Search Results for utsc

The UTSC '97 saw the release of a new wave of HVOF related technologies with the promise of high quality coatings allied to lower costs and simpler operation. This trend was seen by some experts as signifying the future of HVOF development. The emphasis was on increasing the cost effectiveness/competitiveness of HVOF coatings and making the technology more attractive to the general coatings market. One route was to use microchip technologies to control the process therefore reducing operation involvement in addition to reducing parts and system cost. Further features included using higher oxygen inlet chamber pressures for higher quality and higher deposition rates. The more compact and portable designs also allow HVOF to expand into field applications and a lower capital cost enabled non-specialists to adopt HVOF. This paper summarises the significant features of this technology wave in the light of practical operational experience and applications. One key to the success of the technology has been its correct matching to the coating type and application. Total coating cost analysis is performed to highlight its economic benefits and there is a comparison with other established forms of coating such as chrome plating, plasma and combustion spraying. This includes a description of the coating quality and wear performance.

Preface (in German and in English) for the United Thermal Spray Conference 1999.

Preface for the United Thermal Spray Conference 1997. Includes a publishing history for proceedings from previous thermal spray conference events.

The damaging of the electrodes during spraying can affect the reproducibility of the plasma spray process. Indeed, this may influence the plasma characteristics and the energy transfer to the sprayed particles resulting in significant changes in the coating attributes. In this paper, results from a detailed investigation on the stability of plasma spraying are presented. Specifically designed diagnosis tools were used to study the evolution of key parameters of a plasma spray process during a long-term experiment. A comprehensive analysis is carried out on the collected set of data, with an emphasis on the correlation that may exist among them. Results show significant variations in the particle state and gun characteristics with the spraying time. These variations are reflected in the microstructure of the sprayed coatings. The investigation also gives some indication on how the spray process could be controlled.

Listing of the organizing committee for the United Thermal Spray Conference 1997.

This paper shows how in-flight particle diagnostics can be used to optimize parameter sets for new layer materials and to detect drift in the control of thermal spraying lines. It describes the equipment and methods used to measure the temperature, velocity, and diameter of spray particles in a plasma jet and explains how torch current, plasma gas composition, carrier and total gas flow, and stand-off distance are varied according to a statistical design plan to determine their effect. The results are presented in the form of process maps and data plots, from which several conclusions are drawn. Paper includes a German-language abstract.

Three actual applications of spray plume sensors for industrial coating operations are presented. Two of these are in the aeronautic industry and one in the automotive industry. Depending on the application, different types of sensors were used ranging from plume shape monitoring (particle trajectories) to full plume characterization including in-flight measurement of individual particle properties. In each case, the process monitoring scheme developed depended on the manufacturer's requirements as well as the nature of the information provided by the sensor. The significant differences in usage and working conditions compared to an R&D environment are examined. Advantages and drawbacks in each of the three situations are detailed. A tentative forecast of coming developments in this field is also given.

Revealing the true properties is of utmost importance for the optimized use of thermal sprayed coatings and for the realization of the ultimate spray booth. The necessity of the true properties for a successful correlation as well as development of process windows for on-line control cannot is emphasized. Only the true properties can be expected to correlate to the spray parameters or the particle properties in the flame. What is actually meant when stating the following? - The coating has 5% porosity - Tensile bond is 50MPa - Hardness is 1000HV - Coating thickness is 100 nm Different loopholes during the steps of metallographic preparation, hardness and tensile bond strength testing are highlighted and discussed. The microstructure of a thermally sprayed coating typically consists of a multiphase matrix (often a mix between hard, soft and amorphous), pores, oxides, delaminations, cracks, grit residues and unmelted particles. Due to this complexity in the structure there are a number of possible errors that often can be made in metallographic laboratories. Several examples and explanations are given. It is shown that improper handling in the materials laboratory may lead to smearing and pullouts etc. This will ruin the results and effectively hide the true microstructure. Furthermore the use of different epoxies and curing methods effectively varies the tensile bond strength test results by more than 300% for various coatings. By using different preparation routines the micro hardness can be varied by more than HV 0.3 100.

In this paper, two long-term experiments are conducted in order to investigate the evolution of the arc root fluctuations and the evolution of the in-flight particle state during plasma spraying. Voltage as well as the acoustic fluctuations measured at three different angles are characterized while particle state was monitored using an optical integrated system, the DPV2000. A detailed study of the evolution of the gun power, in-flight particle state (temperature, velocity, diameter, particle flux) and coating microstructure is was carried out. Results showed that the microstructure of the deposited coating significantly changed during the forty-hour spraying period. Paper includes a German-language abstract.

This paper assesses the abrasion resistance of plasma and HVOF sprayed WC-Co and Cr 3 C 2 coatings under dry friction conditions. It is observed that WC-Co layers produced by HVOF spraying have the most regular layer structure, the best abrasion resistance, and the highest hardness. Paper includes a German-language abstract.

Studies on atmospheric plasma spraying have generally focused on the influence primary parameters such as gas flows and plasma current. However, the APS process is also influenced by a large number of disturbance variables including electrode wear, cooling system irregularities, and disruptions in powder injection. This study investigates both the cause and effect of each of these factors in the context of aluminum oxide spraying. Numerous measurements are made showing how electrode wear, cooling fluctuations, flow measurement inaccuracy, and variations in powder feed rates affect in-flight particle characteristics, deposition efficiency, and layer thickness. Paper includes a German-language abstract.

