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1.
Abstract

It is important to optimize the properties of a material for a particular application, hence, to find the suitable material for tribological applications, the wear and friction behaviour of AA5052 in situ composites with different kind of reinforcements have been investigated. For present study, three in situ formed composites have been produced with different reinforcements namely Al3Zr, ZrB2 and combination of both (Al3Zr + ZrB2) by direct melt reaction (DMR) technique. The as-cast composites and base alloy have been characterized by X-ray diffraction (XRD), optical microscopy, electron microscopy, tensile testing, hardness and dry sliding wear and friction tests. XRD results indicate the successful formation of second phase reinforcement particles in all composites. Wear test results indicate that the cumulative volume loss increases with an increase in sliding distance while coefficient of friction shows a fluctuating tendency, whereas with increasing applied load, wear rate shows an increasing trend while coefficient of friction shows decreasing trend. The variation of wear rate with composites indicates that the composite with multiple reinforcement (Al3Zr + ZrB2) has lowest wear rate among all as-cast composites and base alloy, while coefficient of friction is higher. The responsible mechanisms concerned with wear and friction results have been discussed in detail with the help of the observation on worn surface analysis by scanning electron microscope (SEM) and 3D-profilometer. All tribological results have been correlated with the microstructural properties, strength parameters and bulk hardness of the composites.  相似文献   

2.
Abstract

Aluminum-based composites containing either SiC (Al10%SiC) as the hard phase or a combination of SiC and MoS2 (Al10%SiC4%MoS2) have been synthesized following stir casting route. To overcome the poor wetting characteristics, magnesium was added in one of the composites (Al10%SiC4%MoS24%Mg) to improve the bonding between matrix and second phase. The results suggested an enhancement in hardness and strength of the composite containing SiC–MoS2 and Mg, thus indicating the effectiveness of Mg addition in improving the interfacial bonding strength. Tribological performance of the composites has been examined by carrying out pin-on-disk wear tests under dry sliding conditions at different normal loads of 9.8, 14.7, 19.6, and 24.5 N and at a constant sliding speed of 1 m/s. Both the friction coefficient and the wear rate have been found to reduce with addition of MoS2; however, bonding between the matrix and reinforcements was not good. Al10%SiC4%MoS24%Mg has shown the best tribological performance at all the loads in terms of the lowest friction coefficient and the lowest wear rate. The wear mechanism has been found to be a combination of adhesion and abrasion as indicated by the presence of some abrasive grooves and delaminated flakes at the worn surface and the X-ray examination of wear debris for all the materials used in the present investigation.  相似文献   

3.
Carbon fabric reinforced phenolic (CFRP) composites filled with nano-Al2O3 were prepared by a dip-coating and heat molding process and the tribological properties of the resulting composites under different sliding conditions were investigated systematically on a block-on-ring test rig. The worn surfaces were observed in a scanning electron microscope (SEM) to understand the mechanism. Nano-Al2O3 particles, as the filler, were effective in reducing the friction coefficient and wear rate of the CFRP composites. The steady state friction coefficient of the CFRP composites filled with 4 wt.% nano-Al2O3 particles was about 65.5% of that of unfilled CFRP composites, and the wear rate, in this case, was about 74.7% of that of unfilled CFRP composites. Tribological tests under different sliding conditions revealed that the filled CFRP composites seemed to be more suitable than unfilled CFRP composites for tribological applications under higher sliding speed and load. Moreover, the wear resistances of the unfilled and filled CFRP composites were found to be related to the stability of the transfer film on the counterface.  相似文献   

