Browsing by Author "Prieto, Germán"

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    Effect of Composition and Thickness on the Tribological Performance of Epoxy-MoS2 Composite Coatings in Reciprocating Block on Ring Test
    (2023) Zanin, Maximiliano; Prieto, Germán; Tuckart, Walter; Failla, Marcelo
    Over the past two decades, there has been an increasing adoption of protective and lubricant coatings for their usage in threaded connections in the oil and gas industry to reduce both failed connections due to galling and environmental contamination due to lubricant spillage. In this work, the influence of composition and thickness on the tribological performance of MoS2-epoxy matrix composite coatings in reciprocating block-on-ring tests was studied. Epoxy resins with 2.5, 5, and 10 wt.% MoS2 were deposited on SAE 4140 steel blocks using a manual procedure, and after curing, hardness and thickness were measured. The tribological evaluation was performed using a block-on-ring test at low speed (30 mm/s), with reversing sliding direction and continuously varying loads between 0 and 5000 N. These conditions are similar to those encountered on the thread flanks during make-and-break operations in OCTG (Oil Country Tubular Goods) threaded connections. Wear surfaces were examined by optical and scanning electron microscopy (SEM). The wear resistance of coatings containing 2.5 and 5 wt.% of MoS2 strongly depends on their thickness, with a threshold around 70 μm. Coatings with lower thicknesses displayed constant wear rates, which decreased as the MoS2 concentration increased. On the other hand, coatings with thicknesses exceeding 70 μm showed an increase in wear rate proportionate to their thickness. In the case of coatings with 10% MoS2, the friction and wear were not influenced by coating thickness. These coatings exhibited the lowest average coefficient of friction (COF) values (0.06 ± 0.015) and wear rates (3.1 ± 1.3 × 10−8 mm3/N mm) compared to the other compositions tested. This performance is attributed to the formation of tenacious tribofilms on the surfaces.
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    Plasma nitriding and plasma nitrocarburizing of a low alloy steel selected to produce camshafts for diesel engines
    (2015-05-14) Cabo, Amado; Brühl, Sonia Patricia; Prieto, Germán; Tuckart, Walter Roberto
    Camshafts are a relevant part of diesel engines of extended use today. These components work under torsion and are also prone to fatigue and wear damage. Usually they are manufactured by casting, forging or machining from forged bars of low alloy steels. In most cases, the machined surfaces are quenched and tempered by induction heating. To withstand the efforts imposed on the active surfaces and improve tribological and fatigue properties, the industry used for decades thermochemical technologies such as: salt bath or gaseous nitriding and nitrocarburizing processes. This work studied the effects of plasma nitriding and plasma nitrocarburizing, on the tribological behavior of the steel SAE 1045HM3 proposed to produce camshafts. Results show that plasma nitrided samples present the best tribological behavior compared to the nitrocarburized and quenched and tempered ones. The influence of the roughness produced by the thermochemical processes also appears to be important.