Influence of the morphology of ZrO 2 particles stabilized with Y 2O 3 on thermomechanical properties of plasma-sprayed coatings

Abstract

Plasma spraying conditions of two size distributions (Pratt and Whitney Aircraft 1375 size specification −106+10 μm and −90+45 μm respectively) of Y 2O 3-stabilized ZrO 2 (8 wt.%) with different morphologies (fused and crushed, sintered and crushed, agglomerated, agglomerated and sintered) have been studied. The torch was custom made (cylindrical nozzle diameter, 8 mm) working with an Ar-H 2 mixture (75 standard 1 min −1 and 15 standard 1 min −1 respectively) at two power levels: 28 and 40 kW. A study of particles collected in water showed very different behaviour. The dense particles were almost completely melted but showed porosities and thus had a density that decreased with increasing torch power. Part of the fine agglomerated powders (diamter less than 40 μm) exploded on penetration but were partly densified, and the agglomerated and sintered as well as the agglomerated large particles (diameter greater than 40 μm) exhibited a molten shell surrounding an unmolten core; the shell for the agglomerated and sintered particles was thicker than that of the agglomerated particles. The molten shell is due to enhanced heat propagation with such porous particles. The highest densities, the best cohesion (characterized by their hardness under a load of 5 N), the lowest porosities and the smallest pore diameters of the coatings were obtained with the particles in the size range −106 + 10 μm which had been either sintered or melted. In good correlation with these results the highest thermal diffusivities at room temperature were also obtained with dense particles.