Study the erosion of Eurofer-97 steel with the linear plasma device GyM

Abstract

This work reports on the investigation of Eurofer-97 erosion behaviour when exposed to the deuterium plasma of the linear device GyM. The erosion dependence of Eurofer-97 on the deuterium ion fluence, Φ≤2.3×1025 m−2, and temperature of the samples, T = 600 K and 990 K, was addressed. A bias voltage of −200 V was applied to GyM sample holder during the experiments. Samples were deeply characterised by: profilometry, scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry, Rutherford backscattering spectroscopy and particle-induced X-ray emission.The behaviour of Eurofer-97 erosion rate with the ion fluence strictly depends upon temperature. At 600 K, it was ∼0.14 nm/s after 4.7 × 1024 m−2, then decreased, reaching a steady state value of ∼0.01 nm/s from 8.0 × 1024 m−2. At 990 K instead, the erosion rate was roughly constant around 0.019 nm/s for Φ≤1.24×1025 m−2. The value at 2.35 × 1025 m−2 was slightly lower. The erosion rate at 990 K was greater than that at 600 K for every ion fluence.Microscopy and surface analysis techniques showed that Eurofer-97 erosion rate dependence on Φ at 600 K was primarily determined by the preferential sputtering of iron and other mid-Z elements of the alloy, leading to a surface rich in W and Ta difficult to be sputtered. The erosion behaviour at 990 K was dominated by the morphology dynamics, instead. The different properties of the morphology developed at the two temperatures can explain the higher erosion rate at 990 K for all the ion fluences.