The Corrosion Behavior of TiN Coated and Uncoated Incoloy 800 Alloy

Incoloy alloy 800 is used in a variety of applications in industry as well as in domestic appliances for sheeting on electric heating elements. The composition of the alloy enables it to resist deterioration in many corrosive environments. However, resistance of the alloy to corrosion in aqueous media needs to be further examined. The present study examines the corrosion properties of Incoloy 800 alloy of both coated and uncoated workpieces obtained in a 0.1N H₂SO₄ + 0.05N NaCl solution. TiN coating is achieved using a physical vapor deposition (PVD) technique while corrosion tests are carried out using electrochemical polarization methods. Moreover, in order to examine the influence of hydrogen diffusion, reduction of hydrogen at the Incoloy 800 surface is carried out in a solution of 0.1N HNO₃ + 1 g/L thiourea. Tensile tests are conducted on the workpieces to determine the influence of hydrogen embrittlement on the resulting mechanical properties of the substrate. To examine the pit formation and stress induced microcracking, scanning electron microscope (SEM) analysis is carried out. The results show that the corrosion resistance of the alloy improves after TiN coating. In addition, no specific pattern or differentiation on the pit geometry is observed. The pitting rate and its size reduce considerably for TiN coated workpieces.