Fatigue in Hard Metals and Cermets
The behaviour of hardmetals and cermets under cyclic bending has been investigated by a new experimental method. Both coated and uncoated materials have been tested, at temperatures varying between 25°C and 900°C. The results show a strong fatigue effect.
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H.G. Sockel, P. Kindermann, P. Schlund, S. Kursawe, M. Herr and Ph. Pott University of Erlangen-Nurnberg, Erlangen, Germany U. Schleinkofer and W. Heinrich Kennametal Hertel AG, Germany K. Gorting Plansee AG, Austria
KEY WORDS: Hardmetals, Cermets, Fatigue, Testing of Fatigue, ABSTRACT The behaviour of hardmetals and cermets under cyclic bending has been investigated by a new experimental method. Both coated and uncoated materials have been tested, at temperatures varying between 25°C and 900°C. The results show a strong fatigue effect. The endured stress amplitudes and lifetimes are strongly reduced under cyclic loads in comparison to the behaviour under static loads. Strong negative influences come from temperature and hard coatings. The conclusions advise the engineer to take fatigue into account in strength and lifetime calculations.
1. INTRODUCTION Hardmetal and cermet tool materials are very well known in the area of production engineering. They have their most important field of technical application in the area of cutting tools [1,2]. In this field they cover the area between HSS-materials with very high toughness and ceramic materials including diamond and cBN with very high hardness [2]. Since their initial developement between 1920 and 1930 they have found increasing fields of application as cutting tools due to the fact that the toughness and the hardness can be changed in relatively large ranges by changing the composition and microstructure. This
Published in: E. Kuljanic (Ed.) Ad!•atJced Manufacturing Systems and Technology. CISM Courses and Lectures No. 406, Springer Verlag, Wien New York, 1999.
H.G . Sockel, P. Kindermann et al.
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allows the adaptation of the materials to special cutting processes with their characteristic loading profiles. In their application the materials are subjected to wear and to different thermo-mechanical loads, at 25°C and at elevated temperatures up to about 1200°C at the cutting edge [4,5]. The mechanical loads consist of static, monotonically increasing and cyclic loads. The complete exploitation of the intrinsic wear resistance of the tool material requires that the lifetimes under the mechanical loads are higher than under the wear load alone. Until 1992, the mechanical properties of hard metals and cermets were largely characterised by hardness, bending strength, and toughness measurements, and thus only the material response to static or quasi static loading conditions was investigated. The material response to cyclic loading was generally not investigated, due to the absence of any simple, inexpensive laboratory test. In consequence of this experimental difficulty there was very little knowledge in the literature about the fatigue of these materials before 1992 [4,6]. A short survey is given in reference [7]. 11. I '
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