BEHAVIOR OF HARD METALS AND CERMETS UNDER CYCLIC MECHANICAL LOADS

Fatigue of materials is a consequence of a deterioration of strength p roperties as a result of cyclic loading. The investigation of this phe nomenon for cyclic mechanical loads in hard metals and cermets is the topic of this work. These materials are related to ceramics. Therefore a new method has been applied for these investigations, which has bee n developed to investigate the fatigue of ceramics. One very important aspect of this method is that it yields access to information about t he growth of small natural cracks. In the experiments the materials, a typical hard metal and a typical cermet, are investigated under stati c, monotonously increasing, and cyclic loads (22 Hz) in air at room te mperature. For these experiments a special apparatus was built. The be haviour of the materials under the different loads is presented and di scussed. The investigations of microscopic features on fracture surfac es and of the microstructure in the volume in front of growing cracks by SEM and TEM give additional information about the processes which o ccur during the fatigue of these materials under cyclic loads. From th e mechanical behaviour under the different loads and the results of th e microstructural investigations, conclusions concerning the processes responsible for the reliability and for the lifetime can be drawn.