Notch Fracture predictions using the Phase Field method for Ti-6Al-4V produced by Selective Laser Melting after different post-processing conditions

TL;DR

This study uses a Phase Field method to predict notch fracture behavior of Ti-6Al-4V produced by Selective Laser Melting, considering different post-processing conditions and their effects on fracture resistance.

Contribution

It introduces a brittle-elastic-plastic Phase Field framework for accurate prediction of notch fracture in additively manufactured Ti-6Al-4V under various post-processing treatments.

Findings

As-built SLM condition exhibits elastic behavior.

Heat treatment and HIP require elastic-plastic modeling.

Oxygen uptake causes brittle failures, especially in V-notch geometry.

Abstract

Ti-6Al-4V is a titanium alloy with excellent properties for lightweight applications and its production through Additive Manufacturing processes is attractive for different industrial sectors. In this work, the influence of mechanical properties on the notch fracture resistance of Ti-6Al-4V produced by Selective Laser Melting is numerically investigated. Literature data is used to inform material behaviour. The as-built brittle behaviour is compared to the enhanced ductile response after heat treatment (HT) and hot isostatic pressing (HIP) post-processes. A Phase Field framework is adopted to capture damage nucleation and propagation from two different notch geometries and a discussion on the influence of fracture energy and the characteristic length is carried out. In addition, the influence of oxygen uptake is analysed by reproducing non-inert atmospheres during HT and HIP, showing that oxygen shifts fracture to brittle failures due to the formation of an alpha case layer, especially for the V-notch geometry. Results show that a pure elastic behaviour can be assumed for the as-built SLM condition, whereas elastic-plastic phenomena must be modelled for specimens subjected to heat treatment or hot isostatic pressing. The present brittle Phase Field framework coupled with an elastic-plastic constitutive analysis is demonstrated to be a robust prediction tool for notch fracture after different post-processing routes.