Crack Initiation Behavior and Microstructural Deformation in Commercially Pure Titanium under Low-Cycle Fatigue Loading

Abstract

Low-cycle fatigue tests have been carried out on an annealed commercially pure titanium under strain-controlled conditions with constant strain range. The initiation of fatigue cracks was observed successively with the aid of an optical microscope using the replication technique and microstructural deformations were measured. Results show that fatigue crack initiation was predominantly intergranular ; however, slip band cracks often appeared also in the low strain range. At the specified grain boundaries, irreversible steps attributed to a few slip systems formed under each strain cycle. The accumulation of irreversible steps due to strain cycling is thought to cause intergranular cracking.