In situ observation of microstructure evolution in 4H–SiC under 3.5 keV He+ irradiation

4H-SiC was irradiated with 3.5 keV He+ ions using the MIAMI facility at University of Huddersfield. The evolution of microstructure and gas bubbles during the irradiation at 700°C, 800°C and 900°C was observed by in situ transmission electron microscopy. Under irradiation, isolated bubbles and bubble discs formed in the SiC matrix. Bubble discs lying on {0001} and {10-10} crystal planes were beginning to form at ion fluence above 2.3×1020 He+ /m2 at 700°C. The density of bubble discs increased with increasing irradiation fluence. However, growth rates were different at different of the implantation periods and temperature holding periods. The nucleation and growth of the bubble discs were attributed to be coalescence of the adjacent He vacancies and combination of loop punching and trap mutation, respectively

Effect of He implantation on the microstructure of zircaloy-4 studied using in situ TEM

Highlights • Differences in the evolution of α and βZr microstructures under 6 keV He ion implantation have been analysed as a function of irradiation dose and temperature using in situ TEM. • Both thermal and irradiation stabilities of Zr hydrides particles were studied and were found to dissolve with increasing fluence. • It is suggested that the combination of two different mass-transport mechanisms for He in zircaloy-4 play a major rule in the Zr hydride irradiation-induced dissolution. • He bubble lattices were observed to form during irradiation at 473 K and 1148 K in both crystalline phases, α and βZr, at around the same fluence of 1.7×10^17 ions⋅cm−2 (3.2 dpa)

Nano-scale chemical evolution in a proton-and neutron-irradiated Zr alloy

Proton-and neutron-irradiated Zircaloy-2 are compared in terms of the nano-scale chemical evolution within second phase particles (SPPs) Zr(Fe,Cr)2 and Zr2(Fe,Ni). This is accomplished through ultra-high spatial resolution scanning transmission electron microscopy and the use of energy-dispersive X-ray spectroscopic methods. Fe-depletion is observed from both SPP types after irradiation with both irradiative species, but is heterogeneous in the case of Zr(Fe,Cr)2, predominantly from the edge region, and homogeneously in the case of Zr2(Fe,Ni). Further, there is evidence of a delay in the dissolution of the Zr2(Fe,Ni) SPP with respect to the Zr(Fe,Cr)2. As such, SPP dissolution results in matrix supersaturation with solute under both irradiative species and proton irradiation is considered well suited to emulate the effects of neutron irradiation in this context. The mechanisms of solute redistribution processes from SPPs and the consequences for irradiation-induced growth phenomena are discussed.<br/

Crystallographic techniques and data for transmission electron microscopy of zirconium.

The crystallography of hexagonal close packed metals is discussed briefly in terms of the four-axis hexagonal reference basis and the Miller-Bravais notation which are used throughout the report. Electron diffraction problems are treated with reference to the four-axis hexagonal reciprocal lattice rather than the more usual three-axis hexagonal system. Using these concepts, analysis of electron diffraction spot and Kikuchi patterns is illustrated and applied to orientation and dislocation Burgers vector determinations. Computed values of interplanar spacings, interplanar angles, angles between directions, and extinction distances for zirconium are listed

Calibration of a JSEM-200 electron microscope with a magnetic specimen pole-piece.

This report contains the results of a detailed calibration of the JSEM-200 scanning transmission electron microscope operated with a magnetic specimen pole-piece as supplied by JEOL (Japan Electron Optics Laboratory) Ltd. The microscopy, in this configuration, permits convenient examination of ferromagnetic specimens in the side-entry goniometer specimen stage with a point-to-point resolution better than 2.0 nm

Characterisation of neutron irradiation damage in zirconium alloys - a 'round robin' experiment.

The nature of the damage structure in the neutron-irradiated zirconium specimens supplied as part of an international 'Round Robin1 experiment has been studied using transmission electron microscopy. The damage structure consists entirely of a/3 dislocation loops and no evidence has been found for c_ component loops. Both vacancy and interstitial loops were found in specimens where inside/outside contrast analysis was possible. Quantitative measurements of loop size distributions and loop concentrations are reported. All specimens exhibited corduroy contrast to varying degrees