materials Article Alumina-Toughened-Zirconia with Low Wear Rate in Ball-on-Flat Tribological Tests at Temperatures to 500 ◦ C Marek Grabowy 1, *, Kamil Wojteczko 2 , Agnieszka Wojteczko 2 , Grzegorz Wi ˛ azania 3 , Maciej Luszcz 4 , Magdalena Zi ˛ abka 2 and Zbigniew P ˛ edzich 2, *   Citation: Grabowy, M.; Wojteczko, K.; Wojteczko, A.; Wi ˛ azania, G.; Luszcz, M.; Zi ˛ abka, M.; P ˛ edzich, Z. Alumina-Toughened-Zirconia with Low Wear Rate in Ball-on-Flat Tribological Tests at Temperatures to 500 ◦ C. Materials 2021, 14, 7646. https://doi.org/10.3390/ ma14247646 Academic Editors: Filippo Berto, Abílio M.P. De Jesus and José A.F.O. Correia Received: 15 November 2021 Accepted: 10 December 2021 Published: 12 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 IEN Institute of Power Engineering, Ceramics Division CEREL, 8 Mory St., 01-330 Warsaw, Poland 2 Department of Ceramics and Refractory Materials, Faculty of Materials Science and Ceramics, AGH—University of Science and Technology, 30Mickiewicz Av., 30-059 Krakow, Poland; kamil.wojteczko@agh.edu.pl (K.W.); agdudek@agh.edu.pl (A.W.); ziabka@agh.edu.pl (M.Z.) 3 Department of Machine Design and Technology, Faculty of Mechanical Engineering and Robotics, AGH—University of Science and Technology, 30Mickiewicz Av., 30-059 Krakow, Poland; wiazania@agh.edu.pl 4 Lukasiewicz Research Network—Institute for Sustainable Technologies, 6/10 Pulaski St., 26-600 Radom, Poland; maciej.luszcz@itee.lukasiewicz.gov.pl * Correspondence: grabowy@cerel.pl (M.G.); pedzich@agh.edu.pl (Z.P.) Abstract: An alumina-toughened zirconia (ATZ) material, fabricated using a procedure consisting of the common sintering of two different zirconia powders, was tested using the ball-on-disc method in a temperature range between room temperature and 500 ◦ C. Corundum balls were used as a counterpart. The ATZ composite behaviour during tests was compared with that of commonly used α-alumina and tetragonal zirconia sintered samples. At temperatures over 350 ◦ C, a drastic decrease in the wear rate of the material was detected. SEM analyses proved that, in such conditions, nearly the whole surface of the sliding material was covered with a layer of deformed submicrometric grains, which limited contact with the part of material that was not deformed. The mentioned layer was relatively strongly connected with the material, increased its resistance, and decreased its coefficient of friction. As a reference, commonly used materials, namely commercial alumina and tetragonal zirconia, were tested. The wear parameters of the composite were significantly better than those registered for the materials prepared of commercial powders. Keywords: alumina toughened zirconia; tribology; sliding wear; ball-on-disc test 1. Introduction Continuous development of ceramics technology is a clear condition for the improve- ment of many branches of industry [1]. Each type of ceramic product has a specific technology and an optimal field of application. Alumina-toughened zirconia (ATZ) materi- als are relatively well recognized and commercialized due to their low manufacturing costs and good properties, which, in some applications, are much better than the properties of monophase tetragonal zirconia or alumina products. A good example is knee or hip-joint ceramics endoprosthesis [2,3], but the mentioned ATZ materials have a significantly wider field of application in the machinery industry. ATZ composites are often used as an efficient material for parts of machinery subjected to sliding, rolling, or any other movement usually correlated with mechanical loading and the potential abrasive acting of the environmental elements. The applications of ATZ materials are not only limited to room temperature, as ATZ materials can withstand elevated temperatures (a few hundred Celsius degrees). Many previous studies [4–10] have elaborated the different aspects of ATZ composite pro- cessing, microstructures, and correlations with their final properties. Usually, attention has been focused on the zirconia/alumina ratio, phase composition, and sintering conditions (or methods). The important issue is also residual stress state which is connected with coefficients of thermal expansion mismatch of both alumina and zirconia phases [11,12]. In Materials 2021, 14, 7646. https://doi.org/10.3390/ma14247646 https://www.mdpi.com/journal/materials