

通过喷雾干燥法制备MoSi2包覆Al2O3的壳核结构混合粉,利用该混合粉以等离子喷涂技术制备MoSi2/Al2O3复合涂层材料。研究MoSi2/Al2O3质量比涂层材料的力学和介电性能的影响。结果表明:随着MoSi2含量从0增加到45%,复合材料的抗弯强度和断裂韧性分别从198MPa和3.05MPa·m1/2增加到324MPa和4.82MPa·m1/2,随后又降到310MPa和4.67MPa·m1/2。在8.2-12.4GHz微波频率波段内,随着MoSi2含量的增加,复合材料的介电损耗增加,而介电常数的实部却呈减小趋势。这主要是由于MoSi2颗粒熔化后的凝聚及导电网络结构的形成导致电导率的增加引起的。     

Interfacial structure and mechanical property of Al2O3 and Invar brazed joint

This paper introduces a brazing process between Al_2O_3 ceramic and Invar alloy.Al_2O_3 can be brazed with Invar effectively.The interfacial structure of Al_2O_3/Invar joint can be expressed as:Invar/Ag(s,s)+Cu(s,s)+Fe_2Ti(zone Ⅰ)/Ag(s,s)+Cu(s,s)+Fe_2Ti+NiTi+Cu_3Ti(zone Ⅱ)/Ag(s,s)+Cu(s,s)+Cu_2Ti+Al(s,s)+TiC+TiO(zone Ⅲ)/Al_2O_3.The maximum shear strength of 139 MPa was measured for as-brazed Al_2O_3/Invar joint brazed at 850℃ for 25 min or 900℃ for 15 min.     

Investigation of reaction between LiNH2 and H2

The reactions for LiNH₂ under a H₂ and an Ar flow were investigated, respectively. The results showed that LiNH₂ can be converted into LiH and NH₃ by reacting with H₂ under a H₂ flow condition, whereas LiNH₂ is converted into Li₂NH and NH₃ by decomposition under an Ar flow. Moreover, the reaction between LiNH₂ and H₂ can be accelerated by mixing LiNH₂ with LiH as well as doping LiNH₂ with TiCl₃. The confirmation of reaction between LiNH₂ and H₂ is helpful for the deeper insight in the systems of Li–N–H and Li–Mg–N–H for hydrogen storage materials.     

Thermoelectric properties of Fe0.98Co0.02Si2 with ZrO2 and rare-earth oxide dispersion by mechanical alloying

The n-type Co-doped β-FeSi₂ (Fe_0.98Co_0.02Si₂) with dispersion of several oxides, such as ZrO₂ or several rare-earth oxides (Y₂O₃, Nd₂O₃, Sm₂O₃ and Gd₂O₃), was synthesized by mechanical alloying and subsequent hot pressing. The effects of these oxide dispersions on the thermoelectric properties of Fe_0.98Co_0.02Si₂ were investigated. ZrO₂ was decomposed in the β phase, and the ZrSi and -FeSi phases, which are metallic phases, were formed in the samples with ZrO₂ addition. The Seebeck coefficient and the electrical resistivity were significantly decreased with increasing amount of ZrO₂, indicating that a part of the Zr atoms was substituted for Fe atoms in the β phase. In the case of the samples with rare-earth oxide addition, a decomposition of a large amount of these added oxides did not occur. However, the rare-earth oxide addition caused a slight increase in the amount of the phase. The Seebeck coefficient was significantly enhanced by the rare-earth oxide addition especially in the low temperature range. These facts indicated that a small amount of rare-earth oxides was decomposed in the β phase, and rare-earth elements were substituted for Fe atoms as a p-type dopant, resulting in the decrease in the carrier concentration. The rare-earth oxide addition was also effective in reducing the thermal conductivity.     

Complete flux jumping in nano-structured MgB2 superconductors prepared by mechanical alloying

High density nano-crystalline MgB₂ bulk superconductors with induced pinning centres were prepared from elemental precursors by a sequence of ball milling, heat treatment, and final pressing. The XRD results revealed the main phase was MgB₂ with a minor component of MgO. The magnetic moment versus temperature indicated that the transition temperature of MgB₂ samples was around 34 K, which is less than the typical transition temperature of commercial powders and also the transition temperature strongly depended on the milling time. It is well known that introduction of defects, grain boundaries and impurities act as effective flux pinning centres in MgB₂ and results in increased critical current density, J_c and decreased the transition temperature, T_c. The magnetization measurements were performed using VSM at 10 K, 20 K and 30 K, and the M–H curves indicated a complete flux jump effect, which is a severe problem for the application of superconductors. It was determined that a noticeable amount of heating (0.3 K jumps at 10 K) occurs at these jumps. In addition, it was found that the sweeping rate of magnetic field and the size of bulk sample are very effective to promote the flux jumping and whereas a low sweeping rate (12 Oe/s) avoids these “avalanches”, consistent with a kind of supercritical phenomenon: going slower allows the field gradients to stay close enough to equilibrium so that the avalanche effect is not triggered. In contrast, the sweeping rate of 100 Oe/s leads to numerous jumps.     

