Size-Dependence of Martensite Transformation Temperature of Yttria-Doped Zirconia and the Distribution of Nucleation Sites

Abstract

Specimen-size dependence of M_b temperatures (burst-type martensite transformation temperatures) was measured on many small spherical specimens of 1.5 mol%Y₂O₃-ZrO₂ ranging from 100 to 1000 μm diameter. With decreasing size, both reductions of the average M_b temperature and a significant increase in the scatter in M_b temperatures were observed. These data were used to deduce the density and distribution of the potential nucleation sites (embryos) by comparing with simulated M_b temperatures assuming randomly distributed embryos with various densities and potentials. Adjusting the parameters specifying the density and potentials so that the simulated result fit the observed data, the following characteristics were deduced for the embryos: 1) effective embryos are more likely to reside on the surface of a specimen rather than through the volume; 2) even the most unstable embryo requires under-cooling of more than 650 K from the equilibrium phase temperature; 3) the density of embryos increased nearly linearly with decreasing nucleation temperature; 4) the density of effective embryos with nucleation temperature above 77 K is approximately 32/mm².