Caxias do Sul, Brazil
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Leite M.V.,University of Sao Paulo | Figueroa C.A.,University of Caxias do Sul | Figueroa C.A.,Plasmar Tecnologia Ltda. | Gallo S.C.,Plasmar Tecnologia Ltda. | And 6 more authors.
Wear | Year: 2010

AISI H13 tool steel discs were pulsed plasma nitrided during different times at a constant temperature of 400°C. Wear tests were performed in order to study the acting wear mechanisms. The samples were characterized by X-ray diffraction, scanning electron microscopy and hardness measurements. The results showed that longer nitriding times reduce the wear volumes. The friction coefficient was 0.20 ± 0.05 for all tested conditions and depends strongly on the presence of debris. After wear tests, the wear tracks were characterized by optical and scanning electron microscopy and the wear mechanisms were observed to change from low cycle fatigue or plastic shakedown to long cycle fatigue. These mechanisms were correlated to the microstructure and hardness of the nitrided layer. © 2010 Elsevier B.V.


Corujeira Gallo S.,Plasmar Tecnologia Ltda. | Figueroa C.A.,Plasmar Tecnologia Ltda. | Figueroa C.A.,University of Caxias do Sul | Baumvol I.J.R.,University of Caxias do Sul | Baumvol I.J.R.,Federal University of Rio Grande do Sul
Materials Science and Engineering A | Year: 2010

The premature failure of an aluminium injection die with a duplex surface treatment (plasma nitriding and physical vapor deposition coating) was investigated, in an effort to identify the causes of such premature failure of the component. The manufacturing and the operating conditions were documented. Analytical tools were used, including scanning electron microscopy with energy dispersive X-ray capability, X-ray diffraction, and instrumented microhardness testing. Preliminary observations showed a microstructure of coarse tempered martensite, and a considerably rough surface with porosity and cracks. A detailed analysis of crack initiation sites identified sulfur inclusions in the subsurface, underneath the coating. A further revision of the processing conditions revealed that a sulfur-impregnated grinding stone had been used to polish the die. The chemical composition of such grinding stone matched that of the inclusions found in the subsurface of the failed component. Thus, searched causes of premature failure could be discussed on the lights of the present findings. © 2010 Elsevier B.V.


Petry E.R.,University of Caxias do Sul | Boeira C.D.,University of Caxias do Sul | Cemin F.,University of Caxias do Sul | Leidens L.M.,University of Caxias do Sul | And 5 more authors.
Surface Engineering | Year: 2016

Diamond-like carbon (DLC) coatings show strident properties such as high wear resistance and ultra-low friction. However, a widespread use regarding energy efficiency issues is neglected due to the poor adhesion. Silicon adhesion interlayers (SiCx:H) were deposited at different temperatures from 50 to 500°C with hexamethyldisiloxane followed by DLC. The microstructure was analysed by atomic force microscopy, scanning electron microscopy and Raman spectroscopy. The chemical depth profiling and chemical mapping were performed by glow discharge optical emission spectroscopy and energy-dispersive spectroscopy, respectively. Hardness and critical loads were analysed by nanoindentation tests. At higher deposition temperatures the Si-containing interlayers show lower relative content of H, O and Si and higher relative content of C, allowing the formation of more C–C chemical bonds at the outermost DLC/SiCx:H interface, which is correlated to better adhesion. Finally, an atomistic model is proposed in order to explain the DLC debonding and bonding mechanisms. © 2016 Institute of Materials, Minerals and Mining


Cemin F.,University of Caxias do Sul | Boeira C.D.,University of Caxias do Sul | Figueroa C.A.,University of Caxias do Sul | Figueroa C.A.,Plasmar Tecnologia Ltda.
Tribology International | Year: 2016

DLC is a promising material to be used in technological issues. However, its poor adhesion on steels keeps away from a wide range of applications. Thus, an understanding of the physicochemical structure of the DLC/interlayer/steel system in correlation with a mechanical model is mandatory in order to explain the tribological behavior as a whole. In this work, DLC was deposited on AISI 4140 low-alloy steel through a silicon-containing interlayer. Two different delamination critical loads were determined and they were associated with different failure mechanisms that took place at the outermost and at the innermost interfaces of the silicon-containing interlayer. The Hertz contact theory was used to evaluate the shear stress distribution at the applied normal loads during the scratch tests. © 2015 Elsevier Ltd. All rights reserved.


