Chapter 25 - State-of-the-art in additive manufacturing of Ti–6Al–4V: recent progress and insights into future developments

Abstract

Titanium alloys have excellent biocompatibility, low density, high specific strength, and corrosion resistance, which promoted them for use in biomedical implants, dental repairs, and the aerospace industry. Ti–6Al–4V is an α+β alloy with superior biocompatibility and an interesting balance of properties (moderately high tensile strength and intermediate fatigue toughness). Therefore, it is one of the most consumed Ti alloys. Additive manufacturing (AM) processes have recently received a lot of attention, and remarkable progress is being made in the field of AM of Ti–6Al–4V. The process–structure–property relationships in additively manufactured Ti–6Al–4V parts are characteristically distinctive due to the thermomechanical history the parts experience during processing. Laser powder bed fusion (L-PBF) involves highly localized energy input, large temperature gradients, and high cooling rates; these thermodynamic events significantly affect the microstructure of the parts, leading to high residual stresses, increasing the strength of the part but compromising the fatigue properties and ductility. The harsh processing conditions can also lead to the formation of various types of defects that play a crucial role in the structural integrity and performance of the parts. Furthermore, the layer-by-layer fashion in which L-PBF works yields parts that are intrinsically anisotropic. A lot of researchers’ efforts are currently invested in tailoring the properties of AM Ti–6Al–4V through manipulating the microstructure via in situ and ex situ treatments, such as conventional thermal treatments, hot isostatic pressing, and novel customized rapid heat treatments. In addition to the metallurgical aspect of the process, the fabrication of various geometries with high degrees of intricacy (e.g., nature-inspired lattice structures), exploiting the full potential in the unprecedented degrees of freedom offered by the technology, to customize and engineer the mechanical performance of AM parts is attracting considerable attention. This chapter aims to provide a comprehensive overview of the state-of-the art of AM of the Ti–6Al–4V alloys, focusing on the L-PBF technology and the in situ and ex situ treatments, including feedstock modifications, that can be utilized to obtain the desired microstructures and mechanical properties. Nevertheless, exemplar case studies and proposals on the use of L-PBF Ti–6Al–4V to achieve customized mechanical behavior when manufacturing bone implants are presented.