Investigations on interfaces between light weight alloys (aluminum AA7022 and magnesium AZ91) and optimized cold gas sprayed (CGS) zinc-based coatings are carried out. The analyses include standard optical and scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). By using TEM resolution within nanometric dimensions is realized. Investigations by SEM show areas of an intensive mixing between substrate and coating material with a number of different grey values due to element contrast. By EDXS analyses in a 1 µm broad transition zone increased zinc concentration compared to the substrate material is detected. TEM investigations prove that in this transition zone no homogeneous solid solution exists, but additionally submicron and nanosized intermetallic phases with different concentration of aluminum, zinc and magnesium are found. Due to these results an intensive mechanical interaction must take place at the substrate-coating interface during CGS. Thus bond strength does not only depend on physical and chemical adhesion or thin metallurgically affected zones, but also highly on effects of mechanical alloying.

HVOF sprayed WC/Co(Cr) and Cr₃C₂/Ni20Cr composite coatings have gained high acceptance in many industrial applications for protection of components against wear. The achieved coatings have quite good corrosion resistance for use of chromium containing matrices. Present research in the field of PTA-Surfacing resulted in the development of high chromium and high vanadium containing iron based hard alloys with simultaneous improvement of abrasive wear and corrosion resistance. These properties of the PTA-Surfaced coatings were studied and it was found that the newly developed alloys have nearly same wear resistance and improved corrosion resistance compared to Co-based alloys reinforced with Fused Tungsten Carbides (FTC). One major advantage of high chromium and high vanadium containing iron based coatings is machinability by turning and milling processes. These features make it attractive to be used in thermal spraying. The absence of substrate melting in HVOF-spraying is advantageous, as the coatings preserve the properties of the alloy due to prevention of dilution with substrate material in contrast to PTA-Surfacing. High chromium and high vanadium containing iron based atomized powder was used for HVOF spraying and deposition efficiency was measured. The sprayed coatings were studied metallographically by optical microscopy, SEM, XRD and micro-hardness measurements. Later, abrasive wear and corrosion properties of the coatings are investigated.

There are constantly increasing requirements concerning light-weight concepts in automotive design due to energy saving demands. Additionally reduction of component weight is desired for demountable parts to permit easier handling. One innovative development example in this field is a draw bar consisting of precipitation hardened aluminum featuring significant weight reduction compared to presently applied steel draw bars. However, low wear resistance of aluminum alloys makes sophisticated addition of wear resistant parts in the area of the positive fit necessary. This leads to increased machining time, further costs for purchasing and machining of adapted additional components and further assembling steps. A study on the capability of thermal spray coating deposition in the positive fit area for substitution of the sophisticated wear protection system is carried out. Different HVOF coating systems with variable thicknesses are tested concerning their capability to withstand bending stress. The optimum combination of Ni20Cr bond coats and Cr₃C₂ - 25 Ni20Cr top coats is applied for prototype production. The prototypes are tested concerning their performance under dynamical load and in corrosion tests. All produced prototypes pass both mechanical and corrosion tests. Prototypes, on which arc-sprayed Ni20Cr coatings are deposited as a low-cost solution, are still in tests.

For constant conditions concerning substrate state, feedstock and environment properties of thermal spray coatings depend only on temperature and velocity of particles at impact on the substrate. Two different HVOF spraying guns, the kerosene fuel system Tafa JP5000 with radial powder injection and the ethylene fuel system Sulzer Metco Diamond Jet Hybrid 2700 with axial powder feeding, are characterized concerning the evolution of space resolved velocity and density of particles by LDA. Also influence of process parameter variations is examined. The region of shock diamonds is studied specifically. The influence of different characteristics concerning impact velocity and trajectories on the coatings microstructure is determined by means of optical microscopy and microhardness testing.

