Tetragonal to monoclinic transformation in Y-TZP joined with metallic materials

Joints between Y-TZP (Yttria containing Tetragonal Zirconia Polycrystal) and metallic materials (type SUS304 stainless steel and Mo) were fabricated, using brazing alloy (Ag-Cu-Ti) sheet. Y-TZP disks having different Y₂O₃ contents, grain size were prepared for changing their transformability from tetragonal to monoclinic phase. Y-TZP disks with various thickness were joined with metal disks with constant thickness in order to change the thermal stress states. Transformation in Y-TZP was investigated by changing cooling rates from the joining temperature. Transformed fraction was larger under presence of tensile thermal stress (σ_rr). The transformed fraction decreased when cooled at a faster rate, which was related with time-dependent characteristics of the transformation in Y-TZP. A large fraction of transformation was detected in the coarse grained Y-TZP joined with Mo, although no transformation was detected in the unjoined state when cooled at the same rate. Transformation of Y-TZP joined with metallic materials was discussed, considering the effects of residual stress and the time dependent features of the transformation.