RESEARCH DESIGN TO EVALUATE Zr-2.5Nb AND Zr-2.5Nb-0.5Cu ALLOYS FOR DELAYED FAILURE HYDROGEN EMBRITTLEMENT. Final Report, October 15, 1962-October 14, 1963

In a previous program, the existence of moderate delayed failure of Zr-- 2.5Nb with 500 ppm absorbed hydrogen was established. The present investigation is to determine static fatigue susceptibility of this alloy under various conditions of hydrogen content, heat treatment, and metallurgical condition and includes study of the ternary modification Zr-- 2.5Nb -0.5Cu. Notched and unnotched specimens were evaluated under static loading conditions, primarily at room temperature and with 500 ppm absorbed hydrogen, and the time to failure and fracture characteristics were determined. The metallurgical history which resulted in significant delayed failure susceptibility consisted of water quenching followed by an aging treatment which gave a matrix of entirely transformed beta. If an alphatransformed beta microstructure was produced, static fatigue was markedly attenuated. The results can be accounted for by consideration of whether a crack nucleus cand propagate through the matrix or be stopped by local plastic yielding. The propagation of cracks is therefore determined by matrix strength and ductility, which appear to be strong factors in determining hydrogen embrittlement. (auth