This work aims to improve the adhesion of a hybrid non-isocyanate polydimethylsiloxane urethane (PDMSUr) coating by producing active layers on titanium alloy (Ti6Al4V) and stainless steel (SS316L) applying pulsed Nd:YAG laser and oxygen plasma. The PDMSUr is a hybrid adhesive and, when functionalized with alkoxysilane groups, can bind onto the interfacial hydroxyl groups of a (hydr)oxide/carbonate layer by sol–gel reactions. These reactions are acid catalysed and the silanol groups can bind through Si–O–metal links. The pull-off-strength of such sustainable coatings raised more than 100% for both substrates after the physical treatments, compared with the substrates etched. X-ray Photoelectron Spectroscopy (XPS) of a freshly pre-treated substrate revealed the formation of thin oxide-based reactive layers on the surface of Ti6Al4V and SS316L after the surface treatments. Both physical procedures were efficient to create oxide layers on top of metallic substrates and contributed to the improvement of adhesion strength of PDMSUr on biomedical grade metals
Bearing steels must have high hardness, good wear resistance and dimensional stability. In the present work the AISI 52100 bearing steel was selected as the substrate for a niobium carbide coating produced by a salt-bath thermoreactive deposition process. The present work addresses the effect of niobium carbide coating on the wear and corrosion resistance of the abovementioned steel. A homogeneous layer composed solely by the cubic niobium carbide (NbC) was produced. The carbide coating yielded average hardness and elastic modulus of 26GPa and 361GPa, respectively. No significant decarburization was detected beneath the case by means of hardness fluctuations. Dry wear tests resulted in worn volumes 10 times smaller for the NbC coated steel, comparatively to the untreated substrate, at three different applied loads. Corrosion tests in NaCl solution indicated an improved behaviour for the carbide coated bearing steel at applied potentials inferior than 250mV. At higher potentials the electrolyte appears to penetrate trough the layer yielding wide corrosion caps.
Pack chromising treatment is an environmentally friendly alternative to hard chromium to form wear and corrosion resistant surface layers. In this work, samples of AISI 1060 steel were pack chromised for 6 and 9 h at 1000 and 1050uC using different activator concentrations. Wear tests were performed in dry conditions and corrosion tests in natural sea water for the pack chromised samples and hard chromium. Pack chromising yielded the formation of layers with high chromium concentrations, high hardness and wear resistance. Increasing activator concentration causes no significant change on the morphology and thickness of the layers. The layers produced at 1050uC yielded only a (Cr,Fe) 2 N 12x phase, and those obtained at 1000uC are composed of a carbide mixture with (Cr,Fe) 2 N 12x . The sample treated at 1050uC for 9 h resulted in an optimum condition by means of better wear resistance and corrosion properties, which were close to that exhibited by the hard chrome, indicating that pack chromising is a promising alternative.
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