Mechanical Behaviour and Wear Resistance of Ce-PSZ Alumina Matrix Composites

Abstract

Abstract. Transformation toughening is one of the methods for improving the strength of alumina which has a hardness value of ~2000 HV. In this study, 0wt.%, 5wt.%, 15wt.%, 25wt.% and 35wt.% of Ce-partially stabilised ZrO 2 powders were dispersed homogeneously in alumina powder matrix. Pure α-Al 2 O 3 and α-Al 2 O 3 /ZrO 2 mixtures were shaped by using slip casting method and then they were sintered at 1550 °C. Specimens were tested in order to determine apparent porosity and bulk density, micro-hardness, flexural strength and fracture toughness. Later, wear tests were carried out on specimens by using 60 and 120 mesh abrasive papers, 64.5N, 33.3N and 14.4N loads. By this procedure, the effects of composition, load and mesh size of abrasive paper on abrasive wear behaviour was inspected throughly. Finally, surface analyses were carried out by using SEM to determine the characteristics of worn specimens. Introduction Alumina ceramics have been widely used materials for their thermomechanical and tribo-properties due to their high hardnesses and ceramical and thermal stabilities. In order to increase the toughness of alumina, a well-known metod is to add PSZ(Partially Stabilised Zirconia) to the matrix. Zirconia increases the toughness of the matrix by several different mechanisms [1-3]. The maximum stress concentration occurs at the tip of the crack. (Fig. 1) [4]. In the dual phased structures, which was ZTA(Zirconia Toughened Alumina) in this case, the fracture energy at the tip of the cracks is absorbed by the transformation thoughness effect of PSZ and prevents the further propagation of the crack (Fig. 2). When the alumina-tetragonal zirconia composites are stressed, the tensile strain field that surrounds a crack tip transforms monoclinic zirconia particles, which expand and generate compressive strain in the matrix and tensile stress at the crack tip is decreased. This stress-induced transformation enhances the fracture toughness of ZTA composites [5]. Zirconia particles dispersed in alumina matrix also increase the fracture toughness, due to the formation of a high density of microcracks absorbing energy due to their slow propagation. The microcracks are formed by the expansion of zirconia during tetragonal to monoclinic transformation. Figure 1. Maximum stress concentration at the tip of the crack [4]. Figure 2. Transformation thoughness of the Ce-PSZ in alumina matrix composite [5]. In this study, different volume percentages of Ce-PSZ powder have been added to pure alumina powder matrix. Then the mixtures were shaped by using slip casting method and the samples were sintered. The abrasive wear properties of the samples were investigated by Pin on Disc type wear test device [6].