铝包带包裹高压输电线路导线的微动损伤

在自制的微动试验装置上对铝包带包裹钢芯铝绞导线（ACSR）进行微动试验研究。振幅1．0mm,2．0×107次微动循环后,研究内、外层铝股线及钢芯线的磨损状况,测定其抗拉强度,探讨铝包带包裹导线的微动损伤机制。结果表明：外层铝股线表面经受铝包带的刮擦以及磨粒磨损;内层铝股线微动磨损斑呈椭圆形,部分磨损斑下有疲劳裂纹;而钢芯线的损伤微弱,仅发生镀锌层的磨损、脱落。铝包带对导线有较好的保护作用,内外层铝股线的抗拉强度均高于未包裹导线的抗拉强度。     

Torsional wear behaviours of TiO2/PMMA film against Ti6Al4V alloy and alumina femoral head ball in dry condition

The torsional fretting wear tests of Ti₆Al₄V alloy flat against alumina femoral ball in dry condition were carried out on a new high-precision torsional fretting-wear tester. The TiO₂/P-methoxymethamphetamine (PMMA)/Ti₆Al₄V pair showed higher contact stiffness, friction torque, wear damage and material transfer than that of the presentation of TiO₂/PMMA/Al₂O₃ pairs. The mechanisms of torsional wear under different counterbodies were discussed in detail. The mechanisms of torsional fretting wear of aluminium alloy are mainly oxidative wear, abrasive wear and delamination in the three fretting regimes. The torsional fretting running regimes transferred from partial slip regime (PSR) to SR were analysed; however, the mixed fretting regime was never appeared in this test. In PSR (lower angular displacement amplitudes), only a dint was found after the tests. The kinetics behaviours and damage mechanism of Ti₆Al₄V alloy under different angular displacement amplitudes with friction torque and dissipation energy, which are strongly dependent upon the imposed angular displacement amplitudes and presented in three stages, were discussed in detail.     

Impact of graphite particle on milling of Al/15Al2O3 and Al/15Al2O3/5Gr composites

ABSTRACT

Hybrid Metal Matrix Composites (MMCs) are a new class of composites, formed by a combination of the metal matrix and more than one type of reinforcement having different properties. Machining of MMCs is a difficult task because of its heterogeneity and abrasive nature of reinforcement, which results in excessive tool wear and inferior surface finish. This paper investigates experimentally the addition of graphite (Gr) on cutting force, surface roughness and tool wear while milling Al/15Al₂O₃ and Al/15Al₂O₃/5Gr composites at different cutting conditions using tungsten carbide (WC) and polycrystalline diamond (PCD) insert. The result reveals that feed has a major contribution on cutting force and tool wear, whereas the machined surface roughness was found to be more sensitive to speed for both composite materials. The incorporation of graphite reduces the coefficient of friction between the tool–workpiece interfaces, thereby reducing the cutting force and tool wear for hybrid composites. The surface morphology and worn tool are analyzed using scanning electron microscope (SEM). The surface damage due to machining extends up to 200 µm for Al/15Al₂O₃/5Gr composites, which is beyond 250 µm for Al/15Al₂O₃ composites.     

Microstructures and mechanical properties of Al/Al2O3 surface nano-composite layer produced by friction stir processing

In this study, a new processing technique, friction stir processing (FSP) was attempted to incorporate nano-sized Al₂O₃ into 6082 aluminum alloy to form particulate composite surface layer. Samples were subjected to various numbers of FSP passes from one to four, with and without Al₂O₃ powder. Microstructural observations were carried out by employing optical and scanning electron microscopy (SEM) of the cross sections both parallel and perpendicular to the tool traverse direction. Mechanical properties include microhardness and wear resistance, were evaluated in detail. The results show that the increasing in number of FSP passes causes a more uniform in distribution of nano-sized alumina particles. The microhardness of the surface improves by three times as compared to that of the as-received Al alloy. A significant improvement in wear resistance in the nano-composite surfaced Al is observed as compared to the as-received Al.     

