INTERNAL-FRICTION IN HYDROGEN-CHARGED CRNI AND CRNIMN AUSTENITIC STAINLESS-STEELS

Relaxation and hysteretic phenomena caused by hydrogen in Cr18Ni15, Cr 25Ni20, and Cr18Ni16Mn10 steels have been studied by using a low-frequ ency internal friction (IF) technique. Five IF peaks were observed in the temperature range of 80 to 450 K; three of them are of relaxation nature and two others have a hysteretic;character. The enthalpies of a ctivation have been evaluated by means of thermoactivation analysis. S hort-range migration of hydrogen atoms has been found to be responsibl e for the relaxation peaks, while the hysteretic peaks have been attri buted to the outgassing processes accompanied by cracking. It follows from the data on orientation dependence of the relaxation strength and values of the activation enthalpies that relaxation has a Snoeklike n ature and is caused by reorientation of complexes of hydrogen atoms wi th substitutional solutes causing noncubic defects, the symmetry of wh ich is not higher than orthorhombic. Study of the composition effects has led to the conclusion that different substitutional solutes contri bute to different components of the relaxation spectra in accordance w ith their influence on hydrogen diffusivity. Effect of electron irradi ation on hydrogen-induced relaxation was studied and explained in term s of short-range atomic order. No indication of hydrogen-induced Snoek -Koster (SK) relaxation was observed in accordance with the data avail able evidencing absence of SK relaxation in face-centered cubic (fcc) metals having low values of stacking fault energy.