Papers by Keyword: Nanocrystalline Phase

Abstract: Ni-W alloys were prepared by electrodeposition at diverse processing conditions. The Ni-W alloys were studied by SEM, EDX and XRD analysis to determine composition and morphology of the surface in dependence on electrodeposition conditions. Focus was put on surface with electroactive sites for hydrogen evolution. Stability of the alloys in chloride medium was determined applying chronopotentiometry and potentiodynamic polarization. Electrochemical behavior of the alloys was tested in alkaline solution by cyclic voltammetry. It was found that processing conditions directly influence quality of the Ni-W alloys concerning phase, morphology and composition. Prevailing amorphous phase of Ni-W alloys supports corrosion rate growth.

Abstract: NiTi alloy is known to have a potential interest specially for its superelasticity and shape memory effect (SME). Most of the research undergone up to now investigates such properties in bulk materials. The few works related to overlays (coatings) use magnetron sputtering for thin films and Vacuum Plasma Spray (VPS) for thicker coatings. VPS is the mostly used thermal spray technique regarding the Ti oxidation problems which considerably affect the so desired SME. The present work compares the microstructure of VPS NiTi coatings with those of High Velocity Oxygen Fuel HVOF and a liquid cooling device coupled to a Atmosphere Plasma Spraying (APS+Q), with optimized spraying conditions trying to minimize Ti oxidation. Apart from their characterization by Scanning Electron Microscopy, the main purpose is to further study how particles are retained within the coating so that Transmission Electron Microscopy is also employed. This has allowed the observation of amorphous and nanocrystalline phases as well as to the change from cubic B2 NiTi lattice to metastable lattices.