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

Abstract

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 Cr 100− x Al x coatings with x = 30 at.% and x = 62 at.%, respectively, the annealing process prompts the formation of Cr 2 Al and Cr 5 Al 8 intermetallic compounds. The enhancement of hardness of annealed coatings is primarily caused by the intermetallic formation and secondarily by oxide layer formation.