B. An

Characterization of hydrogen-induced crack initiation in metastable austenitic stainless steels during deformation

Hydrogen-induced crack initiation in hydrogen-charged metastable austenitic stainless steels during deformation at 295 K is characterized by performing a combined tensile and hydrogen release experiment and scanning probe microscopy. Strain-induced martensite (α′) not only provides a path for rapid hydrogen diffusion in austenite (γ) but also promotes crack initiation. Hydrogen rapidly diffuses from α′ and accumulates at the boundary between the α′-rich and γ-rich zones during deformation due to the high hydrogen diffusivity and low hydrogen solubility in α′, resulting in crack initiation at the boundary between the α′-rich and γ-rich zones. The hydrogen-induced crack initially grows along the boundary between the α′-rich and γ-rich zones and then propagates in the α′-rich zone.

Evolution of Ar+-damaged graphite surface during annealing as investigated by scanning probe microscopy

The surface evolution of highly oriented pyrolytic graphite irradiated with Ar+ ions of 1.0 keV at doses between 5×1011 and 1×1013 ions/cm2 during annealing was investigated by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) in the tapping mode. Hillocks were observed by both STM and AFM after ion irradiation, where the height of a hillock measured by STM was larger than that measured by AFM. The ion-irradiated surface was recovered in three stages during annealing: the first stage at 473–873 K, the second stage at 873–1473 K, and the third stage at 1473–1873 K. In the first stage, many of the ion-induced hillocks recovered rapidly and irregular domelike protrusions were formed due to both the recombination of the mobile interstitial clusters with the immobile vacancies and the aggregation of interstitial clusters. In the second stage, the hillocks recovered slightly and domelike protrusions aggregated to larger domelike protrusions. In the third stage, the hillocks recovered complet...

Anomalous plastic deformation and martensitic transformation in metastable austenitic steels at low strain rate characterized by in-situ hydrogen and argon releases and scanning probe microscopy

Plastic deformation behavior and strain-induced martensite (α’) transformation in metastable austenitic stainless steel sheets are investigated during tensile loading at a slow strain rate of 1.7 × 10−4 s−1 at 298 K by in situ hydrogen and argon releases and scanning probe microscopy. Anomalous stress peaks, which occur on the stress-strain curve in the later half stage of plastic deformation, are simultaneous with distinct hydrogen release peaks and argon release valleys, and the α’ content measured at a fixed region increases stepwisely with increasing strain in the corresponding stage of deformation. Such anomalous deformation and α’ transformation phenomena result from repeatedly occurring and propagating of X-shaped strain localization accompanied by the rapid α’ transformation in the later half stage of deformation.

Atomic structure of interface between monolayer Pd film and Ni(111) determined by low-energy electron diffraction and scanning tunneling microscopy

The atomic structure of Pd ultrathin films grown on Ni(111) at 300 K is investigated by low-energy electron diffraction and scanning tunneling microscopy. It is determined atomically that the growth of monolayer Pd films leads to a periodic arrangement of triangular misfit dislocation loops in the underlying Ni(111) surface, resulting in a triangular superstructure on the monolayer Pd surface. The triangular dislocation loops tend to align at an angle of about 5° from the Ni atom row, owing to a slight rotation of the Pd films with respect to the Ni substrate, and appear as a moirelike superstructure on the multilayer Pd surfaces. Atomistic simulations indicate that the slight rotation of monolayer Pd films and the formation of misfit dislocation loops in the Ni surface minimize the Pd–Ni interface energy.