Abstract Environmental protection and worker safety measures against hard chrome plating are increasing and leading many industries to adopt alternatives. HVOF thermal spray technology for applications of tungsten carbide based coatings have proved to be more environmentally friendly and effective than hard chrome. In this study, the results of wear tests for WC-12%Co sprayed coatings deposited onto AFNOR 25CD4 low carbon steel are compared to those for hard chrome. It was shown that WC-12%Co coatings exhibit the adequate tribological properties compared to those of electrodeposited hard chrome.

Abstract The laser-flash method is used to determine the thermal diffusivity of HVOF sprayed WC-Co(Cr) and Cr 3 C 2 -Ni20Cr as well as APS sprayed Cr 2 O 3 and electroplated hard chromium coatings in the temperature range between RT and 600°C. Additionally bond and/or corrosion protective coatings like Ni5Al, Ni20Cr and 316L are characterized taking into account the different manufacturing methods twin wire arc spraying, HVCW and HVOF. With respect to the application example of drying rollers in paper industries the Taber-Abraser wear test is applied to evaluate the wear resistance. Finally the coatings are characterized concerning their corrosion resistance by salt fog test and by exposure to humid SO 2 environment. For WC-CoCr feedstock the effect of carbide size and micro hardness on thermal, wear and corrosion properties are studied. WC-CoCr coatings with maximum micro hardness and fine carbides show the best thermal conductivity. The use of coarse carbide feedstock permits manufacturing of coatings with the highest resistance against dry abrasive wear, but the protective function depends severely on the processing conditions.

Abstract HVOF cermet layers are increasingly viewed as an alternative to galvanic hard chrome layers for applications with high demands on wear and corrosion protection. The WC-Co-Cr layer is one of them. The WC-Co-Cr layers were produced with different HVOF systems: Jet-Kote, Diamond Jet, and JP5000. With all three systems, dense and well-adhering layers could be produced. This article considers HVOF sprayed WC-10Co- 4Cr as a generic coating type for replacing hard chrome plating. The friction, wear, adhesion, and corrosion performance of the HVOF WC-10Co-4Cr coatings are compared against the performance of a commercial hard chrome coating system. The article also evaluates effect on the coating adhesion of corrosion through the coating and penetrating along the interface at the coating edge. Paper includes a German-language abstract.

Abstract This paper compares the corrosion resistance of WC-10Co-4Cr layers, which were produced by means of the y high-velocity oxygen-fueled (HVOF) method and the electrolytic hard chrome (EHC) plating process, whereby two test methods were used: salt spray test according to ASTM B117 and electrochemical measurements in salt water. The test bodies consisted of HVOF samples, EHC samples, and two low alloy steel substrate materials, namely AerMet 100 and 300M. The corrosion resistance of the layer systems is determined in accordance with ASTM B537 in the salt spray tests and by polarization-voltage printouts in the electrochemical investigations. After the end of the test, a metallographic evaluation is carried out to understand the failure mechanisms. The following parameters are discussed: the HVOF spray parameters, the corrosion test results according to ASTM B117, the electrochemical measurement results, and the metallographic findings. Paper includes a German-language abstract.

Abstract Airline and printing industry are looking for new techniques to replace electrolytic chrome plating in their machinery because of the toxic and carcinogenic characteristics of hexavalent chromium used in the ECP. Hard chrome platings are compared to thermal sprayed coatings and different techniques are shown. The article gives examples of Hard chrome replacement in printing applications, shows activities of government, airline and textile industries. Different types of coatings, produced with different spraying techniques, are compared in wear and corrosion tests. The results lead to an economical evaluation of HVOF sprayed alternative coatings and gives a hint to the HCAT-Program.

Abstract The aerospace industry currently applies high velocity oxy-fuel (HVOF) coatings to turbine engine, structural, and landing gear components. An increasing demand for HVOF wear resistant coatings to replace electrolytic hard chrome (EHC) on landing gear components has renewed focus on the spray limitations of HVOF WC/CoCr. One such limitation resulting from the line-of-sight HVOF process is the spray angle. In this study, HVOF WC/CoCr coatings were sprayed at several angles while maintaining consistent combustion characterisitics and standoff distance. The measured responses included tensile bond strength, microhardness, residual stress, coating surface roughness, and dry fretting wear resistance. Fatigue response was also of interest, but no results were available at the time this paper was written. The microstructure of each coating was examined, both normal to the surface and in cross section. Coatings sprayed at 90° exhibited the highest microhardness and most compressive residual stress, both considered favorable for good wear response. But these coatings also exhibited the highest as-sprayed roughness, least homogeneous microstructure normal to the surface, and lower wear resistance compared to the off-angle coatings; however, the off-angle coatings apear to cause greater wear of the contacting surface. The microstructural differences among the coatings are related to the measured responses.

