Nanostructured materials have a high potential to improve properties of thermal spray coatings. High-energy ball milling is an effective process to produce dispersion-strengthened powders with a homogenous nanoscale microstructure and superior mechanical properties compared to unstrengthened material. Because of the relatively low temperatures and heat flux during HVOF spraying, the microstructure of the powder particles can be maintained in the coating. In this study Al 2 O 3 - dispersion-strengthened NiCr powders were synthesised by high-energy ball milling, using optimised milling parameters. Thermal spray coatings were produced using the HVOF process. The improvement of the tribological behaviour and the potential for technical applications were evaluated. The study shows the favourable impact of mechanically alloyed MMCs on the tribological behaviour of HVOF coatings on the basis of an Al 2 O 3 -strengthened NiCr powder

For thermal sprayed coatings, compactness of their constituent particles is required in many applications, e.g. to obtain impermeable anticorrosion coating in marine use. We investigated key factors to improve compactibility of deposited particles in HVOF sprayed coatings by condition measurements of spray particles. The results revealed that plastic deformability of the sprayed particles as well as their molten fraction was important to obtain the dense VHOF coatings.

The use of coatings to improve wear and corrosion resistance of mechanical components has been common for several decades. Various application techniques have been commonly used, including welding, cladding, electroplating, PVD (physical vapor deposition) and CVD (chemical vapor deposition). Thermal spraying has been found to be an interesting and viable alternative for those processes in such applications. Coatings of several types can be used for wear and corrosion protection, including situations when they are combined. The analysis for choice of the ideal coating and of the application process should take into account the environment and related limitations and specificities of each coating material and application process. In this work a study and characterization of tungsten and chrome carbides based coatings was carried out. The coatings were applied by high velocity oxy fuel thermal spraying (HVOF), using two different HVOF systems. Microstructure, hardness, as well as wear characteristics of the coatings were evaluated. The results show that the obtained coatings present great characteristics and can successfully face several wear conditions.

In this paper the development of thermal sprayed, hard phase reinforced aluminum based layers, in particular for coating light metal substrates is described. The aim of the project was to obtain wear resistant coatings for applications on light metal surfaces combined with other advantageous characteristics, especially good thermal conductivity. One possible application for these coatings can be seen in automotive light weight constructions as wear protection for brake discs or drums. Flame shock spraying as well as high velocity oxyfuel flame spraying (HVOF) were used as coating processes. As consumables mechanically alloyed powders consisting of aluminum and ferric oxide were used. Due to the high kinetic process energy developed by the selected procedures in connection with the exothermically reacting spraying material, a new light metal matrix composite was produced. One major advantage of this coating material is the in-situ synthesis of the hard particles in the aluminum matrix during the spray process resulting in good adhesion/cohesion properties. This research project includes an extensive analysis of the consumables including differential thermal analysis, SEM, and EDX. Furthermore, process parameters were optimized. This includes a characterization of the HVOF process using modern particle diagnostics. Besides good bonding properties proven coating characteristics are high thermal conductivity and thermal shock resistance as well as good wear behavior even at elevated temperatures. The results show that the developed coating system is a promising alternative for cast aluminum matrix composite materials used for wear stressed parts even at elevated temperatures.

Although the HVOF process has shown to be a technological alternative to the many conventional thermal spray processes, it would be very advantageous to design a nozzle that provides improved performance in the areas of deposition efficiency, particle in-flight oxidation, and flexibility to allow coating of ceramic powders. Based on a numerical analysis, a new nozzle was modeled, designed, tested, and used to produce thermal spray coatings according to the industrial needs mentioned above. Performance of the new nozzle was investigated by spraying several coating materials including metallic (Nickel, MCrAlY, Stainless Steel), carbide (WC-Co), and ceramic (Al 2 O 3 ) powders. Particle spatial distribution, velocity, and temperature corresponding to the new nozzle and the standard HVOF gun were compared. The new nozzle provides a superior particle spatial distribution, as well as higher and more uniform particle velocity and temperature.

According to aerodynamics and thermodynamics, High Velocity Oxygen/Air Fuel Spray system was successfully developed. The system introduced stream atomization, high-pressure combustion chamber, converging/diverging nozzle, spark plug ignition, radial powder injection with reliable operation. The system has the function of both of HVOF and HVAF. It can not only use air and oxygen to spray respectively, but also the mixture of air and oxygen, so the velocity and temperature of the flame can be changed by adjusting the flux of air and oxygen. The system can produce high quality cermets, metal and alloy coatings for the adjustable of flame velocity and temperature.

Advanced TiC-based spray powders contain molybdenum and nitrogen as alloying elements and consist of core-rim-structured (Ti,Mo)(C,N) hard phases embedded in Ni, Co or mixed Ni/Co binder phases. For the investigations of the present study, four powders with binder phase contents of 29 and 39 mass-%, corresponding to about 20 and 27 vol.-%, respectively, were prepared by agglomeration and sintering. Coating samples were sprayed using JP-5000 equipment and two spray parameter sets. During coating characterization, special emphasis was placed on the changes in chemical (carbon loss and oxygen uptake) and phase compositions during spraying and their correlation to the coating microstructures and properties. It was found that the decreases in carbon and nitrogen contents were practically independent of the spray parameters for all of the four powders, whereas the oxygen uptake was different for each of the powders. The effect of the oxygen content on different coating properties is discussed in detail. All coatings investigated in this work showed excellent properties. It is anticipated that TiC-based coatings sprayed from these types of advanced powders can complement thermal spray coating solutions based on WC and Cr 3 C 2 .

