Microstructure and properties of directionally solidified LaB6 (100)-ZrB2 eutectic composite prepared by the optical zone melting method

Directionally solidified (DS) LaB6 (001)-ZrB2 eutectic composite is successfully prepared by optical zone melting technique. The effect of the solidification rate on the microstructure and properties is systemically investigated. With the increase in the solidification rate from 20 to 100 mm/h, the eutectic rods present a homogeneous eutectic microstructure. The relationship between the average eutectic spacing and the solidification rate is established. The fracture toughness shows an obvious anisotropy. Crack deflection and crack bridging play important roles in improving the fracture toughness of the material. As the solidification rate is increased from 20 to 300 mm/h, the fracture toughness, bending strength and current density firstly increase and then decrease. The highest fracture toughness of 5.16 MPa.m1/2, bending strength of 809.04 MPa and current density of 36.24 A/cm2 at 1873 K belong to the DS LaB6 (001) - ZrB2 eutectic composite obtained at V = 100 mm/h.