Abstract The increasing demand of the industry for high quality coatings with a low cost aspect has led to the development of ultra thin, nearby finishing free carbide coatings. The R&D work performed for this publication was focused on the tailoring of carbide powders together with the development of a new generation of HVOF-Systems working on higher combustion chamber pressures. An as-sprayed surface roughness of less than 1,5µm has to be envisaged for a thin nearly finishing free coating. Therefore, the starting powder has to have fine particles size with a homogenous distribution of carbides and matrix metals. To ensure the corrosion resistance, the matrix metals have to be completely alloyed and the coatings have to be dense. The used HVOF-System must be able to feed and spray these fine powders without any blockage of the powder feeder or nozzle clocking. The coating quality has to fulfil the requirements of hardchrome plating as wear and corrosion resistance is concerned. The low cost level of thin hard-chrome coatings shall be matched. The suitability for using this coating on applications like hydraulic cylinders has been proven. Generally, this technique of thermal spraying can be used as a hard-chrome alternative as well as for new applications where thermal spraying was not put into account due to cost and technical reasons. The aim was to fill the gap between thin film technologies as PVD or CVD techniques and conventional thermal spraying. The new technology enables the industry to coat large components with nearly no restrictions in size and for competitive prices.

Abstract This paper evaluates four tungsten carbide basecoats produced by thermal spraying with a high speed flame spraying system as potential candidates to replace hard chrome in applications subject to abrasive and/or corrosive conditions. It investigates the potential of using WC-based cermet coatings deposited using high velocity oxy-fuel thermal spraying to replace electrodeposited hard chromium. The paper shows that WC-based thermally sprayed coatings are available to replace hard Cr in many applications. Salt spray tests and electrochemical measurements in synthetic sea water showed that the Cr-containing coatings had the highest corrosion resistance. These results indicated that 10Co-4Cr-WC could be the best coating candidate for conditions in which both abrasion and corrosion are present. Paper includes a German-language abstract.

Abstract Based on successful developments in the field of high-speed flame spraying (HVOF) equipment, HVOF spray materials (powder), and HVOF process technology, this paper describes the increasing use of HVOF as a replacement for hard chrome plating. It presents the results of laboratory and operational evaluations of the HVOF-sprayed coatings as a replacement for hard chrome in the aviation industry. Paper includes a German-language abstract.

Abstract One candidate alternative to chrome plating and hard anodizing is a tungsten carbide (WC) coating applied by the High Velocity Oxy-Fuel (HVOF) process. HVOF WC coatings are currently being evaluated in many service life tests, including fatigue. The purpose of this paper is to compare the fatigue life of HVOF WC coated specimens with the fatigue life of hard anodized and bare aluminum specimens. This work examines WC thermal spray coatings as candidates for replacement of hard chrome plating and hard anodizing in aircraft and helicopter applications such as landing gear. In fatigue testing, the results showed an expected fatigue deficit for hard anodizing as compared to bare aluminum. Paper includes a German-language abstract.

Abstract The demand for better paper qualities and for higher speed of the paper web requires a constant technological development of the existing calendering process. An important factor in modern calendering is the heated metal roll. Its surface has an important influence on the gloss and the smoothness of the paper. During operation these rolls are heated to temperatures of up to 200°C. Additionally, the rolls are exposed to severe abrasive wear by fine hard filler materials and to corrosion by the moisture of the paper. The SUMECAL coating systems - especially developed for calender rolls - surpass the hard chromium platings by far regarding the scratch and wear resistance and demonstrate better calendering properties. Paper text in German.

Abstract Tungsten carbide thermal spray coatings have been used for more than twenty years in the commercial aircraft industry in applications such as turbine blade and flap-track wear surfaces. Additionally, the evaluation of tungsten carbide (WC) coatings to replace chrome plating in other aircraft applications has been underway for several years. For example, WC coatings applied by the high velocity, oxy-fuel (HVOF) process are being evaluated for use on aircraft landing gear parts. One factor that affects the suitability of WC coatings is the fatigue life of the coated part. This study compares the fatigue life of electrodeposited chrome plated specimens to the fatigue life of WC HVOF-sprayed specimens on aircraft landing gear alloys. Fatigue tests were run on cantilever flat beam specimens coated on one side and subjected to bending fatigue loads. Residual stress levels for the coatings were determined using the Modified Layer Removal Method on rectangular residual stress specimens processed with the flat beam specimens. Also, the Young's modulus and Poisson's ratio of the coating were determined using the Cantilever Beam Bending Method performed on beam specimens that were processed with the fatigue specimens and the residual stress specimens. Results indicate that certain levels of residual stress in the coating can enhance the fatigue life of the parts. The fatigue lives in bending tests of several WC coated specimens are compared with the fatigue life of chrome plated specimens.

Abstract High-velocity oxyfuel (HVOF) spraying is a viable alternative for hard chrome plating because of its excellent coating properties and substantially lower environmental pollution. Initial applications in ball valves, journals, and hydraulic cylinders on earthmoving equipment have proven successful. This paper discusses the advantages and disadvantages of HVOF spraying as an alternative to hard chrome plating for aircraft components and presents some of the early results of laboratory and in-service testing.