Wear Mechanism of Alumina Ceramic Tools when Machining Austempered Ductile Iron

Abstract

An austempered ductile iron (ADI) exhibits the excellent mechanical properties and the wear resistance. However, ADI has generally the very poor machinability due to the characteristic. This paper describes the tool life behaviour and the wear mechanism, when turning ADI with ceramic cutting tools such as zirconia toughened alumina (ZTA), alumina containing TiC etc. Al₂O₃-TiC tool has the longer tool life at low cutting speeds. In contrast, Al₂O₃-ZrO₂ has the longer tool life at 150 m/min or more, further, the flank wear rate per a cutting distance decreases as rising cutting speeds. In order to investigate this reason, the reaction tests between ceramics and ADI were carried out at 773 K and 1 273 K, in addition the transformation of ZrO₂ contained in ZTA ceramic tool was examined. ZrO₂ consists of a tetragonal phase (T) and a monoclinic phase (M) and the T-phase increases at high temperatures. Therefore, it is assumed that the wear resistance in ZTA ceramic tools depend on a value of T-phase which influences on tool hardness.