A Nucleation Mechanism of Hydrogen Blister in Metals and Alloys

Abstract

The nucleation process of hydrogen blister in metals was investigated through experiments and the mechanism was discussed. Small hydrogen blister in charged Ni-P amorphous coating and steel was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermodynamics and kinetics of hydrogen and vacancies in metals are analyzed. Further, an approach of the nucleation mechanism of hydrogen blister is proposed as follows. Atomic hydrogen can induce superabundant vacancies in metals. The superabundant vacancies and hydrogen aggregate into a hydrogen-vacancy cluster (small cavity). The hydrogen atoms in the hydrogen-vacancy cluster become hydrogen molecules that can stabilize the cluster. And the hydrogen blister nucleates. The pressure in the small cavity increases as the hydrogen atoms enter the cavity. The cluster, that is, the hydrogen blister nucleus, grows through vacancies diffusing into it under the action of cluster-hydrogen binding energy and hydrogen pressure. When the blister nucleus grows to a critical size C cr cracks will initiate from the wall of the cavity due to the internal hydrogen pressure.

Role of Microstructure in Susceptibility of X70 Pipeline Steel to Hydrogen Embrittlement

“…Similar external and internal damage was observed after cathodic hydrogen charging of steels [3][4][5]. Ren et al [4] has proposed that internal cavities can occur by the aggregation of hydrogen atoms and vacancies at trapping sites in the microstructure, resulting in blister formation and growth if cavity is proximate to the surface. On reaching a critical size the internal hydrogen-filled cavity can initiate cracking at the edges of the cavity due to to the internal hydrogen pressure.…”

“…This is typical for pipeline steels and pressure vessels in contact with wet hydrogen sulphide or hydrocarbons [1,2]. Similar external and internal damage was observed after cathodic hydrogen charging of steels [3][4][5]. Ren et al [4] has proposed that internal cavities can occur by the aggregation of hydrogen atoms and vacancies at trapping sites in the microstructure, resulting in blister formation and growth if cavity is proximate to the surface.…”

“…On reaching a critical size the internal hydrogen-filled cavity can initiate cracking at the edges of the cavity due to to the internal hydrogen pressure. It has been reported that grain boundaries, interfaces between inclusions and the matrix and/or phase interfaces can act as hydrogen trapping sites for nucleation of cavities [4][5][6][7][8][9]. Of these, interfaces between oxide inclusions and matrix are deemed to be the most common sites for cavity nucleation and crack extension [8,9].…”

Investigation of the effect of electrolytic hydrogen charging of X70 steel: II. Microstructural and crystallographic analyses of the formation of hydrogen induced cracks and blisters

“…In relation to the initiation of cracking and cavity development, Ren et al [10] proposed a formation mechanism that involves the aggregation of hydrogen atoms and vacancies at trapping sites to form a "blister nucleus", followed by cracking at the edges of the cavity when the internal hydrogen pressure and the stress concentration produce a "nucleus" of critical size. Several publications [10][11][12][13][14] have shown that second phase particles are the most common nucleation sites for cracks that result in the formation of internal cavities.…”

“…Several publications [10][11][12][13][14] have shown that second phase particles are the most common nucleation sites for cracks that result in the formation of internal cavities.…”