EFFECT OF GRAIN-SIZE ON THE KINETICS OF ISOTHERMAL TETRAGONAL TO MONOCLINIC TRANSFORMATION IN ZRO2(2MOL-PERCENT-Y2O3) CERAMICS

In this paper, effect of grain size on kinetics of isothermal tetragon al(t) to monoclinic(m) transformation in ZrO2(2mol% Y2O3) ceramics has been studied by means of thermal expansion analysis (TEA), X-ray diff raction (XRD), scanning electron microscopy (SEM) and transmission ele ctron microscopy (TEM). Experimental results reveal that t-->m transfo rmation in ZrO2(Y2O3) ceramics is essentially isothermal with its time temperature transformation (TTT) curve expressed in the form of C-sha pe, occurrence of which has been analyzed in terms of nucleation and g rowth process. Grain size has been shown to have significant effect on the isothermal kinetics of t-->m transition. With decreasing grain si ze of t-phase, the ''nose'' temperature of the TTT curve is decreased and incubation period is shortened However, the incompleteness of the transformation is enhanced due to higher transformation activation ene rgy. TEM observation also indicates that phase constituents may vary w ith grain size with the implication of the effect of grain size on the stability of t-phase. (C) 1997 Elsevier Science Limited.