QUANTIFICATION OF THE MINOR PRECIPITATES IN UDIMET(TM) ALLOY720(LI) USING ELECTROLYTIC EXTRACTION AND X-RAY-DIFFRACTION

A study on the quantification of the minor precipitates such as a-phas e, carbide and boride in UDIMET(TM) alloy720 (U720) and alloy720LI (U7 20LI) was carried out. A quantitative X-ray diffraction technique comb ined with electrolytic extraction has been used to quantify the micro- constituents. It was shown that U720LI is much less prone to a formati on than U720. At 800 degrees C, the weight fraction of a in U720LI rem ained at a level as low as approximate to 0.1%, even after 3000 h of e xposure. In U720, on the contrary, it increased remarkably with exposu re up to 1000 h and then saturated at,approximate to 5%. A close exami nation of the a formation mechanism using transmission electron micros copy (TEM), shows that sigma forms and grows in consumption of gamma'- phases. M23C6-type carbide and M3B2-type boride precipitates did not s how any significant variations of amount in both alloys, U720LI and U7 20, during long time exposure at 800 degrees C. (C) 1998 Elsevier Scie nce S.A. All rights reserved.