Ni-Nb composite electrocoatings were obtained on carbon steel from Watts bath, containing suspended 20 lm size niobium powders. The effect of cathodic current density, electrolyte stirring rate and concentration of Nb particles in the bath on the deposit morphology and texture, volume fraction of co-deposited Nb particles and microhardness was investigated. The Ni-Nb composite layers presented a rough morphology with randomly oriented Ni grains, whereas pure Ni coatings obtained under the same experimental conditions were smooth and showed highly preferred orientation in the [110] or [100] direction. Stirring rate of the electrolyte and concentration of Nb particles in the bath are the main parameters affecting the incorporation of Nb particles. The Nb incorporated volume fraction was 11-14%, 17-19%, 27-32% and 34-37% for the 20 g L -1 Nb/550 rpm, 20 g L -1 Nb/400 rpm, 40 g L -1 Nb/400 rpm and 40 g L -1 Nb/550 rpm conditions, respectively. The microhardness of the Ni-Nb composite coatings obtained at 20 and 40 mA cm -2 was higher than that of pure Ni layers, due to grain refining. Incorporation of Nb particles in Ni coatings improved the corrosion resistance of the deposits in NaCl and H 2 SO 4 solutions.
Reference materials for the Rockwell, Brinell and Vickers hardness scales are fundamental for the Brazilian industrial sector. Mechanical property Hardness is the most common mechanical test used for quality control of raw materials in finished products as well as in research and development of new products and materials. A description of the main findings of two studies and the revalidation of the last on the demand of hardness reference blocks in Brazil is presented. This paper shows national demand of hardness reference blocks could be supplied on a large scale by Inmetro´s Force Laboratory.
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