Life improvement of unduplicated tool for deformation processing of aluminum alloy by duplex treated TIN coating

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The film life of the TiN duplex treatment was studied as a potential surface modification for tools for deformation processing of aluminum alloy. The following results are obtained.(1) Wear starts with that of coating film at a constant low wear rate irrespective of the tempering duration, and a transition to wear of the substrate at high wear rates takes place in air atmosphere.(2) Transfer of aluminum alloy to the TiN coating film was predominant and the coating film suffered no wear damage in nitrogen atmosphere. After sliding for a certain distance, a small shell-like chipping appeared on the TiN coating film. This small chipping grew downstream within the TiN coating film and along the coating film-substrate interface to cause a macroscopic spalling of the film.(3) TiN-duplex treatment reduces by 80% the wear of plasma-nitrided tool steel.(4) The tempering of the nitrided substrate of duplex-treated tool steel further prolongs the coating film life more than twofold.(5) Applying the appropriate coating bias and the nitrided layer thicker than 70 μm, a markedly long film life, which is about 3 times longer than of the conventional duplex treated surfaces is obtained.(6) On the other hand, for the conventional duplex treated surfaces prepared without the tempering neither optimizing the coating bias nor the increase of the depth of nitrided layer improves the film life.