Characterizing irradiation damage in materials utilized in light water reactors is critical for both material development and application reliability. Here we use both nanoindentation and Laue micro diffraction to characterize both the mechanical response and microstructure evolution due to irradiation. Two different irradiation conditions were considered in 304 stainless steel: 1dpa and 10 dpa. In addition, an annealed condition of the 10 dpa specimen for 1 hour at 500 °C was evaluated. Nanoindentation revealed an increase in hardness due to irradiation and also revealed that hardness saturated in the 10 dpa case. Broadening using Laue micro diffraction peaks indicates a significant lattice strain in the irradiated area that is in good agreement with both the SRIM calculations and the nanoindentation results.

a b s t r a c tMicropillar compression testing was implemented on Equal Channel Angular Pressed copper samples ranging from 200 nm to 10 mm in side length in order to measure the mechanical properties yield strength, first load drop during plastic deformation at which there was a subsequent stress decrease with increasing strain, work hardening, and strain hardening exponent. Several micropillars containing multiple grains were investigated in a 200 nm grain sample. The effective pillar diameter to grain size ratios, D/d, were measured to be between 1.9 and 27.2. Specimens having D/d ratios between 0.2 and 5 were investigated in a second sample that was annealed at 200°C for 2 h with an average grain size of 1.3 mm. No yield strength or elastic modulus size effects were observed in specimens in the 200 nm grain size sample. However work hardening increases with a decrease in critical ratios and first stress drops occur at much lower stresses for specimens with D/d ratios less than 5. For comparison, bulk tensile testing of both samples was performed, and the yield strength values of all micropillar compression tests for the 200 nm grained sample are in good agreement with the yield strength values of the tensile tests.

Characterizing plasticity mechanisms below the ductile to brittle transition temperature (DBTT) is traditionally difficult to accomplish in a systematic fashion. Here, we use a new experimental setup to perform in situ cryogenic mechanical testing of pure Sn micropillars at room temperature and at-142 °C. Subsequent electron microscopy characterization of the micropillars shows a clear difference in the deformation mechanisms at room temperature and at cryogenic temperatures. At room temperature, the Sn micropillars deformed through dislocation plasticity while at-142 °C they exhibited both higher strength and deformation twinning. Two different orientations were tested, a symmetric (100) orientation and a non-symmetric (4 5 1) orientation. The deformation mechanisms were found to be the same for both orientations.

Recent developments in micromechanical testing have allowed for the efficient evaluation of radiation effects in micron-scale volumes of ion-irradiated materials. In this study, both nanoindentation and in situ SEM microcompression testing are carried out on 10 dpa proton beam irradiated 304 stainless steel to assess radiation hardening and radiation-induced deformation mechanisms in the material. Using a focused ion beam (FIB), arrays of 2 μm x 2 μm cross-section microcompression pillars are fabricated in multiple dose regimes within the same grain, providing dose-dependent behavior in a single crystal orientation. Analysis of the microcompression load-displacement data and real-time SEM imaging during testing indicates significant hardening, as well as increased localization of deformation in the irradiated material. Although nanoindentation results suggest that irradiation hardening saturates at low doses, microcompression results indicate that the pillar yield stress continues to rise with dose above 10 dpa in the tested orientation.

The microstructure and mechanical integrity of protective multilayered oxide films grown in liquid metal on F/M steel HCM12A was investigated utilizing Raman spectroscopy, nanoindentation and micro-cantilever testing methods. The Raman spectra showed a Fe 3 O 4 outer layer and a Cr-rich spinel structure inner layer. The nanoindentation results showed a higher hardness value for the inner layer than for the outer layer. In addition, the hardness of the diffusion layer in between the inner layer and the bulk steel was measured. Quantitative fracture properties were obtained of the steel/oxide interface and within the oxide layers utilizing microcantilever testing. Furthermore the strength and elastic properties of the multilayered oxide film were measured and it was found that the porous structure in the inner Fe-Cr oxide limits the integrity of the steel/oxide interface.