High Velocity Oxygen Fuel

High Velocity Oxygen Fuel (HVOF) is an excellent approach to prepare a good, wear-resistant lamella of Chromium Carbide-Nickel Chrome (Cr3C2-NiCr) on carbon steel for high temperature application. This research investigates the effect of a thin, deposited layer of Cr3C2-NiCr on carbon steel in terms of wear and corrosion properties. The microstructure of the HVOF-sprayed Cr3C2-NiCr coating was characterized at each step by scanning electron microscopy. Wear testing was performed with a pin-on-disk tester. Wear weight loss was examined by applying different loads over a 9048.96 m sliding distance. Experimental results show that the wear resistance of the coated sample reduced the risk of seizure compared to the uncoated sample. An electrochemical test was also performed and the behavior of the substrate in the coated sample was investigated in 3.5% NaCl for 27 days. Electrochemical Impedance Spectroscopy (EIS) showed that the HVOF coating has high corrosion resistance and protects th...

In this work the affects of laser characteristics on surface morphology, microstructure, microhardness and wear rates of high velocity oxygen fuel (HVOF) WC-CoCr coatings were investigated. Continuous and pulsed laser treatments were applied on the HVOF coatings using a CO2 laser of 10.6 μm wavelength. Continuous laser treatment significantly improved homogeneity of the coatings. Pulsed laser treatment produced significantly higher discontinuities compared to continuous mode. Microhardness increased by 45% for continuous mode laser modified WC-CoCr coatings. However, wear resistance deteriorated, with a notable 40% increase in wear rate. The variations in coating properties were attributed to the re-melting and rapid quenching of the CoCr bonding matrix allowing for WC redistribution.

j m a t e r r e s t e c h n o l. 2 0 1 9;8(5):4253-4263 w w w. j m r t. c o m. b r High velocity oxygen fuel (HVOF) MCrAlY Thermal-barrier-coating (TBC) Bending test a b s t r a c t High-velocity oxygen fuel (HVOF) and flame spraying (FS) are alternative methods to thermal spraying processes to produce dense high-quality coatings. The aim of this study is to compare the microstructure and mechanical properties for HVOF and FS using a thermally sprayed bond coat NiCoCrAlY and CoNiCrAlY powders on an AISI 304 stainless steel substrate. The microstructure and composition of coatings were characterized by an X-ray Diffraction (XRD) analysis and Electron Microscopy (SEM) coupled to an Energy Dispersive Spectroscopy (EDS) detector. HVOF showed higher quality coatings compared to FS in terms of porosity and the presence of unfused particles for both employed powders. The mechanical properties and results indicated that the yield strength of the NiCoCrAlY (HVOF) coating was 1.4-folds FS, but the flexural bending modulus was almost the same. For the CoNiCrAlY powder, HVOF gave a higher yield strength and a higher flexural modulus than FS as the oxygen affinity of the CoNiCrAlY powder was lower than NiCoCrAlY given the high Co content in the former versus the latter. The results also indicated that hardness increased by about 83%, and by 58% for the NiCoCrAlY HVOF and FS coating alloys, and by 42% and 20% more for the CoNiCrAlY HVOF and FS coatings than the stainless steel substrate hardness, respectively.

The new material class of ceramic nanocomposites, containing at least one phase in nanometric dimension, has achieved special interest in previous years. While earlier research was focused on materials science and microstructural details in laboratory scale the subject of developing suitable manufacturing technologies in technical scale is the challenge for the manufacturing engineer. The same high-performance features which make the nanocomposite materials so interesting in their properties are absolutely detrimental if it comes to production of these materials. Extreme hardness, toughness and abrasion resistance make the state of the art cutting-and-machining operations extremely cost intensive so that, from a manufacturing point of view, true near-net-shape manufacturing is mandatory to accomplish reasonable cost targets.Ceramic feedstocks with both, high solid content to reduce shrinkage and warping and stable processing conditions are required to accomplish this aim of near-net...

Near-nanostructured WC-18 pct Co coatings, with low amounts of non-WC carbide phases, have been synthesized using high velocity oxygen fuel (HVOF) thermal spraying under spraying conditions of varying fuel chemistry, fuel-oxygen ratio, and powder particle size. The results show that the temperature the particles experience during spraying depends on the preceding parameters. Compared to available published results on WC-Co system

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.

Thermally sprayed WC–Co coatings are currently used in numerous contact wear applications in the aircraft, automotive and paper industries. High-cycle fatigue tests were performed at room temperature and 370 °C on SAE 12L14 low-carbon steel and aluminium alloy 2024-T4 thermally sprayed with WC–17 wt% Co using the high-velocity oxygen fuel process. The fatigue life distributions of specimens in the polished, grit-blasted, peened and coated conditions are presented as a function of the probability of failure. Composite beam theory was applied to the coated beam to evaluate the stresses and elastic modulus.The stress–strain curves for the coated and uncoated specimens were used to evaluate the stiffness factor for the aluminium alloy and steel. It is concluded that (i) the coated specimens exhibited significantly high fatigue lives compared with the uncoated specimens, (ii) the mechanisms of deformation for the coated and uncoated aluminium alloy specimens are quite different and (iii) the elastic modulus of the coating plays a significant role in determining the fatigue strength of the coated component. © 1998 Kluwer Academic Publishers