# Impact Wear Behavior of the Valve Cone Surface after Plasma Alloying Treatment
## 4 Conclusions  
Using double glow technology, highly resistant CrN coatings were prepared on the NCF3015 valve surface, enhancing the service stability of the latter. The surface microstructure was characterized via scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The microhardness was examined using a Vickers hardness tester. The adhesion strength was assessed by the scratching method. The impact wear behavior of the valve was studied by means of a bench test device. Based on the findings, the following conclusions can be drawn.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \(\uptheta\)\(\upmu\)m & 90\(\uptheta\)\(\upmu\)m & 180\(\uptheta\)\(\upmu\)m & 270\(\uptheta\)\(\upmu\)m & Average/\(\upmu\)m & Wear Amount/mg \\ \hline Valve substrate & 119.88 & 114.82 & 116.67 & 121.53 & 118.23 & 92.66 \\ CrN coating & 49.82 & 43.41 & 43.63 & 34.86 & 42.93 & 23.49 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Depth and amount of wear marks.  
Figure 10: Wear contour morphology. (**a–d**) Valve substrate; (**e–h**) CrN coating.  
(1) Under the set experimental parameters, the CrN coating develops in an island-like formation, achieving a thickness of approximately 46 \(\upmu\)m. The metal Cr shows a gradient distribution in the diffusion layer and forms a high-strength metallurgical bond with the substrate, exhibiting an adhesion of approximately 72 N.  
(2) The average surface hardness of the CrN coating reaches 903.1 HV\({}_{0.5}\), exceeding the hardness of the valve substrate by approximately 2.4 times. This is mainly attributed to the interstitial phase structure of CrN with a face-centered cubic configuration. The high hardness also enhances the impact resistance of the CrN coating.  
(3) After exposure to a temperature of 650 \({}^{\circ}\)C under a load of 12,000 N over 2 million shocks, the CrN coating and its seat primarily exhibit adhesive wear along with local fatigue peel, whereas the wear mechanism between the valve substrate and its seat involves both adhesive and abrasive wear mechanisms. The average wear depth and wear amount of CrN coating are found to be 42.93 \(\upmu\)m and 23.49 mg, respectively, being 63.7% and 74.6% lower than those of the substrate (118.23 \(\upmu\)m and 92.66 mg, respectively).  
Conceptualization, C.L., Y.Y. and D.W.; methodology, M.L. and P.Z.; software, C.L. and M.L.; validation, C.L., D.W. and P.Z.; formal analysis, Y.Y.; investigation, C.L., D.W. and S.Q.; resources, C.L. and S.Q.; data curation, M.L.; writing--original draft preparation, C.L., Y.Y. and M.L.; writing--review and editing, C.L., D.W. and P.Z.; visualization, D.W.; supervision, C.L.; project administration, C.L. All authors have read and agreed to the published version of the manuscript.  
This project was supported by the Natural Science Foundation for Excellent Young Scientists of Jiangsu Province, China (Grant No. BK20180068), and Fundamental Research Funds for the Central Universities, China (Grant No. NT2022019), Open Project Funding for State Key Laboratory of Engine and Powertrain System, China (Grant No. skleps-sq-2023-080). The equipment for this project was supported by Plasma Surface Engineering Laboratory. Authors [PERSON] and [PERSON] were employed by the company Weichai Power Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.