Peritectic titanium alloys for 3D printing

Pere Barriobero-Vila,Joachim Gussone,Jan Haubrich,Norbert Schell,Andreas Stark,Guillermo Requena

doi:10.1038/s41467-018-05819-9

Pere Barriobero-Vila, Joachim Gussone + Show 4 more

Open Access

https://doi.org/10.1038/s41467-018-05819-9

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Abstract

Metal-based additive manufacturing (AM) permits layer-by-layer fabrication of near net-shaped metallic components with complex geometries not achievable using the design constraints of traditional manufacturing. Production savings of titanium-based components by AM are estimated up to 50% owing to the current exorbitant loss of material during machining. Nowadays, most of the titanium alloys for AM are based on conventional compositions still tailored to conventional manufacturing not considering the directional thermal gradient that provokes epitaxial growth during AM. This results in severely textured microstructures associated with anisotropic structural properties usually remaining upon post-AM processing. The present investigations reveal a promising solidification and cooling path for α formation not yet exploited, in which α does not inherit the usual crystallographic orientation relationship with the parent β phase. The associated decrease in anisotropy, accompanied by the formation of equiaxed microstructures represents a step forward toward a next generation of titanium alloys for AM.

Highlights

Metal-based additive manufacturing (AM) permits layer-by-layer fabrication of near netshaped metallic components with complex geometries not achievable using the design constraints of traditional manufacturing
Owing to the complicated thermal history undergone by materials during selective laser melting (SLM), namely sharp cycles of steep heating (~106–107°C s−1) and cooling (>103°C s−1) rates[9], brittle martensitic microstructures unsuitable for structural applications are usually obtained via diffusionless transformation of parent β grains in the as-built condition of α + β Ti alloys
Our approach consists in adding the solute αstabilizer La to commercially pure titanium (CP Ti) aiming at altering the regular Burgers-related β → α transformation

Summary

Introduction

Metal-based additive manufacturing (AM) permits layer-by-layer fabrication of near netshaped metallic components with complex geometries not achievable using the design constraints of traditional manufacturing. This results in severely textured microstructures associated with anisotropic structural properties usually remaining upon post-AM processing. For titanium-based components, these advantages account for estimated production savings up to 50%, by basically missing out exorbitant machining costs and material loss[3] In aerospace, this focuses on parts with high buy-to-fly ratio (BTF): the weight of the purchased stock material to that of the finished part. The typical resulting microstructures are coarse, columnar prior β grains with strong β orientation along the building direction, normal to synthesized powder layers[5,6] This effect is well known to occur in the popular α + β Ti-6Al-4V alloy, which accounts for more than 50% of the titanium market[7] and leads—by far—AM of Ti alloys[8]. Apart from representing a costly methodology that reduces the economical attractiveness of AM, these post-treatments do not represent an alternative to mitigate crystallographic texture and its effect on mechanical performance of the alloys[17,18,19]

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