Relationship between thermal and sliding wear behavior of Al6061/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> metal matrix composites

Al6061 alloy and Al6061/Al₂O₃ metal matrix composites (MMCs) were fabricated by stir casting. The MMCs were prepared by addition of 5, 10 and 15 wt% Al₂O₃ particulates and the size of particulates was taken as 16 μm. The effect of Al₂O₃ particulate content, thermal properties and stir casting parameters on the dry sliding wear resistance of MMCs were investigated under 50–350 N loads. The dry sliding wear tests were performed to investigate the wear behavior of MMCs against a steel counterface (DIN 5401) in a block-on-ring apparatus. The wear tests were carried out in an incremental manner, i.e., 300 m per increment and 3,000 m in total. It was observed that, the increase in Al₂O₃ vol% decreased both thermal conductivity and friction coefficient and hence increased the transition load and transition temperature for mild to severe wear during dry sliding wear test.     

Tribological properties of Al6061–Al2O3 nanocomposite prepared by milling and hot pressing

Tribological properties of bulk Al6061–Al₂O₃ nanocomposite prepared by mechanical milling and hot pressing were investigated. Al6061 chips were milled for 30 h to achieve a homogenous nanostructured powder. A 3 vol.% Al₂O₃ nanoparticles (∼30 nm) were added to the Al6061 after 15 and 30 h from the beginning of milling. The milling times with Al₂O₃ in these two samples were then 15 h and 30 min, respectively. Additionally, 3 vol.% Al₂O₃ (1 μm and 60 μm) was added to the Al6061 after 15 h of milling; where, the micron size Al₂O₃ in these two samples, was milled 15 h with the matrix. Hot pressing of milled samples was executed at 400 °C under 128 MPa pressure in a uniaxial die. The hot pressed samples were characterized by micro-hardness test, bulk density measurements, pin on disc wear test, and finally scanning electron microscopy observations. Fifteen hour-milled nanocomposite with nanoscale Al₂O₃, showed improvement in wear resistance and bulk density compared with that of 30 min-milled nanocomposites due to better dispersion of Al₂O₃ nanoparticles, improved surface quality of nanocomposite particles before pressing and more grain refinement of Al matrix. Moreover, increasing the reinforcement size increased the wear rate because of reduction in relative density, hardness and inter-particle spacing.     

Spray processing and wear characteristics of Al-Cu-Al2O3-Pb based composites

The spray deposition process has been employed in synthesis of Al-4.5Cu-10Al₂O₃ and Al-4.5Cu-10Al₂O₃-10Pb based composites. The microstructure and wear characteristics of composites were investigated. The rapid solidification inherent in spray deposition processing resulted in a uniform dispersion of Al₂O₃ and Pb particles co-existing in the matrix of the- primary α-phase. The grain size of the Al-4.5Cu-10Al₂O₃-Pb composite was observed to be higher than that of the Al-4.5Cu-10Al₂O₃ composite in various sections of the spray deposit. The wear rate of composite materials decreased with addition of Pb phase. This behavior is discussed in the light of the microstructural modification induced by spray deposition and the morphology of debris particles on the wear track surfaces. The wear characteristics of the composites are compared with that of the liquid immiscible Al-4.5Cu-10Pb alloy.     

Studies on wear rate and micro-hardness of the Al/Al2O3/Gr hybrid composites produced via powder metallurgy

Micro-structural characterization of the composites has revealed fairly uniform distribution and some amount of grain refinement in the specimens. Further, it was observed that the micro-hardness improve when increasing the milling time and the reinforcement content due to presence of hard Al₂O₃ particles. Was also observed a low wear rate exhibited by the Al/Al₂O₃/Gr hybrid composites due to presence of Al₂O₃ and Gr which they acted as load bearing elements and solid lubricant respectively. The observed wear rate and micro-hardness have been correlated with microstructural analyses.     