Luvison C.,University of Caxias do Sul | Sonda V.,University of Caxias do Sul | Rovani A.C.,University of Caxias do Sul | Cemin F.,University of Caxias do Sul | And 9 more authors.
Vacuum | Year: 2012

We investigated the low load friction behavior of plasma post-oxidized, plasma- nitrided AISI 1045 plain steel, using unidirectional sliding tests. The hydrogen content in the post-oxidation plasma was varied between 0 and 25%. The nitrided or oxidized layer thicknesses ranged from approximately 340-380 μm or 0.7-1.1 μm, respectively. The outermost iron oxide layer decreases the friction, whereas the underneath iron nitride layer increases the mechanical strength. The incorporation of hydrogen in the oxidative plasma mixture allows to control the type of iron oxide phase. It is observed that the presence of a superficial magnetite layer leads to a decrease of the friction coefficient with respect to the non-oxidized nitrided steel. The results are interpreted on the lights of crystal chemistry and with a model to explain the in-depth effects of hydrogen in the oxidative plasma. © 2011 Published by Elsevier Ltd.


Dufrene S.M.M.,University of Caxias do Sul | Dufrene S.M.M.,University of Lorraine | Cemin F.,University of Caxias do Sul | Soares M.R.F.,University of Caxias do Sul | And 6 more authors.
Surface and Coatings Technology | Year: 2014

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with attractive properties such as high hardness, low friction, chemical inertness and high wear resistance. In this work, hydrogenated amorphous carbon (a-C:H) thin films were deposited using a plasma enhanced chemical vapor deposition technique by pulsed DC plasma with a simple, low-cost and efficient arrangement of multi-cathodes and multi-anodes in order to enhance the plasma by electrostatic confinement. The samples were characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, Elastic Recoil Detection Analysis, Raman Spectroscopy, and nanoindentation measurements. a-C:H thin films show an homogeneous hydrogen profile along the films deposited at -600V and -800V and variable working pressure. According to Raman spectra, both the ID/IG ratio and the G-peak position increase at higher voltages (more remarkable dependence) and lower working pressures (less remarkable dependence). Moreover, the hardness depends on working conditions such as power supply voltage and total working pressure. The electrostatic confinement enhances the deposition rates of a-C:H thin films up to values of 0.9μm·h-1, which is almost double than those previously published by pulsed DC plasma in similar conditions. The Raman spectra follow the stage 2 of an established model and this structure transition may explain the hardness behavior. © 2014 Elsevier B.V.


Boniatti R.,University of Caxias do Sul | Bandeira A.L.,University of Caxias do Sul | Crespi A.E.,University of Caxias do Sul | Aguzzoli C.,University of Caxias do Sul | And 4 more authors.
Applied Surface Science | Year: 2013

The interaction of bio-ethanol on steel surfaces modified by plasma-assisted diffusion technologies is studied for the first time. The influence of surface microstructure and chemical composition on corrosion behaviour of AISI 4140 low-alloy steel in fuel-grade bio-ethanol was investigated. The steel surfaces were modified by plasma nitro-carburizing followed plasma oxidizing. X-ray diffraction, scanning electron microscopy, optical microscopy, X-ray dispersive spectroscopy, and glow-discharge optical emission spectroscopy were used to characterize the modified surface before and after immersion tests in bio-ethanol up to 77 days. The main corrosion mechanism is pit formation. The pit density and pit size were measured in order to quantify the corrosion resistance which was found to depend more strongly on microstructure and morphology of the oxide layer than on its thickness. The best corrosion protection was observed for samples post-oxidized at 480 °C and 90 min. ©2013 Elsevier B.V. All rights reserved.


