Flattening behavior of micro- and nano-sized yttria-stabilized zirconia particles plasma-sprayed on smooth preheated (610 K) nickel substrate: part I

Abstract

The work presented in this paper is devoted to the impact on Ni substrates of molten oxide particles (yttria-stabilized zirconia (YSZ)) either in the micrometer-sized range (between 20 and 100 µm) or in the submicrometer range (between 0.3 and 1.1 µm). YSZ was chosen because no oxidation occurs when plasma-spraying it in air. Micrometer-sized particles were injected into a hot plasma stream obtained with a DC plasma torch (Oerlikon Metco F4 torch) working with a mixture of Ar and H2 (Ar 33 slm and H2 10 slm). Correlatively an ethanol suspension of submicrometer-sized particles was injected into an Ar–He (Ar 40 slm and He 20 slm) DC plasma jet. Upon impact on a smooth Ni substrate preheated in air at 610 K both sizes of particles flatten and form splats. To achieve a much better understanding of splat formation, measurements of the velocity and temperature of an in-flight single particle just prior to its impact and at its impact were developed. Unfortunately, with submicrometer-sized particles, in-flight measurements of a single particle become impossible and only mean values resulting from a few particles are measured, making interpretation trickier. This study focused on the flattening on smooth substrates, presented as Part I, and will be followed by another study, to be presented as Part II, concerning splat formation on rough substrates adapted to the size of sprayed particles and then splat layering. Of course, the rough surfaces will also be preheated as the smooth ones at 610 K.