MICROSTRUCTURES PROPERTIES RELATIONSHIPS IN ALPHA+BETA TITANIUM-ALLOYS - APPLICATION ON THE TI-6AL-2SN-4ZR-6MO ALLOY IN ULTRASONIC FATIGUE/

The purpose of this research is to bring out the microstructural param eters that control the damage of the Ti-6 Al-2 Sn-4 Zr-6 Mo alloy in v ibratory fatigue at 20 kHz at stress temperatures of 77 and 300 K. A m icrostructural characterization was done at various scales : size and deformation of the beta ex-grains, morphologies of the primary alpha p hase coming from forging, fine precipitation appealing by decompositio n of the beta phase during quenching. Comparison for the various therm omechanical treatment ranges of the results of fatigue tests and quant ification of the microstructure have ended in a better understanding o f the damage mechanisms and in quantifying the influence of the number of alpha(p)/beta interfaces on crack initiation.