Alpha alumina thin film for processing difficult-to-cut material and cast iron

An alpha alumina (α-Al2O3) thin film which has a thickness of T and is formed on a lower layer which is formed on a base material, the α-Al2O3 thin film being divided into:

• a D1 layer which is positioned between an interfacial layer and 0.15T above the interfacial layer;
• a D2 layer which is positioned between 0.15T and 0.4T above the interfacial layer;
• and
• a D3 layer which is positioned between 0.4T and 1T above the interfacial layer,
• wherein S1 (the grain size of the D3 layer/the grain size of the D1 layer) is 2 to 5.5, and S2 (the grain size of the D2 layer/the grain size of the D1 layer) is 1.5 to 4,
• wherein the lower layer comprises:
• a TiN layer formed on the base material;
• a MT-TiCN layer formed on the TiN layer;
• and
• an interfacial layer containing Ti and formed on the TiCN layer, and
• wherein the interfacial layer comprises:
• a TixAl1-xCNO layer formed on the MT-TiCN layer;
• a AlyTi1-yCNO layer formed on the TixAl1-xCNO layer;
• and
• a Ti oxide layer formed on the AlyTi1-yCNO layer.