INFLUENCE OF SOFT ZONES ON THE FATIGUE CRACK NUCLEATION AND PROPAGATION BEHAVIOR OF HIGH STRENGTH β TITANIUM ALLOYS AND ALUMINUM ALLOYS

摘要

Both high strength β Ti-alloys and high strength Al-alloys exhibit soft zones along grain boundaries, resulting from continuous α layers in case of β Ti-alloys and from precipitate free zones (PFZ) in case of Alalloys. In both cases, the preferred microstructure for application is an unrecrystallized pancake shaped grain structure. The present work evaluated HCF strength, the nucleation and propagation behavior of self-initiated microcracks, and the propagation behavior of large fatigue cracks as a function of the inclined angle of the stress axis to the pancakes (0°, 45°, 90°). The lowest HCF strength was measured in the 45° test direction. Large fatigue cracks and self-initiated microcracks exhibited the fastest crack propagation rate under an angle of 90°.