Characterization #alpha# _2 precipitates in a (#alpha# / #beta# )-titanium alloy

摘要

Microstructural characterization of precipitation in Ti-6Al-2Cr-2Mo-2Sn-2Zr-0.2Si (Ti-6-22-22S) has been conducted using optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). The presence of very fine #alpha# _2 precipitates has been identified by electron diffraction. The #alpha# _2 precipitates formed within the #alpha# matrix of the conventional "TRIPLEX" heat treated materials and also in samples cooled from the #beta# phase field with cooling rates less than 5.5 deg C /sec. Dark field and HREM imaging ascertained that the #alpha# _2 precipitates were homogeneously distributed within the #alpha# phase with size of about 1-2nm. Aging between 600 deg C and 650 deg C further stabilized the #alpha# _2 precipitates. No detrimental effect on the mechanical properties has been observed for the TRIPLEX heat treated materials despite of the presence of these very fine ordered procipitates in Ti-6-22-22S.