(La0.5Ba0.5)B6-VB2阴极材料的微观结构及热电子发射性能

Microstructure and Thermionic Emission Properties of (La0.5Ba0.5) B6-VB2 Cathode

摘要:

六硼化镧（LaB₆）是优异的热阴极高温陶瓷材料，然而脆性较高导致难以加工，限制了其进一步的工程化应用。为改善材料的力学性能同时保证其热发射水平，本研究将低功函数的BaB₆和高弹性模量的VB₂加入到LaB₆中，利用放电等离子烧结技术，在1900 ℃-40 MPa-5 min的工艺条件下，获得了致密度为98.57%且基体为单相固溶体的(La_0.5Ba_0.5)B₆-VB₂复合材料。随着烧结温度从1500 ℃升高到1900 ℃，复合材料的平均晶粒尺度从(2.68±1.44) μm增加到(7.21±1.37) μm、维氏硬度从(16.57±0.88) GPa升高到(24.89±1.26) GPa、断裂韧性从(1.95±0.16) MPa·m^1/2提高到(3.81±0.28) MPa·m^1/2、最高抗弯强度达到376.32 MPa，裂纹偏转和裂纹分叉是复合材料的主要增韧机制；(La_0.5Ba_0.5)B₆-VB₂复合材料最高热电子发射电流密度为7.56 A/cm²、最小功函数为2.97 eV。

Abstract:

Lanthanum hexaboride (LaB₆) is an excellent high-temperature ceramic material for thermionic cathodes. However, the high brittleness of LaB₆ makes it difficult to process, limiting the further engineering application. In this study, Barium hexaboride (BaB₆) with low work function and Vanadium diboride (VB₂) with high elastic modulus were added into LaB₆. (La_0.5Ba_0.5)B₆-VB₂ composite with the high relative density of 98.57%, whose matrix is a single-phase solid solution, was prepared by spark plasma sintering (SPS) under the conditions of 1900 ℃, 40 MPa, and 5 min. As the sintering temperature increases from 1500 ℃ to 1900 ℃, the average grain size of the composite increases from 2.68±1.44 μm to 7.21±1.37 μm, Vickers hardness increases from 16.57±0.88 GPa to 24.89±1.26 GPa, fracture toughness increases from 1.95±0.16 MPa·m^1/2 to 3.81±0.28 MPa·m^1/2, and the maximum bending strength reaches 376.32 MPa. Crack deflection and branching are identified as the primary toughening mechanisms in the composite. (La_0.5Ba_0.5)B₆-VB₂ composite exhibits the maximum current density of 7.56 A/cm² and the minimum work function of 2.97 eV.