**6.2 Matching of strength and toughness of SPE coating**

A large number of research results have shown that the high hardness of the hard coating itself can well solve the micro cutting problem of the substrate caused by small attack angle erosion. However, due to the lack of toughness of the monolayer hard coating, the coating is prone to rapid failure in the form of brittle fracture when coping with the erosion of sand and gravel at high angles of attack. Therefore, the matching of strength and toughness of the coating is the key to breakthrough of the erosion resistant hard coating. How to obtain a hard and tough erosion resistant coating is also a research difficulty that has not been overcome so far.

## **6.3 Micro-particles in anti-erosion coatings prepared by arc ion plating**

Arc ion plating technology has been widely used in the preparation of hard coatings. However, due to its physical characteristics of arc discharge, it is difficult to
