MICROSTRUCTURAL EVOLUTIONS AND MECHANICAL PROPERTIES DURING LONG-TERM AGEING OF TITANIUM ALLOY Ti-17

• Published in: MATEC Web of Conferences 2020, Vol.321, p.12004
• Main Authors: Maury, Nicolas, Dehmas, Moukrane, Archambeau-Mirguet, Claude, Delfosse, Jérôme, Aeby-Gautier, Elisabeth
• Format: Article
• Language: English
• Subjects: ageing; Aging; Aging (metallurgy); Beta phase; Chromium; crystallography; Elongation; Grains; Heat treating; Heat treatment; Image analysis; Mechanical properties; Microstructure; Molybdenum; near-β alloy; Precipitates; Spatial distribution; Titanium alloys; Titanium base alloys; Ultimate tensile strength
• ISSN: 2261-236X; 2274-7214; 2261-236X
• DOI: 10.1051/matecconf/202032112004

Microstructural evolutions and resulting mechanical properties have been investigated in the near-β Ti-17 alloy following long- term ageing heat-treatment up to 6000 h at 450 °C. The initial microstructure was bimodal lamellar, consisting of two populations of α grains (α lam-primary and α secondary ) in a β phase matrix. Two microstructures were obtained either via controlled heat- treatments from the β phase field - in order to generate significant differences in the grain fraction, size, density and spatial distribution - or sampled from a part submitted to an industrial processing route. High energy XRD reveals that whatever the initial microstructure, the amount of α phase increases significantly after 1000 h long-term ageing. Complementary SEM and image analysis characterizations enable to deduce that this evolution is the consequence of α secondary growth and/or coarsening. Also, TEM observations and EDX analysis show that the Mo and Cr contents of the β phase increase and that α 2 nano-precipitates form within the α lam-primary grains. Considering the mechanical properties, long-term ageing leads to an increase in the yield and ultimate tensile strength, as well as a decrease in the elongation at failure, at an extent which depends on the ageing time.