A comparison of the galling wear behaviour of PVD Cr and electroplated hard Cr thin films

Abstract

Electroplated hard chromium (EPHC) is used in many industries as a wear and corrosion resistant coating. However, the long term viability of the electroplating process is at risk due to legislation regarding the toxic chemicals used. The physical vapour deposition (PVD) process has been shown to produce chromium and chromium-based coatings that could be a possible alternative for EPHC in some applications. This study investigates the microstructure and properties of two PVD chromium coatings as a possible alternative to EPHC to provide resistance to galling. Two PVD deposition processes are investigated, namely electron beam PVD (EBPVD) and unbalanced magnetron sputtering (UMS). Galling wear tests were performed according to ASTM G98-17. The results show that the two PVD coatings are of similar hardness, surface roughness and exhibit similar scratch behaviour. However, the galling wear resistance of the coating deposited by UMS is approximately ten times that of the EBPVD coating, and similar to that of the EPHC. X-ray diffraction reveals that the EBPVD chromium coating has a strong preferred orientation of the {2 0 0} planes parallel to the coating surface whilst in the UMS PVD coating, preferred orientations of the {1 1 0} and {2 1 1} planes parallel to the surface are observed. The EPHC does not exhibit relative peak intensities which conform to the International Centre for Diffraction Data (ICDD) powder diffraction pattern consistent with chromium. The crystal orientation of the PVD chromium coatings appears to play a significant role in influencing galling resistance.

Galling phenomena in metal forming

“…The galling wear resistance of coatings deposited by UMS is approximately ten times that of the EBPVD coatings (Fig. 12), and the crystal orientation of the chromium coatings appears to play a significant role [53]. In cold sheet metal stamping, a PVD treatment of CrN on the D53 mold surface enhances the hardness to 1,600 HV, and the obtained good anti-adhesive properties of the surface significantly improve its galling resistance [54], as shown in Fig.…”

A review: advancements in fluoro-based polymers for aggrandizing anti-galling and wear resistant characteristics

“…Researchers tried numerous material as surface coat for enhancing anti-galling properties such as hard inorganic coatings of TiC, DLC, VN, graphite, hBN or organic coating of paraffins, microcrystalline, carnauba, polyethylene and amide waxes. Out of the above-mentioned, polytetrafluoroethylene (PTFE) and polyamides have good lubricating property owing to their plastic or viscoplastic behavior under applied frictional loads [63][64][65][66][67][68][69][70]. Global Fluoropolymers Market was valued at $5404 million in 2015, and is expected to reach $9034 million by 2022, registering a CAGR of 7.7% from 2016 to 2022 [71].…”

Microstructure, Micro-Indentation, and Scratch Behavior of Cr Films Prepared on Al alloys by Using Magnetron Sputtering

“…Thus, Cr is commonly employed as protective coating or film for metal parts at aggressive friction condition, corrosion, and high-temperature oxidation [2]. Generally, Cr coatings are fabricated by electroplating [3,4] and physical vapor deposition (PVD) [2,[5][6][7][8]. However, the traditional Cr plating process uses a highly toxic CrO 3 electrolyte, and a large amount of waste liquid discharges cause serious pollution to the environment.…”

“…Moreover, the target materials come from a wide variety of materials including almost all metals, alloys, and ceramics. Several studies have reported the feasibility to deposit Cr films by magnetron sputtering [5][6][7][8]. Compared with CrO 3 electrolyte, metal Cr target could be less hazardous.…”

“…The applied bias and high deposition rate led to the formation of irregular microstructure of Cr films. Recently, Daure [5] found that Cr film deposited by using unbalanced magnetron sputtering (UMS) and electron beam PVD (EBPVD) showed obvious preferred orientations and close hardness (~5 GPa), but UMS Cr film showed similar galling resistance with conventional hard chromium electroplating (EPHC), which was much better than EBPVD Cr. Daure pointed out UMS would have potential to replace EPHC in some tribological applications.…”