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The role of δ-Fe in hydrogen embrittlement (HE) of 17-4 PH steel is studied in this work. Scanning Kelvin probe force microscopy result indicates that δ-Fe is a hydrogen trapping site. Accordingly, δ-Fe can reduce the hydrogen concentration of surrounding martensite and prior austenite grain boundaries (PAGBs) and imped the brittle fracture along lath boundaries and PAGBs, which can be beneficial to the HE resistance improvement. However, a cleavage fracture of δ-Fe can occur under the synergetic action of hydrogen-enhanced localized plasticity (HELP) and hydrogen enhancement of the strain-induced generation of vacancies (HESIV). These findings indicate a new path to improving HE resistance of high strength martensitic steels. • SKPFM result shows that hydrogen tends to segregate in delta ferrite. • Delta ferrite acting as a hydrogen trapping site decreases the tendency of brittle fracture. • Hydrogen segregation in delta ferrite leads to a strain localization and a subsequent transgranular cleavage fracture. [ABSTRACT FROM AUTHOR]

Abstract: Porous materials have drawn attention from scientists in many fields such as life sciences, catalysis and photonics since they can be used to induce some materials growth as expected. Especially, porous Langmuir–Blodgett (LB) film is an ideal material with controlled thickness and flat surface. In this paper, stearic acid (SA), which has been extensively explored in LB film technique, is chosen as the template material with known parameters to prepare the LB film, and then the porous SA monolayer film is obtained by means of etching in salt solution. The main etching mechanism is suggested that the cations in the solution block the electrostatic interaction between the polar carboxyl group of SA and the electronegative mica surface. The influencing factors (such as concentration of salt solution, valence of cation and surface pressure) of the porous SA film are systematically studied in this work. The novel method proposed in this paper makes it convenient to prepare porous monolayer film for designed material growth or cell culture. [Copyright &y& Elsevier]