The slurry erosion resistance of laser-clad NiCoFeCrAl₃ high-entropy alloy (HEA) coating was investigated by using a jet erosion testing machine. When the impingement angle increased from 15° to 90°, the volume loss of the HEA coating was accelerated firstly and then followed with a slight deceleration. The largest volume loss of this HEA coating was 4.1 mm³, which was acquired at a 45° impingement angle after a 30-min erosion time with a 15 wt% SiO₂ particles (350–600 μm) at an impact velocity of 13 m s⁻¹. Under the same erosion situation, the volume loss of 17-7 PH stainless steel was 5.4 mm³, which means that the HEA coating possesses better erosion resistance under this situation. Annealing treatment is beneficial to improve the erosion resistance of HEA coatings. The 950°C annealed HEA coating had the best erosion resistance because the intermetallic compound Cr₃Ni₂ was precipitated from the matrix and the volume loss was reduced to 3.5 mm³ at a 45° impingement angle. The worn surface morphologies of HEA coatings were characterized by grooves, ploughing marks, and a small quantity of brittle fractures, which suggests that plastic deformation and abrasive wear were the predominant mechanisms in the slurry erosion of the HEA coatings.

From the view point of chemical compatibility of elements, the electronegativity difference Δe was investigated as a characterisation parameter to evaluate the formation possibility of solid solution phases. The relationship between the formation of high entropy alloys (HEAs) and Δe indicates that a lower value of Δe is favourable to form solid solution phases. Based on the rule of topological stability and chemical compatibility, a δ − Δe plot was built, and four multicomponent alloys were designed. X-ray diffraction results show that three of the four designed alloys were fabricated as HEAs by arc melting and suction casting. The new HEA FeCoCuNiAgGe with the lowest value of Δe has typical dendrite and interdendrite microstructures, and the phase separation phenomenon is a common characteristic of the designed alloys containing Ag. Therefore, the application of Δe can explore the composition range for the development of new HEAs.

High-entropy alloys (HEAs) have gained extensive attention due to their excellent properties and the related scientific value in the last decade. In this work, Al_xCoCrFeNiTi_0.5 HEA coatings (x: molar ratio, x = 1.0, 1.5, 2.0, and 2.5) were fabricated on Q345 steel substrate by laser-cladding process to develop a practical protection technology for fluid machines. The effect of Al content on their phase evolution, microstructure, and slurry erosion performance of the HEA coatings was studied. The Al_xCoCrFeNiTi_0.5 HEA coatings are composed of simple face-centered cubic (FCC), body-centered cubic (BCC) and their mixture phase. Slurry erosion tests were conducted on the HEA coatings with a constant velocity of 10.08 m/s and 16–40 meshs and particles at impingement angles of 15, 30, 45, 60 and 90 degrees. The effect of three parameters, namely impingement angle, sand concentration and erosion time, on the slurry erosion behavior of Al_xCoCrFeNiTi_0.5 HEA coatings was investigated. Experimental results show AlCoCrFeNiTi_0.5 HEA coating follows a ductile erosion mode and a mixed mode (neither ductile nor brittle) for Al_1.5CoCrFeNiTi_0.5 HEA coating, while Al_2.0CoCrFeNiTi_0.5 and Al_2.5CoCrFeNiTi_0.5 HEA coatings mainly exhibit brittle erosion mode. AlCoCrFeNiTi_0.5 HEA coating has good erosion resistance at all investigated impingement angles due to its high hardness, good plasticity, and low stacking fault energy (SFE).