Characterisation of electrodeposited nanocrystalline Ni?Mo alloys

Abstract

Ni-Mo nanocrystalline layers were electrodeposited using direct current from citrate-ammonia solutions. The quartz crystal microbalance investigation confirms that the discharge process starts with hydrogen evolution before the onset of the alloy deposition. The grain size was estimated from X-ray line broadening. It decreases when the molybdenum content is increased. It is smaller for layers deposited at pH 9.5 than 8.5. The microhardness exhibits a maximum close to 800 Vickers for s Mo around 17 wt%. For higher s Mo a softening is observed showing a deviation from Hall-Petch behaviour due to small grain size. In deaerated hydrochloric solutions, the layers show a large passivation domain without any pitting. The corrosion currents as well as the passivation currents, higher than for the bulk Hastelloy B alloy, decrease when s Mo is increased.

Morphological, structural, microhardness and corrosion characterisations of electrodeposited Ni-Mo and Cr coatings

“…This figure shows that the Cr coating has the noblest corrosion potential, which is -0.328 V. Among the Ni-Mo coatings, the nobler corrosion potential is presented by the Ni-13Mo coating, which is -0.362 V. The experimental value of the corrosion potential for the Ni-Mo coatings are in close agreement with those reported in the literature, 11 while the corrosion potential of the Cr coating is about 0.15 V more positive than that reported by others authors. 15 This difference in the corrosion potential it is explained as to be related to the different surface morphology present by the electrodeposited Cr in this work (Figure 3a) compared to the surface morphology of the electrodeposited Cr coating reported in the literature.…”

“…In addition, some polyhedral grains can be observed, suggesting that they are formed by several nuclei. Cracked morphologies were also observed by Chassaing et al 11 for Ni-Mo coatings containing Mo higher than 30 wt.%, which were electrodeposited from citrate bath and under force hydrodynamic operational conditions. The appearance of the cracks is explained as being caused by relaxation of internal tensile stress in the coating.…”

“…The amorphous/nanocrystalline structures appeared for the deposits content Mo higher than 20% in atom while that obtained with the lower amount of Mo were crystalline. Chassaing et al 11 studied the electrodeposition of Ni-Mo nanocrystalline layers using direct current in citrate-ammonium plating solutions and found that the layers exhibited microhardness comparable with the hard chromium coating (ca. 800 Vickers) and also presented corrosion current higher than Hastelloy B alloy.…”

“…In addition, despite many authors quote the good corrosion resistance properties of the electrodeposited Ni-Mo coatings at room temperature, relatively little reports about this subject are found in the literature. 11 Thus, this work was carried out aiming to perform a comparative study of the corrosion resistance of both electrodeposited Cr and Ni-Mo coatings in chloride medium and also to evaluate the influence of thermal treatments on corrosion resistance, on crystal structure and on microhardness properties of these coatings.…”

Isotropic magnetization response of electrodeposited nanocrystalline Ni–W alloy nanowire arrays

“…Recently, nanocrystalline metallic materials and nanoparticles have received much attention due to their unique physical properties, such as mechanical strength [6], corrosion resistance [7][8], electron transport [9] and magnetic property [10][11]. Nanocrystalline M iron -W alloy thin films are of special value to developers, because they exhibit excellent magnetization response and corrosion resistance [12].…”