Martín Flores

Corrosion of a Zn–Al–Cu alloy coated with TiN/Ti films

Abstract TiN and Ti coatings were deposited by d.c. magnetron sputtering on a Zn–Al–Cu alloy. The coatings were deposited at a relative low temperature of 115–130°C. X-ray diffraction showed that the films were crystalline. A pure titanium interlayer was used to improve the adhesion and corrosion resistance of the titanium nitride films. The corrosion behavior of samples in NaCl solutions was studied using polarization curves. Scanning electron microscopy was used to study the corroded samples. It was found that corrosion resistance of coated alloy was higher than the substrate resistance. Furthermore the corrosion resistance is mainly controlled by the presence of defects in the TiN and Ti films.

Study of the Pull-In Voltage for MEMS Parallel Plate Capacitor Actuators

This paper provides new investigation for the static and dynamic behavior of a MEMS parallel plate capacitor derived by analytical and numerical design modeling programs developed in Matlab. One significant finding is about the role, which has so far overlooked in many analyses, of a dielectric layer normally placed on top of the ground electrode to avoid short circuiting risks. It is demonstrated in this paper that this layer produces an increased force between electrodes that in turns decreases the well-known pull-in voltage, V pi , as compared to the one calculated when this dielectric layer is not considered on the systems static analysis. Expressions for the static V pi and its corresponding maximum stable electrode swing x pi are derived to take the above effect into account. The system dynamic analysis is done with a user-friendly Simulink interface constructed to allow easy introduction of capacitor design dimensions, material parameter values and voltage signal stimuli. The impact of any combination of these parameters on the electro-mechanical system behavior, that is, the voltage-electrode position dependence data can be easily extracted and become of help for design decision making on the early design stages of this type of structures. This modeling tool interface is based on solving the full differential equation that describes the free electrode displacement without relying on linearizing the inverse quadratic electrode separation dependence of the electro-static force term. This approach intrinsically takes into account the voltage dependant k -spring softening effect derived precisely from a linearizing simplification. Finally, by applying a saw-tooth voltage waveform, the dynamic pull-in voltage and the maximum stable electrode travel range are observed to go well beyond the predicted static pull-in voltage and travel range values.

Dynamic behavior modeling of MEMS parallel plate capacitors

This work presented dynamic behaviors of a MEMS parallel plate capacitor using analytical and numerical methods. The differential equation describing the electrode displacement is solved by using a Matlab/Simulink interface developed to serve as a practical fill-the-box design tool. The systems dynamic instability condition (at the pull-in voltage, V/sub dpi/) is reached at much higher bias levels as compared with the static case. We presented the dynamic behavior and the frequency limiting cases for sine and pulse input bias waveforms. For high frequency, the results are given both in analytical and numerical forms.

Influence of plasma density on the chemical composition and structural properties of pulsed laser deposited TiAlN thin films

Incorporation of substitutional Al into the TiN lattice of the ternary alloy TiAlN results in a material with improved properties compared to TiN. In this work, TiAlN thin films were grown by the simultaneous ablation of Ti and Al targets in a nitrogen containing reactive atmosphere. The deposit was formed on silicon substrates at low deposition temperature (200 °C). The dependence of the Al content of the films was studied as a function of the ion density of the plasma produced by the laser ablation of the Al target. The plasma parameters were measured by means of a planar Langmuir probe and optical emission spectroscopy. The chemical composition of the films was measured by energy dispersive X-ray spectroscopy. The results showed a strong dependence of the amount of aluminum incorporated in the films with the plasma density. The structural characterization of the deposits was carried out by Raman spectroscopy, X-ray diffraction, and transmission electron microscopy, where the substitutional incorporation of the Al into the TiN was demonstrated.

Sintering behaviour and mechanical characterisation of Ti64/xTiN composites and bilayer components

ABSTRACT Ceramic particle reinforcement can be used to improve the surface properties of Ti6Al4V (Ti64) alloy. Powder metallurgy route is a promising method to fabricate such reinforced Ti64 components. To assess the relevance of this technique, this work investigates the effect generated by the addition of TiN particles in Ti64 powder during free sintering. TiN reinforcement particles were randomly distributed in the Ti64 matrix with three different concentrations in two configurations: completely reinforced and unreinforced–reinforced bilayer. Dilatometry was used to obtain the shrinkage kinetics of samples at 1200, 1300 and 1400°C under inert atmosphere and to investigate the impact of reinforced particles on the sintering behaviour. The microstructure of sintered materials was shown to be lamellar in the unreinforced material and equiaxed in reinforced materials. Finally, the Vickers microhardness measurement showed the huge benefit of adding TiN particles to increase the mechanical strength of the Ti64 alloy.

Constrained sintering and wear properties of Cu-WC composite coatings

Abstract Coatings of metal matrix composites (Cu-WC) were fabricated by solid-state sintering. WC reinforcing particles in different quantities from 5% up to 30% (volume fraction) were mixed with Cu particles. After mixing, the powders were poured onto the surface of copper substrates. Sintering was carried out at 1000 °C under a reducing atmosphere in a vertical dilatometer. Sintering kinetics was affected by both rigid substrates and WC particles which retarded the radial and axial densification of powders. However, the coatings were strongly attached to the substrate, and WC particles were randomly distributed within the matrix. The addition of the reinforcing particles enhanced the microhardness and reduced the volume loss in wear tests to 1/17 compared to the unreinforced sample. The predominant wear mechanism was identified as abrasion at a load of 5 N. 20% WC (volume fraction) reinforcing particles led to the maximum values of properties for the composite coating.