Walter R. Tuckart

Tin Coatings Electrodeposited from Sulfonic Acid-Based Electrolytes: Tribological Behavior

Abstract A high efficiency methane sulfonic acid electrolyte used for tin electrodeposition was studied, and the properties of the resulting deposits were compared to those of tin coatings obtained from an industrial phenol sulfonic acid electrolyte. Cyclic voltammetry was used to study the effect of organic additives on the reduction process to define the composition of the electrolytic bath. Thick tin electrodeposits were obtained on rotating cylinder steel electrodes, and their surface morphology, preferred crystal orientation, surface roughness, micro hardness, and tribological behavior were measured. Smooth, adherent, and bright tin coatings were obtained from the methane sulfonic acid electrolyte, which differed in morphology and texture from tin electrodeposited from the industrial bath. Influence of organic additives on preferred crystal orientation of the coatings was found to be stronger than changing the supporting sulfonic acid type. Tribological tests showed that the two types of deposits have a similar coefficient of friction. However, tin coatings obtained from methane sulfonic electrolytes presented a lower wear resistance and underwent galling at lower loads.

Tribological behaviour of nitrided and nitrocarburized carbon steel used to produce engine parts

Purpose – The purpose of this study is to select a proper surface treatment to enhance wear resistance of engine camshafts. The camshaft is a relevant part of a diesel engine which works under torsion, fatigue and wear efforts. They are usually manufactured by casting, forging or machining from forged bar of low alloy steels, and in most cases, the machined surfaces are quenched and tempered by induction heating. After that, in many cases, to withstand the efforts imposed on the active surfaces and improve tribology and fatigue properties, the industry used for decades, thermochemical technologies such as salt bath or gaseous nitriding and nitrocarburizing processes. Design/methodology/approach – This paper studied the effects of plasma nitriding and plasma nitrocarburizing, on the tribological behaviour of the steel SAE 1045HM3 proposed to produce camshafts. After the plasma treatments, the change in surface roughness was measured; the modified layers were studied by X-ray techniques and its thickness by...

Influence of the Martensite Volume Fraction on the Reciprocating Sliding Behavior of Ti-Nb Microalloyed Steel

The objective of this work was to evaluate the influence of martensite fraction on the wear mode and the energy dissipation by friction of dual phase (DP) steel tested under reciprocating sliding conditions. For this purpose, a Ti-Nb microalloyed steel was heat treated in a conventional furnace at temperatures between 780 and 880°C (intercritical annealing temperature) for 3 min to obtain DP microstructures with volume fractions of martensite between 25 and 90%. Wear tests were carried out in both DP and as-received samples, using a reciprocating tribometer with ball-on-flat geometry, at two constant applied loads, 2.5 and 4 N. The wear damage of each sample was measured through volume loss and the dissipated energy during the test. The obtained results evidenced a significant influence of the contact load over the wear mode, because at low load the DP wear was reduced with increased hardness but just up to 75% of martensite. At high load, the sliding process promotes an oxide mixture in the ferritic microstructure that acts as a factor in wear reduction.

Effect of crystal size on the tribological behavior of manganese phosphate coatings under lubricated sliding

In this study, the wear and friction behavior of manganese phosphate coatings with different crystal sizes were investigated. Crystal size was controlled modifying the chemical composition of the phosphating bath, particularly the concentration of the activator which modifies the number of nuclei for crystal growth. Activator concentration range used for this work varied from 0 to 0.7 g/L, and crystal size was measured using image analysis software on scanning electron microscopy photographs. Available volume for lubricant retention was determined measuring the phosphated surface with a 3D optical profilometer. At the same time, lubricated wear tests were carried out using a ring-on-block configuration at low speeds (23 mm/s) and high loads (14,500 N). Wear behavior was determined as the sliding distance to failure, which was noticed through signs of removal of the phosphate along with the increase of coefficient of friction. It was found that there is a competition between the availability of volume to hold the lubricant, which increases with the crystal size, and the surface coverage, which diminishes as the crystal size grows. Optimal results were obtained for an activator concentration of 0.3 g/L, which meant an average crystal size of 16 µm.

Bismuth (III) sulfide as additive: towards better lubricity without toxicity

Purpose The purpose of this study is to design a fluid formulation with good lubricant properties by using an environmentally friendly additive for: high and low contact pressure conditions and steel/steel and polymer/steel systems. Design/methodology/approach Bismuth (III) sulfide (Bi2S3, “green chemistry” synthesis) is added to a commercial vinyl-terminated silicone fluid (PDMS-Vi) to obtain different weight-per cent mixtures. Tribological performance of formulations is studied from Reichert’s tests (steel/steel system) and block on ring tests (polymer/steel). The results are compared with formulations prepared with commercial bismuth (III) sulfide (Bi2S3), molybdenum (IV) sulfide (MoS2) and graphite. Findings An orthorhombic crystal lattice (XRD ) and a high-purity product (XRF) are evidenced for synthesized Bi2S3. Lubricant properties increase when the weight-per cent of the synthesized Bi2S3 increases in formulations. The wear area decreases up to 90 per cent according to Reichert’s tests. The synthesized Bi2S3 shows a better tribological behavior when compared to commercial Bi2S3, MoS2 and graphite. Originality/value Replacement of lead derivatives by an environmentally friendly lubricant in extreme pressure (EP) formulations and excellent performance compared to commercially used additives are achieved.

Nanotribological behavior of deep cryogenically treated martensitic stainless steel

Cryogenic treatments are increasingly used to improve the wear resistance of various steel alloys by means of transformation of retained austenite, deformation of virgin martensite and carbide refinement. In this work the nanotribological behavior and mechanical properties at the nano-scale of cryogenically and conventionally treated AISI 420 martensitic stainless steel were evaluated. Conventionally treated specimens were subjected to quenching and annealing, while the deep cryogenically treated samples were quenched, soaked in liquid nitrogen for 2 h and annealed. The elastic–plastic parameters of the materials were assessed by nanoindentation tests under displacement control, while the friction behavior and wear rate were evaluated by a nanoscratch testing methodology that it is used for the first time in steels. It was found that cryogenic treatments increased both hardness and elastic limit of a low-carbon martensitic stainless steel, while its tribological performance was enhanced marginally.