Quantities and distribution of strain-induced vacancies and dislocations enhanced by hydrogen in iron

Abstract

The role of hydrogen in the formation behavior of various lattice defects induced by plastic strain in pure iron specimens has been investigated using low-temperature thermal desorption spectroscopy (L-TDS), which can start measurement from −200 °C. Specimens were subjected to various plastic strains within a uniform elongation range in the absence and presence of hydrogen. Strain-induced lattice defects were quantitatively evaluated using L-TDS for specimens saturated with hydrogen as a probe for detecting lattice defects, not only vacancies but also dislocation cores. The L-TDS spectra contained two hydrogen desorption peaks: a low-temperature peak associated with dislocations and a high-temperature peak associated with vacancies. The tracer hydrogen content corresponding to each peak increased with plastic strain. However, when compared at the same plastic strain of 25%, the low-temperature peak, i.e., dislocations, was not enhanced by hydrogen, whereas the high-temperature peak, i.e., vacancies, was enhanced by hydrogen, increasing by about six times at 25% plastic strain and by seven times at 40% plastic strain. Analyses conducted by electron channeling contrast imaging (ECCI) and electron backscattered diffraction (EBSD) revealed that strain was localized along the vicinity of the ferrite grain boundaries at 25% plastic strain in the presence of hydrogen. Hence, the role of hydrogen in the formation behavior of plastic strain-induced lattice defects is presumably to enhance vacancy formation and the localization of the dislocation configuration near the grain boundaries without affecting the amount of dislocations formed.