FRCU - Grupos de Investigación

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    Evaluation of wear and corrosion resistance in acidic and chloride solutions of PVD-CrN coatings on untreated and plasma nitrided AISI 4140 steel
    (2024-05-24) Maskavizan, Ana Justina; Quintana, Juan Pablo; Dalibón Bähler, Eugenia Laura; Márquez, Adriana Beatriz; Brühl, Sonia Patricia; Farina, Silvia Beatriz
    CrN coatings deposited by Physical Vapor Deposition (PVD) are widely used due to their high hardness and high wear resistance, low friction coefficient and superior corrosion resistance. The latter makes this coating appropriate for protecting forming tools, moulds and components used in chemical processing. In this work, single layer CrN coatings were deposited on plasma nitrided and non treated AISI 4140 steel. The influence of nitriding on the wear resistance, coefficient of friction and corrosion resistance in acidic solutions and chloride solutions was studied. Thickness of the coatings was measured using optical microscopy, and surface hardness was assessed with a Vickers microindenter. Adhesion was determined using Rockwell indentation applying 150 kg and scratch test as well as Scratch test at different constant loads. Sliding wear resistance was studied with Pin-on-Disk tests under different normal loads and sliding distances, the coefficient of friction was registered during the tests and volume loss was calculated. Corrosion test were carried out using a 3.5 % NaCl solution and a 0.5 M H2SO4 solution as electrolytes. Nitrided steel without any coating was used also as comparison. Coating thickness was approximately (2.6 ± 0.4) μm and surface hardness reached a value of (1960 ± 160) HV0.05, being this a composed hardness because of the low film thickness. Adhesion was good for both substrates, non nitrided and nitrided steel, in both cases, it could be classified as HF1 according to VDI 3198 standard. In the case of the Scratch test, in the only coated samples, without nitriding as pre treatment the film cracking was observed at 50 N in the track, whereas in the duplex sample the coating had a better load bearing capacity and reached 70 N without damage. No delamination was detected around the scratch track in all cases. Wear volume loss was undetectable in the pin-on-disk test for the coated systems, whereas it was approximately 30 x 10-3 mm3 for the nitrided steel and 150 x 10-3 mm3 for the untreated steel. In the corrosion tests, the coating showed a passive behaviour as tested in NaCl solution and the corrosion current density was significantly lower for coated samples in the H2SO4 solution, proving that the CrN coating is suitable for protecting steel substrate in both chloride and acidic media.
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    Extensión de durabilidad de pistones de bombas de fractura hidraúlica mediante el empleo de tecnología de nitruración por plasma y PVD
    (Asociación Argentina de Tribología, 2017-10) Cirimello, Pablo; Brühl, Sonia Patricia; Aguirre, Luis Alberto; Morris, Walter; Carfi, Guillermo Rodolfo
    En la industria del Gas y el Petróleo (Oil&Gas), el concepto de fractura hidráulica consiste en “romper” la formación (reservorios) por intermedio de un fluido, básicamente formado por agua y arena (agente de sostén), que bombeado a una determinada presión y un dado caudal, supere la resistencia de la formación (gradiente), de manera de colocar dentro de las fisuras creadas un ordenamiento del agente de sostén, impidiendo el cierre de las mismas . Las bombas de fractura hidráulica son de tipo aspirante-impelente: aspiran el fluido con el agente de sostén y lo bombean a altas presiones a fondo de pozo. Los pistones de estas bombas realizan la succión y la compresión; en su movimiento alternativo se produce el eventual ingreso de finos de arena al huelgo que queda entre la superficie del pistón y los sellos, siendo esta la principal causa de desgaste localizado del pistón, las camisas y los sellos del conjunto. Existen al menos dos mecanismos de desgaste: generalizado, atribuible a los finos del agente de sostén y localizado, atribuible a claras deficiencias en el recubrimiento duro comúnmente aplicado. La tecnología de endurecimiento superficial empleada actualmente para fabricar estos componentes es el Thermal Spray, que presenta ante estas prestaciones, fallas propias de la técnica y de su forma de aplicación: heterogeneidad química y microestructural, porosidad y falta de adherencia entre metal base y recubrimiento. Siguiendo criterios ampliamente difundidos en la ingeniería de superficie, se propuso por tanto reemplazar esta técnica de endurecimiento superficial por la de Nitruración por Plasma, la cual genera una transición gradual de durezas desde el núcleo hacia la superficie, eliminando la presencia de interfases. El tratamiento desarrollado se complementa con un segundo endurecimiento superficial, mediante la técnica de PVD (Physical Vapor Deposition). El tratamiento de endurecimiento descripto, fue utilizado para fabricar nuevos pistones de bomba de fractura hidráulica, y ensayados en un piloto tecnológico de campo.