Abstract The main problem in metal oxidation is the spalling and de-cohesion of the oxide layer, which results in delamination due to strong compressive stress gradient through the layer. Present paper proposes the use of a modified process named Asymmetric Bipolar Pulsed Plasma (ABiPPS) for plasma-oxidation treatment of low carbon steel AISI-1006 samples. Results show that the ABiPPS process ensures high plasma stability and enables the growth of uniform oxide layers (with thickness up to 6 µm) on metal surfaces. Plasma generated through bipolar asymmetric voltage pulses provides better control on surface bombardment through interspersed jets of ions and electrons, during the oxidation process. The control of intermittent ions and electrons bombardment (through voltage peaks up to 1.5 kV and period about 1µs), during plasma oxidation, make it possible to improve the adhesion between the oxide layer and the substrate, moreover the control of crystalline phases, such as hematite and magnetite.

Abstract This contribution reports on an experimental polishing procedure, that is comprised of early grinding in Al2O3 slurries and late polishing in colloidal silica, which is used for preparing the nitrided region of a plasma nitrided austenitic stainless steel, for crystallographic analysis via electron backscatter diffraction (EBSD). The suitability of the polished surfaces for conducting EBSD characterization was assessed through an analysis of both the surface roughness (appraised by atomic force microscopy) and the quality of the Kikuchi diffraction patterns. We observed that as-nitrided virgin surfaces were not suitable for EBSD characterization, due to intense surface roughening, which was induced by the nitriding process itself. At the subsurface region, exposed by on-top mechanical polishing, the flatter nature of the polished surfaces allowed the acquisition of EBSD patterns with enough quality for microtexture analysis. A resolution of 100 nm in the total removed layer was attainable via careful control of the polishing parameters. Close parallelism between the polished and original surfaces was verified.

UNS S31603 stainless steel (SS) substrates were covered by reactive magnetron-sputtering with protective SS coatings of the same steel specification. A mechanical characterization study (through nano-, micro- and macro-hardness tests) of samples obtained under two different sputtering conditions and varying the N2 gas flow rate was carried out. This contribution aimed at appraising the effects of varying the nitrogen flow rate on hardness, elastic modulus, and susceptibility to indentation-induced crack formation of the coated SSs. Nitrogen-free samples displayed body-centered cubic (BCC) films with 9.0-9.4 GPa hardness and 203-206 GPa elastic modulus, while their susceptibility to indentation-induced cracking varied between superior and moderated among the two sets of sputtering conditions studied. Samples alloyed with 4-6 N at-% displayed a predominantly face-centered cubic (FCC) structure, 9.4 GPa hardness, 196-218 GPa elastic modulus, and superior resistance to crack formation. Samples with 11.5-22.0 N at-% were fully composed of the FCC structure, displayed 12.4-15.2 GPa hardness, 188-193 GPa elastic modulus, and moderated resistance to indentation-induced crack formation. Samples with 47.0 N at-% displayed FCC compound nitride structure, for which hardness and elastic modulus were 8.1 GPa and 139 GPa, respectively. These samples displayed low resistance to crack formation.