Cemin F.,University of Caxias do Sul | Bim L.T.,University of Caxias do Sul | Menezes C.M.,University of Caxias do Sul | Maia da Costa M.E.H.,Pontifical Catholic University of Rio de Janeiro | And 4 more authors.
Surface and Coatings Technology | Year: 2015

Diamond-like carbon (DLC) is a hydrogenated amorphous carbon (a-C:H) thin film material owing to its unique tribological properties that may open great opportunities for new applications. However, DLC presents low chemical affinity with metallic alloys and high intrinsic stress, prompting film delamination and poor adherence on the substrate. In the presentwork, we performed a systematic study about structural and tribological properties of a-C:H thin films grown on steel by introducing adhesive silicon-containing interlayers deposited at different processing temperatures and times. The studied bi-layers were deposited by electrostatic confinement plasma enhanced chemical vapor deposition (EC-PECVD) and were characterized by several techniques. The results showed that the adhesive interlayers produced from tetramethylsilane are chemically structured as a nonstoichiometry hydrogenated amorphous silicon carbide alloy (a-SiCx:H). Its structure, chemical composition and thickness are very dependent on deposition conditions. The thickness of the interlayers increaseswith deposition time and decreases with deposition temperature. The interlayer contains less hydrogen and silicon atoms at higher deposition temperatures, with enhanced formation of Si-C bonds in its structure. This last chemical event is correlated with the rise in the critical load values found for a-C:H film delamination when the a-SiCx:H interlayers are deposited from 573 K to 823 K. On the other hand, the interlayer contains less carbon atoms at higher deposition times, decreasing the critical load values for a-C:H film delamination when the a-SiCx:H interlayers are deposited from 5 min to 10 min. © 2015 Elsevier B.V.


Cemin F.,University of Caxias do Sul | Bim L.T.,University of Caxias do Sul | Leidens L.M.,University of Caxias do Sul | Morales M.,University of Campinas | And 4 more authors.
ACS Applied Materials and Interfaces | Year: 2015

Amorphous carbon (a-C) and several related materials (DLCs) may have ultralow friction coefficients that can be used for saving-energy applications. However, poor chemical bonding of a-C/DLC films on metallic alloys is expected, due to the stability of carbon-carbon bonds. Silicon-based intermediate layers are employed to enhance the adherence of a-C:H films on ferrous alloys, although the role of such buffer layers is not yet fully understood in chemical terms. The chemical bonding of a-C:H thin films on ferrous alloy intermediated by a nanometric SiCx:H buffer layer was analyzed by X-ray photoelectron spectroscopy (XPS). The chemical profile was inspected by glow discharge optical emission spectroscopy (GDOES), and the chemical structure was evaluated by Raman and Fourier transform infrared spectroscopy techniques. The nature of adhesion is discussed by analyzing the chemical bonding at the interfaces of the a-C:H/SiCx:H/ferrous alloy sandwich structure. The adhesion phenomenon is ascribed to specifically chemical bonding character at the buffer layer. Whereas carbon-carbon (C-C) and carbon-silicon (C-Si) bonds are formed at the outermost interface, the innermost interface is constituted mainly by silicon-iron (Si-Fe) bonds. The oxygen presence degrades the adhesion up to totally delaminate the a-C:H thin films. The SiCx:H deposition temperature determines the type of chemical bonding and the amount of oxygen contained in the buffer layer. (Chemical Equation Presented). © 2015 American Chemical Society.


Cemin F.,University of Caxias do Sul | Bim L.T.,University of Caxias do Sul | Menezes C.M.,University of Caxias do Sul | Aguzzoli C.,University of Caxias do Sul | And 6 more authors.
Vacuum | Year: 2014

This work reports a systematic study of physical-chemical properties of SiCx:H interlayers deposited by using tetramethlysilane on AISI 4140 at different temperatures (100 °C-550 °C) and its effects on the adhesion of a-C:H thin films. The bi-layers were obtained by pulsed-DC PECVD assisted by electrostatic confinement. The results show that the thickness of the SiCx:H interlayer exponentially decreases as the deposition temperature increases, i.e., a thermally activated kinetic process controls the global chemical reaction in the interlayer. There is a transition temperature (∼300 °C) for interlayer deposition where adhesion of a-C:H is reached. Above ∼300 °C, the a-C:H thin films show critical loads to wedge spallation from 298 (300 °C) to 478 mN (550 °C). At higher temperatures, H and Si contents decrease whereas C content increases in the interlayer. The improved adhesion is associated with the nature of chemical bonds formed in the interlayer. © 2014 Elsevier Ltd. All rights reserved.

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