Improving corrosion properties of high-velocity oxy-fuel sprayed Inconel 625 by using a high-power continuous wave neodymium-doped yttrium aluminum garnet laser

Thermal spray processes are widely used to protect materials and components against wear, corrosion and oxidation, Despite the use of the latest devel opments of thermal spraying, such as high-velocity oxy-fuel (HVOF) and plas ma spraying, these coatings may in certain service conditions show inadequa te performance, e.g., due to insufficient bond strength and/or mechanical p roperties and corrosion resistance inferior to those of corresponding bulk materials. The main cause for a low bond strength in thermal-sprayed coatin gs is the low process temperature, which results only in mechanical bonding . Mechanical and corrosion properties typically inferior to wrought materia ls are caused by the chemical and structural inhomogeneity of the thermal-s prayed coating material. To overcome the drawbacks of sprayed structures an d to markedly improve the coating properties, laser remelting of sprayed co atings was studied in the present work. The coating material was nickel-bas ed superalloy Inconel 625, which contains chromium and molybdenum as the ma in alloying agents. The coating was prepared by HVOF spraying onto mild ste el substrates, High-power continuous wave Nd:YAG laser equipped with large beam optics was used to remelt the HVOF sprayed coating using different lev els of power and scanning speed. The coatings as-sprayed and after laser re melting were characterized by optical microscopy and scanning electron micr oscopy (SEM). Laser remelting resulted in homogenization of the sprayed str ucture. This strongly improved the performance of the laser-remelted coatin gs in adhesion, wet corrosion, and high-temperature oxidation testing. The properties of the laser-remelted coatings were compared directly with the p roperties of as-sprayed HVOF coatings and with plasma-transferred are (PTA) overlay coatings and wrought Inconel 625 alloy.