Due to its oxidation resistance, HVOF thermal sprayed Cr 3 C 2 -NiCr coatings have been widely used for wear resistance at elevated temperatures up to 850ºC. During HVOF spraying deposition, compositional degradation occurs through dissolution of the carbide phase into the metal matrix. The occurrence of carbide dissolution and the high working temperatures affects on the final properties of the coating. The aim of this work is to study the effect on the structure and wear properties at elevated temperatures of Cr 3 C 2 - NiCr coatings using hydrogen as a fuel gas against propylene. The structural characterization was done by SEM-EDS, XRD, and Scanning White Light Interferometry (SWLI). Wear properties at room and high temperatures have been evaluated by Ball-on-Disk (ASTM G99-90). Oxidation resistance of all coatings was carried out using a calorimetric technique Abstract only; no full-text paper available.

Although high-velocity oxyfuel (HVOF) spray coating is a relatively new thermal spraying process, interest is growing rapidly along with the pace of development in areas such as torch design, powder quality, and modelling. The gases used in HVOF spraying are also important because they directly influence the state of the particle striking the substrate. This presentation reviews the HVOF combustion process with an emphasis on the gases used and their influence on coating quality.

Bulk, welded or laser cladded Stellite based materials are widely used in chemical industry due to their excellent combined properties against corrosion and wear processes and as a superalloy they have a high melting point and are designed to withstand high temperature for long periods of time. Problems related with poor inter-splat bonding arise when this kind of materials are sprayed with HVOF because it is characterized by having relatively low flame temperatures and high particle speed, and so dwell time may not be long enough to melt or soften Stellite particles completely. For these reasons, typical structured composed by a superposition of non-melted particles are obtained when spraying with propylene fuel gas. The aim of this work is to study the effect of using Hydrogen as a fuel gas and also to study the effect of the variation of the propylene flame characteristics. The coatings are characterized by SEM-EDS, XRD, and ASTM G99-90 sliding wear test has been done to compare the coatings. SWLI has been used to measure the volume lost after the wear test. Splat morphology studies have been also done in order to compare the melting behavior of the impinging particles.

HVOF spraying process is widely used to improve component life in service due to the high bond strength of the coatings, which is a result of the high particle velocity upon impact, and consequent low coating porosity. However, many parameters can affect metallic coatings properties, especially unmelted particles and oxidation level. Flame parameters, such as calorific power, combustion ratio and temperature, are of prime importance. Moreover, the fuel gas employed in this spraying process can lead to various coating properties and deposition efficiency. The aim of this work was focused on the influence of some fuel gases, namely propane, propylene (LPG) and hydrogen, on stainless steel coating characteristics. A specific domain common for those three gases was determined in order to effectively compare those gases with the same flame parameters. Flame characteristics were computed using a simple model for all the fuel gases considered. Temperature as well as calorific power were fixed. For different substrate temperatures, obtained through a special CO 2 cooling nozzle system, richness was varied from 1.4 to 1.6. Microstructure investigation as well as oxide content and microhardness measurements were conducted. For the same kinetic torch parameters, thickness-per pass gave an idea of the deposition efficiency. In the range studied, deposits properties were quite similar for both LPG fuel gases. Hydrogen led to better characteristics in term of oxide content, although its deposition efficiency was a bit lower. A general law was established to link oxide content within the coatings to the flame parameters. A reasonable regression analysis was obtained for all the coatings sprayed. The combination of cooling efficiency (i.e. CO 2 flow rate) and flame characteristics (i.e. interaction of the particle in flight) led to a good correlation. These correlations were further verified by spraying another metallic powder, namely Inconel 625.

Chromium oxide coatings are currently produced predominantly by the plasma spray process utilizing the high process temperatures required to fully soften the high melting point chromium oxide powder. The development of the HVOF process, combining the relatively high flame temperatures of hydrogen, propylene or propane fuel gases with the notably high particle velocities generated by the process, is known to produces dense, low porosity coatings. By utilizing acetylene, the highest flame temperature fuel gas commercially available, and acetylene based mixtures, the HVOF process can be used to successfully spray chromium oxide powder previously impractical for HVOF systems. This paper describes the results of a programme of work carried out to study the effect of gas related parameters on the properties of Cr 2 O 3 , coatings deposited by HVOF using acetylene and acetylene based mixtures as fuel gases. It further describes the engineering of gas supply systems to overcome the working limitations of acetylene pressures and flowrates to achieve acceptable gas pressures and flow rates and subsequent particle temperature and velocity.