Formation and chemical leaching effects of nonequilibrium Al0.6(Fe25Cu75) alloy powder produced by rod milling

The formation and chemical leaching effects of a nonequilibrium Al_0.6(Fe₂₅Cu₇₅)_0.4 powder produced by rod milling is described. X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and vibrating sample magnetometry were used to characterize both the as-milled and leached specimens. After 400 h of milling, only the bcc AlFe phase with an amorphous phase was detected in the XRD patterns. The crystallite size for the bcc AlFe phase (110) after 400 h of milling was about 5.3 nm. The peak temperature and the crystallization temperature of the as-milled powders were 448.7 and 428.0 °C, respectively. Al atoms leaching from the as-milled bcc AlFe powders in the L1 condition did not alter the diffraction pattern significantly, even though Al atoms had been removed. After the L1 specimen was annealed at 500 °C for 1 h, the bcc AlFe phase transformed to the fcc Cu, Fe, and CuFe₂O₄ phases. The peak widths of L1 and L2 specimens were similar, but became broader than that of the as-milled powder. The saturation magnetization decreased with increasing milling time, and a value of 10.4 emu/g was reached after 400 h of milling. After cooling the specimen from 750 °C, the magnetization slowly increased at approximately 491.4 °C, indicating that the bcc AlFe phase had transformed to the fcc Cu and Fe phases.     

Nb-Cr掺杂原位合成Al2O3/TiAl复合材料的组织与性能

采用原位热压工艺,在Ti-Al-TiO2-Nb2O5体系中加入Cr2O3原位合成Al2O3/TiAl复合材料.借助X射线衍射分析、SEM分析及力学性能分析,研究了Nb-Cr掺杂复合强化Al2O3/TiAl复合材料的反应过程、微观结构及力学性能.结果表明Nb-Cr掺杂原位合成Al2O3/TiAl复合材料能够细化晶粒并通过微合金化增强增韧TiAl复合材料.     

Improvement in hydrogen sorption properties of Mg by reactive mechanical grinding with Cr2O3, Al2O3 and CeO2

We tried to improve the hydrogen sorption properties of Mg by mechanical grinding under H₂ (reactive mechanical grinding) with oxides Cr₂O₃, Al₂O₃ and CeO₂. The hydriding rates of Mg are reportedly controlled by the diffusion of hydrogen through a growing Mg hydride layer. The added oxides can help pulverization of Mg during mechanical grinding. A part of Mg is transformed into MgH₂ during reactive mechanical grinding. The Mg+10wt.%Cr₂O₃ powder has the largest transformed fraction 0.215, followed in order by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. The Mg+10wt.%Cr₂O₃ powder has the largest hydriding rates at the first and fifth hydriding cycle, followed in order by Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. Mg+10wt.%Cr₂O₃ absorbs 5.87wt.% H at 573 K, 11 bar H₂ during 60 min at the first cycle. The Mg+10wt.%Cr₂O₃ powder has the largest dehydriding rates at the first and fifth dehydriding cycle, followed by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. It desorbs 4.44 wt.% H at 573 K, 0.5 bar H₂ during 60 min at the first cycle. All the samples absorb and desorb less hydrogen at the fifth cycle than at the first cycle. It is considered that this results from the agglomeration of the particles during hydriding–dehydriding cycling. The average particle sizes of the as-milled and cycled powders increase in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of hydrogen absorbed or desorbed for 1 h for the first and fifth cycles decrease in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of absorbed or desorbed hydrogen increase as the average particle sizes decrease. As the particle size decreases, the diffusion distance shortens. This leads to the larger hydriding and dehydriding rates. The Cr₂O₃ in the Mg+10wt.%Cr₂O₃ powder is reduced after hydriding–dehydriding cycling. The much larger chemical affinity of Mg than Cr for oxygen leads to a reduction of Cr₂O₃ after cycling.