the crack path, but with a slight increase of growth rate. At the triple point @, where the EM stuo
misorientation angels to the adjacent grains are higher than 30°, the slip band crack b is blocked for
more than 600 cycles. Not until 2500 cycles, the fatigue crack continues its propagation but now Berri
perpendicularly to the loading direction through the highly-misorientated adjacent grain. Similar to (en
this, the microcrack a was blocked at the tripel point © for more than 1300 cycles until it crossed )
the high-misorientated GB.
These observations allow the assumption that low-angle GB do not significantly act as obstacles for { Introd
short crack growth. The influence and the interaction of microstructural effects on short crack ini- fom
tiation and growth in the solution heat-treated metastable beta-titanium alloy LCB are discussed in Howevet,
more detail in ref. (3) and (7). From the sum of experimental results, favourable conditions for the esa
initiation and propagation of microstructurally short fatigue cracks can be deduced: Grain boundary Kon
cracking and slip band cracking take place only when the misorientation of adjacent grains is pra
relatively high, leading to high additional stresses resulting from the elastic anisotropy of the es
material (8). On the other hand, high-misorientation angle conditions hinder short crack propagation dhe and
leading to a chang of the crack path direction and a reduction of the crack growth rate. Under low- ee
misorientation angle conditions, cracks grow directly from one grain into another without changing Se
the crack path direction and without a considerable reduction or increase of the propagation rate. Cn
Conclusions re
By using the EBSD technique, helpful information can be obtained to characterise microstructural with oo
effects on short fatigue crack initiation and propagation. For the single-phase beta-titanium alloy rita
LCB highly-misorientated GBs and slip bands are preferential crack initiation sites during cyclic
loading. The short crack growth occurs mainly along slip bands and the rate at which a GB is
crossed depends on the local crystallographic misorientation between the grains involved. 2 Sampl
Discs of]
(SC papeı
Acknowledgements spre
The financial support by Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority
program "mechanism-oriented lifetime prediction” is gratefully acknowledged. Thanks are also to oe as
Professor Dr. C. Blochwitz and Dr. Tirschler, Institut für physikalische Metallkunde, TU Dresden, fure: 400
Germany, for fruitful discussions. most
tionally,
well ash
References a nitridir
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