Abstract
Isothermal oxidation tests of mechanically treated Ti-Beta-21S (TIMET, Ti–15Mo–3Nb–3Al–2Si, ASTM Grade 21) were performed under dry air at 650, 700 and 750 °C for 100 h and compared to untreated samples. Two different mechanical surface treatments were used: ultrasonic shot-peening (SP) and laser-shock peening (LSP). The study investigates the effect of both treatments on the oxidation kinetics of the process and the role of atmospheric nitrogen insertion. With this aim, oxidation experiments were also performed under pure oxygen. The results show that the oxidation is governed by diffusion after a short transient time. Both SP and LSP treatments improve the high temperature oxidation resistance of Ti-Beta-21S in dry air, but not in pure oxygen. The formation of a nitrogen-enriched layer at the oxide–metal interface, which is promoted by the mechanical surface treatments, explains the increase in the oxidation resistance in air by slowing down the diffusion of oxygen into the metal.
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