Pretreatment of the aluminum substrate, such as Ti and Ni-P interlayer, can improve the adhesion strength and mechanical properties of deposited TiN films. In this work, in order to compare with the effect of Ti interlayer and Ni-P interlayer, aluminum substrate was pretreated by titanium ion implantation prior to the deposition of TiN films by magnetron sputtering in a custom-designed multifunctional ion implanter. A scratch tester was used to assess the coating adhesion by investigating the critical load, L-c, at which delamination or other types of coating failures take place. The effects of different pretreatments on the adhesion strength between the films and substrates were analyzed. Our experimental results show that all the adopted pretreatment approaches can effectively improve the adhesion of TiN coatings on aluminum but the failure modes are different for the different coatings/substrate systems. Among the different processes, the use of a thick Ni-P interlayer (10 mu m) and Ti ion implantation together with a Ti interlayer (300 nm) produce the better effects, as the adhesion strength increases from 0.7 to 3.7 and 4.0 N, respectively. (c) 2005 Published by Elsevier B.V.