# Self-Ginding Silage Knife Strengthened with Ni-WC Alloy Prepared by Laser Cladding
## 1 Introduction  
Cutting tools are used in a variety of agricultural machines for harvest. During usage, the cutting edge interacts with crop stalks and attachments of earth and sand, which induces friction and wear of the cutting edges. Friction is the primary cause of failure for agriculture knives, workpieces touching soil, etc. A gradual loss of materials subjected to abrasion mechanisms consumes more than 500,000 t of steel in China [1]. In addition, the blade angle and radius of the edge curvature increases when knives become dull, which leads to crop damage and poor cutting performance [2]. Self-grinding tool-making technology offers a good scheme for solving the above problems [3]. The cutting edge comprises a layered structure that consists of a wear-resistant layer and a lesser wear-resistant layer. As a result, different amounts of wear are produced at different layers of the cutting edge when cutting crops. The wear-resistant layer is exposed at the tip of the cutting edge. The geometry of the cutting edges can remain unchanged for long periods of time, which improves the service life and cutting quality of the knife [4]. Convenient techniques to induce effective compounds featuring a sharp gradation are coating, diffusion hardening, and local applied strengthening, e.g., one side of thecutting edge is carburized in order to obtain a self-grinding edge [5]. An Fe-Cr-C-V layer was prepared on a 65 Mn steel substrate by plasma surfacing welding technology. The over-lapped Fe-Cr-C cladding layer and dot-shaped Fe-Cr-C cladding layer were deposited by plasma-transferred arc (PTA) cladding on Hadfield steel [6; 7]. Three kinds of steel plates were rolled into hardness gradient materials by vacuum rolling [8]. A two-part dental molding material was used to make casts of the cutting edge. The tip of the cutting edge in this case had a radius of less than 0.2 mm, which showed an excellent demanding operation of self-grinding [2]. Using the laser cladding technique to implement a coat on steel is a convenient approach to inducing a layered structure that overcomes the defects of other coating techniques. Metallurgical bonding can be formed for TIG welding, but the dilution ratio of TIG welding is higher than that of laser cladding, and the precision of the coating thickness does not meet the demands for preparing self-grinding knives. For the electroplating technique, only physical bonding takes place, which is prone to falling off. In addition, the thickness of the electroplating layer is between 1 and 3 \(\upmu\)m, which is considerably lower than that of laser cladding. One the other hand, laser cladding can achieve metallurgical bonding between the layer and the substrate, a lower dilution, and a high precision of coating layer thickness, etc. [9]. Self-grinding knives prepared by laser cladding are used in forage choppers, and demonstrate significantly improved performance characteristics [10]. In addition to the coating technique, the material composition is the other important element influencing the performance of self-grinding knives. Ni-based alloys are an important material used to coat steel to obtain high wear resistance, with carbides and borides forming during coating [11]. Moreover, the wettability of the Ni element is excellent, which is the main element enhancing the bonds' strength and the material's toughness. Ni-based alloys have good compatibility with tungsten carbide (WC), which in particular holds high potential regarding wear resistance. WC can improve the hardness and wear resistance of the coating. The combination of the two can enhance the bonding strength and fracture toughness of the coating [12]. A layer consisting of nickel alloys and WC particles is made on one side of the cutting edge by laser cladding, which combines the hardness and toughness for this layer. Laser cladding also creates metallurgical bonding at interface between the substrate and the strengthening layer.