Microstructural evolution and stress-corrosion-cracking behavior of thermally aged Ni-Cr-Fe alloy

• Effects of long-term thermal aging on the nickel-based Alloy 600 were investigated.
• Heat treatments simulating thermal aging were conducted by considering Cr diffusion.
• Nano-indentation test results show hardening of thermally aged materials.
• Thermally aged materials are more susceptible to stress corrosion cracking.
• The property changes are attributed to the formation and evolution of precipitates.

To understand the effect of long-term thermal aging in power plant systems, representative thick-walled Alloy 600 was prepared and thermally aged at 400 °C to fabricate samples with thermal aging effects similar to service operating conditions. Changes of microstructures, mechanical properties, and stress corrosion cracking susceptibility were investigated mainly through electron backscatter diffraction, nanoindentation, and high-temperature slow strain rate test. The formation of abundant semi-continuous precipitates with chromium depletion at grain boundaries was observed after thermally aged for 10 equivalent years. Also, alloys thermally aged for 10 equivalent years of thermal aging exhibited the highest susceptibility to stress corrosion cracking.

Figure optionsDownload as PowerPoint slide