Nickel and iron-based alloys: hydrogen decohesion mechanism

G. CANTO; C. LANZ; SIMONETTI, S.; I. SALAZAR-EHUAN

San Diego

Conferencia; International Conference on Metallurgical Coating & Tin Films; 2017

ICMCTF

Nickel and iron-based alloys are used for high-temperature industrial devices. These materials are sensitive tosubstances in the operating atmosphere such as hydrogen or water vapor, so that atmospheric degradation.Extensive experimental studies have been conducted to clarify the process but the effect of hydrogen on thematerial behavior is very complicated; thus, so far no definitive hydrogen mechanism on nickel and iron-basedalloys has been established. In this paper, computational calculations have been performed to study the effect ofhydrogen in a vacancy region of a nickel and iron-based alloy. The calculations were performed with a DFTbased code using the SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) code. Theresults show that hydrogen impurities develop a negative charge while the closest iron and nickel atoms resultmore positively charged. This H-metal exchange main contributes to the decohesion process. Hydrogendebilitates the metal-metal bonds by forming interactions with the metallic matrix (see Figure 1). The ironhydrogeninteraction is stronger than the nickel-hydrogen interaction. The metal-metal bond strength decreasesa bigger percent with the introduction of the first hydrogen atom and no additional decohesion is observed in themetallic bonds when additional H atom is present but more bonds are affected. The hydrogen-hydrogeninteraction in the vacancy region is very small; a hydrogen molecule is not formed in the vacancy zone.