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Titanium was powder siliconized and gas nitrided, in order to improve its cyclic-oxidation resistance. Siliconizing was performed in a pure-silicon powder at temperatures in the range of 800-1100 • C for 3-48 h. Gas nitriding was carried out in pure N 2 at 1100 • C/12 h. Cyclic-oxidation experiments with the siliconized and nitrided samples were conducted in air at 850 and 950 • C for up to 560 h. It was found that the siliconized layers grew according to the parabolic law with the activation energy for siliconizing E S being 47.2 kJ mol −1 . Powder siliconizing at 900-1100 • C/3 h produced multi-phase layers, in which Ti 5 Si 3 silicide predominated The siliconizing temperature of 800 • C/3 h appeared to be insufficient, because it led to a non-uniform surface layer with a slight protective effect. The nitrided layers were composed of titanium nitride TiN and α-Ti(N) intestitial solid solution. Measurement of the oxidation kinetics revealed that the titanium siliconized at 900-1100 • C/3 h oxidized much more slowly than pure Ti, Ti-6Al-4V alloy and nitrided titanium. Microstructural investigation revealed the complex substructure of the scales on the siliconized samples which was composed of rutile+silica, rutile and nitrogen-rich sub-layers. The mechanism of high-temperature cyclic oxidation of the siliconized and nitrided titanium is discussed.

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