Microstructure and mechanical properties of Ti-6Al-4V-5% hydroxyapatite composite fabricated using electron beam powder bed fusion. Issue 2 (February 2019)

• Record Type: Journal Article
• Authors: Terrazas, César A.; Murr, Lawrence E.; Bermudez, Diego; Arrieta, Edel; Roberson, David A.; Wicker, Ryan B.
• Is Part Of: Journal of materials science & technology. Volume 35:Issue 2(2019)
• Page Start: 309
• Page End: 321
• Publication Date: 2019-02
• Subjects: Hydroxyapatite (HA) -- Metal-matrix ceramic composites -- Open-cellular (mesh) structures -- Electron-beam powder bed fusion (EPBF) -- Additive manufacturing (AM) -- Mechanical properties -- Microstructure characterization; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2018.10.025
• Languages: English
• ISSNs: 1005-0302

Abstract

Abstract: A novel, Ti-6Al-4V (Ti64)/Hydroxyapatite (HA at 5% by weight concentration) metal/ceramic composite has been fabricated using electron beam powder bed fusion (EPBF) additive manufacturing (AM): specifically, the commercial electron beam melting (EBM ® ) process. In addition to solid Ti64 and Ti64/5% HA samples, four different unit cell (model) open-cellular mesh structures for the Ti64/5% HA composite were fabricated having densities ranging from 0.68 to 1.12 g/cm 3, and corresponding Young's moduli ranging from 2.9 to 8.0 GPa, and compressive strengths ranging from ∼3 to 11 MPa. The solid Ti64/5%HA composite exhibited an optimal tensile strength of 123 MPa, and elongation of 5.5% in contrast to a maximum compressive strength of 875 MPa. Both the solid composite and mesh samples deformed primarily by brittle deformation, with the mesh samples exhibiting erratic, brittle crushing. Solid, EPBF-fabricated Ti64 samples had a Vickers microindentation hardness of 4.1 GPa while the Ti64/5%HA solid composite exhibited a Vickers microindentation hardness of 6.8 GPa. The lowest density Ti64/5%HA composite mesh strut sections had a Vickers microindentation hardness of 7.1 GPa. Optical metallography (OM) and scanning electron microscopy (SEM) analysis showed the HA dispersoids to be highly segregated along domain or grain boundaries, but homogeneously distributed along alpha (hcp) platelet boundaries within these domains in the Ti64 matrix for both the solid and mesh composites. The alpha platelet width varied from ∼5 μm in the EPBF-fabricated Ti64 to ∼1.1 μm for the Ti64/5%HA mesh strut. The precursor HA powder diameter averaged 5 μm, in contrast to the dispersed HA particle diameters in the Ti64/5%HA composite which averaged 0.5 μm. This work highlights the use of EPBF AM as a novel process for fabrication of a true composite structure, consisting of a Ti64 matrix and interspersed and exposed HA domains, which to the authors' knowledge has not been reported before. The results also illustrate the prospects not only for fabricating specialized, novel composite bone replacement scaffolds and implants, through the combination of Ti64 and HA, but also prospects for producing a variety of related metal/ceramic composites using EPBF AM.