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High temperature mechanical properties of Ni-Al intermetallic alloys make them potential candidates as wearresistance materials or coatings to protect components operating in harsh environments. In-situ processing of Ni-Al intermetallic coatings has been successfully carried out previously. The role of interaction with the substrate, measured by the Fe content in NiAl coatings, on the wear performance is addressed in this study. Mixtures of Ni and Al powders were prepared (65 at.%Ni-35 at.%Al) and deposited onto 1020 steel disks. Three deposition current were used (100, 120 and 150 A) resulting in coatings with Fe content ranging from 36 to 50 at.%, as a consequence of the metallurgical bond with the substrate steel. The development of the NiAl was confirmed by X-ray diffraction together with austenite. Dry sliding tests were carried out at room temperature and 710°C, using a ball-on-disk tribometer with a 3.0 mm Al 2 O 3 ball under different normal loads (1, 3 and 5 N). Temperature played an important role on the wear behavior and the wear coefficient was reduced by one order of magnitude at 710°C. At room temperature, wear coefficients increased with the applied load, and abrasion was the main observed mechanism regardless of the iron content in coatings. However, at 710°C the variations on the wear coefficient cannot be associated with the coating hardness and wear was dominated by oxidation. Hematite was identified on all the oxidized surfaces. Notwithstanding, for the coatings with higher Fe content the continuous and thicker scale accounts for the measured stable wear coefficient regardless of the applied load.

The aim of this work was to study the influence of varying nitrogen potential during plasma nitriding of stainless steel ISO 5832-1. The control of nitrogen potential was achieved by pulsing the nitrogen flow for different times (01/19, 02/18, and 05/15), where the numbers represent the time (in minutes) of nitrogen flow on/off, thus creating an intermittent flow of nitrogen during the treatment. For all tested conditions-continuous and pulsed flow of nitrogen-the treatment temperature was kept at 425ºC during 2 and 8 hours. Specimens were characterized by means of X-ray diffraction, scanning electron microscopy, optical microscopy, energy-dispersive X-ray spectroscopy, and nanohardness. Results showed that the layer thickness increases with the increase of total treatment time, and decreased for shorter times of pulsed nitrogen flow. Smaller expansion of the austenite phase, as well as less precipitation of chromium nitrides, were also observed for shorter times of pulsed nitrogen flow. Hence, the use of intermittent nitrogen flow appears to be an efficient approach in order to control the nitrogen concentration within the layer, reducing its brittleness.

The effect of surface finishing on the contact area evaluation of an austempered ductile iron (ADI) with 10% volume fraction of graphite nodules is presented. The nodules were scratched during the roughness measurement made using a stylus. A model based on two functional roughness parameters was used to evaluate the contact area, considering the deformation as elastic. Two sets of ADI specimens were prepared. In the first set, the surfaces were sanded up to 1200‐grit paper, whereas in the second set, the specimens were metallographic polished. The scratches were artificially removed using a specific routine. The results after this removal were compared with those determined for bearing steel, prepared under similar conditions. A reduction of approximately 93% in the contact area values was observed after the artificial removal of scratches caused by the stylus probe for the polished specimens, whereas for the sanded ones, this reduction was about 80%. Copyright © 2012 John Wiley & Sons, Ltd.