Influence of Atmospheric Plasma Spraying Parameters on Porosity Formation in Coatings Manufactured from 45S5 Bioglass (R) powder

摘要

Atmospheric plasma spraying parameters were studied to understand their influence on the splat stacking and the porosity formation in coatings made from commercial Schott 45S5 Bioglass (R) powder onto AISI 304 L stainless steel substrate. The spraying parameters were established from numerical simulation carried out by the Jets&Poudres software. The plasma spraying was performed by using an Oerlikon Metco F4 MB gun with a 6-mm-internal-diameter nozzle. Three Ar/H-2 mixtures were used as plasma-forming gas (95/5, 88/12 and 84/16 vol.%), and the current intensity was varied from 450 to 650 A and the spray distance from 60 to 100 mm. The cooling of the samples during spraying was controlled by air jet pressure. The x-ray diffraction and the scanning electron microscopy were used to determine phases and structural characteristics of coatings, respectively. The numerical simulation results for each set of spray parameters have shown suitable Sommerfeld number for proper splat stacking. However, Na2O and P2O5 evaporation occurred experimentally during spraying of 45S5 Bioglass (R) promoted the porosity formation into the coating structure. Low porosity was obtained for 45S5 Bioglass coatings manufactured under the appropriate relationship between plasma-forming gas mixture ratio, current intensity, spray distance and cooling air jet pressure to achieve thermal energy input enough to overcome the glass transition temperature and to avoid the evaporation of volatile oxides.