Quantitative assessment of intergranular damage due to PWR primary water exposure in structural Ni-based alloys

Two nickel-based alloys, alloy 718 and alloy 600, known to have different resistances to IGSCC, were exposed to a simulated PWR primary water environment at 360 °C for 1000 h. The intergranular oxidation damage was analyzed in detail using an original approach involving two characterization methods (Incremental Mechanical Polishing/Microcopy procedure and SIMS imaging) which yielded a tomographic analysis of the damage. Intergranular oxygen/oxide penetrations occurred either as connected or isolated penetrations deep under the external oxide/substrate interface as far as 10 μm for alloy 600 and only 4 μm for alloy 718. Therefore, assessing this damage precisely is essential to interpret IGSCC susceptibility.

► IG damage occurred on Ni-base alloys during exposure at high temperature water.
► Two characterization methods yield a tomographic analysis of this IG damage.
► Connected or isolated intergranular oxygen/oxide penetrations are quantified.
► Such quantitative description provides information on IGSCC susceptibility.