4.
Abstract

Aluminum-based composites containing 0.06, 0.09, 0.12 fractions of in situ-synthesized TiC (Titanium carbide) particles have been prepared through in-melt reaction from Ai–SiC–Ti system following a simple and cost-effective stir-casting route. The TiC forms by the reaction of Ti with carbon which is released by SiC at temperatures greater than 1073 K. However, some amount of titanium aluminide (Al3Ti) is also formed. The formation of TiC has been confirmed through X-ray diffraction studies of the composite. The hardness and tensile strength have been found to increase with increasing amount of TiC. The friction and wear characteristics of the composites have been determined by carrying out dry sliding tests on pin-on-disc machine at different loads of 9.8 N, 19.6 N, 29.4 N, 39.2 N at a constant sliding speed of the 1 m/s speed. The wear rate i.e. volume loss per unit sliding distance has been found to increase linearly with increasing load following Archard’s law. However, both the wear rate and friction coefficient have been observed to decrease with increasing amount of TiC in the composite. This has been attributed to (i) a relatively higher hardness of composites containing relatively higher amount of TiC resulting in a relatively lower real area of contact and (ii) the formation of a well-compacted mechanically mixed layer of compacted wear debris on the worn surface which might have inhibited metal–metal contact and resulted in a lower wear rate as well as friction coefficient.  相似文献   

5.
Abstract

To investigate the amorphous-crystalline microstructure on the tribocorrosion of bulk metallic glasses (BMGs), 6 mm diameter rods of Cu46-xZr47Al7Agx (x = 0, 2, 4) amorphous-forming alloys with in situ crystalline and amorphous phases were fabricated by arc-melting and Cu-mould casting. Using a pin-on-disc tribometer, the tribo-pair composed by CuZr-based amorphous-forming alloys and AISI 52100 steel were studied in 3.5% NaCl solution. With the increase of Ag content from 0 to 4 at.%, the compressive fracture strength and the average hardness decrease firstly and then increase. Moreover, 4 at.% Ag addition increases the amount of amorphous phase obviously and inhibits the formation of brittle crystalline phase, resulting in the improvement of corrosion resistance and the corrosive wear resistance. The primary wear mechanism of the BMG composites is abrasive wear accompanying with corrosive wear. The tribocorrosion mass loss of Cu42Zr47Al7Ag4 composite is 1.5 mg after 816.8 m sliding distance at 0.75 m s?1 sliding velocity under 10 N load in NaCl solution. And the volume loss evaluated from the mass loss is about 20 times lower than that of AISI 304 SS. Thus, Cu42Zr47Al7Ag4 composite may be a good candidate in the tribology application under marine environment.  相似文献   

6.
Wear resistance of reactive plasma sprayed TiB2-TiC0.3N0.7 based composite coatings and the as-sprayed coating with laser surface treatment was investigated using plate-on-plate tests. Wear tests were performed at different normal loads and sliding speeds under dry sliding conditions in air. The surface morphologies of counterparts against as-sprayed and laser remelted coatings were investigated. The microstructure and chemical composition of wear debris and coatings were studied using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The results show that the wear resistance of the laser remelted coating is improved significantly due to their increased microhardness and reduced flaws. The primary wear mechanism of the remelted coating is oxidation wear and its minor wear mechanisms are grain abrasion and fatigue failure during the course of wear test. In contrast, the primary wear mechanism of the as-sprayed coating is grain abrasion at the low sliding speed (370 rpm) and fatigue failure at the high sliding speed (549 rpm). The oxidation wear mechanism is a minor contributor for the as-sprayed coating.  相似文献   

7.
卢明明  袁杰  温博  刘甲  曹文强  曹茂盛 《中国物理 B》2013,22(3):37701-037701
We investigate the dielectric properties of multi-walled carbon nanotubes (MWCNTs) and graphite filling in SiO2 with the filling concentration of 2-20 wt.% in the frequency range of 102-107 Hz. MWCNTs and graphite have general electrical properties and percolation phenomena owing to their quasi-structure made up of graphene layers. Both permittivity ε and conductivity σ exhibit jumps around the percolation threshold. Variations of dielectric properties of the composites are in agreement with the percolation theory. All the percolation phenomena are determined by hopping and migrating electrons, which are attributed to the special electronic transport mechanism of the fillers in the composites. However, the twin-percolation phenomenon exists when the concentration of MWCNTs is between 5-10 wt.% and 15-20 wt.% in the MWCNTs/SiO2 composites, while in the graphite/SiO2 composites, there is only one percolation phenomenon in the graphite concentration of 10-15 wt.%. The unique twin-percolation phenomenon of MWCNTs/SiO2 is described and attributed to the electronic transfer mechanism, especially the network effect of MWCNTs in the composites. The formation of network plays an essential role in determining the second percolation threshold of MWCNTs/SiO2.  相似文献   

