In this study, the electrochemical polarization tests were performed on tensioned and non-tensioned CUSTOM 450 specimens in a 3.5 wt% NaCl solution to investigate pitting potential and stable pit initiation time. A potentiodynamic test was conducted to determine the exact amount of pitting potentials. According to the potentiostatic tests, a relation between applied potential and the stable pit initiation time was obtained. Concerning this relation, stable pitting time can be predicted without experimental works. Optical microscopy was used to evaluate the shape of the pits. Tensile stress led the pit to experience the "pit to crack" step. The corrosion rate of samples was studied by the determination of mass loss. Mass loss measurements and current density-time curve in potentiostatic tests demonstrated the rate of pitting corrosion decreased as time passed. Finally, the depth of the pits was measured by the eddy current technique. The results showed that tensile stress facilitated deeper pit development.

No abstract

A key application of CUSTOM 450 alloy is in the construction of gas turbine compressor blades. The study of pitting corrosion can prevent the failure of many gas turbine compressor blades. In this study, a reflective digital holography microscopy method was employed to investigate the growth of pitting corrosion in depth. To this end, a constant potential of 350 mVSCE in a 3.5 wt.% NaCl solution was applied to the specimen. The generated pits were simulated in three dimensions, and it was indicated that pitting corrosion rate was decreased as time passed. Comparing the obtained experimental data with the data gathered from the real industrial environment surrounding a compressor installation, an accelerated test was proposed. By the proposed accelerated test, it is possible to produce a pit similar to the one that will be initiated and propagated at any time in the future in real conditions.

pitting corrosion, stress corrosion cracking and corrosion fatigue. Due to erosion of particles in the presence of a corrosive environment, pitting happens on the blade surfaces, which is a source of subsequent cracks. Therefore, it is necessary to get knowledge of its mechanism in order to prevent the phenomena as much as possible. The main purpose of this paper is to investigate the growth of pitting corrosion in CUSTOM 450 stainless steel and to obtain strain values in the growing pits at the maximum bending region. In this regard, a two-point bending specimen was made and subjected to a potentio-static test underthe potential of 350 mVSCE in the 3.5 wt% sodium chloride solution. Then the propagated pits were numerically examined. By the digital image correlation method, the local strain was calculated in the pits and a relation was presented to obtain the maximum strain time. Therefore, growth direction of pitting corrosion could be estimated by having maximum strain region. Finally, by simulating the pitting corrosion process of a stress-free sample under the potential of 350 mVSCE in 3.5 wt% sodium chloride solution in COMSOL Multiphysics software, variations in the concentration of ions, electric potential, and corrosion current density were shown in the existing pit. The potential was decreased by moving in-depth and the maximum current density was found at the depth of 18 μm. Thus, without the need of advanced laboratory facilities for surface scanning and analysis, useful information from surface corrosion conditions could be obtained.