Surface modification of HVOF thermal sprayed WC–CoCr coatings by laser treatment

In this work the affects of laser characteristics on microstructure and microhardness of high velocity oxygen fuel sprayed (HVOF) WC–CoCr coatings were investigated. The coating was deposited with a Sulzer Metco WokaJet™-400 kerosene fuel and the laser surface treatments were applied using CO2 laser with 10.6 μm wavelength. Large variations in surface properties were produced from variation in the laser processing parameters. In total, four levels of peak power (100, 200, 300 and 350 W), four levels of spot diameter (0.2, 0.4, 0.6 and 1 mm) and three levels of pulse repetition frequency (PRF) were investigated. An initial set of tests were followed by a more detailed 33 factorial design of experiments. Pulse repetition frequency and duty cycle were set in order to maintain the same overlap in the x and y directions for the raster scanned sample spot impact dimensions. Overlaps of 30% were used in the initial tests and 10% in the more detailed trials. The results have shown that care must be taken to keep the irradiance at a relatively low level compared to uncoated surfaces. High irradiance can in this case result in rough and porous surfaces. Lower levels of irradiance are shown to provide more uniform microstructures, reduced porosity and increased microhardness

Solid particle erosion protection for the BLOODHOUND SSC front wheel arches

BLOODHOUND SSC is a World Land Speed Record Vehicle designed to travel at speeds of up to 1050 mph (469 m·s−1), with the lower chassis and suspension extremely close to the ground. The shockwave from the nose of the car is expected to fluidise the desert surface of the track in Hakskeen Pan, South Africa. Sacrificial materials must be added to the exterior of the car to limit erosive wear. An open loop gas blast erosion rig was used to test materials at velocities predicted by computational fluid dynamics in the front wheel arches, an area highlighted by the BLOODHOUND SSC engineers as requiring extensive protection. Tests of potential erosion protection materials were performed at 15° and 90° Impact angle using alumina as a substitute for Hakskeen Pan soil. Testing resulted in the use of a 2-mm thick Kevlar 49 laminate and 1.2 mm thick titanium Ti 15 V-3Cr-3Sn-3Al sheet for the wheel arch liner, with titanium Ti 6Al-4V used for the wheel arch lip. The erodent mass flow rate for the application was an unknown variable during testing; the test rig used a specific erodent mass flow rate of approximately 300 kg·m−2·s−1. Depending on in-service erosion rates, the titanium liner may be replaced with either a more durable liner made from Stellite 6B or a less dense liner made from aluminium Al 6082-T6

Tribological performance of nano structured TiO2 coatings prepared by Suspension HVOF spraying

Research conducted in the field of suspension thermal spraying promises an entire new class of nanostructured coatings. In this study a number of parameters for Suspension HVOF spraying were explored, including spray distance and number of passes. Nano-sized TiO2 particles suspended in a water-isopropanol mixture were used to deposit coatings for tribological applications onto a type 304 stainless steel. The surface topography, cross sectional microstructure and phase composition of the deposits were characterized by 3D optical microscopy, scanning electron microscopy and X-ray diffraction. Their sliding friction and wear behaviour were examined under humid air conditions using a reciprocating tribometer. The spray parameters used, the microstructures obtained and the dominating wear mechanisms of the nano-structured TiO2 coating are presented and discussed

Identifying Important Differences in Mass Spectra Generated by Secondary ion Mass Spectrometry (TOF–SIMS) in a Tribochemical Study

In order to better understand the lubricating properties of diesel fuel, species that were present on tribological surfaces were investigated using secondary ion time-of-flight mass spectrometry (TOF–SIMS). Traditionally, only certain species that are expected to be present at the interface are investigated and their presence or absence is used to make conclusions regarding the mechanism of lubrication. In this work, an alternative and complementary approach to data analysis and interpretation is proposed, previously demonstrated for TOF–SIMS and based on multivariate analysis methods, where the mass spectral data are investigated more comprehensively. The main objective was to interpret variation within and between different areas of a tested surface and ultimately to contribute to the understanding of the tribochemical reactions that occur at the interface. The validity of this approach was confirmed when the palmitate ion (which would normally be targeted) was shown to contribute significantly (together with other ions) to chemical differences between scratched and unscratched areas of the surface.Sasol (Sasol Technology,Fuels Research) and the National Research Foundation (DAAD-NRF).http://link.springer.com/journal/112492015-10-31hb201