Improving density and properties of spark plasma sintered LaB6 bulk by Ni addition

The effect of Ni addition on the spark plasma sintering (SPS) densification and properties of LaB 6 is investigated in this study. The results show that the Ni addition not only facilitates the SPS densification of LaB 6 but also enhances its mechanical and thermionic emission properties. Under the conditions of 1800 °C sintering temperature, 50 MPa applied pressure, and 5 min holding time, the LaB 6 -2wt%Ni sample achieves a relative density of 97.5 %, while the pure LaB 6 bulk only reaches 83.4 %. Microstructural analysis reveals that the LaB 6 -2wt%Ni sample has a two-phase microstructure, with the NiB secondary phase mainly distributed along the grain boundaries of the LaB 6 matrix, and the average grain size of LaB 6 grains is 10.11 ± 6.30 μm. The effects of crack deflection and bridge induced by Ni addition enable the LaB 6 -2wt%Ni sample to exhibit an indentation fracture toughness of 1.14 ± 0.04 MPa m 1/2 , nearly twice that of 0.59 ± 0.05 MPa m 1/2 for the SPSed LaB 6 bulk with the same density. At the operating temperature of 1600 °C, the LaB 6 -2wt%Ni sample exhibits a slightly higher thermionic emission current density and lower effective work function compared to the dense LaB 6 bulk. This study provides a novel strategy for the fabrication of dense LaB 6 , and the LaB 6 -Ni composite shows great potential as a thermionic cathode material.