**1. Introduction**

Solid particle erosion (SPE) is one of the common wear modes in engineering field. When solid particulate matter (sand, fly ash, salt, ice crystal, volcanic ash, etc., as shown in **Figure 1**) is entrained by air flow and impacts the surface of components, solid particle erosion will occur. In various applications, including helicopter rotor blades, wind turbines, power generation gas turbines, aircraft windshields, fuselage and engines, etc., they may be subject to severe erosion wear, resulting in the removal of component materials. As early as the Vietnam War in the 1960s, the US military had realized the seriousness of sand erosion. Because Vietnam is in a sand and dust environment, the compressor blades of T53 turboshaft engine of the "Huey" helicopter and the "Cobra" helicopter of the US military mission suffered sand and dust erosion, and serious geometric deformation and structural damage occurred, resulting in engine power reduction, blade crack failure, etc., which necessitated the engine to be replaced in advance, and the average maintenance interval was significantly shortened. By the 1970s, solid particle erosion had become an urgent problem in the field of aerospace. During the Gulf War, the T-64 engine of the US CH53E helicopter had serious erosion and wear problems of compressor blades in this desert environment, which reduced the operating time of the engine from 2000 hours in the ordinary environment to 100 hours in the desert environment. During the war in Afghanistan, the mission of the Russian Mi-17 helicopter in the sand and dust environment, a number of blade fracture failures occurred, resulting in a significant reduction in the service life of the engine and a serious threat to flight safety. In 2010, the Eyjafjallajokull volcano eruption in southern

**Figure 1.** *Gravel, volcanic ash particles, salt and ice crystals erode engine parts to form SPE.*

Iceland led to the closure of the largest civil aviation line since the Second World War, which is precisely due to the reduced visibility of the region and the volcanic ash caused by the volcanic eruption easily entering the engine and endangering flight safety. It is generally believed that when the speed reaches 300 m/s, sand will inevitably enter the turbine engine [1]. Once the engine inhales sand dust, the sand will start to impact and slowly erode the blades. At the same time, corrosive liquids such as rain will accelerate its corrosion. On the contrary, erosion will accelerate the destruction of the integrity of the blades, and the corrosion will intensify. Thus, erosion and corrosion will act together to erode and destroy the blades in a domino manner, leading to catastrophic consequences of the engine.

In other fields, gas turbines are eroded by 5 μm coal fly ash particles. When particles are driven into the gas turbine by the gas flow, they will cause erosion damage to the static and moving blades, which will change the shape and size of the blades, leading to lower working efficiency and worse performance. In 1990, BP conducted an investigation on throttle valve failures in Alaska oil field, which showed that 34% of failures were caused by wear of valve internals and valve bodies [2]. However, in the pipeline system of pumps and heat exchangers, there are huge hidden dangers of safety accidents [3–6]. In a word, erosion wear is very harmful in the industrial production field [7]. In order to effectively reduce the loss caused by erosion wear and improve the service life and reliability of equipment and materials, scholars at home and abroad have carried out a variety of researches. Among them, hard coatings are increasingly used to improve the service life of components, which can significantly improve the anti-erosion performance by endowing the components with surface mechanical properties other than their own.
