Abstract Titanium suboxides form a class of ceramic materials possessing such technically interesting properties as electrical conductivity and solid lubrication. Consequently, these materials have a high potential for application as thermally sprayed coatings. In this paper the preparation and characterisation of two spray powders of different composition by agglomeration and sintering with a narrow range of the value n in Ti n O 2n-1 is described. Powders were characterised by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), thermogravimetric measurements (TG), helium pycnometry, nitrogen adsorption and mercury intrusion techniques. The sprayability was tested by plasma spraying. The coating structures were studied by optical microscopy, XRD, TG and TEM. Although the powders were only partially oxidized as a result of the spray process, the crystallographic structure was changed significantly, according to XRD and TEM investigations. As an alternative method of preparation of titanium suboxide spray powders, the reduction of a fused and crushed spray powder with hydrogen is described. Powder particle shape and size distribution are not changed in this process.

Abstract TiC-based coatings sprayed by different processes, such as detonation gun spraying, high velocity oxy-fuel spraying, atmospheric plasma spraying (APS), and vacuum plasma spraying, using agglomerated and sintered powders have been actively developed over the years. This development is based on the high technical and engineering potential of the hard phase TiC. This paper describes the results of basic studies of the APS for various alloying steps in the production of TiC base coatings from agglomerated and sintered powders as well as the results of the application of APS coatings on piston rings. Paper includes a German-language abstract.

Abstract Oxide-bonded silicon nitride (OBSN) powders have been developed to address thermal spray problems associated with high temperatures. This paper examines how such powders perform when applied via detonation gun (DGS) and atmospheric plasma spraying (APS) with axial powder injection. All coatings were characterized using optical microscopy and X-ray diffraction with additional tests being performed on DGS coatings. For the first time, relatively dense Si3N4-rich coatings with an oxide binder phase were produced, and some of the DGS coatings were found to be sufficiently wear resistance for industrial use.

Abstract Agglomerated and sintered TiC-Ni based powders were sprayed by detonation gun spray (DGS) and high-velocity oxy-fuel (HVOF) spray processes. Influence of the binder content (20 and 27 vol.-%) and some alloying elements, such as Mo, Co and N on the coating properties were investigated. The coating structures and properties were investigated by optical microscopy, hardness measurements, X-ray diffraction analysis and by rubber-wheel abrasion wear test. It was found that alloying the hard phase with Mo and N leads to an improvement of the coating properties. Alloying of the binder phase with Co did not affect the coating properties. Porosity in the powder granules was found to beneficial in order to melt more efficiently the particles in the DGS process and especially in the HVOF process. HVOF spraying of powders with the higher binder content of 27 vol.-% was found to be advantageous for the preparation of coatings with dense microstructures and good wear resistances.

Abstract Thermal spraying of silicon nitride has been considered impossible because the high temperatures involved lead inevitably to decomposition/oxidation of the material. To address these issues, improved silicon nitride-based powders were developed, two of which have been tested as reported in this paper. The powders were applied using low pressure plasma spraying (LPPS) and the resulting coatings characterized based on microhardness, adhesion, and cohesion strength. Phase transformations of the powders during spraying were also investigated and preliminary optimization strategies by statistical variation of plasma spray parameters were tested.

Abstract Hardmetal-like coatings on the base of titanium carbide as a hard phase and nickel as a metal binder were prepared from agglomerated and sintered powders by plasma spray, detonation gun spray and high-velocity oxygen-fuel spray processes. The powders used in the spray experiments were plain TiC-Ni type and alloyed (Ti,Mo)C-NiCo type powders with different binder content. The coatings were characterized by optical and scanning electron microscopy, microhardness measurements, XRD analysis and in an abrasion wear test. The results showed that the sprayability of these novel hardmetal-like powders is good in all spray processes studied and the coatings deposited were found to have dense microstructures and good properties. The XRD analysis showed that the coatings have a phase structure similar to that found in the spray powder. The amount of retained carbides in the coatings was high. Some regions in which the carbides had dissolved with the metallic binder phase during spraying were also found, especially in plasma sprayed coatings. In such microstructural regions submicron size reprecipitated carbides were detected. These were clearly detectable in detonation gun sprayed coatings. HVOF sprayed coatings were found to contain a very high content of retained carbide phase. In this process the heat effect to the material seemed to be the lowest. The wear tests clearly showed the importance of alloying the hard phase and the binder phase in order to improve the wear resistance of the coatings. All studied spray processes produced coatings with nearly similar coating wear properties.