Mechanical Properties of Nanocrystalline Coatings Prepared by Thermal Spraying Process

Abstract

The uniaxial tensile tests are generally used to measure the yield stress and/or tensile stresses. The majority of the results, resulting from this method and deferred in the literature on the mechanical properties of amorphous materials, were obtained in the ribbons form generally produced by melt spinning. This limitation in the shape of the specimens for tensile tests was inherent in the manufacturing techniques of the amorphous materials which required cooling rates of about 106°C/s. The fabrication of amorphous coatings by plasma spraying, in tubular form, should improve rigidity of the specimens, increase their size and especially get a more reliable means to the amorphous coatings under the tensile test. Amorphous coatings of NiCrBSi alloys are produced by thermal plasma spraying. The thickness of the resulting amorphous deposit may be up to 500 μm. The uniaxial tensile tests were carried on Instron machine at room temperature. Microstructural studies are investigated by means of X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopy. The test methodology used in this study shows that it is possible to obtain a comprehensive assessment of the mechanical properties of the amorphous coatings deposited by thermal plasma in tubular form. Plasma sprayed coatings in tubular form, under the uniaxial tensile test in the amorphous state, crystallized and nanocrystallized, fracture without bursting compared to samples in the form of amorphous ribbon.