An investigation of precipitation strengthened Inconel 718 superalloy after triode plasma nitriding

In this study, we investigated the microstructural evolution, surface hardening and general corrosion properties of a precipitation-strengthened Inconel 718 Ni-superalloy after triode-plasma nitriding (TPN) at low treatment temperatures 400–450 °C (i.e. thermodynamic paraequilibrium conditions) high temperature 700 °C. At temperatures, apart from formation nitrogen-expanded austenite (? N ) high-Cr ? matrix, pre-existing ?? ?? intermetallic nano-precipitates appear to exhibit different responses. The spheroidal N-modified (or precipitates were ‘slightly-expanded’, leading slightly shifted XRD peaks, i.e. 2-theta angles ~0.2° substrate (111) ~0.5° (200). contrast, could experience substantial lattice expansion close that matrix. With increasing temperature, nitride started as additional nano-sized (e.g. ~3–6 nm diameter observed 450 °C) grew into laths ~5–10 thick ~15–30 wide °C). Without changing core microstructure/properties, nitrogen modification obtained on alloy TPN ~486 HV 0.025 ~1212 400 No degradation performance was for nitrogen-supersaturated However, TPN-treated showed increased current density in anodic region, which can be associated with early-stage formation. significantly deteriorated is due pronounced segregation substitutional alloying elements. • Triode plasma corrosion-resistant Ni-superalloy, Significant anisotropic peak shifts matrix (and most likely high-Nb ??). A “slightly-expanded” phase corresponds high-Al . “dotted” “woven” precipitation morphology °C, respectively Hard layers without altering microstructure/hardness