Since its commercial introduction in the early 1980s, it has been known that HVOF spraying can produce layers with low oxide levels, high toughness, and excellent adhesion strength. Unlike low-pressure and vacuum plasma spraying, the HVOF process does not require a controlled atmosphere. As a result, the oxygen content of the wettable powder plays a significant role in layer quality. In this paper, the oxygen content of normal MCrAlY powder is varied and its influence on coating quality is examined. It is shown that, by limiting the initial oxygen content in spray powder, higher density HVOF layers with lower oxide proportions can be achieved. Paper includes a German-language abstract.

HVOF spraying is used to produce NiCoCrAlYRe deposits that serve as adhesive layers for plasma-sprayed thermal barrier coatings. This paper investigates the influence of HVOF spray parameters on the structure and properties of the adhesion-promoting layers. Spray parameters are optimized to produce high layer densities with low degrees of oxidation and a surface roughness comparable to that of the thermal barrier coatings. A vacuum-sprayed layer with similar composition is also examined. Following the application of the TBC, the oxidized layers are characterized based on microstructure, oxide layer thickness, proportion of the NiAl phase, and imperfections at the boundary layer. It is observed that the less expensive HVOF layer offers the same protective properties as a vacuum plasma sprayed bond coat. Paper includes a German-language abstract.

This paper assesses the effect of different annealing treatments on the adhesion strength of NiCrAlY coatings. The coatings were HVOF sprayed on superalloy substrates using widely available powders. It was found that the annealing atmosphere has no significant influence on adhesion, indicating that the coatings self-reinforce when subjected to high temperatures. The observed effect is due to the diffusion of elements, forming a metallurgical bonding layer at the coating-substrate interface. Test results show that, in an ambient atmosphere at 1000 °C, this bonding layer becomes stronger with time, more than doubling the adhesion strength of HVOF NiCrAlY coatings on Inconel 738 substrates. Paper includes a German-language abstract.