The practical application of bulk metallic glasses (BMGs) as structural materials is still restricted due to the intrinsic brittleness of BMGs although they have high hardness and strength and even pretty good toughness. As an alternative form of metallic glasses, amorphous coatings based on BMG systems can exactly overcome the drawback of BMGs, but carry forward the superiority in corrosion and wear resistance, thus exhibiting promising applications in surface engineering. However, the monolithic amorphous coatings faces new challenges, such as low adhesion strength and impact toughness. In this presentation, we present some new findings on the design of novel Fe-based amorphous composite coatings by HVOF technique. These include the add stainless steel ductile phase, hard ceramic particles and in-situ carbon phases into the amorphous coating, in addition to form laminar structural coatings. It will be shown that the second phase and their interface structure with amorphous matrix play important role in the resultant mechanical properties of the coatings. The combination of the good mechanical, physical and chemical properties warrants amorphous composite coatings to have extensive applications in industry in near future.

Cr 3 C 2 -25%NiCr, Stellite 6, NiCrBSi and Hastelloy C-276 coatings were deposited on substrate material P91 by HP/HVOF (High Pressure / High Velocity Oxygen Fuel) thermal spraying technology. The resistance against high temperature corrosion was evaluated exposition of coatings to corrosive-aggressive environment in the form of molten salts mixture with composition of 60% V 2 O 5 and 40% Na 2 SO 4 at temperature of 750 °C. Further, coatings were exposed to cyclic conditions. After the corrosion tests, all coatings were analyzed using scanning electron microscope (SEM), and analysis of elemental composition (EDX). Alloys-based coatings showed very similar corrosion mechanism in the selected aggressive environment and the same can be stated about cermet coatings. The obtained results prove that HVOF deposited coatings can replace current surface protection of components in power equipment such as nitriding.

The use of nanoscale WC grain or finer feedstock particles are two possible methods of improving the properties and performance of WC-Co-Cr coatings. Finer powders are being pursued for the development of coating internal surfaces, as less thermal energy is required to melt the finer powder compared to coarse powders, permitting spraying at smaller stand-off distances. Three WC-10Co-4Cr coatings, with two different particle sizes and two different carbide grain sizes, were sprayed using a high velocity oxy-air fuel (HVOAF) thermal spray system developed by Monitor Coatings Ltd. in the UK. The powder and coating microstructure were characterised using XRD and SEM. Fracture toughness and dry sliding wear performance were investigated using a ball-on-disc tribometer with a WC counter-body. It was found that the finer powder had a higher hardness but relatively lower fracture toughness. When performing sliding wear testing at the lower 96N load the nanostructured coating performed best; however at 240N this coating was displayed the highest specific wear rates, with the other two powders performing to a similar, better standard.

This paper presents research results showing how spraying distance affects the bonding strength, porosity, microhardness, and deposition efficiency of HVOF-sprayed NiCrAl coatings. The coatings examined were deposited on quenched 1045 steel substrates at spraying distances of 340, 360, and 380 mm. At the optimal standoff distance of 360 mm with kerosene and oxygen flow rates at 22 L/h and 850 L/min, respectively, NiCrAl coatings were achieved with a bonding strength of 66 MPa, microhardness of 418.56 HV 0.3 , porosity of 1.1%, and deposition efficiency of 65.3%.

In this study, particle image velocimetry (PIV) is used to measure WC particle velocity during HVAF spraying. Measured velocities are compared with calculated velocities obtained using open source CFD software. Numerical simulation is also used to investigate particle temperatures. With the HVAF gun used, maximum particle velocity is reached around 18 mm from the nozzle exit with a corresponding gas temperature of 1400 K.

In this study, a path strategy for robot-based HVOF spraying is developed via deposition simulations. The simulations include the analysis of the spray plume footprint and the consideration of robot dynamics in the path planning strategy. A fine WC-Co powder was used as the feedstock material.

Two agglomerated and sintered powders, WC-Co and WC-Co-Cr, were deposited by HVAF spraying and evaluated based on material decarburization, coating porosity, and microhardness. The role of carbide grain size, contiguity, and binder mean free path is investigated with respect to coating microstructure and wear and corrosion resistance.

This study evaluates an internal diameter HVAF spray system and compares coatings characteristics obtained with WC and Cr 3 C 2 based powders with those achieved via standard HVAF spraying. Coating microstructure, phase composition, hardness, roughness, and corrosion resistance are investigated and the potential for further optimization is discussed. It is also shown that the new system can be used for grit-blasting as well as spraying.

This study evaluates the base mechanical properties of Hastelloy C-276, WC-Co, and Cr 3 C 2 -NiCr coatings produced by HVOF spraying at angles ranging from 60° to 90°. Examinations and tests were conducted to characterize changes in microstructure, density, hardness, wear resistance, surface roughness, and deposition efficiency based on spraying angle. Only minor spray-angle dependencies were found for base mechanical properties, although thickness, roughness, and deposition efficiency varied greatly.