Microstructural origins of high hardness and toughness in cathodic arc evaporated Cr-Al-N coatings

Abstract

Abstract The relation of microstructure and mechanical property in cathodic arc evaporated (CAE) Cr 33 Al 67 N coatings have not yet been fully understood despite their extensive applications. In this work, we prepared Cr 33 Al 67 N coatings using CAE, a more industrially favored technique. The as-deposited coatings show superhardness (41\u202fGPa), superior fracture resistance, adhesion strength and high compressive stress (6.3\u202fGPa). Phase and bonding analyses show that the coatings comprise single fcc -solid solution structure with (111) orientation. Transmission electron microscope investigation revealed a microstructure evolution of the coatings: columnar grains with a diameter of 20–40\u202fnm ripen from nano-composite structure with grain diameter of about 6\u202fnm. The resulting densification of grain boundary (GB) facilitates growth of compressive stress, confirming the GB adatom pinning mechanism. Compressive stress plays a significant role in the concomitant hardening and toughening of the coatings by impeding grain boundary glide. Hall-Petch effect and low-angle grain boundary also contribute to the hardening-toughening. These findings reveal the relation of structural mechanism between hardening and toughening in PVD nitride coatings, and supplement the measures to tune microstructure towards superhard yet tough coatings.