Microstructure, phase transformation and hardness of nanometric Cr-Al multilayer coatings

Nanometric Cr-Al multilayer films are deposited by magnetron sputtering to investigate the influences of composition and annealing on the microstructure, phase transformation, and hardness. The enhancement of hardness of as-deposited coatings is attributed to solid solution strengthening and grain size strengthening. For the Cr100−xAlx coatings with x = 30 at.% and x = 62 at.%, respectively, the annealing process prompts the formation of Cr2Al and Cr5Al8 intermetallic compounds. The enhancement of hardness of annealed coatings is primarily caused by the intermetallic formation and secondarily by oxide layer formation.