In this project we studied the formation of nanoripples in calcite and InP single crystals by continuous scanning using the nanoindenter in the ambient environment and by Argon ion irradiation under ultra high vacuum conditions, respectively. Formation of tip induced nanowear ripples is studied on a freshly cleaved calcite single crystal as a function of scanning frequency and contact load of the diamond tip. At lower loads, initiation of the ripples takes place at the bottom of the surface slope at 3 Hz scanning frequency, which continue to propagate as scanning progresses. The orientation of these ripple structures is perpendicular to the scan direction. As the number of scans increases, ripples fully develop, and their height and periodicity increase with the number of scans by merging ripples together. At 6 mu N normal load, tip induced wear occurred as the tip started removing the ripple structures with increased number of scan cycles. As the contact load increased further, a ripple structure was not initiated and only tip induced wear occurred on the surface. At 1 Hz frequency material removal takes place as the tip moves back and forth and material slides towards the scan edges. Material removal rate increased with contact load and it is observed that the number of scans required to create a new surface is inversely proportional to the contact load. Possible mechanisms responsible for the formation of ripples at higher frequencies are attributed to the slope of the surface, piezo hysteresis,system dynamics or a combination of effects. Single crystal calcite hardness of 2.8 GPa and elastic modulus of 80 GPa were measured using nanoindentation. Evolution of nanostructures on the InP surface due to ion bombardment has been studied with scanning tunneling microscopy in UHV environment. InP crystal surfaces were irradiated by Argon ion incident beam with 3 KeV energy at an incident angle of 75 degrees. Self-organization of the surface was studied by varying the ion fluence from 7.7E13 to 4.6E17 ions per square centimeter. The observed nanoripple morphologies have been explained based on the concept of interplay between roughening and smoothing processes. Wavelength of the nanostructures linearly increases with the logarithm of the fluence. The rms roughness is approximately linear with the logarithm of the fluence. Nanoindentation experiments were performed on InP surface before and after ion bombardment to determine variation in hardness and elastic modulus. Surface of irradiated InP has higher H and E values as the surface become amorphized after Ar+ ion bombardment.

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Uranium-zirconium (U-Zr) alloys comprise a class of metallic nuclear fuel that is regularly considered for application in fast nuclear energy systems. The U-10wt%Zr alloy has been demonstrated to very high burnup without cladding breach in the Experimental Breeder Reactor-II (EBR-II). This was accomplished by successfully accommodating gaseous fission products with low smear density fuel and an enlarged cladding plenum. Fission gas swelling behavior of the fuel has been experimentally revealed to be significantly affected by the temperature gradient within a fuel pin and the multiple phase morphologies that exist across the fuel pin. However, the phase effects on swelling behavior have not been yet fully accounted for in existing fuel performance models which tend to assume the fuel exists as a homogeneous single phase medium across the entire fuel pin. Phase effects on gas bubble nucleation and growth in the alloy were investigated using transmission electron microscopy (TEM). To achieve this end, a comprehensive examination of the alloy system was carried out. This included the fabrication of uranium alloys containing 0.1, 2, 5, 10, 20, 30, 40, and 50 wt% zirconium by melt-casting. These alloys were characterized using electron probe micro-analysis (EPMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Once the alloys were satisfactorily characterized, selected U-Zr alloys were irradiated with 140 keV He^(+) ions at fluences ranging from 1 × 10^(14) to 5 × 10^(16) ions/cm^(2). Metallographic and micro-chemical analysis of the alloys indicated that annealing at 600 °C equilibrates the alloys within 168 h to have stable α-U and δ-UZr_(2) phase morphologies. This was in contrast to some reported data that showed kinetically sluggish δ-UZr_(2) phase formation. Phase transformation temperatures and enthalpies were measured using DSC-TGA for each of the alloys. Measured temperatures from different time annealed alloys have shown consistent matches with most of the features in the current U-Zr phase diagram which further augmented the EPMA observed microstructural equilibrium. Nevertheless, quantitative transformation enthalpy analysis also suggests potential errors in the existing U-Zr binary phase diagram. More specifically, the (β-U, γ2) phase region does not appear to be present in Zr-rich (> 15 wt%) U-Zr alloys and so further investigation may be required. To prepare TEM specimens, characterized U-Zr alloys were mechanically thinned to a thickness of ~150 μm, and then electropolished using a 5% perchloric acid/95% methanol electrolyte. Uranium-rich phase was preferentially thinned in two phase alloys, giving saw-tooth shaped perforated boundaries; the alloy images were very clear and alloy characterization was accomplished. During in-situ heating U-10Zr and U-20Zr alloys up to 810 °C, selected area diffraction (SAD) patterns were observed as the structure evolved up to ~690 °C and the expected α-U → β-U phase transformation at 662 °C was never observed. For the temperature range of the (α-U, γ2) phase region, phase transformation driven diffusion was observed as uranium moved into Zr-rich phase matrix in U-20Zr alloy; this was noted as nonuniform bridging of adjacent phase lamellae in the alloy. From the irradiation tests, nano-scale voids were discovered to be evenly distributed over several micrometers in U-40Zr alloys. For the alloys irradiated at the fluences of 1 × 10^(16) and 5 × 10^(16) ions/cm^(2), estimated void densities were proportional to the irradiation doses, (250 ± 40) and (1460 ± 30) /μm^(2), while void sizes were fairly constant, (6.0 ± 1.5) and (5.2 ± 1.2) nm, respectively. Measured data could be foundational inputs to the further development of a semi-empirical metal fuel performance model.