Influence of Aggressive Media on the Mechanical Behavior of the Uranium--0.20Wt % Vanadium Alloy the Role of Hydrogen Embrittlement.

摘要

The tests comprised tensile tests under constant load or up to the fracture point using cylindrical or flat,trapezoidal test pieces,tests in which disks were ruptured under gaseous pressure,and tenacity tests. The alloy was found to be sensitive to: (1) intrinsic brittleness (I.B.) due to dissolved residual hydrogen from the preparation stage. This manifested itself mainly by cracking at an elongation threshold of about 3percent. (2) Cracking due to stress corrosion (S.C.C.) in the true sense,which is made possible under certain conditions by an imperfect passivation of the metal surface. The process is initiated either by the appearance of microcracks which appear at the surface,or by corrosion pits. (3) Generalized corrosion accelerated by the stress (S.A.C.),whose microscopic appearance is similar to that observed with corrosion under gaseous hydrogen. Below pH 2there is no stress corrosion. Stress rupture tests in moist air at 80and 100exp 0 C measure I.B. + S.C.C. under high stress,giving rise to short lifetimes. I.B. + S.C.C. + S.A.C.,with S.A.C. predominant,occurs under lower stresses that give long lifetimes. Stress rupture tests measure at 20and 60exp 0 C I.B. + S.C.C. with I.B. predominant. Under high stresses (short lifetimes) the magnitude of the S.C.C. component increases as the temperature increases. The most serious effects are those of S.A.C. at 80and 100exp 0 C,and of I.B. at all temperatures. The way this alloy behaves can only be changed by an effective reduction in the quantity of residual hydrogen present,or by coatings that will in no case allow the ingress of hydrogen. 62fig, 82references, 15tables.