Utilization of a microstructure sensitive fatigue model for additively manufactured Ti-6Al-4V

Abstract

Purpose The purpose of this study is to calibrate a microstructure-based fatigue model for its use in predicting fatigue life of additively manufactured (AM) Ti-6Al-4V. Fatigue models that are capable of better predicting the fatigue behavior of AM metals is required to further the adoption of such metals by various industries. The trustworthiness of AM metallic material is not well characterized, and fatigue models that consider unique microstructure and porosity inherent to AM parts are needed. Design/methodology/approach Various Ti-6Al-4V samples were additively manufactured using Laser Engineered Net Shaping (LENS), a direct laser deposition method. The porosity within the LENS samples, as well as their subsequent heat treatment, was varied to determine the effects of microstructure and defects on fatigue life. The as-built and heat-treated LENS samples, together with wrought Ti-6Al-4V samples, underwent fatigue testing and microstructure and fractographic inspection. The collected microstructure/defect statistics were used for calibrating a microstructure-sensitive fatigue model. Findings Fatigue lives of the LENS Ti-6Al-4V samples were found to be consistently less than those of the wrought Ti-6Al-4V samples, and this is attributed to the presence of pores/defects within the LENS material. Results further indicate that LENS Ti-6Al-4V fatigue lives, as predicted by the used microstructure-sensitive fatigue model, are in close agreement with experimental results. The used model could predict upper and lower prediction bounds based on defect statistics. All the fatigue data were found to be within the bounds predicted by the microstructure-sensitive fatigue model. Research limitations/implications To further test the utility of microstructure-sensitive fatigue models for predicting fatigue life of AM samples, future studies on additional material types, additive manufacturing processes and heat treatments should be conducted. Originality/value This study shows the utility of a microstructure-sensitive fatigue model for use in predicting the fatigue life of LENS Ti-6Al-4V with various levels of porosity and while in a heat-treated condition.