时间：9月24日（周三）下午14:30

地点：文萃路园区扇形报告厅

Topic

New insights about the synergistic action of hydrogen embrittlement mechanisms in metals: HELP+HEDE model

Abstract

The HELP+HEDE model is a comprehensive concept that explains the coexistence of hydrogen embrittlement (HE) mechanisms in metallic materials [1,2]. This model involves the interplay and competence between two groups of HE mechanisms: HELP and/or other plasticity-mediated HE mechanisms, and HEDE mechanism [1-3]. The confirmed competition and transition in dominance between hydrogen provoked localized plasticity, i.e., hydrogen-induced dislocation activity (HIDA) HE mechanisms (HELP and others), and HEDE, depending on the global/local hydrogen (H) concentration and distribution, microstructural characteristics, and stress state, are of utmost importance to achieve a unified model for HE. The HELP+HEDE model defined that the previous HELP, or other HIDA mechanisms activity, is not always necessary for the activation and the complete predominance of the HEDE mechanism (non-HELP mediated decohesion) at high local/global hydrogen concentrations. The recently updated unified HELP+HEDE model [3] introduced the "local HEDE micro-incidents" concept as the appearance of discrete micro-scale, i.e., hydrogen-induced crack initiation (HICI) incidents, at a high local H concentration above the critical one, particularly at HEDE-prone H traps in microstructure. These incidents happen even in the case of HIDA predominance, i.e., plasticity-mediated HE mechanisms dominance, on the global level [1-6]. For the shift from HIDA to HEDE macroscopic predominance, followed by a sharp drop in ductility and other mechanical properties, the necessary prerequisite is the macro-volume appearance of "local HEDE micro-incidents" [3]. This means an accumulation of a high enough number of such HEDE micro HICI incidents throughout the volume of a hydrogenated sample. In that case, the degree of activity of the HELP mechanism and other plasticity-mediated (HIDA types) HE mechanisms can become minor and negligible [1-6]. This paper presents new insights about the HELP+HEDE model, validated through experiments [2,4] and modeling studies [5], i.e., "local HEDE micro-incidents" concept, conditions for particular HE mechanism dominance, and HEDE-prone H traps, highlighting its significance in the fundamental understanding of HE phenomena.

References

[1] M. B. Djukic,V. Sijacki Zeravcic,G. M. Bakic,A. Sedmak,B. Rajicic. Hydrogen damage of steels: A case study and hydrogen embrittlement model. Eng. Fail. Anal. 58,485-498 (2015)

[2] M. B. Djukic,G. M. Bakic,V. Sijacki Zeravcic,A. Sedmak,et al. The synergistic action and interplay of hydrogen embrittlement mechanisms in steels and iron: Localized plasticity and decohesion. Eng Fract Mech 216,106528 (2019)

[3] M. Wasim,M. B. Djukic,T. D. Ngo. Influence of hydrogen-enhanced plasticity and decohesion mechanisms of hydrogen embrittlement on the fracture resistance of steel. Eng. Fail. Anal. 123,105312 (2021)

[4] A. Behvar,M. Haghshenas,M. B. Djukic. Hydrogen embrittlement and hydrogen-induced crack initiation in additively manufactured metals: A critical review on mechanical and cyclic loading. Int. J. Hydrogen Energ. 58,1214-1239 (2024)

[5] H. W. Lee,M. B. Djukic,C. Basaran. Modeling fatigue life and hydrogen embrittlement of bcc steel with unified mechanics theory. Int. J. Hydrogen Energ. 48(54),20773-20803 (2023)

[6] X. Li,J. Zhang,Y. Cui,M. B. Djukic,H. Feng,Y. Wang. Review of the hydrogen embrittlement and interactions between hydrogen and microstructural interfaces in metallic alloys: Grain boundary,twin boundary,and nano-precipitate.  Int. J. Hydrogen Energ. 72,74-109 (2024)

Short biography

Milos B. Djukic is a Full Professor at the University of Belgrade, Faculty of Mechanical Engineering, Serbia, and an Adjunct Professor at Ohio University, Russ College of Engineering and Technology, Department of Chemical and Biomolecular Engineering, Athens, OH, USA. He leads the Hydrogen-Materials Interaction Laboratory, with research spanning hydrogen embrittlement, hydrogen–materials interactions, corrosion and materials science, materials degradation, and the mechanical behavior of structural materials.

Prof. Djukic has been recognized among the Top 2% of Most Cited Researchers Worldwide in 2023 and 2024, according to the Stanford University–Elsevier database. He is actively involved in shaping national and international hydrogen initiatives, serving as a team member in the preparation of the Hydrogen Strategy of the Republic of Serbia. Within the European Structural Integrity Society (ESIS), he is an Executive Committee Member, an elected Fellow (FESIS), and Chair of the ESIS Technical Committee TC21 on Hydrogen Embrittlement and Transport. He also contributes to the scholarly community as Assistant Subject Editor for the International Journal of Hydrogen Energy and as a board member of 18 international journals. With over 25 years of teaching and research experience, Prof. Djukic has authored 5 books, 10 book chapters, 1 patent, 3 technical solutions, more than 100 peer-reviewed scientific papers, and 120 conference contributions. In addition, he has participated in over 200 industrial studies, technical reviews, and expert evaluations. His scientific contributions focus on advancing the fundamental understanding of hydrogen embrittlement mechanisms in metallic materials. He proposed the widely recognized unified HELP+HEDE model of hydrogen embrittlement, which integrates multiple mechanisms into a synergistic framework. This model has gained significant traction in the field and has been cited more than 1,000 times.