[en] Atomistic modeling of segregation in Ni-Ti alloys is performed using the Bozzolo-Ferrante-Smith (BFS) method for alloys. It is found that Ti segregation to the surface decreases rapidly even for small increases in Ni concentration. A competing process is identified in the vicinity of surface defects, leading to excess Ti coverage of the exposed surface and the creation of Ti-covered pits. A simple explanation based on an atom-by-atom energy analysis is found to satisfactorily explain the observed effects

[en] In this work, we have studied the effects of swift heavy ion irradiation on the creation of new functional groups in high and low density polyethylene (HDPE and LDPE). Polymers were irradiated with different ions (6.77 MeV He and 47 MeV Li) and fluences. The induced changes were analyzed by Fourier transform infrared (FTIR) spectroscopy. Creation and damage cross sections for some groups were compared for two different types of PE.

[en] The energy deposition of a heavy ion in a latent track gives rise to a central partially melting core zone surrounded by a larger region where some physico-chemical modifications take place. When these latent tracks start to overlap some interference effect occurs. A previous irradiated zone of one latent track can be eliminated by the core zone of others. In the present, work a Monte Carlo simulation program that permits us to determine the track dimensions is described. The core and chemical radii are obtained from fitting the FTIR absorption as a function of fluence. This new method was applied specifically on ultra-high molecular weight polyethylene (UHMWPE) irradiated with a 72 MeV S beam. The inner core radius value obtained was 5 ± 1 nm

[en] The equilibrium volume, compressibility, and coefficient of thermal expansion of B2-based Al-Ni-Ru-M alloys (M = B, Si, Ti, Sc, V, Cr, Mn, Fe, Co, Cu, Zn, Nb, Mo, Tc, Rh, Pd, Zr, Ag, Ta, Hf, W, Re, Os, Ir, Pt, and Au) are determined as a function of concentration of the additive M. Details of the phase structure and determination of these properties are obtained from large-scale simulated annealing of the quaternary alloys using the Bozzolo-Ferrante-Smith method for alloys for the calculation of the energy.

[en] The behavior of ternary and quaternary additions to NiTi shape memory alloys is investigated using a quantum approximate method for the energetics. Ternary additions X to NiTi and quaternary additions to Ni-Ti-Pd, Ni-Ti-Pt, and Ni-Ti-Hf alloys, for X=Au, Pt, Ir, Os, Re, W, Ta,Ag, Pd, Rh, Ru, Tc, Mo, Nb, Zr, Zn, Cu, Co, Fe, Mn, V, Sc, Si, Al and Mg are considered. Bulk properties such as lattice parameter, energy of formation, and bulk modulus of the B2 alloys are studied for variations due to the presence of one or two simultaneous additives.

[en] Reverting the traditional process of developing new alloys based on one or two single elements with minority additions, the study of high entropy alloys (HEA) (equimolar combinations of many elements) has become a relevant and interesting new field of research due to their tendency to form solid solutions with particular properties in the absence of intermetallic phases. Theoretical or modeling studies at the atomic level on specific HEA, describing the formation, structure, and properties of these alloys are limited due to the large number of constituents involved. In this work we focus on HEA with refractory elements showing atomistic modeling results for W-Nb-Mo-Ta and W-Nb-Mo-Ta-V HEA, for which experimental background exists. An atomistic modeling approach is applied for the determination of the role of each element and identification of the interactions and features responsible for the transition to the high entropy regime. Results for equimolar alloys of 4 and 5 refractory elements, for which experimental results exist, are shown. A straightforward algorithm is introduced to interpret the transition to the high entropy regime.

[en] When ions suddenly pass through a polymeric material a very complex path of excited and ionized molecules is induced. Experimental data of grafting yield and new chemical groups formation present a maximum as a function of radiation fluence. We have found a correlation between this characteristic ion fluence and the stopping power. Their values lie approximately on a straight line with a negative slope and this correlation persists for an extended range, almost two orders of magnitude in stopping power variations. In the present work we will try to explain the observed correlation applying a known radial distribution of deposited energy induced by ion interaction with polymers

[en] Poly(propylene) foils were irradiated with Ag ions and then chemically etched to produce samples with structured surfaces. After the etching procedure the active sites that remain on the latent track were used to graft acrylic acid. Nuclear tracks before grafting were visualised using a transmission electron microscope. The grafting yields were determined by weight measurements as a function of ion fluence, etching and grafting time, and were also analysed using Fourier transform infrared spectroscopy. Both measurements suggest that the acrylic acid was grafted on etched tracks using the active sites produced by the swift heavy ion beam

[en] Structural analysis with infrared spectroscopy was carried out on ultra-high molecular weight polyethylene (UHMWPE). The polyethylene was irradiated using Li, C, N, S and I heavy ion beams with different fluences. The analysis showed that the absorbance of the C=C stretching vibration from trans-vinylene groups containing hydroperoxides presents a maximum at certain ion fluence and is correlated with the ion stopping power. The results were analyzed by a Monte Carlo simulation program that models the irradiation process from a geometrical point of view, in which the latent tracks consist in a central core zone surrounded by a larger perturbed region. This study suggests that it is possible to estimate the core dimension from absorbance measurements as a function of fluence. A possible relationship between this C=C structure with the cross-link of two polymeric chains is discussed

[en] When polymers are irradiated with heavy ions new chemical groups are created in a few microns of the material. The irradiation changed the polarity and wettability on the surface so that could enhance the biocompatibility of the modified polymer. The study of chemistry and nanoscale topography of the biomaterial is important in determining its potential applications in medicine and biotechnology, because their strong influence on cell function, adhesion and proliferation. In this study, thin films of Polystyrene and Polypropylene samples were modified by irradiation with low energy ion beams (30-150 keV) and swift heavy ions both with various fluences and energies. The changes were evaluated with different methods. Adhesion of NIH 3T3 fibroblasts onto unirradiated and irradiated surfaces has been studied by in vitro techniques. The correlations between physicochemical properties as a function of different irradiations parameters were compared with cell adhesion on the modified polymer surface.