Cathodic Cage Plasma Pre-treatment of TiN-Coated AISI-304 Stainless Steel for Enhancement of Mechanical Strength and Wear Resistance

Abstract

Although austenitic stainless steels (ASSs) are known for their superior corrosion resistance properties, the use of such materials in motion contact parts is limited due to their low wear resistance. Previous studies reveal that titanium nitride (TiN) coating of ASS significantly improves its hardness and surface morphology but not the wear resistance due to weak interfacing with the substrate. Since plasma nitriding is a flexible and multifunctional case-hardening process, an attempt was made to improve the wear resistance of TiN-coated AISI-304 stainless steel by subjecting it to pre-treatment by pulsed DC cathodic cage plasma nitriding (CCPN) in the abnormal glow region. The hardness of the TiN-coated steel samples (with and without CCPN pre-treatment) was measured using Vickers micro-hardness tester. This test revealed maximum hardness of 2284 HV after plasma treatment of TiN-coated steel. The untreated TiN-coated steel exhibited 10.6 times lower hardness than the plasma pre-treated TiN-coated steel (CCPN-TiN). XRD analysis of the untreated TiN-coated steel showed strong diffraction peaks of TiN (311) and (400) in the spectrum, whereas plasma pre-treated sample contained dominant peaks of TiN (111), (200) and (220). The ball-on-disk wear tester was used to investigate the wear behavior of the samples. Very small wear rate and friction coefficient were reported for CCPN-TiN-coated steel. The observed low wear rate was probably due to the development of a subsurface (i.e., nitrided surface) on TiN-coated steel during CCPN pre-treatment.