An important aspect in the successful commercialisation of thermal spray processing is a safe and cost efficient gas supply system. As coating techniques such as High Velocity Oxygen Fuel spraying, (HVOF) High Pressure Plasma spraying (HPPS), High Pressure High Velocity Oxygen Fuel kerosene based systems (HPHVOF) and the recent developments in Cold Gas Dynamic spraying become more prominent, so the requirements on existing standard gas delivery systems designed for less demanding applications such as flame and plasma spraying need to be up-rated and improved. This work highlights recent developments in gas safety supply equipment dedicated to the thermal spray sector, the use of gas detectors in thermal spray workshops, more cost efficient gas delivery systems for fuel gases such as hydrogen, LPG propane, propylene and acetylene, and also covers improvements in gas delivery systems for the process gases such as oxygen, nitrogen and argon. The paper looks at various gas supply options, comparing compressed gas cylinders, liquid gas cylinders and bulk liquid supply vessels outlining the benefits and limitations of each systems in relation to the individual spray techniques. The higher pressures and flow rate associated with the growth of kerosene based fuel guns has resulted in an increased demand on the conventional compressed oxygen supply systems making them less cost effective and unworkable in a production environment. The paper covers new liquid oxygen supply cylinders and novel bulk tank systems that reduce cylinder holdings while reducing gas wastage due to lack of pressure. With the increase in higher thermal energy systems, necessity to more closely control the temperature of sprayed the component has outstretched the demands on conventional compressed air cooling systems. In the past, the use of cryogenic cooling gases such as carbon dioxide has been restricted by increased cost. However it has been shown in a number of cases that often the hidden costs of running air compressors, including the use of moisture traps, and oil filters can be greater than using clean, high purity cryogenic liquid gases such as carbon dioxide and nitrogen. The paper outlines the details of such cooling systems. The commercial success of Cold Gas Dynamic spraying may in future rely on a cost efficient, high pressure and high volume gas delivery systems for either helium or nitrogen. The paper describes a novel high pressure supply system presently used in another application suitable for Cold Gas Dynamic spraying with nitrogen able to generate pressure in-excess of 30 bar and flow rates above 120m3/hr from a liquid vessel.

This paper informs about the potential dangers associated with the gases used in thermal spraying. These include fuel gases, oxygen, inert gases, and carbon dioxide. The paper addresses the following: flammability, explosion, oxygen enrichment and tolerance, asphyxiation, and low-temperature technology. It presents regulations and leaflets relating to the safe storage, handling, and use of gases with various supply options. Safe working techniques are recommended along with a brief description of the relevant safety equipment. Paper includes a German-language abstract.

The high technical level of thermal spraying is based on four segments: available know-how, equipment and installations, spray materials, and industrial gases. This article discusses the application of industrial gases used in thermal spraying. It describes the processes involved in the production, provision, and storage of industrial gases as well as their properties. In addition, the article also discusses the influence of quality on the individual fuel gases used in thermal spraying.

The basic idea when using common plasma gases for arc spraying with their varying levels of energy was first of all to achieve higher system efficiency and to produce coatings with fewer oxides. The differentiation between the open arc process and plasma spraying is the advantage using active gases with a much higher energy level, for example using fuel gases to influence the process characteristics and to get high end coatings. As these results from this work in arc spraying show, the increased need for research into this technology at the moment is definitely of importance. The main market of arc spraying can be found in the area of corrosion protection, the technology’s growth stems from those areas which are interested in manufacturing high-quality coatings with substantially more cost-effective wire. In order to broaden the range of thermal spray applications, we have endeavored to investigate the issue of the right gas mix for arc spraying. In doing so, it was concluded that, by using wire as the spray material, this cost-effective process can often be used as an equally viable alternative to other methods. The optimization of costs and tailoring of coating properties to suit specific applications are just some of these influencing variables.

