Composite coating for surface layer of valve rod piece of internal combustion engine and preparation method of composite coating

The invention belongs to the technical field of internal combustion engine part surface treatment, and particularly relates to a composite coating for an internal combustion engine valve rod piece surface layer and a preparation method of the composite coating. The surface of a valve rod base body sequentially comprises a Ti metal bonding layer, a TiAlN middle supporting layer, a TiAl-DLC gradient working layer and a corrosion-resistant coating from inside to outside; the TiAl element content of the TiAl-DLC gradient working layer is sequentially reduced from bottom to top according to component gradient design, so that the coating structure is transited to an amorphous structure from a nano-composite structure; according to the prepared composite coating, friction between the composite coating and the valve guide pipe can be effectively reduced, and the surface abrasion resistance of a rod piece is improved; and the composite coating has good corrosion resistance and strong oxidation resistance, so that the