Synthesis of TiB2 -Ni3 B nanocomposite coating by DC magnetron sputtering for corrosion-erosion protection

Abstract

Significant contribution on corrosion-erosion resistance of Ni3B-TiB2 nanocomposite coating of 1 μm of thickness, deposited by DC magnetron Sputtering on stainless steel 304 substrates was studied. Nickel phase (γ Ni) plus Ni3B-TiB2 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 Ni3B-TiB2with 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 μm. The average hardness of 537.4 HV(5265.0 MPa) and wear coefficient at room temperature of 2.552E-10 m2 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/Na2SO4 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