José Rubens Gonçalves Carneiro

XPS, XRD and laser raman analysis of surface modified of 6150 steel substrates for the deposition of thick and adherent diamond-like carbon coatings

Although the 6150 steel has an excellent fatigue and impact resistance, it is unsuitable to operate it when the corrosion is a limited factor. We propose here a sequence of steel pre-treatment by carburizing, carbonitriding and nitriding in order to improve the poor adhesion between Diamond Like-Carbon coatings on steel. This sequence is our attempt to reduce the difference between the coefficients of thermal expansion of steel and DLC through the graded interface. This work demonstrates the quantitative analysis of the molecules present at surface using X-ray photoelectron spectroscopy. The crystallographic structures are investigated by X-ray diffraction which shows the formation of carbides and nitride phases. Raman spectroscopy reveals the carburizing surface characteristics where DLC coating is nucleated and grown at the substrate. At the end of the analysis it is possible to verify which molecules and phases are formed on the steel surface interface after each step of pre-treatment.

Methods of data analysis for the ball cratering test on TiN and DLC coated steel

Titanium nitride (TiN) coatings are widely used in machining because of its mechanical characteristics which modify the surface of the substrate increasing the capacity of load support and reduction of friction, while a coating as diamond-like carbon (DLC), which also has interesting mechanical properties, needs better attention. In this sense, the development of new coatings such as DLC is as important as wear analysis techniques. This work discusses the methods available to assess abrasive wear of coatings. For this, it has been used the data of the crater volume formed in ball cratering test and compared the difference between the specific wear coefficients of substrate and coating (ks and kc). These coefficients depend of the methods used for data analyses, thus, it has been used four equations to calculate ks and kc. Moreover, profilometry (pf) has been used to calculate the volumes, and thus ks and kc. Also, the roughness of the coatings, the thickness, the images corresponding to the crater formed, the coefficient of friction, the data obtained in wear tests due to the volume removed and, in the end, a comparison between ks and kc by different methods of data analyzes are presented.

Influence of Ethanol as a Carburizing Agent on Carbon Surface Concentration and Microstructure of DIN 17NiCrMo7 Steel Gears

In the present work, the addition of ethanol to endothermic gas during the carburizing process of DIN 17NiCrMo7 steel gears was investigated with the objective of determining the impact on carbon surface concentration and microstructure. The materials were carburized at 870°C and 930°C, oil quenched, tempered and subsequently shot peened. Carburizing was carried out in a continuous industrial furnace for a total of 280 min. After quenching and tempering, the in-depth carbon concentrations were determined through quantitative chemical analysis and the resulting profiles were modeled in order to obtain carbon diffusivity constants. The amount of retained austenite and austenite grain size, determined by X-ray diffraction and optical microscopy, were found to increase with carburizing temperature. Residual stress profiles were also determined by X-ray diffraction before and after the shot-peening process. The microstructure of the specimens was further investigated by transmission electron microscopy, which revealed the presence of BCC martensite before and after shot-peening. The enrichment of the endothermic gas carrier with ethanol could be shown to be a viable option, allowing for surface concentrations of up to 0.8%C.Copyright