Browsing by Author "Ramos-Moore, E."

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    A Thermo-metallurgical Model for Laser Surface Engineering Treatment of Nodular Cast Iron
    (2021) Boccardo, A. D.; Catalan, N.; Celentano, D. J.; Ramos-Moore, E.
    Heat treatments are frequently used to modify the microstructure of cast irons according to experimental parameters. Among these, laser surface engineering (LSE) has become relevant for being a highly localized treatment with rapid heating and cooling of the irradiated area resulting in minimal distortion of the workpiece. This work presents and experimentally validates a thermo-metallurgical model able to predict the phase transformations occurring during the LSE treatment of nodular cast iron when it is subjected to different laser beam powers and scanning velocities. For this purpose, an experimental characterization of the thermal history and final microstructure is performed for several operating scenarios. In particular, significant changes in the microstructure can be seen at high powers and low scanning velocity where the matrix is transformed into ledeburite and martensite. The final phase volume fractions predicted by the proposed model along the depth of the sample are compared with the corresponding experimental measurements. The results obtained in the simulation are in good agreement with the experimental measurements. This work highlights the use of our model to be systematically applied for the design and optimization of LSE treatments on cast irons.
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    Analysis of student perceptions of scientific models: validation of a Spanish-adapted version of the Students' Understanding of Models in Science instrument
    (2020) Villablanca, S.; Montenegro, M.; Ramos-Moore, E.
    We present the results of a study of Chilean students' understanding of scientific models, using a Spanish-adapted version of the Students' Understanding of Models in Science instrument (Treagust, D. F., Chittleborough, G., & Mamiala, T. L. (2002). Students understanding of the role of scientific models in learning science. International Journal of Science Education, 24(4), 357-368. doi:10.1080/09500690110066485). The study covered 290 students in three schools in different parts of Chile. Results showed a Cronbach's alpha of 0.86 and medium correlation between the dimensions of the instrument. A confirmatory factor analysis showed that the five dimensions' theoretical structure is supported by the data, and one-way ANOVA and a t-test showed a balanced, non-discriminatory instrument that is suited for use in the Spanish language. The instrument also showed that Chilean students most need improvement in two of the dimensions - 'understanding of scientific models in terms of exact replicas' and the 'use of scientific models'. This reflects the original data analysed by Treagust et al. (2002) and suggests that these factors are common issues in the teaching and learning of scientific models. Future research will review the data by year and group to determine how students develop the idea of a scientific model and relate this information to science curricula. It will also investigate the link between students' understanding of scientific models and Anderson & Krathwohl's (2001) cognitive taxonomy.
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    Effect of microstructure on thermoelastic stresses in Al2O3/Ti(C,N,O)/Ti (C,N) coating systems studied by Finite Element Method simulations
    (2021) Espinoza, C.; Ramos-Moore, E.; Celentano, D.
    Finite Element Method (FEM) simulations were performed to qualitatively study the effects of texture anisotropy, bonding interlayer thickness, and average crack spacing on the evolution of thermoelastic stress in coatings systems containing Al2O3 and Ti(C,N) layers bonded with a Ti(C,N,O) interlayer. Commercial WC-Co tools were considered as substrates, including a superficial gamma-free phase. Significant stress differences are observed between the Al2O3 and Ti(C,N) layers due to differences in the Coefficient of Thermal Expansion (CTE) relative to the substrate. No significant differences were observed when considering axis-dependent CTE and elastic data of the Al2O3 layer, nor introducing a Ti(C,N,O) interlayer. Cracks across the coatings resulted in a significant reduction of stress in both layers, reaching values near zero in the cracks' vicinity, this effect being more prominent for shorter crack distances. Differences among our FEM simulations and experimental residual stress reports on similar systems highlight the need to develop more complex models to understand the effect of nucleation processes and microstructure on the residual stress. (C) 2021 Elsevier B.V. All rights reserved.
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    Effect of surface etching and electrodeposition of copper on nitinol
    (2017) Ramos-Moore, E.; Rosenkranz, A.; Matamala, L.F.; Videla Leiva, Alvaro Rodrigo; Durán, A.; Ramos-Grez, J.
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    Growth, characterization and thermo-mechanical analysis of Al/Al2O3 core/shell nanoparticles obtained under H2 atmosphere
    (2020) Diaz-Droguett, D. E.; Ramos-Moore, E.; Roble, M.; Muecklich, Frank
    In this work, growth, characterization and thermo-mechanical behavior of Al/Al2O3 core/shell nanoparticles (NP) is performed. The growth was carried out by gas condensation methods using H-2 as carrier gas at a pressure of 100 Pa and with a temperature of the evaporation source of 1315 degrees C. The prepared NP were characterized by Energy Dispersive X-ray Spectroscopy for chemical information, transmission electron microscopy for morphological study, and electron diffraction patterns for structural information. The prepared Al NP exhibit a thin Al2O3 passivating oxide shell due to the air exposure when removed from the preparation vacuum chamber. Afterwards, the growth of the Al2O3 oxide shell of the Al NP and the thermo-mechanical interaction between this growing oxide shell and its Al core was studied by performing in-situ thermal X-ray diffraction from RT up to 505 degrees C. Coefficients of thermal expansion of both Al core and Al2O3 oxide shell were obtained by means of X-ray strain analysis. It was found that the thickness of the Al2O3 shell increases with temperature and the thermal stress induced in the system increases linearly with temperature. Our results highlight that these NP overcome higher values of fracture toughness compared with Al2O3 NP used in micro-nano composites, thus improving their mechanical properties for nanofluid applications.
