Synthesis of TiB 2 -Ni 3 B nanocomposite coating by DC magnetron sputtering for corrosion-erosion protection

Significant contribution on corrosion-erosion resistance of Ni 3 B-TiB 2 nanocomposite coating of 1 μ m of thickness, deposited by DC magnetron Sputtering on stainless steel 304 substrates was studied. Nickel phase ( γ Ni) plus Ni 3 B-TiB 2 phases were synthesized previously by Mechanical Alloying (MA). Solid cathode (76.2 mm of diameter and 3 mm of thickness) used to grow thin films was manufactured with the alloyed powders, applying a uniaxial load of 70 MPa at room temperature and sintered at 900 °C for two hours. Microstructure and mechanical properties of the coatings were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation, and wear test with a ball-on-disc tribometer. Compact coating of Ni 3 B-TiB 2 with a microstructure of prismatic crystals after annealing treatment, showing a uniform coating with good adherence and low friction coefficient of 0.5, correlated with a low roughness of Ra ≈ 0.0439 ± 0.0069 μ m. The average hardness of 537.4 HV (5265.0 MPa) and wear coefficient at room temperature of 2.552E-10 m 2 N −1 correspond with medium-hard phases with an elastic-plastic behavior suitable for fatigue applications. Geothermal fluid modified was synthesized in the lab with NaCl/Na 2 SO 4 to evaluate the corrosion resistance of the films in a standard three electrodes cell, characterizing a corrosion rate of 0.0008 and 0.001 mm*year −1 at 25 and 80 °C respectively during 86.4 ks (24 h) of exposition; showing a resistive coating without corrosion products and with good response to the geothermal environment.