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Cui, Yuchi

Publications and source records attributed to Cui, Yuchi.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

In Situ Micro-Pillar Compression to Examine Radiation-Induced Hardening Mechanisms of FeCrAl Alloys

Here, the effects of 5 MeV Fe 2+ ion irradiation at 300°C on the microstructure evolution and deformation behavior of a FeCrAl C26M alloy are presented. It has been found that dislocation loop density increases an order of magnitude from 1 dpa to 16 dpa irradiations, whereas, the dislocation loop size saturates with increasing damage. Micropillars, 600 nm in diameter and 1.3 µm in height, were fabricated and compressed inside grains with <001>, <011> and <111> crystallographic orientations, respectively. {112} <111> has been identified as the primary slip system in both unirradiated and irradiated alloy. The increase in yield stress after irradiation is observed with measurable variation along <001> and <011> vs. along <111>. By applying the Orowan dispersed barrier model, the increase of yield stress is found mainly due to the slip resistance of radiation generated defect loops. Detailed transmission electron microscopy (TEM) studies were performed to quantify the Burgers vector and the distribution of irradiation induced dislocations at elevated strains. It is revealed that localized shear instability is caused by avalanche slip events of ½<111> dislocations gliding out of tested pillars. Simultaneously, a large number of sessile/immobile <100> dislocations formed in the vicinity of slip band, leading to the hardening at elevated strains.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Microstructure and mechanical properties of nanoscale Cu/(Ta50Nb25Mo25) multilayers

Nanoscale Cu/(Ta50Nb25Mo25) multilayers comprised of medium entropy alloy Ta50Nb25Mo25 and pure Cu are found to exhibit similar length-scale-dependent deformation mechanisms as metallic multilayers with elemental individual layers, i.e., confined layer slip at layer thickness of tens of nanometers and shear localization at several nanometers. The hardness of the nanoscale Cu/(Ta50Nb25Mo25) multilayers is higher as compared to the pure element FCC/BCC multilayers due to the extra solid solution strengthening contribution in the BCC layer. The synergy between the size effect and solid solution strengthening mechanism is discussed. In conclusion, this is an early report of the multi-component multilayers, which serves to provide directions for developing novel multilayer materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Fracture resistance of hierarchical Cu–Mo nanocomposite thin films

We report the fracture behavior of high-temperature co-sputtered Cu/Mo nanocomposite thin films was investigated through in situ 3-point bend testing of pre-notched microbeams in SEM. The as-synthesized nanocomposites present hierarchical nano/microstructures composed of a matrix of phase-separated Cu–Mo with nanoscale ligaments dispersed with sub-micron scale Cu-rich islands containing Mo nano-precipitates. Results show a significant crack growth resistance in the hierarchical nanocomposite, several times higher than that measured in Cu/Mo nanoscale multilayers. Based on electron microscopy characterization, three mechanisms of crack growth resistance in the hierarchical structures are proposed: crack bridging by the Cu-rich layer, crack deflection via shear along the Cu/Mo interface, and multiple cracking. This work demonstrates an approach to increase toughness in high strength nanocomposites through interface micro-structure design.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Micropillar Tests of As-received and Irradiated FeCrAl C26M Alloys

The present report summarizes the efforts to investigate the deformation behavior of a FeCrAl C26M alloy before and after irradiation. In order to clarify the mechanical effects of radiation-induced defects along different crystallographic orientations, micropillars with the dimension of 600 nm in diameter and 1.3 um in height have been fabricated inside grains with different orientations. When compressed along [001] direction, it was found that the yield stress has increased from 630 MPa to 750 MPa at an average dpa level of 1 (peak dpa ~ 2.7), and to 850 MPa at 16 average dpa (peak dpa ~ 42.7). In addition, due to the appearance of radiation-induced defects, strain hardening response has been changed as well. Especially, when the flow stressis lower than 1.5 GPa, hardening response has been captured, which is due to the collective interaction of various shear bands. However, when the flow stress increases to larger than 1.5 GPa, another mode of shear band has been captured. The correlated process is at least ten times faster, corresponding to the sudden load drop in the stress strain plot. When the compression has been applied along [011] and [111] direction, the increase of yield stress after irradiation has also been captured. However, the correlated magnitude is different: yield stress of [011] increases from 500 MPa to 700 MPa at 1 dpa and to 1200 MPa at 16 dpa. On the other hand, when the compressive loading has been employed along [111], the correlated yield stress changes from 500 MPa to 700 MPa at 1 dpa and to 1400 MPa at 16 dpa. Moreover, the second mode of shear band has also been recorded in the 16 dpa irradiated sample when stress applied along [011], but not shown along [111] direction.

36 MATERIALS SCIENCE↗
DOE OSTI2019

An overview of interface-dominated deformation mechanisms in metallic nanocomposites elucidated using in situ straining in a TEM

Nanostructured multiphase metallic materials present extraordinary properties, such as high strength, enhanced fatigue and radiation resistance, and thermal stability, compared to conventional bulk metallic materials. Previous research studies have shown that their deformation and fracture behavior are dominated by defect interactions at internal interfaces. In situ straining, including nanoindentation, compression, and tension, in a transmission electron microscope (TEM) has emerged as a powerful tool to investigate the physics of defect–interface interactions at the nano-scale and even atomic scale. Here, the mechanistic insights gained from these experiments coupled with dislocation theory and atomistic modeling has helped develop a fundamental understanding of the mechanical properties. In this article, through some recent investigations on observing dislocation and interface activities, crack propagation, and nanopillar compression, we present current progress in utilizing in situ TEM straining to examine interface-dominated deformation mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Design of bicontinuous metallic nanocomposites for high-strength and plasticity

We demonstrate design of Cu/Mo nanocomposite thin films with bicontinuous intertwined morphologies for high strength and plastic deformability. Through co-sputtering Cu and Mo at different temperatures, nanocomposites with lateral and random concentration modulations (LCMs and RCMs) were fabricated. Ligament size and coherency of the Cu/Mo interfaces was also controlled via the deposition conditions. It was discovered that nanocomposites with LCM structure and coherent interfaces have high strength but limited deformability. Enhanced deformability was achieved when the interface was altered to semi-coherent, although plasticity was localized in kink bands. The RCM structure design with semi-coherent interfaces showed an excellent combination of high flow strength and plastic deformability due to suppression of shear and kink bands.

36 MATERIALS SCIENCE↗