US Patent 7785700 Surface-coated cutting tool

A coating layer formed from an outermost layer and an inner layer disposed on a substrate surface of a surface coated cutting tool. The inner layer is formed from a periodic table group IVa, Va, VIa metal, Al, Si, B compound. The outermost layer is formed from aluminum nitride or aluminum carbonitride. The outermost layer has a chlorine content of more than 0 and no more than 0.5 atomic percent. The protective coating on the tool surface is made easier to form during cutting by further adding a predetermined amount of chlorine to the film formed from aluminum nitride, which provides thermal stability and lubricity. Lubricity can be increased by using this protective coating.