Effect of rare earth Y addition on the microstructure and mechanical properties of high entropy AlCoCrCuNiTi alloys

A series of AlCoCrCuNiTiYx (x values in molar ratio, x = 0, 0.5, 0.8, 1.0) alloys have been prepared using vacuum arc melting. Classical high entropy diffraction peaks corresponding to a BCC crystal structure and some Cu, Cr peaks are observed for the AlCoCrCuNiTi alloy. However, with the incorporation of rare earth element Y, the BCC diffraction peaks disappeared and were replaced by new compounds like Cu2Y and AlNi2Ti. A typical cast dendrite structure with Cu-rich dendritic regions and Cr-rich rosette-like shape precipitations are found in the AlCoCrCuNiTi alloy. In the AlCoCrCuNiTiYx alloys, Y segregated preferentially to Cu and combined as bulky Cu2Y compound. The maximum stress of the AlCoCrCuNiTi alloy is 1495 MPa, but reduces intensively after the incorporation of Y due to the formation of bulky Cu2Y. For all the alloys, the compressive fracture mechanism is observed to be cleavage fracture.