Evaluation of sensitization of ni base alloys using electromagnetic nondestructive evaluation method

Ni base alloys are widely used as the materials of high temperature components for nuclear power plants because of their high mechanical strength, heat resistance and corrosion resistance. Intergranular Stress Corrosion Cracking (IGSCC) is one of serious problems for this material. Because the sensitization of Ni base alloys is one of the main factors of IGSCC, the establishment of nondestructive evaluation of sensitization is highly required. It is well known that alloy 600, one of Ni base alloys, is paramagnetic after solution heat treatment, but as sensitization increases, its magnetic properties change. In this study, feasibility of nondestructive evaluation of sensitization of alloy 600 is discussed focusing on its magnetic properties. To investigate the relationship between magnetic properties and sensitization, alloy 600 were heated in different temperatures and durations. Then, the relationship between magnetic properties and sensitization is discussed based on hysteresis curves, and microstructure observed by TEM (Transmission Electron Microscope) and numerical analysis. Finally, nonlinear eddy current method is applied and the feasibility of nondestructive evaluation of sensitization is discussed.