Abstract
Ti-6Al-4V is commonly used in orthopaedic implants, and fabrication techniques such as Powder Bed Fusion (PBF) are becoming increasingly popular for the net-shape production of such implants, as PBF allows for complex customisation and minimal material wastage. Present research into PBF fabricated Ti-6Al-4V focuses on new design strategies (e.g. designing pores, struts or lattices) or mechanical property optimisation through process parameter control–however, it is pertinent to examine the effects of altering PBF process parameters on properties relating to bioactivity. Herein, changes in Ti-6Al-4V microstructure, mechanical properties and surface characteristics were examined as a result of varying PBF process parameters, with a view to understanding how to tune Ti-6Al-4V bio-activity during the fabrication stage itself. The interplay between various PBF laser scan speeds and laser powers influenced Ti-6Al-4V hardness, porosity, roughness and corrosion resistance, in a manner not clearly described by the commonly used volumetric energy density (VED) design variable. Key findings indicate that the relationships between PBF process parameters and ultimate Ti-6Al-4V properties are not straightforward as expected, and that wide ranges of porosity (0.03 ± 0.01% to 32.59 ± 2.72%) and corrosion resistance can be achieved through relatively minor changes in process parameters used–indicating volumetric energy density is a poor predictor of PBF Ti-6Al-4V properties. While variations in electrochemical behaviour with respect to the process parameters used in the PBF fabrication of Ti-6Al-4V have previously been reported, this study presents data regarding important surface characteristics over a large process window, reflecting the full capabilities of current PBF machinery.
Highlights
Titanium-based alloys, Ti-6Al-4V, are the most commonly used materials for orthopaedic implants, due to properties such as low cytotoxicity and high mechanical strength [1,2,3,4]
The samples produced with low volumetric energy density (VED) (< 50 J/mm3) had comparatively fewer partially melted particles across their x/y surfaces than those produced with higher VED (> 55 J/mm3), likely due to comparatively exaggerated cooling rates/heat transfer between the final layer and the surrounding powder caused by the higher thermal energy supplied per unit volume
Powder Bed Fusion has the potential to produce effective and long-lasting customised Ti-6Al4V orthopaedic implants, with the careful control of process parameters used during fabrication
Summary
Titanium-based alloys, Ti-6Al-4V, are the most commonly used materials for orthopaedic implants, due to properties such as low cytotoxicity and high mechanical strength [1,2,3,4]. Successful orthopaedic implant fixation requires good osseointegration, with osseointegration being defined as the formation of a direct structural and functional connection between living bone and the surface of a load-bearing implant [5,6,7]. For permanent fixation, the host bone must be active enough to form a stable chemical bond with the orthopaedic implant surface. Ti-6Al-4V surfaces exhibit low cytotoxicity, but are bio-inert, and so do not interact well with host bone cells; only weak interfacial bonds are formed following implantation, leading to inferior long term fixation [8,9,10,11]. Conventional implant manufacturing processes cannot accommodate the need for supplementary features or patient-specific implants, advances in additive manufacturing allow for the production of previously un-manufacturable complex shapes, structures and features
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