Research ArticleHEALTH AND MEDICINE

High hardness in the biocompatible intermetallic compound β-Ti3Au

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Science Advances  20 Jul 2016:
Vol. 2, no. 7, e1600319
DOI: 10.1126/sciadv.1600319

Figures

  • Fig. 1 Hardness of Ti1−xAux and other intermetallic alloys and compounds.

    Hardness as a function of x (top axis) or mass density ρ (bottom axis) in Ti1−xAux. Blue squares, medical alloys; green triangles, intermetallic compounds.

  • Fig. 2 Structural analysis of the Ti0.75Au0.25 alloy.

    (A) Crystal structure of the α-Ti3Au phase along with the cuboctahedron local environments of the Au (left inset) and Ti (right inset) atoms. (B) Crystal structure of β-Ti3Au along with the icosahedron local environment of Au (left inset) and the 14-vertex Frank-Kasper polyhedron local environment of Ti (right inset). (C) XRD pattern was fitted with the β-Ti3Au phase (blue vertical symbols). Small inclusions of α-Ti3Au and α-Ti are marked by asterisks. arb. units, arbitrary units. (D and E) HRTEM (high-resolution transmission electron microscopy) images of the Ti0.75Au0.25 sample, taken for the [111] and [100] orientations, respectively. (F and G) SAD (selected area diffraction) images of the [111] and [102] orientations, respectively.

  • Fig. 3 DOS of Ti–Au stoichiometric compounds.

    DOS (solid lines) as a function of energy for β-TiAu (black), TiAu (yellow), TiAu4 (blue), and β-Ti3Au (red), with the pronounced valley around the Fermi energy in β-Ti3Au marked by a dotted line and highlighted in yellow (inset).

  • Fig. 4 Wear analysis of Ti1−xAux alloys against a diamond-SiC disc.

    (A) COF as a function of time for x = 0, 0.25, 0.30, and 0.50. Inset: An alumina container showing that Ti1−xAux adheres to this ceramic component. (B) Wear volumes of Ti1−xAux (dashed) compared to diamond-SiC (solid).

  • Fig. 5 SEM images of pin and disc wear tests.

    (A, C, E, and G) Ti reference ingot (A), Ti1−xAux pins for (C) x = 0.25, (E) x = 0.30, and (G) x = 0.50. (B, D, F, and H) Corresponding wear tracks on the diamond-SiC disc. Red rectangles (right panels) identify the regions of contact between the disc and the pin. For the (E) and (F) pair, there is little wear on both surfaces, indicating the wear resistance of the Ti0.75Au0.25 sample.

Tables

  • Table 1 Composition and wear test summary for the Ti1−xAux alloys.
    xPhase-determinedTi1−xAux discDiamond-SiC disc
    from TEMfrom XRDWear
    volume
    (mm3)
    Wear typeWear
    volume
    (mm3)
    Wear type
    0Reference (commercial specimen)0.038Abrasive, adhesive0.183Adhesive
    0.25β-Ti3Auβ-Ti3Au + α-Ti3Au + α-Ti0.012Abrasive,
    adhesive
    0.163Abrasive, adhesive
    0.33β-Ti3Au + β-TiAuα-Ti3Au + β-Ti3Au + β-TiAu0.010Abrasive, adhesive0.153Adhesive
    0.50β-TiAu + α-Tiβ-TiAu + α-Ti + α-Ti3Au0.017Adhesive0.093Adhesive
  • Table 2 Summary of crystallographic and electronic parameters of the Ti–Au phases.
    Space
    group
    dTi–Au (Å)VED (Å−3)Pseudogap
    W (eV)H/H0
    α-Ti3AuEmbedded Image2.93237 (31)0.18
    β-Ti3AuEmbedded Image2.84478 (57)0.2014
    β-TiAuPmma2.79248 (71)0.1510.4
    TiAu2I4/mmm2.80056 (72)0.120.22
    TiAu4I4/m2.85050 (73)0.10