Effect of nitriding treatment on corrosion behaviour of Co–Cr–Mo alloy in liquid Al

•Co–29Cr–6Mo alloy is nitrided in pure nitrogen.•Sample surface after nitriding is observed using transmission electron microscope.•Sample subsurface after nitriding is observed with electron backscatter diffraction.•Corrosion of nitrided samples in liquid Al is evaluated with immersion test.•Nitriding treatment is compared and discussed with oxidation treatment.

Effects of nitriding treatment on the corrosion behaviour of Co–29Cr–6Mo alloy in liquid Al were investigated. Because of the high solubility and high diffusion coefficient of nitrogen in Co, Cr2N and π phases formed from sample surface into alloy matrix during nitriding at 1273 K; however, the nitride layer was not continuously formed on sample surface even in a prolonged process. The Cr2N showed obviously higher resistance to liquid Al compared to alloy matrix, but owing to its discontinuous distribution, the formed Cr2N did not obviously improve the corrosion resistance of the alloy to liquid Al.