The mechanism of nucleation of hydrogen blister in metals

Abstract

The nucleating, growing and cracking of hydrogen blister have been investigated experimentally and theoretically. The results show that atomic hydrogen induces superabundant vacancies in metals. The superabundant vacancies and hydrogen aggregate into a hydrogen-vacancy cluster (microcavity). The hydrogen atoms in the microcavity become hydrogen molecules which can stabilize the cluster. And the hydrogen blister nucleates. With the entry of vacancies and hydrogen atoms, the blister nucleus grows and the pressure in the cavity increases. When the stress induced by hydrogen pressure on the blister is up to the cohesive strength, cracks will initiate from the wall of the blister.hydrogen blister, vacancy cluster, nucleation, cracking Hydrogen blister or hydrogen crack appears in many materials in the absence of external stress when the hydrogen concentration is high enough [1][2][3] . The mechanisms of the formation of the blisters or cracks have been discussed widely [4][5][6] . Most of the mechanisms suggest that hydrogen atoms combine into hydrogen molecules in the interface of second phase and matrix, and the hydrogen molecules produce high hydrogen pressure to induce microcracks. The propagation and connection of the microcracks induce the formation of the hydrogen blisters or hydrogen cracks. Hydrogen atoms cannot combine into hydrogen molecules which induce hydrogen pressure when there is no interspace to accommodate the hydrogen atoms. Hydrogen atoms can be trapped in pre-existing microvoids or microcracks in a material and become hydrogen molecules. The microvoids or microcracks containing hydrogen molecules become hydrogen blisters (a lacuna full of H 2 in the interior of materials also is called a hydrogen blister in this paper). For some materials with good plasticity and even single crystalline metals, there are neither microvoids nor microcracks in them, but hydrogen blisters or hydrogen cracks can appear if they are charged. How are the lacunas containing H 2 (hydrogen blister) produced?There are abundant supersaturated vacancies in metals quenched from high temperature. The supersaturated vacancies can aggregate into vacancy clusters (microlacuna) and then collapse into dislocation loops or stacking fault tetrahedral [7] . If the supersaturated vacancies can be induced by hydrogen and can aggregate into vacancy clusters to accommodate molecular hydrogen, the hydrogen blisters will be formed during charging. This work is an attempt to confirm this hypothesis through experiments and theoretical analysis. Here a mechanism describing the nucleating, growing and cracking of hydrogen blister in metals is presented.

Non-Pd BCC alloy membranes for industrial hydrogen separation

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Neutron imaging of hydrogen in iron and steel

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Tratamientos Térmicos y Corrosión en Niebla Salina en acero inoxidable AISI 316L

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