This research examined the use of 4-point bend testing, with in-situ acoustic emission analysis, for the characterization of the deformation of WC-Co coatings sprayed by the high-velocity oxy-fuel method. Coatings were deposited from WC- 17wt.%Co powders using a Praxair JP5000 system. Two sets of gun operating parameters were employed to produce coatings with distinctly different structures. In the present studies the cracking behaviour of the coatings was investigated through analysis of the acoustic emission (AE) data. In particular, AE data recorded has shown clear differences between the two coating types, in terms of the critical strain level and amount of energy released during cracking. The critical strain levels for the different coatings were 0.32% and 0.6% respectively. Analysis of the coatings by scanning electron microscopy and X-ray diffraction has allowed correlations to be made between the principle microstructural features of the coatings and the mechanical behaviour under bending. The AE responses for these cermet coatings were highly reproducible.

Four-point bend test using acoustic emission (AE) was used to compare coating properties under mechanical solicitation, mainly the toughness and the spalling behaviour. Coatings are made from the same material; the 2005NS (WC-17Co), sprayed with an HVOF gun at various spray parameters. Coatings deposited on thin rectangular substrates were tested with the coating bent in tension and in compression. AE features like the event number, energy per event and cumulative energy were used to assess the damage in the coatings. The results are analyzed in relation with the coating microstructure.

In the case of thermal spraying of cermet powders using HVOF with longer barrel, such as a JP-5000 and a Diamond Jet 2700, spitting and clogging troubles tend to be brought about on the inner wall of the barrel. This phenomenon comes from the existence of fine particles (in spray powders) which tend to fully melt through barrel. This investigation has been carried out to realize the influence of powder particle strength and particle size distribution of agglomerated and sintered Cr 3 C 2 -25%NiCr powders during HVOF spraying. It is found that the finer and weaker the powder particles, the higher the deposit efficiency. However, the finer and weaker the powder particles, the easier is the onset of spitting and clogging phenomena. On the contrary, it is found that the coarser and stronger the powder particles, the lower the deposit efficiency with less spitting and clogging phenomena. Finally optimum powder particle strength and particle size distribution of Cr 3 C 2 -25%NiCr powders have been found in this study using a JP-5000 system.

Aluminium-based plain bearings for gasoline internal combustion engines are traditionally manufactured by casting and rolling, followed by forming and boring. The application places severe demands on the bearing material and a combination of properties such as fatigue, seizure and wear resistance are required. These properties are achieved by using a multi-phase material comprising of a distribution of tin in an aluminium alloy matrix. HVOF has been investigated as an alternative process for bearing manufacture and as a route to producing novel bearing materials with microstructures that cannot be achieved using the conventional casting route. The work reported describes the use of different HVOF spraying systems and powder types to develop aluminium-tin based coatings for advanced bearing applications. The coatings are described in terms of microstructure characteristics. The fatigue performance of the advanced sprayed bearings is compared with conventional cast bearings.

A high velocity oxy-fuel spraying system using liquid fuel (HVOLF) has produced Stellite 6 (CoCrWC) and NiCoCrAlY coatings from gas atomised powders of both alloys. Comparative coatings were prepared by weld 0verlay (Stellite 6) and vacuum plasma spraying (VPS) of NiCoCrAlY. The original powders and coatings were characterised by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The presence or absence of cored dendritic microstructures in etched surfaces was used to interpret the degree of melting which took place during spraying, i.e. >80% in VPS and <20% in HVOLF. Low levels of oxide were formed in HVOLF coatings due to the reduced level of thermal transfer during the short heating cycle involved in spraying. For the same reason less melting occurred which permitted sufficient plastic deformation of the solid fraction to occur, reducing voidage between particles and then allowing the liquid fraction to weld them together. This pattern of short cycle heating with both NiCoCrAlY and Stellite 6 particles influenced second phase formation. In NiCoCrAlY coatings the β (Co Ni Al) phase remained as relatively coarse precipitates in the as - sprayed condition whilst in Stellite 6 little carbide eutectic formed. HVOLF spraying can produce coatings with different hardness values when compared with VPS coatings and weld overlays. This may widen the range of coating applications as well as reduce costs.

The paper analyzed microstructure and property of WC-17Co coatings sprayed by High Velocity Oxygen/Air Fuel Spray under three kinds of spray conditions, which are HVOF, HVO-AF and HVAF. Coatings bond well with the substrate. The average bonding strength exceeds 70Mpa. Coatings are dense and hard, and the average porosity is about 1%. Microhardness of coatings is between HV1000 0.2 and HV1200 0.2 . Coatings are mainly composed of WC with little W 2 C and Co 3 W 3 C. With the increasing of Nitrogen, decarburization of WC was reduced.

Spinel soft ferrites such as NiZnFe 2 O 4 are of great interest due to their extensive applications in magnetic-optics, microelectronics, and microwave devices. This study deals with the production of thick Ni 0.5 Zn 0.5 Fe 2 O 4 magnetic films (>50 microns) using high velocity oxy-fuel (“HVOF”) thermal spray. With the HVOF process, high density films more than 98% theoretical density were prepared, apparently due to the high velocity of droplets in the process. The influence of the fuel composition on coating structure, deposition efficiency, and magnetic properties of the Ni-Zn ferrite films was investigated. Better magnetic properties were obtained in the as-sprayed film formed with a neutral or oxygen-rich flame. The decomposition of the ferrite material occurred with a fuel-rich flame and resulted in a reduction in magnetic properties. However, the magnetic properties could be improved dramatically after heat treatment. Pellet and toroid samples of these films were produced for evaluation of magnetic properties by saturation magnetization and magnetic permeability. The permeability exhibited a very flat response to high frequencies up to 13 MHz.