This paper shows how thermal spraying, with an additional thermal treatment, can be used to join metal parts and fill surface defects. The joining and surface repair methods demonstrated in this work involve a wide range of materials and processes, and the results are characterized based on microstructural and elemental analysis and various property measurements. Paper text in German.

Arc spraying is an economical method for applying metallic layers due to its high spray rates and uniform melting of spray particles. The main disadvantage is the difficulty in achieving sufficient particle velocity to ensure good layer adhesion. This study investigates the influence of nozzle geometry, arc power, and gas pressure on the size and velocity of particles in an arc spray jet. The experiments were conducted using particle image velocimetry (PIV) to measure the spatial and velocity distribution of particles in flight. For X45Cr13 steel, particle velocities were found to be between 85 and 95 m/s at a gas volume flow of around 1 m 3 /min. Velocities of up to 150 m/s were ultimately achieved, but at the expense of higher atomizer gas consumption. Paper text in German.

The properties of thermal sprayed coatings depend mainly on the thermal and kinetic energy of the spray particles. Increase of thermal energy of sprayed particles can be realized using exothermic reactions between components in sprayed particles. Self propagating high temperature synthesis (SHS) is especially suitable to benefit from released energy in the spraying process. At present most commonly used spray material with exothermal reaction is Ni+Al. However, the highest amount of heat is produced in the reactions of aluminium and metal oxides. Of special interest are Cr 2 O 3 , NiO, CuO and V 2 O 5 because they obtain high reaction energies. Furthermore products of the reaction are of special, functional interest like NiAl as bonding agent or alumina as a wear resistant coating. To assure good contact between reacting substances (Al/Oxides) powders for plasma spraying were prepared by mechanical alloying. Calorimetric investigations of plasma sprayed coatings prove that during spraying Al reacts exothermically with oxides. Increase of oxide contents improves coating adhesion/ cohesion properties, hardness, and reduction of porosity. Results are discussed on the base of light microscopy, scanning electron microscopy (SEM) and X-ray structure analysis (XRD).

TiN reinforced Ti coatings were produced by using the arc spraying process. TiN hard phases were synthesized during spraying using Ar/N 2 reactive atomizing gas. The spray process was realised in an air atmosphere with a shrouded gun and in a chamber with closed loop Ar/N 2 -gas atmosphere. The content of TiN phases in Ti-coatings was increased by rising the N 2 -amount in atomizing gas during spraying. Sprayed coatings obtained a graded hardness ranging from 450HV 0.1 near the substrate up to 650HV 0.1 near the top (mean values). TiN-particle precipitations exhibited micro hardness up to 1350HV 0.1 . Structure investigations of manufactured coatings proved that they consist of pure titanium, titanium nitrides and small amounts of titanium oxides. Wear resistance of the coatings, tested by Taber Abraser and Pin on Disc, decreases from the coating surface to the substrate. According to Kesternich test, Ti/TiN-arc sprayed coatings exhibit good corrosion resistance.

For obtaining higher particle velocities and consequently dense coatings, a closed nozzle system for atmospheric arc spraying was developed. The proposed system is characterized by a nozzle geometry which allows an expansion of the atomizing gas only in downstream direction. First coatings, obtained with this system exhibited promising results due to dense structure and high adhesion. Paper text in German.