1,563 research outputs found
Investigation into laser re-melting of inconel 625 HVOF coating blended with WC
No full textHigh 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
Obtaining Crack-free WC-Co Alloys by Selective Laser Melting
No full textAbstractStandard hardmetals of WC-Co system are brittle and often crack at selective laser melting (SLM). The objective of this study is to estimate the range of WC/Co ratio where cracking can be avoided. Micron-sized Co powder was mixed with WC nanopowder in a ball mill to obtain uniform distribution of WC over the surface of Co particles. Continuous layers of remelted material on the surface of a hardmetal plate were obtained from this composite powder by SLM at 1.07μm wavelength. The layers have satisfactory porosity and are well bound to the substrate. The chemical composition of the layers matches the composition of the initial powder mixtures. The powder mixture with 25wt.%WC can be used for SLM to obtain materials without cracks. The powder mixture with 50wt.%WC cracks because of formation of brittle W3Co3C phase. Cracking can considerably reduce the mechanical strength, so that the use of this composition is not advised
Abrasive wear behaviour of detonation sprayed WC-Co coatings on mild steel
No full textThe main objective of the present investigation is to evaluate the abrasive wear behaviour of detonation sprayed WC-Co coatings and to compare them with plasma sprayed WC-Co coatings and carburised and nitrided surfaces. Mild steel was coated with WC-12Co and WC-17Co using detonation and plasma guns. The abrasive wear rates of these coatings were determined at three different loads and compared with wear rates of as received, carburised, and nitrided mild steel. The abraded surfaces and the surfaces beneath the abraded surfaces were characterised by SEM. The results indicate that the detonation sprayed WC-12Co coating has the best abrasive wear resistance at all loads. Maximum improvement in wear resistance is obtained at an intermediate load (i.e. at 5 kg). The wear of detonation sprayed coatings is by abrasion of the soft Co matrix followed by the pullout of hard WC particles
Abrasion resistant glass-ceramic coatings reinforced with WC-nanoparticles
No full text© 2021 The Author(s)The glass ceramic coatings reinforced with nano-WC hard ceramic particles used in the study were designed to remove stress points in the vitreous matrix. Coatings were applied to cast iron surfaces by the wet spraying method and fired at 770 °C for 12 min. The abrasion resistance of the samples was evaluated with a Taber abrasion device with H18 wheels and the changes in SEM, color, gloss, mass loss, and surface roughness values were analyzed before and after the abrasion test of the samples. The results showed that, the addition of 2.5 wt% nano-WC (W25) created the lowest mass loss and the lowest change in the surface properties. The lowest amount and the size in the pores were also observed in the W25 sample. It was observed that agglomeration occurred with the increase of nano-WC ratio in the samples and the abrasion resistance decreased
Composition regulation of composite materials in laser powder bed fusion additive manufacturing
No full textUnderstanding and controlling the composition segregation during powder spreading is of key importance in the additive manufacturing (AM) of composite materials. Under this circumstance, the segregation behavior of WC/316 L composite powders during spreading in laser powder bed fusion (LPBF) AM was numerically investigated by the discrete element method. The effects of process conditions (i.e., spreader velocity and geometry) and powder properties (i.e., size and shape of the WC powder) on the powder bed composition segregation and related characteristics were systematically analyzed. Corresponding mechanisms were identified from microscopic scale in terms of particle velocity, motion trajectory, mechanical behavior, and energy information. Finally, proper solutions in designing and constructing WC/316 L composite materials with desired gradient structures were proposed. The results show that the small blade velocity (V) will enhance the negative segregation, increase the average packing density ρ¯, and decrease uniformity ρvc in the WC/316 L composite powder bed. Compared with the blade, the roller can increase the negative segregation (Seroller = −0.027 < Seblade = −0.019) and the average packing density (ρ¯roller = 0.31>ρ¯blade = 0.20). When the WC/316 L size ratio increases from 25 μm/45 μm to 45 μm/45 μm, the negative segregation becomes weaker, and its value increases from −0.084 to −0.007. When the size ratio increases to 65 μm/45 μm, the powder behaves positive segregation with Semax = 0.017; in this case, the packing density is the lowest (0.14), and the uniformity is the worst (0.17). In comparison with spherical shape, polyhedral WC powder can reduce the negative segregation of the powder bed (Sesphere = −0.019 < Sepolyhedron = −0.008), while the WC shape has less effect on the packing density and uniformity. The density difference of the WC and 316 L powders leads to the difference in energy and force, resulting in different motion and segregation behaviors in the composite powder bed. For WC/316 L composite powder with a fixed composition, the condition of V = 0.025 m/s, WC/316 L size ratio = 25 μm/45 μm, roller spreader, and spherical WC can realize the proper composition gradient along the spreading direction in the composite powder bed.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Resources & Recyclin
Vaccinations, infections and antibacterials in the first grass pollen season of life and risk of later hayfever
No full textPublished source: Bremner, S. A., Carey, I. M., DeWilde, S., Richards, N., Maier, W. C., Hilton, S. R., Strachan, D. P. and Cook, D. G. (2007), Vaccinations, infections and antibacterials in the first grass pollen season of life and risk of later hayfever. Clinical & Experimental Allergy, 37: 512–517. doi: 10.1111/j.1365-2222.2007.02697.
