WC-based coatings have found extensive application in industries requiring wear resistance. WC-12% Co coatings were applied with a variety of high speed combustion spray guns (including HVAF) with various spray parameters. This paper aims to investigate the influence of the particle velocity, the particle temperature and the spray atmosphere on the decarburisation reactions and phase changes that take place during spraying. XRD and SEM used BSE image processing to characterize and quantify these responses. A comparison between temperature and speed measurements as well as the XRD results showed that the decarburisation is influenced not only by the temperature but also by the residence time and the entrainment of oxygen. Paper includes a German-language abstract.