Guerrero Fernández, Margie R.

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    Experimental benchmarks for mechanical properties of highly-loaded carbon nanotube- reinforced polyether ether ketone
    (2018) Guerrero Fernández, Margie R.; Marín Martín, Carlos; College of Engineering; Cancelos Mancini, Silvina; Martínez Iñesta, María M.; Pérez, Nestor J.; Department of Mechanical Engineering; Tarafa, Pedro
    Composites of carbon nanotubes (CNTs) and polymers have been proposed for several engineering applications, this due to the elevated mechanical, thermal and electrical properties of the nanotubes. However, effective manufacture of these compounds has not yet been achieved because the nanotubes tend to agglomerate, do not disperse homogeneously in the polymer matrix and low percentage of nanotubes can be used in the mixture. For polyether-ether-ketone (PEEK) and CNTs composites, evidences show that PEEK seems to coat along nanotubes under certain heat treatments. Based on this premise, this work proposes a new methodology for the manufacture centimeter scale PEEK/CNT composites with high load of CNTs through thermal treatment under controlled pressure. Mechanical properties were determined from strain-stress curves and structural homogeneity and porosity was determined nanoscopically using high-resolution electron microscopes. A correlation between the mechanical properties and the degree of porosity of the fabricated material was obtained. Samples with record structural reinforcement of 115% in the Young modulus of PEEK/CNTs composites were reproducibly fabricated and characterized.
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    Cold gas spraying copper metal on AlN ceramic as an alternative to thick DBC substrates
    (2024-12) Guerrero Fernández, Margie R.; Quintero Aguiló, Pedro O.; College of Engineering; Suárez, O. Marcelo; Resto Irizarry, Pedro J.; Colón Curiel, Brandon J.; Department of Mechanical Engineering; Isaza Brando, Clara E.
    This dissertation investigates the use of Cold Gas Spraying (CGS) to deposit copper onto aluminum nitride (AlN) substrates as a viable alternative to thick Direct Bond Copper (DBC) substrates in power electronics packaging. The research begins by functionalizing the AlN surface through potassium hydroxide (KOH) etching, significantly increasing surface roughness and area, which enhanced the adhesion properties critical for effective CGS copper deposition. Key CGS parameters such as temperature, pressure, nozzle standoff distance, travel speed, substrate roughness, and deposition angle were systematically studied to optimize the copper coating quality. The deposition angle, in particular, emerged as a critical factor, with a 60-degree angle yielding the smoothest coating. A uniform 300 μm thick copper layer, comparable to that of commercial DBC substrates, was successfully achieved. The bonding mechanisms between copper and AlN were found to involve mechanical interlocking, plastic deformation, dynamic recrystallization, and grain refinement driven by temperature increases during particle impact, with the copper particle temperature reaching up to 693 K. These mechanisms contributed to strong interfacial bonding and minimal coating defects. Overall, this study demonstrates that CGS offers a promising alternative to conventional DBC substrates, providing high bond strength, excellent thermal stability, and defect-free coatings. The findings provide valuable insights into metal-ceramic bonding in CGS and establish a foundation for future research to further refine this technique for industrial applications in high-voltage and power electronics.