Energy dissipation in depth-sensing indentation as a characteristic of the nanoscratch behavior of coatings

Wear behavior of coatings has usually been described in terms of mechanical properties such as hardness (H) and effective elastic modulus (E*). Alternatively, an energy approach appears as a promising analysis taking into account the influence of those properties. In a nanoindentation test, the dissipated energy depends not only on the hardness and elastic modulus, but also on the elastic recovery (W(e)). This work aims to establish a relation between plastic deformation energy (E(p)) during depth-sensing indentation method and the grooving resistance of coatings in nanoscratch tests. An energy dissipation coefficient (K(d)) was defined, calculated as the ratio of the plastic to the total deformation energy (E(p)/E(t)), which represents the energy dissipation of materials. Reactive depositions using titanium as the target and nitrogen and methane as reactive gases were obtained by triode magnetron sputtering, in order to assess wear and nanoindentation data. A topographical, chemical and microstructural characterization has been conducted using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), wave dispersion spectroscopy (WDS), scanning electron (SEM) and atomic force microscopy (AFM) techniques. Nanoscratch results showed that the groove depth was well correlated to the energy dissipation coefficient of the coatings. On the other hand, a reduction in the coefficient was found when the elastic recovery was increased. (C) 2009 Elsevier B.V. All rights reserved

Corrosion behavior of carbon steel protected with single and bi-layer of silane films filled with silica nanoparticles

The electrochemical behaviour of carbon steel coated with bis-[trimethoxysilylpropyl]amine (BTSPA) filled with silica nanoparticles in naturally aerated 0.1 mol L-1 NaCl solutions was evaluated. The coating was prepared by adding different concentrations of silica nanoparticles (100, 200, 300, 400 and 500 ppm) to the hydrolysis solution and then a second layer without silica nanoparticles was applied. The electrochemical behavior of the coated steel was evaluated by means of open-circuit potential (E-OC), electrochemical impedance spectroscopy (EIS) and polarization curves. Surface characterization was made by atomic force microscopy (AFM), and its hydrophobicity assessed by contact angle measurements. EIS diagrams have shown an improvement of the barrier properties of the silane layer with the silica addition, which was further improved on the bi-layer system. However, a dependence on the filler concentration was verified, and the best electrochemical response was obtained for samples modified with 300 ppm of silica nanoparticles. AFM images have shown a homogeneous distribution of the silica nanoparticles on the sample surface; however particles agglomeration was detected, which degraded the corrosion protection performance. The results were explained on the basis of the improvement of the barrier properties of the coating due to the filler addition and on the onset of defective regions on the more heavily filled coatings allowing easier electrolyte penetration. (C) 2007 Elsevier B.V. All rights reserved

Ni-based Mar-M247 superalloy as a friction stir processing tool

The authors acknowledge FAPESP (State of Sao Paulo Research Foundation) to the scholarship funding (Process Number 2014/13772-4). The authors appreciate all experimental support provided by LNNano (CNPEM/MCTI) and recognize Petrobras by financial support.Ni-based superalloy Mar-M247 was evaluated as a potential tool material for friction stir processing (FSP) of X70 steel. The superalloy consists of a γ-γ’ structure and minor precipitates, such as MC carbide. FSP tests evaluated the tool performance at different rotation and welding speeds and the effect of shielding gas was also analyzed. Prior to FSP tests, hot compression tests showed that the tool material microstructure was stable below 950 °C, which affected positively its mechanical strength. It was observed the FSP tool overheating at rotation speed of 400 rpm. In this condition the γ-γ’ structure was destabilized forming “γ’ free zones” at the tool shoulder. In these zones new γ-grains were formed by recrystallization. Oxygen diffusion occurred at γ-grain boundaries embrittling the γ’ free zones that were ripped out by abrasion during FSP tests. The tool wear damage was mitigated by controlling friction processing parameters, such as rotation and welding speeds, Z-force values and gas shielding. The FSP made in this work improved surface properties of X70 steel.preprintpublishe