MATEC Web Conf.
Volume 321, 2020The 14th World Conference on Titanium (Ti 2019)
|Number of page(s)||6|
|Published online||12 October 2020|
Gaseous thermochemical synthesis and characterization of mixed interstitial phases in the Ti-C-O system
Technical University of Denmark, DK 2800 Kgs. Lyngby, Denmark
1 Department of Mechanical Engineering
2 Department of Chemistry
Titanium grade 2 thin foils were carbo-oxidized at 800 °C in a thermogravimetric analyzer in CO gas for 20 - 100 hours. The synthesized thin foils were characterized by infrared carbon determination for composition analysis, transmission X-ray diffraction (XRD), light optical microscopy (LOM) and nanoindentation. Thermodynamic equilibrium predictions were performed using ThermoCalc. Oxygen and carbon expanded h.c.p. α and NaCl type δ carbo-oxide were identified from the XRD patterns. Rietveld refinements of the XRD patterns revealed an increase in expansion of the h.c.p. α lattice from interstitially dissolved C and O: the c/a ratio increases from 1.588 for interstitially free h.c.p. α to 1.607 after 100 hours of exposure. The overall carbon and oxygen content after 100 hours was 4.2 wt% and 5.5 wt%, respectively; these overall compositions correspond to the two-phase α + δ region in the calculated ternary phase diagram. The microstructure from LOM revealed large grains of expanded α-phase and a surface zone consisting of porous δ carbo-oxide. The hardness, as determined by indentation, of the expanded α increased linearly with the c/a ratio, resulting in an increase to 11748 MPA after 100 hours exposure from 2193 MPa for the untreated Ti grade 2.
Key words: Titanium / Transmission X-Ray diffraction / Rietveld refinement / Gaseous carbo-oxidation / Light optical microscopy / Nanoindentation / ThermoCalc
© The Authors, published by EDP Sciences, 2020
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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