8.
Two types of PEO coatings, one consisting of magnesium oxide (MgO) and the other comprising zirconium oxide (ZrO2) as the main phase composition were produced on AM50 magnesium alloy from alkaline and acidic electrolytes, respectively. The ZrO2 coating was found to be spongy and thicker with a higher roughness, whilst the relatively more compact MgO coating was having contrasting features. In the dry sliding oscillating wear tests under two different loads viz., 2 N and 5 N, the ZrO2 coating exhibited a very poor wear resistance. The MgO coating showed an excellent resistance to sliding wear under 2 N load; however, the load bearing capacity of the coating was found to be insufficient to resist the wear damage under 5 N load. The higher specific wear rates of the MgO coating under 5 N load and that of the ZrO2 coating under 2 N and 5 N loads were attributed to the poor load bearing capacity and a three-body-abrasive wear mechanism.  相似文献   

9.
Polymer composites based on polystyrene and modified SiO2 are synthesized. Effect of the SiO2 concentration on the surface (thermostatic) properties of the composites is analyzed. Surfaces of composites with different SiO2 concentrations are microscopically studied. Minor amounts of spherical agglomerates are obtained at relatively high SiO2 concentrations, and the size of the agglomerates may amount to 80 μm at a SiO2 concentration of 30 wt %. Variations in the integral absorbance of solar radiation are studied for the polymer composites irradiated with vacuum-UV radiation at a temperature of 125°C.  相似文献   

10.
《Composite Interfaces》2013,20(5):395-414
The dry sliding wear characteristics of glass-epoxy (G-E), graphite-filled G-E and functionally graded graphite-filled G-E composites were investigated using pin-on-disc test rig. The specific wear rate was determined as a function of applied load, sliding velocity and sliding distance. The results revealed that the specific wear rate increases in all the tested composites with increasing wear parameter. But, the admirable wear resistance was obtained with functionally graded graphite-filled G-E composite. The scanning electron microscope studies of worn-out surfaces support the involved wear mechanisms and are well indicated in the worn-out surface features such as matrix wear, fibre exposure, fibre breakage, fibre and matrix deboning, microcracking, debris formation, fibre cracking and removal of fibres.  相似文献   

11.
A series of photochromic phosphotungstic acid (PWA)/SiO2 composites were synthesized using the sol-gel method. Depending on the feeding schedule of PWA during synthesis, the size of the formed PWA/SiO2 particles varied considerably from as small as 1.2 nm to ca. 10 nm. With decreasing silica particle size, the total contact area/interaction between SiO2 and PWA increases, as revealed by FT-IR and solid-state 29Si-NMR analyses. Particularly, when the size of PWA/SiO2 is ~1 nm, crystallization of PWA is inhibited, and PWA presents as amorphous molecular entities distributing uniformly in the SiO2 host, which is in evidence in the XRD spectroscopy and HR-TEM imaging. In contrast, substantial crystallization of PWA takes place when PWA/SiO2 particles are as large as 10 nm, in which case less amount of surface free Si-OH is available for PWA to make bonds with. Photochromism occurs activated by ultraviolet light irradiation. The rate of coloration/bleaching is found to depend strongly on the particle size of PWA/SiO2; specifically, the rate increases twice when the particle size is reduced from 10 nm to 1.2 nm.  相似文献   

