Electrically conductive and flexible Aluminium coatings using powder and wire flame spraying were successfully deposited onto diverse textiles. The influence of different process parameters as well as the fabric materials on the electrical conductivity and microstructure of the metal-fabric composites were studied. Preliminary results show that in order to obtain excellent coating surface conductivity values, a specific coating quantity higher than 20 mg/cm 2 is necessary. After further optimization of the spraying parameters, a very good specific surface conductivity (~500 S i ) could be obtained even with reduced coating quantities. This corroborates that by performing an adequate parameter optimization a reduction of the specific coating quantity could be done while still keeping high conductivity values. Furthermore, when the coating quantity is reduced, the flexibility of the fabric substrates is better conserved. This study illustrates that optimized electrically conductive composites with flexible fabric substrates can be produced, without any preliminary thermal or chemical fabric specifications.

Flame sprayed Al-12Si coatings were produced onto the surface of composite castings parts in order to enhance the adhesion of such castings. Due to the high surface roughness and the presence of pores in the coatings combined with the formation of an intermetallic phase at the interface, the adhesion of flame sprayed composite castings could be enhanced by a factor of 2 in comparison to blank castings and by a factor of 1.3 when compared to sand-blasted castings. However, results also show that gaps are mostly present at the interface between the Al profiles and the flame sprayed coatings and these gaps have a negative effect on the adhesion values of the composite casting parts. Therefore, an optimization of the adhesion of the coating on the Al profiles through an optimization of both the sand-blasting and the flame spraying parameters would be beneficial for further enhancement of the adhesion of composite casting parts.

By cold spraying, coatings are produced without significant heating of the spray powder and the substrate material. The powder particles are accelerated in a preheated gas stream to velocities of more than 500 m/s without melting and form a dense and tightly bonded coating. Bonding occurs only due to plastic deformation and the heat created thereby. Due to the absence of melting of the powder particles during cold spraying, several negative phenomenon, such as oxidation and phase transformations associated with thermal spray processes, such as HVOF, arc, flame and plasma spray can be minimized or avoided. This paper presents an overview of cold spray process developments and of coating characteristics. A variety of metallic powders having a low or high melting temperature including Cu, Al, Ti as well as alloys were sprayed onto different substrate materials, and the microstructure and properties of the coatings were evaluated.

It is well known that thermally sprayed aluminum and aluminum alloys can be used to protect low-alloyed steel against marine corrosion in offshore applications. The efficiency and service life of this protection can be, however, severely limited by the amount and distribution of defects, which are usually present in coating microstructures. In thermal spraying, microstructures and properties are strongly influenced by the type of spray system used for the production of coatings. To investigate the influence of defects like pores, oxides and cracks on the corrosion performance, coatings were processed by conventional thermal spray techniques, such as Flame Spraying (FS) and Arc Spraying (AS). In addition, the more recently introduced High Velocity Combustion Wire (HVCW) spraying technique was used, which, due to higher particle velocities, results in lower porosity and finer coating microstructures as compared to conventional processes. The influence of spray conditions and related microstructures on the performance in corrosion tests was investigated for protective coatings of Al99.5, AlMg5 and Al - 30 wt. % W2C. The resistance against corrosion was analyzed by different electrochemical methods, such as corrosion potential monitoring, polarization resistance and potentiodynamic anodic polarization measurements. Additionally, the microstructures of the coatings were examined before and after the electrochemical tests. The results from these tests are correlated and attributed to the different microstructures obtained by the various spray techniques and different compositions of the feedstock material.

Various metals such as aluminum, copper, zinc, steel, nickel, titanium, and niobium have been deposited on a wide range of substrate materials via cold spraying. This paper provides a detailed overview of the cold spray process and the coatings typically produced. It discusses the powders and gases used, the dynamics of gas-particle flow in spray nozzles, the effect of temperature and pressure, and the concept of critical velocity. It also presents examples of the properties and microstructures recently achieved in cold sprayed aluminum, zinc, NiCr, MCrAlY, and Cu-Al coatings. Paper includes a German-language abstract.

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.

Thermal spraying of a nanograined WC-12Co cermet powder using high velocity oxy-fuel was employed to produce nanostructured coatings. The spray conditions were varied by employing a wide range of thermal spray parameter settings and using either hydrogen or propylene as fuel gas. By determining the characteristics of the spray jet for each set of spray conditions and by studying various aspects of the coatings, including the microstructure, properties, and performance in dry abrasion tests, conclusions were drawn regarding the effect of the spray parameters on the properties and performance. When comparing the effect of using hydrogen or propylene as fuel on in-flight particle characteristics, the results indicated that, for a given particle temperature, the particle velocity tended to be higher with hydrogen than propylene. As well, it was found that the coatings produced using hydrogen tended to have a higher microhardness and a lesser degree of carbide degradation. The resistance to wear in dry abrasion was significantly higher for coatings produced using hydrogen as fuel. For both series of coatings, it was found that the abrasion resistance increased with the particle temperature at the point of impact during thermal spraying and with the hardness of the coating. The abrasion resistance of coatings produced using propylene appeared to be much more sensitive to changes in hardness. For the thermal spray system studied in this work, the results indicate that nanostructured WC-12Co coatings having a maximum abrasion resistance are obtained by using hydrogen as fuel under conditions such that the particles achieve temperatures above approximately 1850-1900°C and a speed greater than 575-600 m/s.

