Impact of plastic strain amplitude on the cyclic behavior of commercially pure titanium grade 2

Abstract

The present study focuses on investigating the impact of plastic strain amplitude on the mechanical behavior of T40 (Grade 2) under low cycle fatigue (LCF) at room temperature with a strain rate of 2 × 10−3 s−1. The mechanical behavior is analyzed in terms of effective and back stress evolution, and the relationship between the microstructural observations, based on analyses using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The evolution of stress amplitude as a function of cyclic number highlights a competition between hardening and softening processes. Both effects can be related to a specific evolution of internal stresses with dislocation patterns and dislocation/oxygen interactions. Crack initiation and propagation regimes are studied using the measurement of striation spacing and TEM-FIB samples on the crack surface. Crack initiates along (10–12) twins and propagates with a crack growth rate directly proportional to the dislocation inter-wall spacing.