DEVELOPMENT OF A SURFACE ULTRASONIC WAVE TECHNIQUE FOR THE STUDY OF H ENTRY INTO METALS

Rayleigh acoustic waves were propagated along the surface of sheet samples of Ni and Fe alloys during cathodic charging. The waves were propagated at frequencies from 2 to 8 MHz, and their velocity and attenuation were measured. Attenuation and velocity both decreased during charging, and then increased again after the charging current was removed. These effects could arise from H entering solid solution or from such extraneous phenomena as the influence of bubbles on wave propagation, the formation or decomposition of films on the metal or polarization effects in the electrolyte. A series of experiments are described which establish that the attenuation and velocity changes were in fact due to H entry upon charging and H egress after charging. The process dominating the changes is the interaction of H atoms with dislocations within the outer 100 to 1000Å of the sample surface region

RAYLEIGH WAVE STUDIES OF CATHODIC H-CHARGING OF Fe

The attenuation of 2-6 MHz Rayleigh waves /RW/ was measured in sheet samples of Fe which were undergoing electrolytic charging with H. The cathodic polarization and As2O3 addition into electrolyte were found to effect the attenuation and velocity of the surface waves. The attenuation changes were retarded by the deposition of a thin /2µm/ layer of Cu on the Fe surface, with the Cu acting as a H-permeation barrier. The decrease in attenuation was caused by the entry of H into solid solution at the surface region. The mechanism of attenuation decrease appears to be associated with the decrease of dislocations mobility in the near-surface region by H-atoms. The long time polarization caused by RW attenuation to increase due to the formation of H-induced blisters on or immediately below the sample surface

INTERNAL FRICTION OF HYDROGEN CHARGED AUSTENITIC STAINLESS STEEL

Internal friction of the 18Cr-14Ni austenitic stainless steel subjected to the annealing, cold work and different hydrogen charging treatments has been studied in term to distinguish the effects of hydrogen-dislocation interaction and those caused by the microcracks formation

IN SITU SURFACE ELASTIC WAVE STUDY OF THE METAL - ELECTROLYTE INTERFACE

Les procès d'electrochimie sur des interface métal-électrolyte et absorption d'hydrogène dans les minces couches superficielles influencent comme on peut voir, pour propagation des élastique ondes superficielle.Some electrochemical processes on the metal - electrolyte interface and an absorption of hydrogen within a thin subsurface layer were shown to affect the propagation of the surface elastic waves

Effect of Hydrogen Precharging on Grain Boundary Relaxation in Iron of High Purity

Irreversible change of grain boundary structure due to the different hydrogen charging of annealed and cold worked iron of high purity was studied by internal friction measurements of grain boundary relaxation. Two relaxation modes are involved in the main process of grain boundary relaxation : high temperature mode associated with the GB sliding, and low temperature mode associated with the motion of near grain boundary dislocations

Effect of the Hydrogen Induced Degradation of Steel on the Internal Friction Spectra

The internal friction method was applied to study the process of the formation of hydrogen induced voids in a pipe line steel. Hydrogen precharging to a content, lower than that established in permeation tests as the critical one for void formation, affected the IF spectrum associated with the grain boundary relaxation. This implies the possibility for application of the mechanical spectroscopy methods for detection of initial stages of the hydrogen induced degradation of steels. The effect of hydrogen precharging on the grain boundary structure and on relaxation processes are discussed