U. Schleinkofer et al., FATIGUE OF HARD METALS AND CERMETS, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 209(1-2), 1996, pp. 313-317
The mechanisms of failure in hard metals and cermets have been studied
at room temperature under cyclic loads with a new method which yields
information about the growth of small cracks. The growth of these sma
ll cracks is important for the behaviour of the materials in the techn
ical application as cutting tools. In the experiments, the materials h
ave been investigated under static, monotonically increasing, and cycl
ic loads (22 Hz, 11 Hz) in air at room temperature. For these experime
nts a special apparatus was built. The behaviours of the materials und
er the different loads are presented and discussed. Electron mciroscop
y including SEM, TEM and SAM were used to investigate the micro-mechan
isms of damage during fatigue. The results are used to interpret the o
bserved mechanical behaviour. The mechanical behaviours of the materia
ls under cyclic loads are found to be different compared with that und
er static and monotonically increasing loading conditions. The corresp
onding damage processes are also completely different. Subcritical cra
ck growth under the cyclic loads occurs along special crack paths whic
h are different from those under the other loading conditions. From th
e mechanical behaviour under the different loads and the results of th
e microstructural investigations, conclusions regarding the damage pro
cesses responsible for the reliability and for the lifetime under cycl
ic loads can be drawn.