AN SEM STUDY OF BETA-PHASE DECOMPOSITION DURING THE ANNEALING OF ZR-2.5-PERCENT NB ALLOY

The effect of annealing on the decomposition of the beta-phase in Zr-2 .5% Nb pressure tube material was studied by SEM (scanning electron mi croscopy). Annealing was carried out at 400 degrees C for 0, 24 and 10 00 h. Previous to annealing, the specimens were electrolytically hydri ded, the final hydrogen amount being about 60 mu g/g. Long time anneal ing causes the beta-phase ligaments to decompose into smaller particle s. Hydrides are formed along the beta-phase ligaments and they become shutter as the lengths of the ligaments decrease with annealing. The S EM technique proved to be useful in studying the decomposition of the beta-phase ligaments.