# Impact Wear Behavior of the Valve Cone Surface after Plasma Alloying Treatment
## 1 Introduction  
Valves are crucial components in engines, designed to open and close in a timely manner through the valve mechanism, thus ensuring the control of exhaust emissions in the cylinder [1]. However, due to the large amount of heat released by the combustion of fuel in a thermal engine, this heat cannot be quickly transferred outward, exposing valves to high-temperature conditions exceeding 600 \({}^{\circ}\)C. During the operation of the valve, reciprocating collisions between the cone surface and the valve seat occur. These significant impact forces result in severe wear of the cone surface, thereby reducing the service life of the valve [2, 3]. The service condition, macroscopic structure, and impact wear failure of a valve are shown in Figure 1.  
In recent years, the escalating demand for engine performance has promoted industrial progress, whereby valve wear and failure have increasingly became a crucial issue. In this respect, research focusing on valve protection has gained prominence [4; 5]. It has been shown that the valve-seat friction pair endures harsh and complex conditions upon operation. Valves are prone to wear because of high load impact and high-temperature gas erosion, directly affecting the performance of the engine [2]. [PERSON] et al. [6] pointed out that the repeated elastoplastic deformation of the valve will increase the dislocation density on the surface of the material under the impact of a high-frequency seating force. Moreover, the wear of the valve-seat friction pair will be aggravated in high-temperature and corrosive environments. [PERSON] et al. [7] have found that the two main factors affecting the performance of the valve train are friction and wear. Among them, energy loss caused by friction accounts for 10-20% of the engine output, and wear is the main cause of valve train failure. Addressing the impact wear of valves, which initiates from the surface, entails the application of surface strengthening technologies. Preparing coatings with a favorable combination of properties on the surface of the valve represents an effective method to avoid the direct contact between the seat ring, the high-temperature gas, and the valve [8; 9]. As a binary material, CrN has been widely applied in the field of surface protection. The atoms in CrN crystals are arranged in an interstitial phase face-centered cubic structure, ensuring excellent mechanical properties [10; 11]. [PERSON] et al. [12] prepared a CrN coating with a hardness of 18.84 GPa and [PERSON]'s modulus of 255.41 GPa on the surface of a metal valve seat via multi-arc ion plating technology. After surface strengthening, the friction coefficient and width and depth of wear scars were effectively reduced, improving the wear resistance of the valve seat significantly. [PERSON] et al. [13] produced TiHFN/CrN nano-multilayer films and CrN composite multilayer films on the mold by means of DC magnetron sputtering technology. The results showed that the wear resistance of the mold was increased and the punching pressure was reduced during the forming process, thereby improving the service life of the mold. [PERSON] et al. [14] have established that a nitriding  
Figure 1: (**a**) Service condition, (**b,c**) macroscopic structure, and (**d**) impact wear failure of a valve. layer, formed at a temperature of 550 \({}^{\circ}\)C and comprising CrN, Fe\({}_{4}\)N, and Fe\({}_{2.3}\)N, can significantly enhance the wear resistance of valve materials. However, the studies on the impact wear behavior of CrN coatings at high temperatures are still scarce. Double glow plasma surface metallurgy technology (referred to as \"double glow technology\") represents a new type of surface strengthening method, with the technical principle shown in Figure 2. In this technology, argon atoms are excited and ionized under low-vacuum and high-energy conditions, decomposing into argon plasma and free electrons.