Ring on block sliding experiments were carried out in nitrogen atmosphere in order to evaluate wear behaviors and film lives of coated tool steels prepared by CVD, aiming at improving performances of tools for aluminum plasticity processes such as extrusion dies. Coated blocks of tool steels, SKD61 and SKH51, with three layers of TiC/TiCN/TiN or single TiC layer were examined sliding against rings of aluminum alloy, A6063-T5, under a dry condition comparing with gas-nitrided ones. A characteristic growing process of failures for coated specimens was observed: after slid to a certain distance, a small damage on the film surface took place under a transfer layer of aluminum alloy, and with a little increase of sliding distance, the damage expanded rapidly toward downward. It seems to resemble the generation of the failures, which was observed in TiC/TiCN/TiN coated extrusion dies. The film lives of coated specimens were longer than the life of gas-nitrided one and a TiC coated specimen of SKH51 had a marked longest film life.
