Consistency and homogeneity is one of the major requirements for plasma sprayed coatings. However, conventional plasma torches and processes enjoy only limited success in achieving these requirements. The limits are first of all associated with plasma parameters drifting, as well as pulsing within 1-5 kHz range. The pulsing results in significant differential in particle temperature and velocity and, consequently, in morphology of splats and related coating properties.

The paper presents the results of analysis of zirconium oxide splats formed by conventional and cascade plasma generators (CPG). CPG generates very stable plasmas and doesn’t display practically any drifting or pulsing, which are inherent to the conventional torches. In addition, CPG offers an extremely wide operating window, which  allows for better control of plasma parameters, particle dwell time and, consequently, a wide range of particle temperature and velocity, which are achieved by generating high enthalpy quasi-laminar plasmas, medium enthalpy transient plasmas, as well as relatively low enthalpy turbulent plasmas. All three types of plasmas are under consideration in the paper. Narrow distributions of particle size were used during experiments minimizing influence of powder inconsistency on splat formation.

Particles temperature and velocity were measured before their collision with a substrate by using a diagnostic setup modified to study the splat formation. 3 wavelengths pyrometer included in the modified setup provided more accurate temperature measurements in comparison to the conventional 2 wavelength pyrometers. Experimental data and theoretical analysis show that for a particular set of plasma parameters, CPG offers a significantly more consistent morphology of splats when compared with that of conventional plasma torches. In addition, wide operating window of the CPG-based plasma torches allows for the formation of splats with a variety of morphologies, thus satisfying different present and future technological needs.