Abstract
A method to uniformly slurry coat ceramic bar specimens to produce a compressive surface layer was investigated by systematically changing critical slurry variables that included the content of the powder, binder, and dispersant. The rheology of the slurries was determined as a function of these three variables. The coating contained a large fraction of alumina relative to the 3 mol% Yittria‐stabilized transformation‐toughened zirconia (TTZ) bars, which enabled the development of compressive stresses during cooling from the densification temperature. After densification, the coating thickness was determined with the optical microscope, and the residual compressive stresses were determined with calibrated Raman microspectroscopy. Before dip coating, the ceramic bars were slightly densified to enable the coating to shrink slightly more than the bar. Also, before coating, the porous bars were filled with water to prevent both slip casting and flaws produced by the out venting of air. Additions of a latex binder to the slurry circumvented cracking when the coating shrank during drying. Too much binder produced a porous coating and reduced the compressive stresses. It was shown that the optimum slurry composition, defined here as the “standard slurry,” would increase the flexural strength by ∼30%, namely 1120±10 MPa, relative to 867±68 MPa for the uncoated 3Y‐TTZ bars.
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