Plasticity and damage mechanisms in Ti-6Al-4V printed with selective laser melting

TL;DR

This study investigates the microstructural damage mechanisms in Ti-6Al-4V produced by selective laser melting, revealing hierarchical martensitic structures and their influence on deformation and fracture behavior.

Contribution

It provides detailed microstructural analysis of additively manufactured Ti-6Al-4V, linking hierarchical phases to damage mechanisms during tensile deformation.

Findings

Hierarchical microstructures with primary, secondary, and tertiary {} martensite.

Strain localization causes micro-void formation and brittle fracture.

Interfacial plasticity influences deformation at grain boundaries.

Abstract

The ability to create complex geometries with tailored material properties has brought interest in using additive manufacturing (AM) techniques in various industrial applications. However, the complex relationship between AM process parameters, microstructure, and resultant properties of metals needs to be fully understood for the widespread use of metal AM. In this study, selective laser melting is used to print Ti-6Al-4V. In-situ tensile tests with concurrent detailed microstructural analysis using electron backscatter diffraction, electron channeling contrast imaging, and digital image correlation are performed to understand the damage mechanism and its relation to the microstructure. Our results show that the as-printed part develops a hierarchical microstructures, consisting of primary, secondary, and tertiary {\alpha}^' martensite. This hierarchical structure is formed as a result of cyclic heat treatment during the course of selective laser melting. Upon deformation, strain localization within primary {\alpha}^' martensite results in microscopic ductile micro-void formation and coalescence, as well as macroscopic brittle fracture. In addition to localization inside primary {\alpha}^', surface steps at the boundaries of these high aspect ratio grains are formed which reveal the contribution of interfacial plasticity to the overall deformation of the material.