A theory for hydrogen embrittlement of transition metals and their alloys

In this paper, a general hydrogen (H) embrittlement mechanism is proposed alongside an empirical model to facilitate successful H embrittlement predictions for various transition metals and alloys. This model's simplicity enables quick predictions through basic hand calculations. To comprehend H embrittlement in complex alloys, it is crucial to explain the embrittlement of pure metals and their binary alloys effectively. The validity of this theory is substantiated by accurate embrittlement predictions for over 22 pure elements and 55 alloy compositions stemming from 18 specific binary alloys, based on the author's extensive test data and literature review. The theory posits that H embrittlement is linked to the electron density of states N(E) at the Fermi energy level, characterized by a unique electrons-per-atom (Zi) number that must be determined from the element's periodic table position and the net charge transfer upon alloying. A universal H embrittlement constant is derived, demonstrating a direct correlation with electronic specific heat coefficients at elevated temperatures. This theory aims to unify the interrelationships across physical, chemical, and metallurgical sciences, with a future focus on detailed assessments of its predictions for common stainless steels and complex alloys.