Crystallization and residual stress formation of sol-gel-derived zirconia films

Abstract

Thin ZrO 2-films have been deposited on stainless steel substrates by a sol-gel deposition process based on zircon-tetra- n-propoxide. Various heat treatments were carried out. The comparison between the expected film thickness determined by coating mass and the real film thickness measured by ball cratering method indicates a porosity of 40 to 50 vol.% for rapidly annealed films. Films heated at a heating rate of 0.5 K/min show only a low porosity. X-Ray diffraction measurements were carried out in order to examine the crystallization behavior of these films as a function of annealing parameters. An interesting correlation between heating rate and crystallization was found and is explained by the temperature dependence of nucleation rate and crystal growth. Crystallite sizes and microstrains were determined by peak profile analysis. The crystallite sizes of the metastable cubic zirconia range between about 13 nm up to about 20 nm. X-Ray residual stress measurements indicate a close correlation between the observed phase transformation and the residual stress formation.