Hypoeutectic AlSi engine blocks of modern passenger cars are generally equipped with cast iron liners in order to provide cylinder running surfaces that meet the tribological requirements. A very promising alternative to the use of cylinder liners lies within the application of thermally sprayed coatings onto the walls of cylinder bores as friction partners for the piston rings. This work describes the development of a novel iron based wire feedstock as well as its application by the Plasma Transferred Wire Arc internal diameter coating system. The material developed within the frame of this work leads to partially amorphous coatings with embedded nanoscale precipitations if processed by thermal spraying. The coatings were applied onto the inner diameters of test liners made of Aluminium EN AW 6060 and onto cylinder bore walls of in-line 4 cylinder engines. All substrates were mechanically roughened in order to obtain high bond strengths of the sprayed coatings. The coatings microstructure was analysed by light optical microscopy, hardness measuring by transmission electron microscopy. Furthermore the oil storage capacities of the honed surfaces were determined.

Crank cases of modern car-engines are made in general of light metal alloys, mostly aluminium alloys. Due to the low hardness of these materials, the use of cylinder liners, in general made of grey cast iron is required. The use of cylinder liners also leads to several disadvantages, such as the increase of the engines weight. The aim of this work in the long term is to replace these cylinder liners with a thermally sprayed nano-structured composite coating, characterised by high hardness. Therefore in this study a coating process employing a plasma transferred wire arc unit and a cored wire are used.

HVOF-, arc- and plasma sprayed coatings are widely used for wear protection. Today these type of layers are dominant if thin coatings from 50 up to 500 µm and low heat input into the work piece are required. The main disadvantage of thermally sprayed coatings is the adhesion to the substrate and the early failure when cyclic loaded. In both cases a metallurgical bonding to the substrate can improve the life cycle time. Plasma transferred arc (PTA) welded coatings show a metallurgical bonding to the substrate. The main disadvantages of this coating technology are the dilution of about 5%, the heat input into the substrate and that nowadays all welding positions seem to be impossible to carry out. In this paper the theoretical background for welding thin coatings (less than 500 µm) with a decreased dilution and in all welding positions is given and experimentally proved.

This study assesses the wear performance of HVOF-sprayed nanostructured TiB 2 composite coatings and the use of mechanical alloying for powder preparation. In order to prevent the formation of undesired secondary borides, TiB 2 particles are processed with a nickel-base self-fluxing matrix alloy. XRD analysis shows that the minimum average TiB 2 crystal size is 22 nm after high-energy milling and only slightly larger and uniformly distributed after HVOF spraying. The resulting TiB 2 layers are characterized based on morphology and wear behavior and are shown to hold promise for abrasive wear applications. Paper includes a German-language abstract.

This paper discusses some of the recent improvements in plasma powder surface build-up welding technology and provides examples of its use in different areas of industry. It describes the coating properties achievable with newly developed filler alloys and how they compare with conventional hardcoats. It also discusses the growing use of manual overlay PTA welding among small and midsize companies and the factors behind it. Paper text in German.

Cored wires expand the spectrum of coating materials, that can be processed from wire feedstock. In particular they allow to provide a custom-made alloy composition. For many industrial applications a low thermal expansion coefficient is desirable to adapt the expansion behavior to specific needs. Bulk material alloys within the system Fe-Ni-Co show thermal expansion coefficients below 5 10 –6 K –1 at temperatures below 600 °C. Thermal spraying is a suitable technology to manufacture coatings, that provide a gradient of the thermal expansion behavior, or free standing bodies for components with low shape changes due to thermal interference. Detailed research has to be done on the influence of the alloy composition regarding the specific metallurgical requirements on wire feedstock material for arc spraying. Fe-Ni(-Co) coatings are produced from cored wires by arc spraying. Guidelines for the choice of the optimum process parameters with respect to coating properties and economical effects are worked out. The coatings are characterized with concern to porosity, oxide content, surface roughness, deposition efficiency, power consumption and deposition rate. The coefficient of thermal expansion is determined by dilatometry.

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.