Papers by Author: Javier Andres Muñoz Chaves

Abstract: The purpose of this study was to evaluate the TiO₂ nanotubes growth and the variation in its diameter to improve the surface properties of Ti-7.5Mo to use for biomedical applications. For the nanotubes TiO₂ growth, the samples were anodized in glycerol and ammonium fluoride and divided according to the anodizing potential at 5V to 10V and 24 hour time. The surfaces were examined by scanning electron microscope (SEM), X-ray analysis (XRD) and contact angle measurements. The average tube diameter, ranging in size from 13 to 23 nm, was found to increase with increasing anodizing voltage. It was also observed a decrease in contact angle in accordance with the increase in the anodizing potential. The X-ray analysis showed the presence of anatase phase in samples whose potential was 10V and this condition represents a simple surface treatment for Ti-7.5Mo alloy that has high potential for biomedical applications.

Abstract: Anelastic properties of Bulk Metallic Glasses (BMG) were studied by mechanical spectroscopy using a flexural vibration apparatus. BMG’s samples, with nominal composition Cu₄₈Zr₄₃Al₉ and Cu₅₄Zr₄₀Al₆, were produced by skull push-pull casting technique in rectangular cavity cooper mold. In both samples, the differential scanning calorimeter patterns have evidenced the presence of amorphous structure, although the X-ray diffraction for Cu₄₈Zr₄₃Al₉ composition has shown a heterogeneous microstructure embedded in the amorphous matrix. Anelastic relaxation spectra were obtained using an acoustic elastometer system with vibration frequency in the kilohertz bandwidth, a heating rate of 1 K/min, vacuum greater than 10^-5 mBar in the temperature range of 300 K to 620 K. In the flexural apparatus, an acoustic elastometer system, the internal friction (energy loss) and the elastic modulus were obtained by free decay of vibrations and by the squared of the oscilation frequency, respectively. Internal friction spectra were not reproducible among the measurements, which may imply atomic rearrangement in the samples due to consecutive heating. Normalized elastic modulus data showed distinct behavior from the first to the other measurements evidencing irreversible microstructural alterations in the samples possibly associated with mechanical relaxation due to the motion of atoms or clusters in the glassy state.

Abstract: This study consists of the characterization of the anelastic properties of a Bulk Metallic Glasses (BMG) by mechanical spectroscopy, which can be defined as an energy absorption technique. The equipment used was the acoustic elastometer system, the anelastic relaxation spectra were carried out with a heating rate of 1 K/min and vacuum better than 10-5 torr, in the temperature range of 300 K to 640 K. The amorphous sample studied, with nominal composition of Cu53.5Zr42Al4.5, was processed by skull push-pull casting technique in a rectangular cavity cooper mould. Differential scanning calorimeter (DSC) curves have evidenced the amorphous structure although the X-ray diffraction (XDR) pattern has indicated a heterogeneous microstructure with amorphous matrix and some metaestable nanocrystalline phases which have not been identified yet. The dynamical elastic modulus of this alloy (between 54 GPa and 58 GPa at room temperature) and internal friction patterns as temperature function implied an increase of the crystalline phase during the measurements. This effect was confirmed with new X-ray diffraction measurements after the internal friction experiments.

Abstract: Measurements of anelastic relaxation (internal friction and frequency) as a function of temperature were carried out in samples of Ti-13Nb-13Zr using two experimental apparatus: Flexural Vibration of the first tone of samples in Acoustic Elastometer System (Vibran Technology®) operating in a kilohertz bandwidth, and Torsional Vibration of the samples in Kê-type Torsion Pendulum operating in a hertz bandwidth. Experimental spectra of anelastic relaxation were determined in the temperature range from 300 K to 450 K for a heating rate of 1K/min under pressure of 10-5 Torr, in both apparatus. The results show a relaxation structure strongly dependent on the microstructure of the material. The dynamical elastic modulus (E) of Ti-13Nb-13Zr alloy can be determined by flexural vibrations by frequency (f) measurements (f  E1/2). The anelastic relaxation spectrum of Ti-13Nb-13Zr alloy was a function of temperature obtained by torsional vibrations, not revealing the presence of interstitial solutes in solid solution in the temperature range of measurements.