HVOF-sprayed stainless steel coatings are potential candidates for protection against water corrosion. However, the process parameter "window" leading to acceptable corrosion behavior has yet to be determined. With potentiodynamic tests, this paper examines the corrosion behavior of metallic, thermally sprayed coatings under carefully controlled conditions in order to gain an insight into their performance "in service". The influence of the variations in the fuel:oxygen ratio, in the total gas volume and in the spraying distance, on the corrosion process of HVOF-sprayed stainless steel coatings on steel substrates with a low carbon content is determined by means of potentiodynamic measurements. The results are correlated with a characterization of the microstructure to understand the influence and role of oxide content, porosity, and coating morphology. Some comparisons with VPS coatings are also made. Paper includes a German-language abstract.

In this paper, the corrosion characteristics of two HVOF-sprayed coatings made with self-fluxing NiCrSiB powders are assessed in the as-sprayed condition. One of the coatings is also investigated after post-spray treatment with polymer sealing and after vacuum furnace fusion. It was found that cracking at lamellar boundaries dominates the corrosion behavior of the layers in the as-sprayed and sealed states, while pitting corrosion resulting from the failure of hard phases plays the main role in the melted layer. Paper includes a German-language abstract.

This paper describes the production of self-lubricating chromium carbide-nickel coatings using the HVOF spraying process. The present work deals with the preparation of Cr 3 C 2 -Ni + CaF 2 multicomponent powders and to spray them with a minimum loss of the CaF 2 solid lubricating phase. The powders are processed by atomization with subsequent sintering and qualification processes. The microstructure of the powder and resulting layers is characterized by SEM. The content of calcium fluoride in the sprayed layer is determined using the EDS method and compared with its content in the spray powder. Wear resistance is measured using a rubber wheel tester. Paper includes a German-language abstract.

Silicates represent a broad group of industrially important ceramic materials. The only silicate that is widely used for plasma spraying is zirconium silicate. Other silicates are generally not used, although they can offer interesting application properties. This paper presents results with other silicates: synthetic wollastonite, stoichiometric mullite, cordierite, and steatite. The input materials were produced in selected sizes from ceramic in industrial quality and applied with the water-stabilized plasma spray system PAL160 to form free-standing panels. The morphology of the microstructure, the thermal expansion, the bulk and filling densities, the open and closed porosity, the phase, and the chemical changes were evaluated. Paper includes a German-language abstract.

The aim of this work is to study the adhesion of WC-Co coatings using acoustic emission testing. The coatings were produced by HVOF spraying then subjected to four-point bending while in situ acoustic emission measurements were made. The test specimens were then examined under a microscope, revealing regularly spaced transverse cracks on the coating surface as well as interfacial cracking. An analysis of the acoustic emission data revealed two types of acoustic events based on absolute energy and amplitude. This appears to be linked to the cracks that were observed forming the basis for an interfacial cracking model.

Since plasma jets, which have been used as heat sources of thermal plasma spraying process, expand adiabatically under a low pressure environment, the plasma temperatures drastically fell down to 2000K at the nozzle out let at 30Pa chamber pressure. However, the plasma jets still had enough reactivity to form hard nitride layer on the surface of the titanium samples by only a few minutes treatment. In this study, in order to obtain useful information for the practical applications of this plasma as low temperature and high rate surface modification processes, nitriding of nitriding steel and carbon steel using supersonic expanding hydrogen/ nitrogen mixture plasma jets were carried out. Consequently, though surface hardening was occurred slightly in the case of carbon steel, surface hardening was obviously promoted in the case of nitriding steel. In both cases, surface hardening was promoted with increasing hydrogen flow rate and thermal damages of the samples due to heat transfer from plasma jets weren't observed. Besides, according to the results of wear testing, wear mass loss of nitrided samples were much lower than that of non-nitrided samples. From these results, this process was found to have a high potential even in the case of surface modification of steel materials.

This paper introduces a new three-cathode plasma burner and explains how it functions in comparison to conventional plasma guns. Paper text in German.

The tribological behaviour of WC-Co-Cr coatings deposited by HVOF and HVAF and WC-Co coating deposited by HVAF was investigated in pin-on-disc tests. Wear rates were determined and wear tracks on the coatings and counterbodies were investigated in SEM. The HVAF sprayed coatings showed greater wear resistance compared to the HVOF coatings. The main wear mechanism in the WC-Co coatings was adhesive wear. The cobalt matrix is lubricious, resulting in very low wear rates and low debris generation. The main wear mechanisms in the WC-Co-Cr coatings were adhesive and abrasive wear. Adhesive wear results in pull-outs that are trapped in the contact zone and act as a third-body abrasive. Particle pull-out of the coating significantly increases the wear rate of the coated specimen. The HVAF WC-Co-Cr coatings proved to have a better resistance to particle pull-out which reflected in a considerably lower wear rate than the HVOF WC-Co-Cr coatings.

This paper presents a simulation of the simultaneous spraying of a metal and a ceramic powder with different configurations for the injection of the powder into the plasma jet. The plasma jet and the behavior of the injected particles were modeled with a commercially available computational model of the dynamics of liquid bodies. The particles are modeled as discrete Lagrangian objects. Three series of numerical tests were carried out: simultaneous spraying of the powder in a three-dimensional plasma jet in a stable state; simulation of the 3-D plasma flow, assuming that it fluctuates at the same frequency as the arc voltage; and simulation of the effect of the current fluctuation on particle behavior. A pre-calculation with an analytical model made it possible to determine the suitable gas flow rate so that the "average" trajectories of the metal or ceramic powders coincide at the same point on the surface. Paper includes a German-language abstract.