Ti6Al4V合金在血清溶液中的扭动微动腐蚀行为研究

在新型恒温扭动微动腐蚀实验装置上,通过改变角位移幅值,在恒温37℃的25%血清溶液中对Ti6Al4V合金的扭动微动腐蚀行为进行了研究。实验结果表明,角位移幅值对扭动微动的运行区域及腐蚀行为有重要的影响,摩擦扭矩-角位移幅值(T-θ)曲线分别呈直线型、椭圆型和平行四边形型,Ti6Al4V合金的扭动微动运行区分别呈现部分滑移区、混合区及滑移区等3个微动运行区。当角位移幅值较小时,扭动磨损发生在接触边缘,损伤轻微;扭动微动对腐蚀几乎不产生影响,腐蚀电流和腐蚀电位随时间的曲线波动不大;随着角位移幅值的增大,接触表面产生强烈的塑性变形,损伤严重。腐蚀电流和腐蚀电位随时间的变化曲线表明,扭动微动对腐蚀的影响较大,呈磨损加速腐蚀的特征。     

Microstructural, mechanical and wear behavior of A390/graphite and A390/Al2O3 surface composites fabricated using FSP

In the present investigation, A390/graphite and A390/Al₂O₃ surface composite (SC) layers were fabricated using friction stir processing (FSP). The effect of tool rotational and traverse speeds on the microstructural, mechanical and wear characteristics of the surface layers was studied. The results revealed that increasing the tool rotational speed increases the hardness of the composite layers. The traverse speed has less significant influence on the hardness of the composite layer than the tool rotational speed. The A390/Al₂O₃ surface composites exhibited higher hardness than the A390/graphite surface composites. The surface composites exhibited better wear resistance than the matrix alloy. The A390/Al₂O₃ surface composites exhibited lower wear rates than the A390/graphite surface composites. Increasing the tool rotational reduces the wear rate of both A390/Al₂O₃ and A390/graphite surface composites.     

Electrochemical corrosion behavior of Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript>w/Al composite

The effects of the volume fraction of alumina borate (Al₁₈B₄O₃₃) whisker and the scan rate of potentiodynamic technique on the localized corrosion behaviors of Al₁₈B₄O₃₃w/Al composite were investigated. Potentiodynamic polarizations and cyclic polarizations were performed to examine the electrochemical corrosion behavior of the composites. The surface morphologies of the as-cast composite were observed by optics microscopy and the surface morphologies of the composite after corrosion tests were observed by scanning electronic microscopy (SEM). The results of electrochemical measurement indicated that the anodic passive region reduced with the increasing in the volume fraction of Al₁₈B₄O₃₃ whisker in the composites (at the same scan rate), and the anodic passive region reduced with the decreasing in the scan rate of potentiodynamic technique (in the same volume fraction of whisker). The results of cyclic polarization indicated that increase in the volume fraction of Al₁₈B₄O₃₃ whisker in the composites results in a significant decrease of protection potential and an increase of the area of cyclic hysteresis loop.     

The effects of environment on the dry sliding wear of eutectic Fe30Ni20Mn35Al15

The wear of as-cast eutectic Fe₃₀Ni₂₀Mn₃₅Al_15, which consists of lamellar f.c.c. and B2 phases, was studied using pin-on-disk tribotests in four different environments: air, dry oxygen, dry argon, and a 4% hydrogen/nitrogen mixture. The counterface in all the tests was yttria-stabilized zirconia. Wear debris and wear tracks were examined in detail to investigate the surface effects during dry sliding and these were correlated with the wear properties. It was found that the wear rate was about 40% lower in tests performed under argon, compared to tests conducted in either air or oxygen. However, the wear rate was about 1000% higher when the tests were conducted in a hydrogen-containing environment. The near-surface regions of the pins were examined using transmission electron microscopy of cross-sectional specimens produced by focused ion beam milling. For tests in oxygen-containing environments, abrasive particles were produced by oxidation. These, protruded and peeled off from the matrix and mixed with the debris from the counterface, producing a combination of a two-body and three-body abrasive wear-controlled processes. In contrast, for tests under argon, plastic flow mechanisms dominated. The dramatic increase of wear in 4% hydrogen/nitrogen was due to hydrogen embrittlement, which meant that little plastic flow occurred, a feature consistent with the results of prior tensile tests.     

