Structure evolution of the Al2O3-ZrO2 alloys under nonequilibrium conditions

Abstract

ZrO2 alloys are widely used in the electronic, abrasive and refractory industries~ The alloys containing approximately 75%* A1203 and 25% ZrO2 (zirconic electrocorundum) are used as an abrasive material. The physical, mechanical, and operational characteristics of the alloys are determined by the dimensions of the structural constituents and their quantitative ratio which, in turn, depend on the cooling conditions of the melt during its solidification.The Al2Os--ZrO2 system belongs to the eutectic-type systems [1][2][3][4][5][6]. The coordinates of the eutectic points (C E and T E) and the regions of existence of the solid solutions have not been established accurately in the phase diagram of the Al2Os--Zr02 system (1983~ <~. T E <~.i 2193~ 32% Zr02 .<~ C E < 55% Zr02). Primary corundum (~-Al2Os) crystals (grains) and the eutectic form the main structural constituents of the 75% Al20s + 25% ZrO2 hypoeutectic type alloys.Eutectic solidification (crystallization) has been a subject of extensive investigation, particularly in view of the promising applications of the eutectic alloys as composite materials. The studies on the metallic systems are concerned with the conventional aspects such as the identification of the phase leading to eutectic solidification, the structural anomalies, and the classification of the eutectic structures [7,8]. It was established that depending on the degree of supercooling of the melt during its solidification, different types of eutectic structures can emerge from the same eutectic [8]. Consequently, by varying the cooling conditions of the melt, it is possible to obtain structurally different materials having identical chemical composition. However, there have been no systematic studies on the structural constituents (primary crystals and eutectic) of the AI~O3--Zr02 alloys and their general structure.Moreover, the regularities in the structure evolution of the alloys under nonequilibrium conditions have not been established. *Here and elsewhere, chemical composition is expressed in terms of weight content.