The aim of this investigation was to determine the influence of a metallic coating on the LTD behavior of an ATZ ceramic. Therefore, a 300 μm thick titanium layer was deposited by plasma spraying on a commercial ATZ ceramic containing 20 wt% alumina and 80 wt% 3Y-TZP. After aging the coated and uncoated samples in water vapor at 134 °C and 2 bar for 5 h and 30 h, respectively, the monoclinic phase content was determined using X-ray diffraction, and its impact on the mechanical properties was assessed in biaxial flexural strength tests. The results revealed an increase in strength with increasing aging time. Furthermore, the Ti-VPS-coating slows down the aging of the ceramic because it acts as a diffusion barrier for the hydroxide ions. As a result, after 30 h of aging, the monoclinic phase content of the coated samples is up to 30% lower than of the uncoated samples.