An interlaboratory exercise on the magnetic properties of various WC hardmetals
No full textAn interlaboratory comparison exercise has been conducted to investigate the reproducibility of coercivity and magnetic moment/saturation measurements on a range of WC based hardmetals. The measurements were made at seven collaborating organisations, six of which were industrial companies, and analysed at NPL. Seven materials were evaluated with a range of WC grain sizes from 0.3-3 #mu#m and cobalt contents from 3-15 wt%. It was found that the standard deviation of the magnetic coercivity value was dependent on WC grain size, with a higher uncertainty associated with the higher values of coercivity (smaller grain size). In contrast there was no clear dependence of the uncertainty in magnetic moment on structure, except for the materials with the very lowest values and they had a larger standard deviation. (author)Available from British Library Document Supply Centre-DSC:6180.5139(78) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo
The reason why orthopaedic surgeons perform total knee replacement: results of a randomised study using case vignettes
No full text10.1007/s00167-015-3961-5KNEE SURGERY SPORTS TRAUMATOLOGY ARTHROSCOPY2482697-270
Investigation into coatings produced from nanoparticle blended feedstock for rotating equipment repair applications
No full textCoating of carbon steel with conventional and nano particle blended feedstock material is considered in relation to repair applications of rotating equipment. Gas Metal Arc Welding (GMAW) and Wire Arc Spray (WAS) processes are used to produce the coatings on carbon steel workpieces. The wire arc sprayed workpieces are heat treated at temperature similar to the operating temperature of hot-path components of power gas turbines. The microstructure and metallurgy of the workpieces are examined using the Scanning Electron Microscope (SEM), Optical Microscope, Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD). The indentation tests are carried out to assess the microhardness variation across the coatings. In the case of coatings produced by GMAW, it is found that fine structures are formed in the coating due to the presence of nano particles and they resulted in increased microhardness of the coatings. In the case of the wire arc sprayed workpieces, the formation of dimples like structure at the surface increases the surface roughness of the coatings. In addition, the microhardness of the resulting coating is significantly higher than that of the base material. The heat treatment does not alter the microstructure and microhardness of the coatings significantly
The influence of Si on the microstructure and sintering behavior of ultrafine WC
No full textThe microstructure of sintered nano scale tungsten carbide powders with 1wt. % Si addition was found to be populated by an abnormally large number of elongated grains. Interrupted sintering experiments were conducted to clarify the origins of the excessive abnormal grain growth seen in the microstructure. It was observed that rapid coarsening occurred at high temperatures owing to the formation of a liquid phase. However, the grain shape evolution during this coarsening period was found to be a consequence of excessive stacking faults and micro twins on the basal planes probably generated by reaction of WC with Si. Analyses of the microstructures and the isothermal and non isothermal coarsening behaviors suggested that the platelet morphology evolved by defect-assisted nucleation and growth on faceted grains. Based on experimental evidence from samples interrupted at low temperatures and crystal growth theories, we discuss the possible mechanisms that eventually led to the rampant platelet-type morphology. Further, the influence of such rapid grain growth on the shrinkage rate during sintering is also discussed. In comparison with the cyclic coarsening-densification process of sintering in pure nano scale WC, the addition of Si leads to only two distinct sintering stages: either densification dominated or coarsening dominated. Concurrent densification and coarsening cannot be sustained particularly in the presence of a liquid phase that significantly enhances coarsening
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