Three dimensional microstructure study of oxide scale formed on a high-speed steel by means of SEM, FIB and TEM

Characteristics of the oxide scale formed on a high-speed steel (HSS) material in the temperature range 550–650 °C were examined. The surface morphologies of oxidised sample indicate that the temperature has a significant influence on the oxidation behaviour of the HSS samples. Differential oxidation is expected to occur due to high-alloyed components in the material. The carbide-free matrix has a good oxidation resistance due to the dissolved chromium; while vanadium rich carbide (MC) regions were oxidised heavily because of high free energy at the carbide/matrix interface and low thermal stability of the MC carbides. FIB/TEM cross-section observation shows that the oxide scale formed on the surface has a duplex-layer structure with vanadium oxides covering the top of the scale.

► Site-specific oxidation behaviour of a HSS was studied by FIB, SEM and TEM.
► A duplex-layer oxide scale formed after oxidation.
► Selective oxidation forms inhomogeneous surface morphology and scale thickness.
► A compact Cr-oxide sub-layer leads to a good oxidation resistance of the matrix.
► The growth mechanism of oxide scale was analysed by ion diffusion.