MICROINDENTATION-INDUCED TRANSFORMATION IN 3.5-MOL-PERCENT-YTTRIA-PARTIALLY-STABILIZED ZIRCONIA SINGLE-CRYSTALS

The temperature dependence of the Vickers microhardness was studied in 3.4-mol%-Y2O3-partially-stabilized ZrO2 (Y-PSZ) single crystals up to 1000-degrees-C; the samples had previously been annealed at 1600-degrees-C for 150 h to develop "colony" precipitates of tetragonal ZrO2 in the cubic ZrO2 matrix. Indentation caused extensive stress-induced martensitic transformation of the colony precipitates to monoclinic symmetry in zones which extended in extreme cases up to several hundred micrometers from the indent. For indents made at 500-degrees-C and above, the M(d) and M(f) temperatures are 450-degrees and 310-degrees-C, respectively; A(s) is approximately 600-degrees-C (M(d) is the temperature of initial transformation (the "martensite start temperature") in deformed samples; M(f) is the temperature at which the final transformation occurs; A(s) is the temperature at which the reverse (monoclinic --> tetragonal) transformation begins). However, extensive transformation zones are also found for indents made at 200-degrees, 300-degrees, and 400-degrees-C. The dislocation density introduced during indentation is responsible for nucleating the transformation in a zone adjacent to the indent. However, the transformation zone extends further than the plastic zone around the indent, indicating extensive autocatalytic transformation. Transformation within the zone appeared to occur in individual plates with {110} habit planes. The plate dimensions (approximately 100-mu-m x approximately 175-mu-m x approximately 10-mu-m) are large compared to the size of the colony precipitates (approximately 2-mu-m in maximum dimension).