HIGH TEMPERATURE BEHAVIOUR OF TI ALLOYS IN MOIST AIR

Titanium alloys are very interesting for applications because of their low density, high mechanical resistance and good resistance to corrosion in aggressive environments. However, recent developments impose the use of these materials at higher temperatures than those initially defined, revealing some uncertainties on their behaviour (above 400 degrees C). Apart from temperature, the humidity of the exposure environment can also significantly influence the material behaviour. This study aims to evaluate the behaviour of three Ti alloys (TA6V, Ti6242S and beta 21S) at 560 degrees C under real ambient atmospheres. The tests are done under laboratory air and in air enriched with water vapour in order to evaluate the behaviour of these grades in complex exposure conditions. The alloys evolution after 600 hours exposition was characterised by using several technics: SEM observations (surface and cross-section), XRD and micro-hardness profiling on cross sections.