Sintering Characteristics of Plasma Sprayed Zirconia Coatings Containing Different Stabilisers Articles uri icon

publication date

  • June 2009

start page

  • 1069

end page

  • 1074

volume

  • 203

International Standard Serial Number (ISSN)

  • 0257-8972

Electronic International Standard Serial Number (EISSN)

  • 1879-3347

abstract

  • Zirconia powders with different types of stabiliser (Y2O3, Dy2O3 and Yb2O3) have been air plasma sprayed onto metallic substrates. The coatings were detached and dimensional changes during heat treatment were measured by dilatometry. Ytterbia-stabilised specimens exhibited the highest rates of shrinkage, in both inplane and through-thickness directions. However, it was noted that these specimens had higher initial porosity levels, and a finer microstructure, than coatings containing the other stabilisers. In-plane stiffness and through-thickness thermal conductivity were also measured after different heat treatments. These increased at greater rates for specimens with higher porosity levels (ie the Yb-stabilised coatings). Changes in pore architecture during heat treatments were also studied. Fine scale porosity is rapidly reduced during heat treatment. This correlates with enhanced inter-splat bonding and healing of intra-splat microcracks. In general, the sintering behaviour, and consequent changes in microstructure and properties, appear to be more sensitive to the pore architecture than to stabiliser type. This is correlated with theoretical expectations that it is grain boundary and surface diffusion which will dominate the sintering behaviour, rather thanlattice diffusion, and these are more likely to be affected by pore structure, and possibly by the presence of certain types of impurity, than by stabiliser content. It is also noted that thermal cycling appears to retard sintering, at least in terms of the rate of shrinkage. This effect, which could be of practical significance, isbriefly discussed.