Clean fabrication strategy of diamond crystals containing nanocomposite films for corrosion and wear protection of AISI-321 alloy

Abstract

This study focused on the synthesis of Niobium/Hexagonal-Diamond/Amorphous-Carbon (Nb/H-D: a-C) films on AISI-321 alloy. The substrate heating used as a vital deposition parameter to tailor structure of the films in an unbalanced magnetron (UB-M) sputtering system for the first time. The substrate heater temperature (Th) ranged between (RT) to 150 °C. The results indicated that increasing the substrate heater temperature promoted the abundance of hexagonal diamond (H-Diamond) crystals through the solid phase separation. Therefore, the film deposited at the highest temperature (150 °C) demonstrated the highest plenty of H-Diamond. Electrochemical impedance spectroscopy (EIS) measurements (after 2, 8, 24, 72, and 168 h immersion) and polarization tests (after 168 h immersion) disclosed that increasing the substrate heater temperature positively affects the corrosion resistance of (Nb/H-D: a-C) films. The results proved that the film deposited at the highest temperature of 150 °C, demonstrated the exceptional corrosion protection efficiency of 99.69 %. Moreover, this film presented acceptable low-frequency impedance (|Z|10KHz) and total resistance (Rt) values of >108 Ω·cm2 and >117 MΩ·cm2 at all immersion times in 3.5 wt% NaCl solution. The highest abundance of the H-Diamond phase, with remarkable chemical inertness at higher substrate heater temperatures, can be an effective reason for elevating anti-corrosion performance of the films. Additionally, as the substrate heater temperature enhanced from RT to 150 °C, mechanical properties illustrated an remarkable increment trend (increasing hardness from 20 to 32.7 GPa and the elasticity modulus from 407 to 470 GPa). Moreover, the anti-wear performances of the films significantly improved with increasing substrate heater temperature, reducing the wear rate from 9.4 × 10−6 to 9 × 10−7 mm3/N·m. These results are mainly attributed to the highest abundance of the superhard H-Diamond phase in the film deposited at higher substrate heater temperature. In conclusion, the (Nb/H-D: a-C) film synthesized at 150 °C represented a promising candidate for tailoring the electrochemical and anti-wear performances of AISI-321 alloy.