Silicon-boronising of Nimonic 90 superalloy

In the present work, Nimonic 90 alloy surface has been modified to increase its abrasive wear resistance by using a self-protective silicon-boronising paste agent. A multilayer consisting of intermetallic compounds, or a composite layer containing different intermetallic compounds, was formed at the surface. In the former case, the multilayer coating consisted of an outer layer of (Ni,Co) 2Si, an intermediate layer of (Cr,Co) 2B, and an inner layer of Ti-rich nickel silicide. The total thickness of these layers was 40–90 μm, depending on the temperature and the holding time. In the latter case, the composite layer contained lathlike (Ni,Co) 5Si 2, ‘flower patterns’ of CrB and modified nickel alloy matrix. The composite layers were about 500 and 800 μm thick after 2 h and 8 h of treatment, respectively. The microhardness of the coatings was about 3 times higher than that of the Nimonic 90 substrate. The abrasive wear resistance of Nimonic 90 was raised by 2.5–5 times, depending on the employed surface treatment parameters.