The performance under dry abrasive wear conditions is studied for HVOF sprayed cermet coatings in comparison to APS Cr₂O₃ and electroplated hard chromium coatings in Taber Abraser tests. Investigations on the wear behaviour depending on the use of different abrasive wheels as well as on the influence of hard phase size, microhardness and chemical composition of the metallic matrix alloy in HVOF sprayed cermet coatings are carried out. For applications in the field of heat transferring components facing strong abrasive wear stress also the influence of hard phase size and microhardness on the thermal diffusivity of HVOF WC-CoCr 86-10 4 is studied. In general HVOF sprayed cermet coatings show superior wear resistance compared to APS Cr₂O₃ and electroplated hard chromium coatings in Taber Abraser tests with H-22 abrasive wheels. The chemical composition of the metallic matrix of HVOF cermet coatings proves to be decisive concerning optimized wear resistance. The size of hard phases shows only minor influence. Coatings produced with coarse carbides make the highest wear resistance accessible, but the wear behaviour depends much more severely on an optimized processing compared to coatings with fine carbides.

The laser-flash method is used to determine the thermal diffusivity of HVOF sprayed WC-Co(Cr) and Cr₃C₂-Ni20Cr as well as APS sprayed Cr₂O₃ 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 SO₂ 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.

The main tendencies in the development of tungsten carbide coating applications are presented. General properties of WC based coatings and their dependence on different factors are discussed. For comparative examination of the abrasive wear resistance of thermal spray coatings detailed Taber Abraser wear tests are carried out. Besides HVOF sprayed cermet and APS Cr₂O₃ also electroplated hard chromium coatings are studied. The best results have been obtained for HVOF sprayed cermet coatings. For this kind of wear conditions the difference in wear behaviour depending on carbide size in WC-CoCr coatings is insignificant compared to the difference depending on the matrix composition.

With the aim to elaborate a coating technology for improved wear resistance of AA2017 alloy surfaces Cr₃C₂/Ni20Cr 75/25 top coats and Ni5Al, Ni5Ti as well as Ni20Cr bond coats are produced. Bond coats are deposited by arc spraying as well as HVOF and top coats by HVOF only. Optimum spraying parameters are determined. The resulting adhesion of bond coats to AA2017 is in the order of 50 MPa. Microscopic investigations point at metallurgical reactions at interfaces both between bond and top coats and between bond coats and substrates. In oscillating wear tests on top coats with alumina balls as counterbody only the coatings are worn, while hardened 100Cr6 steel balls cause no wear of the coatings.

Silicides in general and MoSi₂ in particular are promising materials for high temperature oxidation protection. Besides a comparatively low density of 6.25 g/cm³ and a high melting temperature (2030 °C) MoSi₂ features a good ductility in the temperature range exceeding the brittle - ductile transition temperature (800 - 1100 °C) and a high thermal conductivity (~ 15 W/m•K, 1200 - 1800 °C). Therefore it is interesting e.g. for applications in the field of aviation engines and gas turbines.
However, the use of MoSi₂ is restricted by its brittle failure behavior at room temperature and the comparatively low creep resistance at temperatures exceeding the brittle - ductile transition temperature. Investigations on sintering ceramics show, that these properties can be improved significantly by ceramic additives (Al₂O₃, SiC or TiB₂).
Mild steel substrates are coated by vacuum plasma spraying of MoSi₂-TiB₂ composite powders. In order to prevent an influence of the substrate material on the characterization of the coatings oxidation behavior, the coatings are detached and tested as free standing bodies. Investigations on the isothermal oxidation behavior in the temperature range between 500 and 1,500 °C are carried out by gravimetric analyses. For characterization of the microstructure of the coatings both in the as sprayed state and after the oxidation tests including the formed oxide scale SEM and XRD investigations as well as micro hardness measurements are carried out.

Molybdenum disilicide (MoSi₂) is a suitable material for high temperature applications especially because of its excellent high temperature oxidation resistance. For several high temperature applications MoSi₂ shows high potential to be used as a protective coating. The oxidation behaviour of HVOF sprayed MoSi₂ coatings is studied at 1500 °C. The oxidation tests are carried out in a simultaneous thermogravimetric device and the mass change is measured in dependence on the oxidation time. The microstructure of the coatings before and after oxidation is examined by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXS). The mass of the coating increases according to a parabolic function. During the oxidation test the microstructure changes significantly from a typical thermal spray coating microstructure with lamellae, pores and a phase mixture of MoSi₂ and Mo₅Si₃ to a two phase system with sharply separated grain boundaries. On the surface of the coating a silicon dioxide layer with a thickness of less than 10 µm is formed.