One of the tubular cell designs for solid oxide fuel cells is based on a closed-end tube made from the cathode material, with an electrolyte layer coating the outside of the cathode tube, and the anode coating the electrolyte layer. The outer anode layer of one tubular cell is connected to the inner cathode layer of the next tube by the interconnect material. High density is required in the interconnects to prevent mixing of the air and fuel gases. The fabrication of interconnect strips in tubular fuel cell stacks by DC-arc plasma spray deposition has been demonstrated in the past, both in air (APS) and in low pressure (vacuum) conditions (VPS). The High Velocity Oxy Fuel (HVOF) spray deposition technique typically yields among the highest density coatings of all common thermal spray techniques due to the high gas and particle velocities achieved, and therefore would appear to be an excellent method for depositing the interconnects if the powder could be sufficiently melted during spraying. The most common material choice is a doped LaCrO3, a ceramic material with a good thermal expansion coefficient match with the other components of the cell and an acceptable electrical conductivity. The microstructure, phase and chemical composition, and electrical properties of doped LaCrO3 deposited on (La,Sr,Mn)2O3 cathode tubes by HVOF was examined as a function of deposition conditions. Abstract only; no full-text paper available.

In this paper, the production of NiCr-TiC powder by SHS, suitable for HVOF spraying, is discussed together with results on the microstructure and coating properties. Compacts for SHS were prepared by mixing elemental Ti and C with pre-alloyed Ni-20wt.% Cr powder to give an overall composition of 35wt.% NiCr and 65wt.% TiC. These were then ignited and a self-sustaining reaction proceeded to completion. Reacted compacts were crushed, sieved, and classified to give feedstock powders in size ranges of 10-45 µm and 45-75 µm. All powder was characterized prior to spraying based on particle size distribution, x-ray diffraction (XRD), and scanning electron microscopy (SEM/EDS). Thermal spraying was performed using both H2 and C3H6 as fuel gases in a UTP/Miller Thermal HVOF system. The resulting coatings were characterized by SEM and XRD analysis, and the microstructures correlated with powder size and spray conditions. Abrasive wear was determined by a modified 'dry sand rubber wheel' (DSRW) test and wear rates were measured. It has been found that wear rates comparable to those of HVOF sprayed WC-17wt% Co coatings can be achieved.

Coatings have been produced by HVOF spraying of four different WC-Co powders, using two fuel gases and two oxygen contents in the flame, and characterised in terms of microstructure and resistance to abrasive wear. It is concluded that there is a close correlation between high levels of chemical reaction, occurring during spraying (and possibly during powder production), and poor wear resistance. Good wear resistance is favoured by using low porosity powders, which interact with the atmosphere less readily during spraying, and also by using a flame with a relatively low oxygen content. This probably minimises the degree of reaction by ensuring that conditions are reducing. Use of propylene rather than hydrogen gives coatings with slightly better wear resistance, despite the fact that the flame temperatures are higher. It is concluded that, for this relatively small rise in temperature, the positive effect on inter-splat cohesion seems to outweigh the negative effect of increased decarburisation.

In the course of this investigation, thermal spraying with different fuel and shroud gas combinations was investigated in terms of its effect on the in-flight particle properties (temperature, velocity) and on the final coating properties (coating thickness, porosity, oxygen content and corrosion behaviour). Independent on the shroud gas, the particle in-flight temperature and velocity were highest when using ethylene as fuel gas and lowest when using propane. Methylene resulted in intermediate properties. The change in the shroud gas from air to nitrogen generally resulted in lower in-flight particle temperatures and also lower velocity. The coating properties in terms of porosity and oxygen content directly correlated to the particle in-flight properties. With decreasing velocity and increasing temperature, the porosity and the oxygen content increased, respectively. The corrosion behaviour of the nickel coatings was studied in 0.5 M sulfuric acid media by means of potentiodynamic polarization curves. Good corrosion properties were observed when methylene and air served as fuel gas and shroud gas, respectively.

