Microstructure and tribological properties of CrN and CrSiCN coatings

Three CrN based coatings were deposited on 17-4PH precipitation hardening stainless steel substrate using plasma enhanced magnetron sputtering (PEMS) technique. The three coatings evaluated in this study assumed the nominal compositions of Cr0.68N0.32 (sample CrN), Cr0.55Si0.013C0.14N0.3 (sample CrSiCN-1), and Cr0.43Si0.034C0.25N0.29 (Sample CrSiCN-2). The microstructure, mechanical properties and wear and erosion resistance of the coatings were evaluated to examine the effect of Si and C additions to CrN. The results indicated that with the incorporation of Si and C, the microstructure transformed from hexagonal Cr2N (for CrN coating) to B1 structure containing crystalline Si3N4 (for CrSiCN-2). The initial addition of Si (1.3 at.%) and C resulted in increase of hardness (H), Youngʹs modulus (E) and the ratio of H3/E2. With further increase in Si (3.4 at.%) and C, the hardness and Youngʹs modulus decreased. The coefficient of friction was observed to decrease with the addition of Si and C, irrespective of microstructure changes. The combination of reduced coefficient of friction and microstructure modifications has resulted in improved wear resistance for sample CrSiCN-2 (with a wear rate ∼ 60% lower than CrN). The erosion resistance test results showed brittle erosion characteristics for samples CrN and CrSiCN-1 where erosion rate increased with erodent impingement angle and reached the highest rate at 75° and 90°, respectively. CrSiCN-2 coating, while exhibiting higher erosion rate at low impingement angle, demonstrated reduced erosion rate at higher angle due to the ductile nature of the coating under erosion test condition.