12.
A methylcellulose–polysulfide gel polymer electrolyte has been prepared for application in quantum dot-sensitized solar cells (QDSSCs) having the configuration FTO/TiO2/CdS/ZnS/SiO2/electrolyte/Pt(cathode). The electrolyte with the composition of 30.66 wt.% methylcellulose, 67.44 wt.% Na2S, and 1.90 wt.% sulfur exhibits the highest conductivity of 0.183 S cm?1 with the lowest activation energy of 6.14 kJ mol?1. CdS quantum dot sensitizers have been deposited on TiO2 film via the successive ionic layer absorption and reaction (SILAR) method. The QDSSC fabricated using the highest conducting electrolyte and CdS QD prepared with five SILAR cycles exhibits a power conversion efficiency (PCE) of 0.78%. After deposition of zinc sulfide (ZnS) and silicon dioxide SiO2 passivation layers, the PCE of the QDSSC with photoanode arrangement of TiO2/CdS(5)/ZnS(2)/SiO2 increased to 1.42%, an improvement in performance by 82%.  相似文献   

13.
《Applied Surface Science》2001,169(1-2):34-43
Thin films of SiO2 and La2O3 were prepared on a glass substrate by a dip-coating process from specially formulated sols. The tribological properties of the resulting thin films sliding against a Si3N4 ball were evaluated on a one-way reciprocating friction and wear tester. The morphologies of the unworn and worn surfaces of the films were examined by an atomic force microscope (AFM) and a scanning electron microscope (SEM). La2O3 shows the best tribological performance. The coefficient of friction is about 0.1 and the wear life is over 5000 sliding passes both under higher (3 N) and lower load (1 N). The SiO2 film derived from a specially formulated aqueous solution shows much better performance in resisting wear and reducing friction than the one derived from an ethanol solution. The wear mechanisms of the films are discussed based on SEM observation of the worn surface morphologies. SEM observation of the morphologies of worn surfaces indicates that the worn surface of La2O3 is too slight to be observed by SEM. The wear of SiO2 derived from TEOS solution is the characteristic of delaminating, which is responsible for the abrupt failure of the film. The wear of SiO2 derived from aqueous solution is the characteristic of fracture. Brittle fracture and severe abrasion dominate the wear of glass substrate.  相似文献   

14.
ZrC/TiN and ZrC/ZrN multilayers thinner than 350 nm were grown on (100) Si substrates at a temperature of 300 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser (λ=248 nm, pulse duration τ=25 ns, 8.0 J/cm2 fluence and 40 Hz repetition rate). Cross-sectional transmission electron microscopy, Auger electron spectroscopy depth profiling and simulations of X-ray reflectivity curves indicated that there was intermixing between the deposited layers at the interfaces as well as between the first layer and the substrate. Nanoindentation investigations found hardness values between 35 and 38 GPa for the deposited multilayers. Linear unidirectional sliding wear tests were conducted using a ball-on-plate tribometer under 1 N normal force. Wear tracks were produced in a Hysitron nanoindenter with 1 μm radius diamond tip under a 500 μN load. High-resolution cross-sectional transmission electron microscopy studies of the wear tracks showed that the multilayers withstood these tests without significant damage. The results could be explained by the use of a high laser fluence during deposition that resulted in very dense and strongly adherent nanocrystalline layers.  相似文献   

15.
Low cost arc spraying and cored wires were used to deposit composite coatings consisting of TiB2 and TiB2/Al2O3 hard particles in a Ni(Cr) and stainless steel 304L matrix. Four coatings were prepared namely Ni(Cr)-TiB2, Ni(Cr)-TiB2/Al2O3, 304L-TiB2 and 304L-TiB2/Al2O3. The microstructural characteristics of powders and coatings were observed by scanning electron microscopy (SEM). Phase compositions of powders were analyzed by X-ray diffraction (XRD). Although all the analyzed coatings exhibited similar lamella structure, remarkable differences not only in the morphology of hard phase and matrix but also in the size and distribution of hard phases were observed from one coating to another. Tribological behavior of the coatings was analyzed in room temperature dry sliding wear tests (block-on-ring configuration), under 75 N at low velocity (0.5 m/s). The coatings showed far high wear resistance than low carbon steel substrate under same conditions examined. Wear loss of 304L-TiB2 and Ni(Cr)-TiB2 coatings were lower nearly 15 times than that of steel substrate. TiB2 hard phases in coatings bonded well with metal matrix contributed to high wear resistance.  相似文献   