The trend in thermal spraying is more and more towards a globally uniform level of high-grade spray coatings. It is therefore extremely important that auxiliaries such as spray materials or industrial gases undergo precise examination in order to exactly define their influence. Based on their application, these auxiliary materials can always be supplied at the required purity level. In order to guarantee such high levels, the gas industry invests a great deal in analysis and supply concepts which ensure this purity from the tank or cylinder through to the point of delivery. A further point is of particular significance in today’s business world. With ever-increasing raw material prices, it is absolutely essential that spray processes are optimized to the maximum. This is not only made possible by selecting the right system, but also by choosing the right gas and gas mixture.

The trend in thermal spraying is more and more towards a globally uniform level of high-grade spray coatings. It is therefore extremely important that auxiliaries such as spray materials or industrial gases undergo precise examination in order to exactly define their influence. A further point is of particular significance in today’s business world. With ever-increasing raw material prices, it is absolutely essential that spray processes are optimized to the maximum. This is not only made possible by selecting the right system, but also by choosing the right gas and gas mixture. The optimization of costs, extended lifetime of systems and tailoring of coating properties to suit specific applications are just some of these influencing variables. Gas producers test countless facilities and thermal spray systems in their own laboratories and are therefore always in a position to provide the right solution for existing and new applications.

Equipment engineering, materials, gases and know-how are integral to the smooth operation of any system. The user often focuses on the attributes of the individual systems, but it is only in conjunction with all their components that the merits of the process can be exploited to the full. Here, industrial gases serve as essential building blocks which positively affect the process in an endless variety of ways. The optimization of costs, extended lifetime of systems and tailoring of coating properties to suit specific applications are just some of these influencing variables. Gas producers test countless facilities and thermal spray systems in their own laboratories and are therefore always in a position to provide the right solution for existing and new applications.

Not least because of the multitude of the possibilities which this process has to offer, has thermal spraying established itself in an extremely wide range of industrial sectors. In quest of new applications, special attention is frequently paid to the properties of individual systems. However, the trumps of the process can only be played out in combination with all the components as a whole. In industry nowadays, it is often the costs alone which are hotly disputed, and especially so when it comes to industrial gases. Yet precisely here infinite opportunities present themselves to positively influence the process. Starting with the optimization of costs, followed by the lifetime of the systems, through the variety of coating properties which can be tailored to the application, the influencing variables are endless. Investigations into this potential are already in full swing. Powder manufacturers are testing the many possibilities in their laboratories and have put their heads together with the R&D departments of hardware and gas suppliers in an effort to continually broaden the coating spectrum.

Being able to offer a consistently high level of spray coatings on a global scale has become more and more the trend in thermal spraying. For this reason it is extremely important that auxiliary materials such as industrial gases or spray materials of a high quality are provided world-wide. In connection with their respective applications, industrial gases must always be available at a specified purity level. In order to ensure such a purity, industrial gas producers invest a great deal of time and energy in analysis and supply concepts which guarantee this purity from the tank or cylinder through to the transfer point. This paper will provide an overview of state-of-the-art supply and purity concepts, as seen by the gas industry, and the influence of fluctuating gas quality. Examples will also be given for the differing gas qualities in individual countries.

High velocity oxy-fuel (HVOF) experiments were carried out with Diamond Jet (DJ) 2600 and 2700, P-5000, Jet Kote and Top Gun to investigate the influence of the spray system and of the spray parameters on microstructure and properties of Cr3C2-NiCr coatings. The results show that with all applied HVOF systems Cr3C2-NiCr coatings of high density, high bond strength and high wear resistance can be produced. However, microstructure and properties of the coatings mainly depend on the degree of oxidation and carbon loss of the material during the spray process. Due to the relatively low heating of the spray material the decarburization of CrsCa-NiCr was found to be very low using the HVOF systems DJ 2600, DJ 2700 and JP-5000. Additionally favored by the increased particle velocities coatings sprayed with the Diamond Jet systems and the JP- 5000 exceed coatings produced with the traditional HVOF systems with regard to hardness, wear resistance and bond strength.

Gas and Liquid fuel HVOF thermal spray torches have been commercially available for the past 20 years. These torches have different fundamental operating characteristics, such as gas flows, exit gas velocities, and thermal efficiencies. This paper will examine the fundamental operating and design characteristics of the Diamond Jet, WokaJet, JP5000, and WokaStar HVOF torches. Results for total heat input to the torch, thermal efficiency, and design conditions are presented.