Abstract
Cr-N films with various compositions and structures are deposited by reactive sputtering on A2 tool steel. The composition analysis indicates that the nitrogen contents in the deposited films are increased as the nitrogen flow rates are raised during deposition. Phase identification indicates that the films with lower nitrogen contents exhibit the Cr and Cr2N phases, while the CrN phase is observed in the films with nitrogen contents higher than 58 at.%. With the aid of AFM, the morphology, surface roughness, and grain sizes of the depositied films are evaluated. The microhardness of the deposited films ranges from 1482 to 1771 HK at the load of 3 gf, in which corresponding penetration depths are less than 1/10th of the average film thickness. In pull-off test, failure always occurs in the epoxy side, indicating that the adhesion between the film and the substrate is better than the measured strength. The scratch test if further applied to evaluate the adhesion of the deposited films. The critical loads of the films are determined by the detected acoustic emission signals and the observation of the scratch channels. Serious failures are found in the films with poor adhesion, both cohesive and adhesive failures are observed in these films in the scratch test. In the films with goog adhesion, only localized failures are observed. The corrosion tests indicate that the films with the CrN phase show bettercorrosion resistance than the other films. The corrosion currents for the films are in correlation with the film structure. The oxide Cr2O3 are formedon the top of the films after oxidation. The phase analysis of the oxidizedsamples indicates that the pre-existed Cr and Cr2N phases in the films are transformed to CrN phase due to the incorporation of nitrogenreleased by the oxidized layers. Moreover, the oxidation resistance of thefilms with the CrN phase is better than those with Cr and Cr2N phases.