Influência da adição de boro na microestrutura e resistência à cavitação de revestimentos à base de Fe-Mn depositados por plasma de arco transferido

Abstract

The cavitation is a big problem occurred in the hydraulic turbines. This is a main cause of decrease on the efficiency of the turbines. The profile recover is performed using coatings based on cavitation resistant alloys. These coatings can be deposited by MIG/MAG and can be deposited by Plasma Transferred Arc (PTA), using powder as deposition material. This work aims to study the effects of Boron on microstructure, weldability and cavitation resistance of coatings deposited by Plasma PTA, evaluating his effects on microstructure, microhardness, grain formation and phases generated. Was realized the metallographic preparation of coatings, analysis in optical microscopy, scanning electron microscopy and in x-ray diffraction, calculating the dilution, Vickers hardness test and accelerated cavitation. The addition of boron reduces the alloy melting point, promotes the dilution increase and improves wettability. Boron promotes the formation of refined dendrites, decreasing the interdendritic spacing, but this is only for the range of Boron 2X to 5X%, because when adding 10X% of boron, there is formation of the rich needles in Fe-B and large amount of phase eutectic Fe-B. Boron added until 5X% promotes the increased cavitation resistance of the alloy.