Synthesis of Ni/nano-Al 2 O 3 coatings by brush plating with magnetic fields

In the process of electrodeposition, the magnetic field would generate the magneto hydrodynamic (MHD) effect, which affects the flow and mass transfer of hydrogen evolution. Thus, the performance of electrodeposition coatings will be affected. In this work, Ni/nano-Al 2 O 3 coatings prepared by brush plating with magnetic fields were studied. The results show that the magnetic field indeed influences the morphology, texture and wears resistance. The morphology of Ni/Al 2 O 3 coating is smooth and uniform; the (200) plane of Ni/Al 2 O 3 coating is preferentially oriented in the same direction of a magnetic field; the wear resistance of Ni/Al 2 O 3 composite coatings increases due to the uniform distribution of Al 2 O 3 particles; and the wear mechanism of coating belongs to adhesive wear. The optimal intensity of magnetic field for Ni/Al 2 O 3 composite coatings to obtain a good performance is 0.1 T.

Fragilización por hidrógeno y Brush Plating

Se hace una revisión de los mecanismos de daño por hidrógeno, incluyendo el ampollado por hidrógeno, la precipitación interna de hidruros, el agrietamiento por precipitación de hidruros, el ataque por hidrógeno y la fragilización por hidrógeno. Se analizan los tipos de fractura en función de los puntos de residencia del hidrógeno y la interacción del hidrógeno con los aceros, estudiándose las etapas de disolución, difusión y transporte de hidrógeno. Se describe el proceso de “Brush Plating” que se aplica a una superficie con el fin de reparar los daños en los recubrimientos anticorrosivos. Finalmente, se describe el procedimiento para evaluar el daño por hidrógeno en aceros, a través del método de la carga incremental detallado en la norma ASTM F1624-12, analizándose el caso de un acero SAE 4340 sometido a brush-plating en comparación con el mismo acero sometido a carga de hidrógeno. El resultado muestra la validez de la norma aludida en la determinación del daño por hidrógeno en aceros. Palabras Clave: Daño por hidrógeno; Brush-plating; Método de carga incremental.

Microstructure and Properties of Cr-Fe2B Composite Coatings Prepared by Pack-Preboronizing Combined with Electro Brush-Plating

Cr-Fe2B composite coatings were prepared on carbon steels by pack-boronizing followed by electro brush-plating. The microstructure and properties of the coatings annealed at different temperatures were studied. The coatings show a gradient structure composed of a Cr-layer and a Fe2B-layer and have excellent thermal stability, and no new layers and/or transition layers are formed in the coating during annealing up to 1000 °C. The Cr-layer has an amorphous structure and is transformed into nanosized grains when the annealing temperature increases to 700 °C. As the annealing temperature is further increased, the nanograins grow rapidly. The microcracks in the Cr-layer increase sharply after annealing at 550 °C and then decrease significantly with any further increase of the annealing temperature. The pre-deposited Fe2B-layer prevents the formation of carbon-poor zones in the steel substrate during annealing. It is considered that high-temperature (>700 °C) annealing helps to eliminate coating defects, increase the coating density and obtain better wear resistance and corrosion resistance. Surprisingly, the as-plated and low temperature annealed samples also show good wear resistance and corrosion resistance, which may be related to their amorphous structure and nanocrystalline structure.