16.
17.
It has been already published that, at nanoscopic level, zircon exhibits wide regions of aperiodic material not detected by the ordinary techniques used to analyse the obtained product in the production of ceramic materials. In this paper it is reported how the Perturbed Angular Correlations (PAC) technique has assisted the interpretation of a mismatch between experiment and theoretical estimation of a mechanical property in some zircon-mullite composites. In fact, it has been proved that the difference observed between the calculated and the experimental value of the elastic modulus in composites of the form (1?x) ZrSiO4 ? x 3Al2O3.2SiO2 (with x = 15, 25, 35 and 45 wt.%) behaves very similarly as the relative amount of aperiodic zircon determined by PAC. This result allows to re-interpret the mullite role during the materials preparation.  相似文献   

18.
Iron supported systems are frequently used as catalysts in the Fischer–Tropsch synthesis being the Fe0 the active phase for the reaction. We have studied the influence of the calcination atmosphere (air or nitrogen) on the iron oxide reducibility and the metallic iron particle size obtained in Fe/SiO2 system. We have impregnated a silicagel with Fe(NO3)3·9H2O aqueous solution and the solid obtained was calcinated in air or N2 stream. These precursors, with 5% (wt/wt) of Fe, were characterized by Mössbauer Spectroscopy at 298 and 15 K. Amorphous Fe2O3 species with 3 nm diameter in the former, and α-Fe2O3 crystals of 48 nm diameter were detected in the last one. Both precursors were reduced in H2 stream. Two catalysts were obtained and characterized by Mössbauer spectroscopy in controlled atmosphere at 298 and 15 K, CO chemisorption and volumetric oxidation. α-Fe0, Fe3O4 and Fe2+ were identified in the catalyst calcined in air. Instead, only α-Fe0 was detected in the catalyst calcined in N2. The iron metallic crystal sizes were estimated as ≈2 nm for the former and ≈29 nm for the last one. The different oxide crystal sizes, obtained from the diverse calcination atmospheres, have led to different structural properties of the reduced solids. It has been possible to reduce totally the existing iron in an Fe/SiO2 system with iron loading lower than 10% (wt/wt).  相似文献   

19.
Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polytetrafluoroethylene (PTFE) composites filled with both glass fibers and Al2O3 were investigated in a ground-based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 1015/cm2 s. It was found that AO irradiation first induced the degradation of PTFE molecular chains on the sample surface, and then resulted in a change of surface morphology. The addition of Al2O3 filler significantly increased the AO resistance property of PTFE composites. Friction and wear tests indicated that AO irradiation affected the wear rate and increased the friction coefficient of specimens. The PTFE composite containing 10% Al2O3 exhibit the best AO resistance and lower wear rate after long time AO irradiation.  相似文献   

20.
TiCu2Al ternary intermetallic compound coating has been in situ synthesized successfully on pure Ti substrate by laser cladding. Tribological properties of the prepared TiCu2Al intermetallic compound coating were systematically evaluated. It was found that the friction coefficient and wear rate was closely related to the normal load and sliding speed, i.e., the friction coefficient of the prepared TiCu2Al intermetallic compound coating decreased with increasing normal load and sliding speed. The wear rate of the TiCu2Al intermetallic compound coating decreased rapidly with increasing sliding speed, while the wear rate first increased and then decreased at normal load from 5 to 15 N.  相似文献   

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