No abstract

The experiments of Heller and of Au and Birnbaum on the anelastic relaxation and the magnetic after‐effect of hydrogen in iron in the temperature range of 20 to 60 K are repeated with high‐purity iron that had been hydrogen‐charged by electrolysis or quenched under hydrogen atmosphere (500 at, 1100 K). Heller's relaxation peak is observed but is found to be identical with the α‐peak obtained on the same iron after room‐temperature cold‐work without hydrogen. A magnetic after‐effect is also found but with an amplitude ten times smaller than that of the earlier experiments. It is concluded that the peak observed by Heller is created by cold‐working during hydrogen charging and that either the non‐cubic distortions associated with isolated hydrogen interstitials in α‐Fe are very small or the relaxation effects due to hydrogen must occur below 4 K.

on the occasion of his 75th birthdayThe internal friction spectrum of pure iron specimens, deformed at room temperature, presents near 25 K (1 Hz) a peak a attributed t o the generation of kink pairs on non-screw dislocations. When such specimens arc subsequently irradiated or plastically deformed at low temperatures, peak a is suppressed and replaced by peak PI, attributed to the interaction between non-screw dislocations and intrinsic point defects. The evolution of p1 and its final reconversion into a during successive annealing treatments yields information about the arrival, clustering, and final annihilation of defects on the dislocation segments. The interpretation of the results is consistent with the long-range migration of interstitials at 125 K and of vacancies a t 220 K.Apres deformation it temphratnre ambiante. un Bchantillon de fcr pur presente un pic CI situB vers 25 K (1 Hz) a t t r i b d B la generation de double dBcrochements sur les dislocations non vis.Quand cct Bchantillon est ensuite irradiB, ou bien deform6 plastiquement A bassc temperature. le pic a est supprime e t remplace par un pic PI, attribu6 B I'interaction entre les dislocations non vis e t des dkfaut,s ponctuels intrinshques. L'~vo1ution du pic B1 e t sa reconversion finale en un pic a a u cows de traitements thermiques successifs donne dcs informations a u sujet de I'arrivhe des defauts sur les segments de dislocations, puis de leur agglom6ration e t de leur annihilation. L'intcrpretation des rksultats est compatible avec I'hypothbse d'une migration tridiniensionnelle a longue distance des interstitiels B 125 K e t des Iacunes B 220 K. l ) 85X, 38041 Grenoble CBdex, France.

The fracture toughness of AISI 304 and 316L stainless steels and their welds irradiated to 7 × 1025 neutrons (n)/m2 (50 percent of this was at E > 0.1 MeV) was investigated on 10- and 20-mm-thick three-point bend specimens. Measurements of critical values of the J-integral, Jc, and the crack-opening displacement, δc, defined at the onset of stable crack growth, were performed at 20 and 400°C. The electric potential method was adapted to hot-cell operation for the detection of the initiation point. Drastic reductions of fracture toughness occur when combining welding, irradiation, and high temperature. As an example, the value δc = 0.51 mm of base-material nonirradiated specimens tested at 20°C drops to 0.011 mm for welded irradiated specimens tested at 400°C. The consequences on liquid metal fast breeder reactor (LMFBR) structural design are illustrated in the case of the French LMFBR Super Phénix.

The internal friction spectrum of pure iron deformed and then charged with hydrogen present,s the experimentally well established hydrogen Snoek-Koster peak together with a second peak which occurs initially a t about 4 K. Like the Snoek-Koster peak, this second peak requires the presence of both, hydrogen and dislocations. It is attributed to the interaction between hydrogen and preexisting geometrical kinks on the dislocations. The absence of a hydrogen Snoek-type relaxation invalidates many of the previous determinations and estimates of the diffusion coefficient of hydrogen in iron a t low temperatures. Indirect proof of the long distance migration of hydrogen is given by dislocation unpinning experiments a t 4 K. The subsequent repinning occurs in several stages the first of which is a t 18 K.Le spectre de frottement interne du fer pur deform6 puis charge en hydrogene prksente, en plus du pic de Snoek-Koster bien connu, u n second pic qui se situe initialement a environ 4 K. De m6me que le pic de Snoek-Koster, ce second pic necessite la presence a la fois d'hydroghe e t de dislocations. I1 est attribuk Q I'interaction entre I'hydrogkne e t les dkcrochements geoni6triques preexistants sur les dislocations. L'absence d'une relaxation de type Snoek retire toute valeur aux determinations antkrieures du coefficient de diffusion de I'hydroghe dans le fer basse temperature. Des preuves indirectes btablissant la migrat.ion a longue distance de l'hydrogkne sont donnees par des expkriences de des6pinglage a 4 K. Le rkbpinglage se produit en plusieurs stades, le premier se situant Q 18 K.