In situ growth of elongated Al2O3 grains induced by Al nanoparticles

We have reported the in situ growth of elongated grains induced by Al nanoparticles for the fabrication of high-pure and high toughness Al₂O₃ ceramics. It is found that the introduced Al nanoparticles have a profound effect on the anisotropic growth of Al₂O₃ grains. As compared to the conventional techniques by adding impurities to induce the anisotropic grain growth, Al particles could be transformed into Al₂O₃ after sintering in air, leading to the formation of high-pure Al₂O₃ ceramics without contamination. The elongated grains induced by the Al nanoparticles make noticeable improvements of bending strength and fracture toughness of Al₂O₃ ceramics. Current work might benefit the fabrication of high-pure and high toughness Al₂O₃ ceramics with in situ grown elongated grains.     

磁控溅射Al掺杂Al2O3薄膜耐蚀性能研究

采用中频电源反应溅射在Si和SS304不锈钢表面制备两种不同成分的Al-O涂层,利用X射线衍射、扫描电镜、纳米压痕仪、电化学工作站和Cu装饰实验对涂层的结构及性能进行了分析。结果表明:室温下制备的涂层,掺Al后沉积速率是纯Al_2O_3的10倍,两种非晶涂层截面无明显的形貌特征,纯Al_2O_3涂层表面有微裂纹存在,掺杂Al的Al_2O_3涂层表现出更为优异的耐腐蚀性能,这与其表面的Al发生钝化氧化反应有关。     

Surface modification of titanium alloy with laser cladding RE oxides reinforced Ti3Al–matrix composites

Ti₃Al–matrix composites were prepared by laser cladding of the Al₃Ti/TiB₂/Al₂O₃ pre-placed powders on the Ti–6Al–4V alloy, which can improve the wear resistance of the substrate. With addition of the proper content of RE oxides (nano-Y₂O₃), this composite coating exhibited finer microstructure and better wear resistance. Nevertheless, excessive RE oxides could lead to the production of the micro-crack, and also decrease the temperature of the molten pool leading to the present of the un-melted TiB₂ block, which can significantly decrease the wear resistance of this composite coating.     

Characterization of microstructure and properties of Al–Al<Subscript>3</Subscript>Zr–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite

Aluminium-based metal matrix composite strengthened by in situ Al₂O₃ and Al₃Zr particles were synthesized by powder metallurgy route. Phase analysis by X-ray diffraction and scanning electron microscopy revealed that the reaction between Al and ZrO₂ produced Al₂O₃ and Al₃Zr phases in the sintered composites. The hardness of the composite is a strong function of sintering temperature as well as the volume fraction of reinforcements. The dry sliding wear test results clearly indicated that increasing the volume fraction of zirconia particles in the composite improved the wear resistance. Microcutting, ploughing, delamination and oxidation were the main mechanisms of wear.     

Wear properties of high pressure torsion processed ultrafine grained Al–7%Si alloy

In this paper, Al–7 wt% Si alloy was processed via high pressure torsion (HPT) at an applied pressure 8 GPa for 10 revolutions at room temperature. The microstructure and hardness of the HPT samples were investigated and compared with those of the as-cast samples. The wear properties of as-cast and the HPT samples under dry sliding conditions using different sliding distances and loads were investigated by reciprocated sliding wear tests.The HPT process successfully resulted in nanostructure Al–7 wt% Si samples with a higher microhardness due to the finer Al matrix grains and Si particles sizes with more homogeneous distribution of the Si particles than those in the as-cast samples.The wear mass loss and coefficient of friction values were decreased after the HPT process. The wear mechanism was observed to be adhesive, delamination, plastic deformation bands and oxidization in the case of the as-cast alloy. Then, the wear mechanism was transformed into a combination of abrasive and adhesive wear after the HPT process. The oxidization cannot be considered as a mechanism that contributes to wear in the case of HPT samples, because O₂ was not detected in all conditions.     

