Effect of plasma nitriding on nanostructure of TRD coating

Abstract

In this study, the effect of conventional plasma nitriding on chromised tool steel was investigated. The samples were chromised at 11008C for 12 h using thermoreactive diffusion/deposition (TRD). Subsequent tof TRD, specimens were nitrided at 6008C using a DC plasma set-up. Phase composition and surface morphology of the coatings were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. Corrosion resistance of the samples was investigated by polarisation corrosion test. X-ray diffraction analysis indicated that after chromising, the coating mainly consisted of Cr 7 C 3 , Cr 23 C 6 and Fe 3 C and surface hardness increased from 330 to 1400 HV 0.01 . However, after plasma nitriding, nanosized Cr 2 N, CrN, Fe 3 N and Fe 4 N phases with particle sizes ranging from 32 to 54 nm were formed. The results of polarisation corrosion tests showed that by applying duplex TRD and plasma nitriding, the corrosion resistance was improved.

Microstructures and Wear Resistance of Boron-Chromium Duplex-Alloyed Coatings Prepared by a Two-Step Pack Cementation Process

“…Nowadays, diffusion coatings on gear materials via carburizing, nitriding, carbonitriding, boronizing, and chromizing to improve the wear resistance of carbon steels has been widely reported [7][8][9][10]. In addition to improvement on the hardness and wear resistance, boronizing and chromizing treatment can also improve the corrosion resistance and high-temperature oxidation resistance of carbon steels.…”

Current failure mechanisms and treatment methods of hot forging tools (dies) - a review

“…In this method, only carbon (or nitrogen) substrates can be used, and component distortions may occur due to the process requiring higher temperature than the austenite start temperature of the steel. It has reported that applying TRD technique with plasma nitriding can improve the corrosion resistance [115].…”

Effect of duplex coating (VC–VN) on forming mandrel for better wear resistance

“…Previous studies show that carbon's affinity towards oxygen is always higher compared to nitrogen during the salt bath TRD process. So, plasma-nitriding sputtering and recondensation [22,23] processes were carried out with increased processing time to form a nitride phase with the vanadium carbide coating. The main objective of this cyclic process was to form larger primary carbides in a fine-tempered martensitic matrix and secondary carbides in a nanoscale during precipitation hardening [15].…”

“…Energy spectrum (Table 5) shows that zone 'Y' has enriched vanadium (66.61%), carbon (25.64%) and nitrogen (4.22%) due to dense VC-VN coating up to 6-8 µm. The thickness of VC and VC-VN coatings remains same, and the reason behind this could be mainly because of the replacement of carbon atoms by nitrogen atoms during the plasma-nitriding process [23].…”

“…From Figure 9(c,d), it is clear that VC-VN coating has increased the transfer layer, which can be clearly seen as dark spots on the wear disc tracks when the temperature was increased to 150°C. From the wear track EDS analysis, as shown in Tables 8 and 9, an increase in oxygen percentage from wear area to near surface area indicates that oxidation has occurred on wear disc worn tracks, and this would have been mainly because of oxygen's affinity towards carbon [22,23]. So, the presence of oxide layer on the surface of the wear disc reduces the co-efficient of friction and acted as a solid lubricant.…”