Characterization of Nano-Sized Features in Powder Bed Additively Manufactured Ti-6Al-4V Alloy

TL;DR

This study explores the nano-sized features in Ti-6Al-4V alloy produced through additive manufacturing and heat treatment.

Contribution

The paper identifies and characterizes previously overlooked nano-sized α-Ti regions formed during incomplete β-Ti precipitation.

Findings

Nano-sized particles inside α-Ti laths are not a new phase but strained α-Ti regions.

Incomplete β-Ti precipitation leads to isolated relaxed α-Ti regions surrounded by strained α-Ti.

High-resolution transmission electron microscopy reveals atomic position shifts in strained α-Ti.

Abstract

In this study, we delve into the intricate microstructural features of Ti-6Al-4V alloy additively manufactured and heat-treated at 800 °C for 4 h. Our in-depth analysis will enable us to gain a better understanding of the β-Ti precipitation process, its dependence on temperature, and its ultimate effect on the overall mechanical properties. As well as α-Ti martensite grains and β-Ti particles interspersed in the α-Ti grain boundaries, there is a third microstructural feature, overlooked by many researchers. This feature is observed as nano-sized particles homogeneously embedded inside the α-Ti laths. Using high-resolution transmission electron microscopy, we reveal that these nano-sized features do not constitute a different phase. Instead, they define isolated regions of α-Ti in its relaxed form, surrounded by the heavily strained form of the α-Ti phase. This phenomenon is a result of the “incomplete” precipitation of the β-Ti phase following the heat treatment stage. The straining of the α-Ti phase appears as a shift in the equilibrium atomic position.

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