Material dependence of electronic sputtering induced by MeV-energy heavy ions

Masses, yields and emission energies of secondary ions have been systematically measured for solid targets bombarded by Si ions over an energy range between 0.5 and 5 MeV for studying roles of the electronic collision in the formation process of secondary atomic ions. The targets used were insulators (Al₂O₃, SiO₂), semiconductors (Si, GaP, GaAs, GaSb and InSb) and a metal (Al). The obtained feature of the secondary ion emission depends characteristically on the target species. Singly and multiply charged positive ions are produced for Al, Si and P, respectively, from the Al, Al₂O₃, Si, SiO₂ and GaP targets. In the cases of GaAs, GaSb and InSb, however, the production rates of positive As and Sb ions are strongly depressed. The obtained emission energy distributions of atomic ions from the conductor and the semiconductors are very broad and have gradually decaying tails at the high-energy side in contradiction to those of singly charged atomic and cluster ions from the insulators. The most probable and mean energies of atomic ions are proportional to their electric charge irrespective of the target conductivity. Large cluster ions are produced from the SiO₂, Al₂O₃, GaSb and InSb targets. The yields of clusters from SiO₂, GaSb and InSb show power-law dependences on their sizes and the yield of clusters from Al₂O₃ decreases exponentially with increasing size. These results show that the clusters from SiO₂, GaSb and InSb are emitted directly from the surface. The clusters from Al₂O₃ may be indirectly produced by coagulation of molecules in a selvage region near the surface.     

Structural and mechanical characterization of Al-based composite reinforced with heat treated Al2O3 particles

In this study, the addition of 1.00 wt.% Al₂O₃ crystals to the metal matrix of the liquid aluminum was studied. In order to investigate the influence of heat treatment on activation of Al₂O₃ powders and mechanical properties of Al–Al₂O₃ composites, the Al₂O₃ particles were heated at 1000 °C. X-ray Diffraction (XRD) analysis used to characterize the crystal lattice of Al₂O₃ and its variation during heat treatment. The size and morphology of the Al₂O₃ grains was evaluated by Scanning Electron Microscopy (SEM). The results showed a considerable change in morphology of Al₂O₃ grains during the heat treatment. Mechanical evaluation such as hardness, compression and wear tests showed enhancement in the properties of Al–1.00 wt.% heat treated Al₂O₃ vs. Al–1.00 wt.% Al₂O₃ composite.     

Fabrication and wear properties of Al2O3-SiC ceramic coatings using aluminum phosphate as binder

Refractory and wear-resistant Al₂O₃-SiC ceramic coatings have been fabricated on A₃ steel using abrasive ceramics (Al₂O₃, SiC), aluminum phosphate binder (inorganic binder), and aluminate (Al₂O₃ · CaO) as starting materials. The Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques are used to investigate the chemical compositions of the in-house synthesized aluminum phosphate binder and the morphologies of the fabricated ceramic coatings after abrasion test. The XRD results indicate that monoaluminium phosphate (Al(H₂PO₄)₃) is the most effective binding phase in aluminum phosphate binder, and that aluminum phosphate binder at high temperatures is a mixture of several phases. It is also found that the addition amount of the stabilizer (oxalic acid) has remarkable effect on the storage life of aluminum phosphate binder. The wear test results show that the wear resistance of the A₃ steel covered with Al₂O₃-SiC ceramic coatings is about two times higher than that of the uncoated A₃ steel. The results also indicate that the wear properties of Al₂O₃-SiC ceramic coatings are dependent on fabrication conditions, such as the weight ratio of ceramics to the binder (RCB), the particle size distribution of ceramics, the density of the aluminum phosphate binder, and the Al/P atomic ratio in the aluminum phosphate binder. The optimal fabrication conditions for achieving good wear resistance of Al₂O₃-SiC ceramic coatings are suggested based on the above results.