Advanced Duplex Coatings for Wear and Corrosion Resistance
Creators: Hossain, Saddam
Publisher: name: University of Alberta Library
Year: 2023

<p>Tribocorrosion, a synergistic impact of wear and corrosion, impacts the lifespan of machine parts in most sectors. Consequently, duplex coating has emerged as the most promising solution to address tribocorrosion. In this work, advanced noble duplex coating systems of TiAlN/WC-NiBSi/steel and TiAlN/TiC-SS/steel were developed by utilizing PVD/PTA techniques to combat the simultaneous impact of wear and corrosion. The coatings were used to assess the mechanical, wear, corrosion, and tribocorrosion properties. Indentation and scratch tests were used to investigate mechanical properties, and wear properties were investigated using a ball-on-flat tribo-system with an alumina ball. The corrosion behavior of the various coatings&#39; architecture was studied using a three-electrode cell system, and tribocorrosion characteristics were tested by immersing the ball-on-flat tribo-system in 3.5 wt.% NaCl electrolyte. SEM and EDS analysis were done to investigate the microstructure and surface morphology of the coatings.<br>
From indentation test results, the hardness was improved in the order of steel &lt; TiC-SS/steel &lt; WC-NiBSi/steel &lt; TiAlN/TiC-SS/steel &lt; TiAlN/steel &lt; TiAlN/WC-NiBSi/steel. Scratch test results revealed an early disintegration of the TiAlN layer due to the brittle character of the TiAlN layer, whereas the harder intermediate layer of TiC-SS/steel and WC-NiBSi/steel coating improved the crack resistance of TiAlN. <br>
Single-thick TiC-SS or WC-NiBSi coatings revealed good wear resistance after dry sliding testing, with the WC-NiBSi/Steel coating system exhibiting the best tribological behavior due to its high load-bearing capacity. However, the addition of a TiAlN layer didn’t improve the wear resistance. This may be due to the reduced adhesion of TiAlN, the high surface roughness of thick coatings, or the brittle nature of the nitride. Nevertheless, the wear performance improved for the duplex coatings compared to the single TiAlN coating due to the higher load-bearing capacity of the hard intermediate layer. <br>
The TiC-SS/Steel system showed the highest corrosion resistance without serious dissolution of stainless-steel matrix and TiC; while thick WC-NiBSi/steel and thin TiAlN/steel coating showed poor corrosion behavior due to surface defects which attracted the electrolyte to infiltrate through the pores. Moreover, the addition of TiAlN on the TiC-SS/Steel coatings system did not improve corrosion since oxidation occurred on the surface of the top TiAlN layer. However, when TiAlN was added to the WC-NiBSi/Steel coating, the top TiAlN layer sealed the pores, greatly improving the corrosion performance. <br>
From the tribocorrosion studies at OCP, TiAlN/steel and WC-NiBSi/steel coatings showed poor corrosion resistance due to the defects on the surface. The TiAlN/steel coating surface showed rupture, fractures, and layer breakdown as mechanical wear initiated the cracks, and chloride ions exacerbated the surface cracking. TiC-SS/steel coating showed excellent tribocorrosion resistance while adding a TiAlN cannot help further. However, the addition of the TiAlN layer improved the tribocorrosion performance of WC-NiBSi/steel coating at OCP. At potentiostatic polarization, all the coatings demonstrated more pronounced material deterioration than wear, corrosion, or tribocorrosion at OCP due to the applied external potential. The duplex coating of TiAlN/WC-NiBSi/steel experienced a significant material loss due to the galvanic coupling between TiAlN and WC-NiBSi. <br>
Overall, the TiC-SS/steel system offers superior corrosion and tribocorrosion resistance due to the hard TiC, and corrosion resistance of stainless steel, while the WC-NiBSi/steel system provides excellent wear resistance due to the wear-resistant nature of WC hard particles. Duplex coating of TiAlN/WC-NiBSi/steel showed good tribocorrosion resistance at OCP conditions.</p>