Structure and mechanical property evaluation of Cr–Ti–B–N coatings

• We deposit five Cr-Ti-B-N coatings with different B content.
• B content influences the mechanical properties and wear resistance of the coatings.
• Addition of Ti element resulted in solution hardening.
• Best mechanical properties are achieved when the B content is 4.0 at.%.

In this study, five Cr–Ti–B–N thin films with different B/(Cr + Ti) ratios ranging from 0.1 to 0.69 were fabricated on silicon substrates and AISI420 stainless steel disks by pulsed DC magnetron sputtering using the Cr and TiB2 targets. It was found that the B content had strong influences on the structures and mechanical properties of Cr–Ti–B–N coatings. When the boron content reached 17 at.%, the microstructure changed from the nanocolumnar structure to a nanocomposite structure with nanograins around 4 nm in diameter embedded in the amorphous matrix. As compared with Cr–B–N coating, the solution hardening effect was found to result from the addition of Ti element. The average surface roughness, hardness and elastic modulus of Cr–Ti–B–N film decreased with increasing B content due to the amorphous BN phase. No chipping failures were found adjacent to the scratch track or indentation craters of each coating. In this study, the 37.3 Cr-2.3 Ti-4.0 B-56.0 N (in at.%) coating provided an optimal combination of hardness, wear resistance and adhesion.