Microstructure Evolution and High-Temperature Fracture Toughness of Al_0.3CrFeNiCu_1.5Mo_x (x = 0,0.1,0.2,0.3) High-Entropy Alloys

In order to enhance the high-temperature fracture toughness of high-entropy alloy, the phase composition, microstructure evolution, fracture toughness and crack propagation behavior of Al_0.3CrFeNiCu_1.5Mo_x alloy with Mo alloying are studied. The results show that the Al_0.3CrFeNiCu_1.5 alloy is composed of FCC + BCC solid solution. When Mo element increases, σ phase is gradually appeared near the main peak of (111)_FCC. The atomic size of Mo element is large, which is easy to cause lattice distortion. The diffraction peaks of (111)_FCC and (110)_BCC are separated. The Al_0.3CrFeNiCu_1.5Mo_x alloys are composed of typical dendrites. The fracture toughness test shows that the value decreases continuously at 25 °C; the value increases first and then decreases at 200 °C (Mo-01 alloy average value is 73.291 MPa·m^1/2) and 300 °C (Mo-01 alloy value is 49.260 MPa·m^1/2); the fracture toughness value first remains unchanged and then decreases at 400 °C. The addition of Mo element plays a strengthening role, the secondary dendrite wall is obviously thickened. The crack propagation path is long, and the crack deflection is obvious. Most of the dendrites have a certain angle with the crack propagation direction, which hinders the crack propagation.