5,848 research outputs found
Consolidation of WC-Co nanocomposites synthesised by mechanical alloying
Full text linkA thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of PhilosophyThe influence of mechanical alloying (MA) milling time, temperature, sintering method and microstructure on the mechanical properties of a tungsten carbide-cobalt (WC-Co) hardmetal, based on 10wt% Co, has been established. The effects of high-energy milling for 30, 60, 180 and 300 min and the interrelation between milling time and powder properties, and the resultant effects on the mechanical properties of the consolidated WC-10Co material, has been obtained for a horizontally designed ball mill. Nanostructured WC-10Co powder was synthesised after 60 min cyclic milling at room temperature with an average WC domain size of 21 nm. In direct comparison, a WC-10Co composition MA at -30°C for 60 min produced an average WC domain size of 26 nm with a higher lattice strain. WC domain size showed a slight increase with milling time, measured at 27 nm after 300 min ball milling. Extended ball milling (300 min) reduced the mean particle size from 0.148 μm for 60 min milling to 0.117 μm. Thermal analysis showed that the onset temperature of the WC-Co eutectic was related to particle size with increased milling time reducing the onset temperature from 1344°C after 60 min milling to 1312°C after 300 min milling. Onset temperature was further reduced by the addition of vanadium carbide (VC), reducing the onset temperature to 1283°C after 300 min milling. Powder contamination increased with increased milling time with Fe content measured at ~ 3wt% after 300 min ball milling. Milling at -30°C reduced Fe contamination to an almost undetectable level. Increased ball milling time resulted in decreased levels of green density with the powders milled for 30 and 300 min achieving 62.5% and 59.5% TD, respectively. Relative density increased for the powder milled at -30°C compared to the RT milled powder due to its flattened, slightly rounded morphology. A large difference in VC starting particle size compared to WC and Co led to non-uniform dispersion of the inhibitor during milling. Densification and hardness reached optimum levels for the 60 min milled powder for both pressureless sintering and sinter-HIP. Both properties decreased with increased milling time, regardless of the sintering method. Low temperature milling resulted in a higher hardness value of 1390 HV30 compared to 1326 HV30 for the 60 min, RT milled material after pressureless sintering. Densification levels of the doped materials were restricted to < 90% TD for both sintering methods due to inhomogeneity in the microstructures. Palmqvist fracture toughness (WK) of the RT milled powders increased with increased milling time and increasing WC grain size for both sintering methods. WK reached 11.6 MN.m3/2 with 300 min milling after pressureless sintering but reached 16.1 MN.m32 for the same material after sinter-HIP due to the effect of mean WC grain size and binder phase mean free path. The -30°C milled powder exhibited higher fracture toughness for both sintering methods than the 60 min, RT milled material. Spark plasma sintering (SPS) showed that the onset of densification was dependent upon particle size with the powder from 300 min milling showing an onset temperature of ~ 800°C compared to ~ 1000°C for the 60 min milled powder. The low temperature milled powder showed an onset temperature of ~ 980°C, which suggested that low temperature milling provided enhanced densification kinetics
Investigation into laser re-melting of inconel 625 HVOF coating blended with WC
Full text linkHigh velocity oxy-fuel (HVOF) spraying of Diamalloy 1005 powders mixed with WC particles onto steel (304) is considered and laser re-melting of the resulting coatings is examined. Laser re-melting process is modeled to determine the melt layer thickness while temperature increase is formulated using the Fourier heating law. The morphological and metallurgical analyses prior and post laser re-melting process are carried out using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) technique is used to determine the residual stress developed in the coating while the analytical formulation is adopted to predict the residual stress levels at the coating base material interface. The indentation tests are carried out to determine the Young’s modulus and fracture toughness of the coating prior to laser re-melting. Corrosion resistance of coating is measured using potentiodynamic polarization technique prior and post laser treatment process. The predictions of the melt layer thickness are in good agreement with experimental results. The presence of WC particles modifies temperature rise and its gradient in the coating while affecting the Young’s modulus, residual stress levels, and fracture toughness of the coating. The differences in the thermal properties of Inconel 625 powders and WC particles result in formation of small size cellular structure through polyphase solidification. WC dissolution in the central region of the large polycrystalline cells is observed due to the loss of carbon through carbonic gas formation. The results of corrosion tests prevail that significant improvement of corrosion resistance can be achieved after laser treatment process
Theoretical analysis on the geometries and electronic structures of fluorene-based conjugated polymers
No full textNew fluorene-acceptor random copolymers: Towards pure white light emission from a single polymer
No full textSynthesis and Properties of New Small Band Gap Conjugated Polymers: Methine Bridged Poly(3,4-ethylenedioxypyrrole)
No full textNew Fluorene-Pyrazino[2,3-g]quinoxaline-Conjugated Copolymers: Synthesis, Optoelectronic Properties, and Electroluminescence Characteristics
No full textTribological Properties of WC-Reinforced Ni-Based Coatings Under Different Lubricating Conditions
No full textIn order to improve the tribological properties of aluminum alloy cylinders and cylinder bore walls, WC-reinforced Ni-WC coatings were deposited on an aluminum substrate by atmospheric plasma spraying. The composition and microstructure of Ni-WC coatings with different WC contents were investigated and the tribological properties were tested under oil lubrication, lean oil lubrication and dry friction. The results showed that Ni-WC coatings consisted of a lamellar structure. Friction and wear testing results demonstrated that Ni-WC coatings had much better tribological performance than gray cast iron under different lubricating conditions. These Ni-WC composite coatings exhibited excellent mechanical properties and tribological properties due to the strengthening effect of the WC phase
Tribological Properties of Cr/WC/DLC Film in Multiple Environments
No full textMultilayer gradient diamond-like carbon (Cr/WC/DLC) film was successfully fabricated on 304 stainless steel substrate by using magnetron sputtering technique. Microstructure and mechanical properties of the Cr/WC/DLC film were characterized by SEM, Raman spectroscopy, nanoindentor and scratch tester. Tribological performances of the Cr/WC/DLC film were investigated by UMT-3 multi-functional tribometer in the atmosphere, distilled water and engine oil. The results show that: the design of multilayer gradient transition of the Cr/WC/DLC film makes the hardness of the film amount to 32.6 GPa, and significantly improves the bonding force between the film and the substrate, and its tribological properties are excellent under the three environments. In the atmosphere, the film shows a lower average friction coefficient and leds to the greatest wear rate,which are 0.094 and 7.86*10~(-8) mm~3 (N ? m)~(-1). In the water, the film has a higher average friction coefficient of 0.124, and has a lower wear rate of 5.26*10~(-8) mm~3 (N ? m)~(-1). In the engine oil, the film has the minimum average friction coefficient and wear rate, which are 0.065 and 4.44 * 10~(-8) mm~3 (N ? m)~(-1),respectively
Fabrication and characterization of high-T-c YBa2Cu3O7-x nanoSQUIDs made by focused ion beam milling
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