In this work, a low-temperature melting composition located within the glass-forming region of the Y 2 O 3 -Al 2 O 3 -SiO 2 (YAS) system is proposed and tested as a protective coating for SiC ceramics. Glassy coatings 197 µm thick were obtained by flame spraying YAS granules on SiC substrates that had been grit blasted and coated with a Si bond layer. Bulk glasses of the same composition were also produced for use as a reference material. The hardness, elastic modulus, and thermal conductivity of the coatings and bulk specimens were evaluated and compared and the effect of heat treatment was investigated. Crystallization occurred in both the bulk glass and coating during isothermal treatments in air at 1100-1350 °C, but it did not compromise system integrity due to crack healing.

Sensor technology is becoming more of a production tool to help improve production quality, reliability and reduce manufacturing costs. Combustion sprayed abradable seal products are a family of materials where this technology will be helpful to the applicator and end user. Although these materials have been used for over forty years with wide success in the aerospace and industrial gas turbine industries they can be sensitive to spray process variables. Changes in spray processing conditions during spraying will change the desired microstructure and coating properties. This paper looks at a commercially available combustion powder and how process parameters such as gas flows and powder feed rates affect output process variables such as particle velocity and temperature. This paper will also discuss the importance of understanding the influences that particle temperature and velocity have on coating properties such as hardness, erosion and coating strength. Deposit efficiency of these combustion powders is also measured as a function of particle temperature and velocity. Based on particle temperature and velocity, sensor diagnostic tools can provide warnings about process changes resulting in fast corrective action. The benefits of this sensor technology are the potential for less inspection requirements, improved microstructure control, reduced in-service failures, and less time and labour required for stripping coated components that may not meet specification standards.

The combustion assisted thermal spray systems are being used to apply coatings to prevent surface degradation. They offer a highly attractive way to modify the surface properties of the substrate to extend the product life. The quality of combustion assisted thermal spray coating depends greatly on the flow behavior of reacting gases and particle dynamics. The present study investigates the effect of gas phase and its interaction with particles through the nozzle of a thermal spray gun by developing a comprehensive mathematical model. The objective is to develop a predictive understanding of various design parameters of combustion assisted thermal spray systems. The model was developed by considering the conservation of mass, momentum and energy of reacting gases. The particle dynamics was decoupled from the gas phase dynamics since the particle loading in the spray process is very low. The developed model was employed to investigate the influence of various design parameters on the coating quality of thermal spray process.

The High Velocity Continuous Combustion (HVCC) Spray System was invented in 1993. The HVCC process uses wire as a consumable feedstock. Atomization takes place in a supersonic air jet, which is produced using a converging-diverging nozzle arrangement. The arc point is located within this supersonic air stream, which produces extremely finely atomized particles averaging 30 µm in diameter. The morphology of the HVCC produced coatings are homogeneous and consist of flat splat platelets with thin, adherent oxides. Permeation by gases and liquids through coating structures is significantly lower than that typically seen for twin wire arc spray coatings. Wear and erosion resistance of materials are significantly better than the same material applied with twin wire arc spray. The HVCC process has been successfully deployed over the past 7 years. It has been successfully used in confined space, in-situ applications, where traditional High Velocity Oxy-Fuel (HVOF) processes cannot be used for reasons of safety and practicality. These include applications in the petrochemical, paper and pulp, utility and independent power generating industries. Many other more specialized workshop and in-situ applications have also been performed with success.

This paper investigates the microstructure and corrosion resistance of Hastelloy C-276 and 316L coatings produced by various thermal spray methods, including arc spraying, flame spraying, HVOF spraying, and a recently developed method called high-velocity combustion wire spraying. The microstructures of the coatings were examined before and after corrosion testing in order to gain information on corrosion mechanisms. Several corrosion tests were performed on each sample and various coating properties were measured including thickness, hardness, oxygen content, porosity, and adhesion strength. Test results for sealed coatings and detached layers are also presented in the paper, giving additional insight into corrosion behavior. Paper includes a German-language abstract.

A computational model of the effect of the tail end of the flame on the temperature of polymer coatings during thermal spraying is presented. The low thermal conductivity of polymers results in a substantial build up of temperature at the surface of the coating and large temperature gradients are developed throughout its thickness. This is particularly problematic for polymer deposition owing to their low decomposition temperatures. The model quantifies the heat transfer from the impinging flame and the in-coming feedstock particles to the coating and the subsequent heat flow into the substrate and surroundings. The work shows that the heat input from the in-coming particles can be neglected in first-order computations. The scanning action of the flame across the substrate is simulated and the temperature profiles within the coating and substrate are calculated. The predictions are consistent with the experimental measurements. The model shows that overheating of polymer coatings can readily occur during combustion flame spraying and indicates remedial measures.

Cored wires show a high potential for production of protective coatings for combined corrosion and wear applications. Iron and nickel based grooved cored wires without and with different reinforcing carbide fillers have been sprayed by arc- and high velocity combustion wire (HVCW) spraying with a Praxair Type 216 gun. Depending on the wear mechanism coatings with a similar abrasive or oscillating wear resistance like HVOF WC/Co/Cr 86/10/4 have been produced. For effective protection against oscillating wear wires with a large diameter and therefore a high content of reinforcing carbide filler have to be applied. All nickel based coatings with chromium addition show an improved corrosion resistance compared to HVOF-sprayed WC/Co/Cr 86/10/4. For coatings from wires with NiCr 80/20 velum no effect of severe sulphurous corrosion in the DIN 50018 test is observed. HVCW-spraying is especially suitable, when only a low degree of interaction between velum and filler material is wanted as for cermet-like coatings. Conventional arc-spraying rather meets the demands of a high degree of interaction between velum and filler necessary for the production of pure metallic coatings like NiCrBSi. All manufactured coatings show good machinability.