Performance of Y-TZP-Al2O3 composite ceramics in dry high-speed turning of thermally hardened steel 0.4 C-Cr (AISI 5135)

Introduction. Analysis of contemporary data in the fields of materials science and the application of ceramic cutting tools for machining difficult-to-machine iron- and nickel-based alloys reveals a limited amount of experimental data concerning the use of the promising Y-TZP-Al2O3 ceramic, which is based on submicron yttria-partially-stabilized zirconia and reinforced with alumina. Purpose of the work. To study the performance of RNGN 120400-01 removable cutting inserts made from Y-TZP-A12O3 ceramic during dry high-speed (200 m/min) cutting of 0.4 C-Cr (AISI 5135) steel (HRC 43…48). Research Methods. Characterization of the initial powders and the sintered ceramic, both before and after cutting tests, was performed using X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses, as well as scanning electron microscopy (SEM) in BSE mode. The physical and mechanical properties of the sintered ceramic were determined using the hydrostatic weighing method, three-point bending, and Vickers microhardness and fracture toughness measurements. Cutting tests were conducted on a high-rigidity lathe in a production shop conditions, involving dry high-speed turning of hardened 0.4C-Cr steel (AISI 5153) (HRC 43…48) in two stages. The first stage involved establishing the allowable variation limits for cutting modes (cutting speed and feed rate) and investigating the wear and failure characteristics of the cutting insert rake and flank faces. The second stage utilized ceramic cutting inserts with a chamfered cutting edge. Results and discussion. It was established that for Y-TZP-A12O3 ceramic, the use of cutting modes V > 200 m/min, S > 0.4 mm/rev, and t > 0.2 mm is not advisable due to the short service life of the cutting edge. A chamfer on the cutting edge is necessary to provide controlled edge blunting. The observed wear patterns and analysis of failure areas indicate a dominant brittle fatigue failure mechanism, caused by the thermal effects of high-speed friction combined with tangential stresses from the chip flow. It is concluded that the Y-TZP-Al2O3 ceramic composite is promising for use as a cutting tool material for dry high-speed turning of both hardened steels and, potentially, wear-resistant cast irons. Based on the conducted research and described observations, recommendations are formulated for the use of Y-TZP-Al2O3 ceramic in future studies.