Slip intermittency and dwell fatigue in titanium alloys: a discrete dislocation plasticity analysis

TL;DR

This paper investigates slip intermittency and stress oscillations in titanium alloys using a discrete dislocation plasticity model, revealing dislocation escape mechanisms and the influence of oxygen on stress behavior relevant to jet engine safety.

Contribution

It introduces a DDP model that explains slip intermittency and stress oscillations in titanium alloys, highlighting the role of dislocation escape and oxygen effects.

Findings

Dislocation escape from obstacles causes slip intermittency.

Stress oscillations are influenced by thermal activation and oxygen content.

<a>-basal slip exhibits larger stress drops than <a>-prism slip.

Abstract

Slip intermittency and stress oscillations in titanium alloy Ti-7Al-O that were observed using in-situ far-field high energy X-ray diffraction microscopy (ff-HEDM) are investigated using a discrete dislocation plasticity (DDP) model. The mechanistic foundation of slip intermittency and stress oscillations are shown to be dislocation escape from obstacles during stress holds, governed by a thermal activation constitutive law. The stress drop events due to <a>-basal slip are larger in magnitude than those along <a>-prism, which is a consequence of their differing rate sensitivities, previously found from micropillar testing. It is suggested that interstitial oxygen suppresses stress oscillations by inhibiting the thermal activation process. Understanding of these mechanisms is of benefit to the design and safety assessment of jet engine titanium alloys subjected to dwell fatigue.