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    Influence of crystallographic texture on friction in a-Al2O3/Ti(C,N) ceramic tool coatings
    (2022) Ramos-Moore, E.; Rosenkranz, A.; Diaz-Droguett, D. E.; Espinoza, C.; El Azahri, I.; Muecklich, F.
    This work explores the influence of the crystallographic texture on the resulting frictional response in two ceramic coatings systems containing top alpha-Al2O3 layer with no and fiber texture. The microstructure was analyzed by electron backscatter diffraction, the surface roughness was characterized by white light interferometry, and the micro hardness was measured by standard Vickers testing. The coefficient of friction (COF) was measured using ball-on-disk tribometry under linear reciprocating sliding motion. Our results verified a strong correlation between the crystallographic texture of the top alpha-Al2O3 layer and the resulting COF. This effect can be mainly attributed to the lowest critical shear stress within the basal dislocation slip {0001} < 11-20 >, which facilitates the generation of plastic deformation at the top surface layer. This work highlights the understanding of the complex correlations between microstructure and tribological performance of ceramic coatings.
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    Modification of ferroelectric hysteresis in Pb(Nb,Zr,Ti)O3 thin films induced by CO2 adsorption
    (2011) Ramos-Moore, E.; Lederman, D.; Cabrera, A. L.
    We report on the modification of ferroelectric hysteresis in Pb(Nb,Zr,Ti)O-3 thin films under the adsorption of CO2 gas. The samples were exposed to the gas in ultra high vacuum while different voltages between the top (Ag) and bottom (Pt) electrodes were applied. After dosing, the samples were heated from room temperature at 1.8 K/s, and a mass spectrometer was used to detect the desorbed molecules. The effective molecular sticking was demonstrated by the appearance of the carbon Auger peak in the surface of the sample and by the presence of CO2 in the desorption curves. After +(-) 9.9 V were applied to the bottom electrode during dosing, we found a shift of 0.52 (+0.58) mu C/cm(2) in the remnant polarization. These evidences suggest the existence of a depolarizing field induced by molecular adsorption at the surface of the top electrode, and contribute to highlight the potential use of ferroelectric thin films as gas sensors. (C) 2011 Elsevier B.V. All rights reserved.
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    Modification of ferroelectric hysteresis in Pb(Nb,Zr,Ti)O3 thin films induced by CO2 adsorption
    (2011) Ramos-Moore, E.; Lederman, D.; Cabrera, A. L.
    We report on the modification of ferroelectric hysteresis in Pb(Nb,Zr,Ti)O(3) thin films under the adsorption of CO(2) gas. The samples were exposed to the gas in ultra high vacuum while different voltages between the top (Ag) and bottom (Pt) electrodes were applied. After dosing, the samples were heated from room temperature at 1.8 K/s, and a mass spectrometer was used to detect the desorbed molecules. The effective molecular sticking was demonstrated by the appearance of the carbon Auger peak in the surface of the sample and by the presence of CO(2) in the desorption curves. After +((-)) 9.9 V were applied to the bottom electrode during dosing, we found a shift of -0.52 (+0.58) mu C/cm(2) in the remnant polarization. These evidences suggest the existence of a depolarizing field induced by molecular adsorption at the surface of the top electrode, and contribute to highlight the potential use of ferroelectric thin films as gas sensors. (C) 2011 Elsevier B. V. All rights reserved.
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    Second nearest neighbor modified embedded atom method interatomic potentials for TiCxN1-x ternary systems
    (2024) Araya-Barr, A.; Garcia, G.; Arias-Camacho, I.; Espinoza, C.; Lee, Byeong-Joo; Ramos-Moore, E.
    New potential parameters for the Ti-C-N ternary system based on the second nearest neighbor modified embedded atom method (2NN MEAM) are reported. The parameters were developed starting from published binary systems for Ti-C and Ti-N and fitted using published data of lattice constants, formation enthalpy, bulk modulus, elastic constants, and surface properties for several C/N ratios in the cubic B1 structure. The simulated systems using the new parameters show agreement with structural and elastic experimental and first-principles values. Our results highlight novel methods to calculate several mechanical and thermal properties of TiCxN1-x systems.
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    Study of thermally induced phase transformations and microstructural changes in porous MoO3 nanostructures for the design of tribological additives
    (2021) Diaz-Droguett, D. E.; Ramos-Moore, E.; Roble, M.; Muecklich, Frank
    The thermal behavior of MoO3-nanostructures is relevant for the design of tribological additives containing Mo-oxides. We report on thermal behavior of porous MoO3-nanostructures analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The nanostructures were grown by gas condensation under H-2. Our results revealed 3 stages of phases behavior as a function of temperature. We found dehydration of MoO3-0,33 H2O after 180 degrees C followed by the formation of beta-MoO3 after 230 degrees C, then to alpha-MoO3 after 280 degrees C, and finally formation of suboxide gamma-Mo4O11 at similar to 330 degrees C. The formation of the latter is mainly due to the crystallization and reduction of the porous oxide matrix. Our results highlight that both thermal and chemical processes must be taken into account when designing tribological additives that contain MoO3. (C) 2021 Elsevier B.V. All rights reserved.