Abstract
In a previous work we have underlined that the in-flight particle oxidation occurs by classical surface oxidation and mass transfer from the surface to the interior of particles, due to convective movements, forming oxide nodules. The later intervenes in the particles during their dwell in the plasma jet core when the plasma-particle kinematic viscosities (nu(i) = nu(g)/nu(p)) ratio>55 and particles Reynolds number (Re)>20. This paper focuses on the influence of spraying parameters on the in-flight particle oxide content.
Two austenitic stainless steel powders, Metco 41C (-106+45 mu m) and Techphy (-63+50 mu m) were air plasma sprayed using a dc plasma gun (PTF4 type) and were collected in an argon atmosphere. Varying plasma current intensity (1), H-2 content of the plasma forming gases and sprayed powder particle size (d), it was confirmed that spraying conditions that promoted superior vi ratio and particle Re led to higher percentages of oxide nodules within the particles and vice-versa. Oxide nodules content increased proportionally with 1, H-2 flow rate and inversely with d. In Techphy powder, the collected particles oxygen content decreased linearly with l. While varying H-2 content in plasma, maxima of oxygen content in collected Techphy and Metco particles was obtained for H2 flow rates of 5.0 and 7.5 slm, respectively. Though similar trends were recorded while spraying Metco powder, the oxygen amount in it, owing to the coarser particle size, in all spraying conditions remained 20% to 60% lower than that in Techphy.