Refusão a arco elétrico de revestimento aspergido termicamente: efeito das variáveis da corrente em regime pulsado sobre a microestrutura e microdureza

Abstract

Thermal spraying is a surface engineering technique that allows to obtain coatings with optimized characteristics, expanding the application field of many engineering materials. This is due thermal spray process allows the use of raw materials with specific properties, and the obtaining of functional gradients coatings, while at the same time, minimally affects the coated components original properties. This method is known for its ease operation and low cost, which makes the thermally sprayed coatings application widely explored in the industrial environment. In some applications, however, the coating high porosity and oxidation make that remelting methods are applied in order to promote the coating densification, and thus improve its adhesion to the substrate and cohesion. Thus, taking into account the different remelting techniques used and considering their peculiarities, a study is necessary to optimize these process, aiming to defining the most appropriate conditions that allow to achieve the best results. Thus, this work aims to evaluate the effect of the TIG electric arc remelting parameters operating in pulsed regime, on the microstructure and microhardness of Fe-Cr-Ni based alloy coatings deposited by electric arc thermal spray technique on plain carbon steel substrate. In this sense, the effect of relationship among peak current intensities – Ip and base – Ib (Ib of 50, 70 and 90% of Ip), pulse times (20, 50 and 80 s), and pulse frequency (1, 5 and 10 pulses/s) were evaluated. As-sprayed and remelted coatings were characterized using optical microscopy, X-ray diffraction and Vickers microhardness measurements. The obtained results show that the pulsed current parameters have an effect on remelted coatings microstructure and microhardness. Remelting coating present a dendritic microstructure, being constituted by the phases Fe-, Fe-, Fe3O4 and Cr23C6. All employed conditions promoted the complete remelting and dilution of the coating to the substrate. The fused zone width decreases with increasing on pulse frequency, and increases with the Ib and tp increasing, the superficial plateau hardness, in turn, increases with the increase in the pulse frequency and with a the Ib and tp reduction, while the hardening depth increases with pulse frequency decrease and an increase in the Ib and tp. Finally, it is possible to conclude that the TIG process can be successfully used to thermally sprayed coatings remelting, promoting a greater bond of the coating to the substrate and reducing its porosity and internal oxidation.