HVOF processes represent the state of art for the spray deposition of wear and corrosion resistant coatings since their supersonic gas velocities in combination with moderate flame temperatures allow the deposition of optimal coatings with very high bond strengths, fine surface finishes and low oxide levels. However, new generation coating materials (fine powders), stringent quality requirements and the high productivity demanded by the industry, push the HVOF technologies to their limits. Recently, a novel air-oxygen controlled high velocity combustion process has been development by Tecnalia. The system operates within the supersonic regime using a broad range of fuel/oxidant ratios thanks to the use of air-oxygen mixtures and a carefully optimized gun design. Extremely low flame temperatures can be achieved while keeping a supersonic flow of combustion products, thus allowing the solid state deposition of almost all industrially relevant metal alloys with superior deposit qualities. In this work, a systematic investigation of the influence of the powder particle size and gun configuration on resulting coating microstructural features has been performed. For comparison, two fine structured commercially available WC10Co4Cr powders with different particle size distributions have been investigated. The coating structure has been characterized with by high resolution SEM cross-section imaging and X-ray diffraction analysis. Resulting coatings are characterized by highly dense structures, a high retention of the primary carbides, average microhardness of up 1885 HV0.3 and fracture toughness varying between 3 and 7 MPa.m -1/2 depending on the powder particle size distribution and the process conditions used.

An air-oxygen controlled high velocity combustion spraying process has been developed that uses a special HVOF gun and a broad range of fuel-oxidant ratios. Extremely low flame temperatures can be achieved while maintaining a supersonic flow of combustion products, thus allowing the solid state deposition of almost all industrially relevant alloys. This work deals with the development of superhard cermet coatings using conventional and fine WC-Co(Cr) powders, optimized spray parameters, and different nozzle geometries. Results are compared based on coating microhardness, toughness, and sliding wear resistance.

The Oxy-Fuel Ionization system (OFI) is a new thermal spray process which consists basically on a high velocity combustion process enhanced by a low energy plasma source. The system is characterized by its stability over a relatively large range of fuel/oxidant conditions, the possibility to use poor fuels like natural one (with low gas consumption) and the high deposition rates that can be achieved in comparison to conventional HVOF guns. The OFI gun has been designed following a modular concept, which in combination with the high flexibility of the system is expected to allow the deposition of coating materials with the most different physical and chemical natures. This work deals with the experimental analysis of the process using methane as fuel gas and its correlation with the deposition of WC-base materials. Two in-flight particle diagnostic systems were used: the Spray Watch diagnostic system (from OSEIR) and the Spray and Deposit Control (SDC) system (developed by the SPCTS laboratory of the University of Limoges). Results are presented for the most representative properties of the optimized coatings (micro hardness distributions on the coating cross section and crystallographic analysis).

The high frequency pulse detonation (HFPD) process has shown to be a cost effective spray technique for the deposition of highly dense and erosion resistant YSZ ceramic coatings. In comparison to the coatings produced by conventional APS, a significant improvement of the wear performance can be achieved by the HFPD process as result of the high coating compactness. This work deals with the deposition of different ZrO 2 and Al 2 O 3 based ceramic powders by the HFPD technique, for the development of highly dense and wear resistant ceramic layers. During this development, the gun configuration and the process parameters (gas flows, explosion frequency, spray distance and cinematic conditions) have been optimised to get the best deposition performance. The resulting coatings have been characterised in terms of the microstructure, the microhardness and the sliding wear performance under dry conditions. In comparison to the plasma sprayed coatings produced with equivalent process conditions, the coatings deposited with the HFPD process are significantly harder and their sliding wear resistance is two–three-fold higher for YSZ coatings and five-six-fold higher for Al 2 O 3 coatings. Furthermore, the HFPD process is able to produce highly dense and hard functional coatings in one spray pass, suitable for wear protective applications.

Different YSZ powders have been deposited by the high frequency pulse detonation (HFPD) thermal spray process leading to highly dense and hard coatings in comparison to standard APS zirconia layers. During this development, the gun configuration and the process parameters (gas flows, explosion frequency, spray distance and cinematic conditions) have been optimised to get the best deposition performance. In order to explore the potential of the HFPD system to process YSZ base materials, different type of commercial spray powders (agglomerated, fused & crushed, fully or partially stabilized compositions) and size distributions, have been investigated and the resulting coatings characterized. A qualitative comparison of the coating performance at elevated temperatures is presented and discussed. For this purpose, an experimental set-up was designed. Potential applications of these types of zirconia coatings in advanced thermal barrier coating systems, high temperature wear protection or ionic conductors (sensors and fuel cells) are discussed.

Structuring coating materials in the nanoscale can significantly enhance the performance of Fe-based coatings. Nanostructured steel coatings with a very high hardness, the strength of carbon-based fibers and a corrosion resistance superior to nickel-based super alloys are currently commercially available. This work deals with the development of wear resistance nanostructured coatings using a commercial steel powder by high frequency pulse detonation. Results concerning the deposition of this powder using two different high velocity oxy-fuel spray systems are presented for comparison. The process parameters were optimized on the basis of the achieved coating features hardness, thickness, porosity and surface roughness. The microstructure of the coatings achieved with the different systems as well as the resulting adhesion and cavitation erosion resistance are compared. These results are also compared with the performance of standard WC-CoCr coatings.

This paper demonstrates the capabilities of a new thermal spray process based on cold gas spraying and detonation gun technology. The method, called high-frequency pulse detonation, uses combustion pulses to heat powders to a temperature that allows good substrate-layer adhesion without the powder being melted. Superalloy, copper, and steel layers so produced are examined and compared with layers deposited by conventional thermal and cold spray processes. Paper includes a German-language abstract.

Ceramic oxides can be deposited by the High Frequency Pulse Detonation process leading to coatings with unique properties as result of simultaneous melting and high velocities of the sprayed particles. In this paper, several Al 2 O 3 based powders have been HFPD sprayed and the resulting coatings characterized. For this purpose, microstructural evaluation, XRD phase analysis and functional behavior (dielectric strength and wear resistance) have been tested.

A combination of pulsed combustion and advanced thermal spray technology has led to the development of the novel High Frequency Pulse Detonation (HFPD) spray technology by Aerostar Coatings. In the HFPD process, the flow of gaseous products from cycled explosions in the spray gun, is used to accelerate and heat the spray particles. This paper provides a fundamental description of this cyclical process, with the main differences to spray processes with stationary flow and also to traditional detonation spraying techniques in the center. Paper includes a German-language abstract.

The High Frequency Pulse Detonation (HFPD) thermal spray process represents a novel cost-effective alternative for the production of premium quality coatings. In this paper, the HFPD spray technique is characterized by very flexible capabilities which allow to deposit a wide range of materials according to different specifications. The spray parameters are carefully selected and adapted to the respective material or specification. The qualitative effect of each parameter on the coating properties and the reliability of the system are checked. Examples of different coatings are presented. Paper includes a German-language abstract.