THE EFFECT OF MICROSTRUCTURE ON FATIGUE-CRACK PROPAGATION OF ALPHA-ALLOYS - IN-SITU OBSERVATION OF SHORT FATIGUE-CRACK GROWTH(BETA TITANIUM)

Fatigue crack initiation and early stage of crack growth for Ti-6Al-4V and Ti-4.5Al-3V-2Fe-2Mo were investigated on notched specimens. In-si tu observation on fatigue cracking processes was made on a fatigue tes ting machine mounted in a scanning electron microscope. It was found t hat Ti-4.5Al-3V-2Fe-2Mo alloy with very fine a grains of approximate t o 2 mu m exhibited a much higher fatigue strength at 107 cycles than t hat of Ti-6Al-4V alloy. However, an opposite trend in fatigue life was obtained in the short life regime for the materials tested in the pre sent study. The observed fatigue behavior in both the long and short l ife regimes is discussed in terms of metallurgical factors responsible for the fatigue behavior of the present materials. (C) 1998 Elsevier Science S.A. All rights reserved.