Scientific Events

Room: Large Conference Room No. 203

Atomistic Dynamics of Deformation, Fracture and GB Migration in Oxides

In order to clarify the deformation and fracture mechanism in oxides such as Al2O3 and STO, TEM in situ nanoindentation experiments were conducted for their single crystals and bicrystals. We successfully observed the dynamic behavior of twin formation, twin-GB interaction, pile-up dislocation, jog and kink formation and jog drag dynamics and so on. The mechanism of each dynamic behavior will be discussed in detail in this presentation. GB migration plays an important role in considering the high temperature mechanical properties. Recently, we have found that GB migration behavior in Al2O3 can be precisely controlled by the aid of the high-energy electron beam irradiation. This technique was applied to directly visualize the atomistic GB migration. It was revealed that the GB migration is processed by a cooperative shuffling of atoms in GB ledges along specific routes. References [1] S. Kondo, T. Mitsuma, N. Shibata, Y. Ikuhara, Sci. Adv., 2[11], e1501926(2016). [2] S. Kondo, A. Ishihara, E. Tochigi, N. Shibata, and Y. Ikuhara, Nat. Commun., 10, 2112 (2019). [3] J.Wei, B.Feng, R.Ishikawa, T.Yokoi, K.Matsunaga, N.Shibata and Y.Ikuhara, Nat. Mater.,20 (7), 951 [4] J.Wei, B.Feng, E.Tochigi, N.Shibata and Y.Ikuhara, Nat. Commun., 13(1), 1455, (2022) [more]

Local Phase Transformations: A New Creep Strengthening Mechanism in Ni-Base Superalloys

Polycrystalline Ni-based superalloys are vital materials for disks in the hot section of aerospace and land-based turbine engines due to their exceptional microstructural stability and strength at high temperatures. In order to increase operating temperatures and hold times in these engines, hence increasing engine efficiency and reduction of carbon emissions, creep properties of these alloys becomes increasingly important. Microtwinning and stacking fault shearing through the strengthening g’ precipitates are important operative mechanisms in the critical 600-800°C temperature range. Atomic-scale chemical and structural analyses indicate that local phase transformations (LPT) occur commonly during creep of superalloys. Furthermore, the important deformation modes can be modulated by LPT formation, enabling a new path for improving high temperature properties. [more]

High-resolution micro-plasticity in advanced high-strength steels

The persistent demand for green, strong and ductile advanced high strength steels, with a reduced climate footprint, calls for novel and improved multi-phase microstructures. The development of these new steels requires an in-depth understanding of the governing plasticity mechanisms at the micron scale. In order to address this challenge, novel numerical-experimental methods are called for that account for the discreteness, statistics and the intrinsic role of interfaces. This lecture sheds light on recent and innovative developments unravelling metal plasticity at the micron scale. Multi-phase through-thickness samples allow for a full characterization of the underlying microstructure. Using computational crystallographic insights, a slip system based local identification method has been developed, which provides full-field crystallographic slip system activity maps. The resulting deformation maps are directly used to assess the model predictions. Heterogeneous spatial variations are introduced by sampling the slip system properties of individual atomic slip planes from a probability density function. This allows to recover naturally localized slip patterns with a high resolution. It is demonstrated that this discrete slip plane model adequately replicates the diversity of active slip systems in the corresponding experiment, which cannot be achieved with standard crystal plasticity models. Recent experimental observations on dual-phase steels demonstrate substructure boundary sliding parallel to the habit plane in lath martensite, for which a habit-plane slip enriched laminate model is developed. This model adequately captures the role of the substructure boundary sliding on the deformation of the martensite aggregate. [more]

Effect of droplets on inhibitor performance for steel and galvanized steel

Effect of droplets on inhibitor performance for steel and galvanized steel
[more]

Real-time hydrogen visualization system with high spatial and temporal resolutions: Imaging the preferential hydrogen permeation at grain boundaries of pure Ni

Real-time hydrogen visualization system with high spatial and temporal resolutions: Imaging the preferential hydrogen permeation at grain boundaries of pure Ni
[more]

Stability of electrochemical hydrogen charging into iron in an aqueous solution containing NH₄SCN

Stability of electrochemical hydrogen charging into iron in an aqueous solution containing NH₄SCN
[more]

There’s plenty of Room at the (Grain) Boundary

There’s plenty of room at the grain boundary (GB), in which we can manipulate its energy and structure for particular properties in polycrystalline materials. Recently, we observed that the aesthetic of the room quantified by the electrical conductance was changed dramatically by simply by turning on/off a UV laser. Specifically, based on photoelectron spectroscopy and complementary conductive atomic force microscopy, we demonstrate that the hundredfold increases in the electrical conductance measured at the GB are strongly associated with the ultraviolet-induced oxygen vacancies, and thus offering novel strategies for optoelectronic or neuromorphic computing applications. Historically, it is a challenge to optimize the room especially in the case of body-centered cubic (bcc) metals due to the lack of quantitative relations between GB energies and populations or microstructure-property-processing relationships. Here, we present a universal function for computing the energies of arbitrary GBs in the bcc metals. The effectiveness of the universal function in describing the variations of the GB energies is demonstrated by consistency between the output of the function and the energies of ~ 2,500 GBs simulated by the embedded atom method. Large-scale comparisons between the interpolated energies and measured GB populations reveal that the population distributions are governed by local energy minima located at the Σ1, Σ3, Σ9, Σ11, and Σ33a misorientations, representing a major step forward for the GB engineering of bcc metals. [more]
Show more
Web-View
Print Page
Open in new window
Estimated DIN-A4 page-width
Go to Editor View