The influence of soft, precipitate-free zones at grain boundaries in Ti and Al alloys on their fatigue and fracture behavior

This paper discusses the effect of the presence of soft zones along grain boundaries in high-strength Al and (beta)-Ti alloys. Soft zones are deformed preferentially and therefore have a strong effect on fracture related properties. The presentation focuses on the ductility, the high-cycle fatigue strength, and the fracture toughness. For microstructures with pancake-shaped grains, the anisotropy of the mechanical properties is discussed on the basis of the effective slip length, determined by the length of the soft grain boundary zones. In high-strength Al alloys, the presence of hard inclusions additionally affects the fracture behavior. For (beta)-Ti alloys, the role of the strength difference between the age hardened matrix and the soft grain boundary layers is discussed.