WC-Co based cermets are extensively used in wear applications due to their hardness and toughness. Recent work has demonstrated the potential for using nanoscale constituents to improve the wear properties of these materials. In the present study, two WC-Co powders containing a nanosized WC phase were used to produce coatings by HVOF thermal spraying. These powders had similar properties except for the volume percent binder present: WC-8C0 and WC-12Co. The thermal spraying conditions were varied in order to identify their effect on the microstructure, properties and phase composition of the sprayed coatings. The as-sprayed coatings possess porosity values ranging between 1% and 2% and microhardness values (HV100) from 1150 to 1550, which are quite similar to values obtained for conventionally sized WC-based coatings. For all the coatings, phase analysis indicated significant degradation of the WC phase to produce W2C, W, CO3W3C and Co6W3C. For some spray conditions, even WO3 phase was found in the coatings. The JP-5000 HVOF system produces coatings with lower porosity, similar microhardness values and, more importantly, with lower WC degradation than the coatings produced with the DJ-2700.

For components that are required to function in sliding or rubbing contact with other parts, degradation often occurs through wear due to friction between the two contacting surfaces. Depending on the nature of the materials being used, the addition of water as a lubricant may introduce corrosion and accelerate the degradation process. To improve the performance and increase the life of these components, coatings may be applied to the regions subject to the greatest wear. These coatings may be engineered to provide internal pockets of solid lubricant in order to improve the tribological performance. In the present study, coatings containing a solid lubricant were produced by thermal spraying feedstock powders consisting of a blend of tungsten carbide-metal and a fluorinated ethylene-propylene copolymer-based material. The volume content of this Teflon-based material in the feedstock ranged from 3.5 to 36%. These feedstocks were deposited using a high velocity oxy-fuel system to produce coatings having a level of porosity below 2%. Sliding wear tests in which coated rotors were tested in contact with stationary carbon-graphite disks identified an optimum level of Teflon-based material in the feedstock formulation required to produce coatings exhibiting minimum wear. This optimum level was in the range of 7-17% by volume and depended on the composition of the cermet constituent. Reductions in mass loss for the couples on the order of 50% (an improvement in performance by a factor of approximately two) were obtained for the best-performing compositions, as compared to couples m which the coating contained no solid lubricant.

This paper aims to analyze the effect of the nature of the core material, the geometry of the buffer rods, as well as the nature and thickness of the cladding material on the ultrasonic propagation properties of these guidance components. The development of ultrasonic waveguides was studied in order to address the need for operation under strict conditions. The effects of the composition and thickness of the cladding as well as the type and geometry of the core were investigated with straight and tapered aluminum oxide and 1018 steel rods for the core and with plasma-sprayed aluminum oxide or aluminum oxide-chromium oxide for the coating. The results show that tapered plated buffer rods perform better than their unclad straight counterparts. They also indicate that the addition of chromium oxide to aluminum oxide is promising in a broader temperature range in which these conductors can be used. Paper includes a German-language 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.

Ceramic-clad ceramic components were developed to address the need for buffer rods capable of operating under severe conditions. The buffer rods were produced using plasma spraying to build up a 500-nm thick layer of alumina on a solid alumina rod. Both conventional plasma spraying and high power plasma spraying techniques were employed to deposit the alumina coating directly onto a pre-roughened surface. Characterization of the resulting coatings indicated a level of porosity of several percent, substantially higher than that of the dense core. The room temperature wave propagation characteristics exhibited by these clad buffer rods were significantly improved over that of the unclad components.

For applications in which two contacting surfaces are in constant motion relative to each other, materials that are both wear resistant and non-abrasive are often required. Such attributes become even more important when the moving contact occurs with no liquid lubricants present to facilitate sliding. In the present study several WC-based coatings deposited using the HVOF process and containing one or more metal constituents as the binder (or matrix) phase were evaluated to determine their performance under conditions cf sliding wear. Image analysis of the coatings indicated a level of porosity of less than 1%. Hardness measurements found that values for the Vickers microhardness number were in the range of 1100-1500. For the wear tests, the test couple consisted of a coated ring (thrust washer type design) rotating against a stationary carbon disk. For each test, the contact load, speed of rotation and duration were controlled. During the test, the temperature of the carbon disk and the torque were recorded using a data acquisition system. This data was used to determine the coefficient of friction for each couple which, together with the results of measurements of weight change, provided a measure of the comparative performance of the various coatings. The preliminary results indicated that the values for the coefficient of friction for the various couples ranged from 0.15 to 0.29. The three coating compositions consisting of lONi-WC, 12Co-WC and 17Co-WC were found to out-perform other WC-based materials in these sliding wear tests.

In this study, Acoustic Emission (AE) signals are used to monitor the degradation of plasma sprayed Thermal Barrier Coatings (TBC) using cyclic four point bend tests. Signal analysis both in time and frequency domains is carried out in order to identify the key parameters which can be used to classify the acoustic emission signals as a function of the damage mechanisms. This classification offers a mean of prediction of the long-term behavior of the thermal barrier coating based on the acoustic emission signal signature at the early stages of bench testing. The samples consist of a Nickel-based alloy blade coated with a duplex TBC made of a 150 μm thick bond coat covered with a 300 μm thick partially-stabilized zirconia coating. Tests were performed on unnotched and perpendicularly notched samples in order to discriminate the AE from perpendicular cracks. Two broadband transducers are used for acquisition of acoustic emission signals. Measuring the time between signal detection by each of the two transducers provides a means of determination of the location of the source of the acoustic signals. A classification of the signals based on their energy and their maximum peak frequency is presented. A comparison is made between the degradation mechanisms of TBC under thermal cycling conditions that were presented elsewhere (1) and the results of four point bend tests presented here.