摘 要

热电材料是一种能够实现热能和电能之间相互转换的功能型材料。方钴矿基热电材料就是其中一种非常具有应用潜力的热电材料，这种材料在中温区具有优异的电性能。在实际应用中，由于温差以及热电器件中热电材料与电极材料热膨胀系数不一致等原因，热电材料会受到温度应力的作用。另外，热电材料在服役条件下会受到长期热载荷的作用，所以热电材料在长时间热载荷作用后的力学性能也越来越受到关注。

本文采用固相反应法合成了方钴矿材料Co₄Sb_11.5Te_0.5，通过超声分散结合高能球磨的方法将x vol%SiC晶须（SiC_w）（x=0,1,2）和y vol%纳米颗粒（SiC_p）（y=2,1,0）均匀分散至Co₄Sb_11.5Te_0.5粉末中，再利用放电等离子方法将混合粉末烧结成块状。研究了晶须和纳米颗粒的含量对方钴矿材料Co₄Sb_11.5Te_0.5结构与力学性能的影响，并研究了退火对该材料结构与性能的影响。

研究结果表明：

1. 通过放电等离子烧结，得到了较为致密的晶须-纳米颗粒复合方钴矿材料，密度大致在7.3~7.4g/cm³（标准方钴矿的密度为7.6g/cm³）。退火后各组试样密度在7.1~7.2g/cm³，说明退火后材料内部孔隙增加。
2. 在退火前，2 vol%晶须 0 vol%颗粒、1 vol%晶须 1 vol%颗粒和0 vol%晶须 2 vol%颗粒的方钴矿材料的弯曲强度分别是100.13MPa、127.04MPa、135.31MPa。材料对应测得压缩强度分别是387MPa、450MPa、486MPa，断裂韧性分别为0.850MPa·m^1/2、0.974MPa·m^1/2、0.866MPa·m^1/2。结果表明退火前纳米颗粒的增韧增强效果优于晶须，另外，晶须与纳米颗粒同时掺加时协同增强增韧效果比较明显。

（3）退火100小时后，2 vol%晶须 0 vol%颗粒、1 vol%晶须 1 vol%颗粒和0 vol%晶须 2 vol%l颗粒的方钴矿材料的弯曲强度分别是85.45MPa、96.42MPa、87.36MPa。材料对应测得压缩强度分别是321MPa、335MPa、290MPa，断裂韧性分别为0.671MPa·m^1/2、0.706MPa·m^1/2、0.531MPa·m^1/2。与退火前相比，各组弯曲强度分别下降了14.7%、24.1%、35.4%；压缩强度分别下降了17.1%、25.6%、40.3%；断裂韧性分别下降了21.1%、27.5%、38.6%。可以看出晶须的抗热衰退性能明显优于纳米颗粒。

关键词：方钴矿；放电等离子烧结；晶须；碳化硅纳米复合；力学性能

Abstract

Thermoelectric material is a kind of functional material capable of realizing the mutual conversion between thermal energy and electric energy. Cobalt-based thermoelectric material is one of the most promising thermoelectric materials, which have excellent electrical properties in the medium temperature range. In practical applications, due to the temperature difference and the thermoelectric device thermoelectric materials and electrode materials, thermal expansion coefficient is not consistent with the reasons, the thermoelectric material will be the role of temperature stress. In addition, the thermoelectric material in the service conditions will be subject to long-term thermal load, so the thermoelectric material in the long-term thermal load after the mechanical properties are more and more important.

In this paper,Co₄Sb_11.5Te_0.5 was synthesized by solid-phase reaction method. The x vol% SiC whiskers (SiC_w) (x = 0,1,2) and y vol% nanometer were obtained by ultrasonic dispersion combined with high energy ball milling.The particles (SiC_p) (y = 2,1,0) were uniformly dispersed in Co₄Sb_11.5Te_0.5 powder, and the mixed powder was sintered into a block using a discharge plasma method. The effects of the content of whiskers and nanoparticles on the structure and mechanical properties of Co₄Sb_11.5Te_0.5 were investigated. The effect of annealing on the structure and properties of Co₄Sb_11.5Te_0.5 was studied.

Research indicates:

(1) The whisker-nanoparticle composite cobalt material was obtained by spark plasma sintering, and the density was about 7.3 ~ 7.4g / cm³ (the density of standard cobalt ore was 7.6g / cm³). After annealing, the density of each group was 7.1 ~ 7.2g / cm³, which indicated that the porosity of the material increased after annealing.

(2) The flexural strength of the 2 vol% whiskers 0 vol% particles, 1 vol% whiskers 1 vol% particles and 0 vol% whiskers 2 vol% particles before annealing are 100.13MPa, 127.04 MPa and 135.31 MPa. The compressive strength of the materials are 387MPa, 450MPa and 486MPa respectively. And the fracture toughness are 0.850MPa·m^0.5,0.974MPa·m^0.5, 0.866MPa·m^0.5. The results show that the toughening effect of the nanoparticles before annealing is better than that of the whiskers. In addition, the effect of the synergistic enhancement and toughening of the whiskers and the nanoparticles is obvious.

(3) After annealing for 100 hours, 2 vol% whiskers 0 vol% particles, 1 vol% whiskers 1 vol% granules and 0 vol% whiskers 2 vol% curvature of skutterudite materials are 85.45MPa, 96.42MPa, 87.36MPa. The compressive strength of the materials are 321MPa, 335MPa and 290MPa. The fracture toughness are 0.671MPa·m^0.5, 0.706MPa·m^0.5and 0.531MPa·m^0.5. Compared with that before annealing, the flexural strength decreased by 14.7%, 24.1% and 35.4% respectively, and the compressive strength decreased by 17.1%, 25.6% and 40.3% respectively. The fracture toughness decreased by 21.1%, 27.5% and 38.6% respectively. It can be seen that the thermal shock resistance of whiskers is significantly better than that of nanoparticles.

Key Words：skutterudite；SPS；whisker；SiC nanocomposite；mechanical propties

目录

第1章 绪论 1

1.1研究背景和意义 1

1.2方钴矿材料的研究进展和现状 1

1.2.1 纳米颗粒增强增韧材料的研究进展与现状 2

1.2.2 晶须增强增韧材料的研究进展与现状 2

1.2.3 复合增韧作用 3

1.3本课题的研究目的和主要内容 3

第2章 晶须-纳米颗粒复合方钴矿材料的制备 5

2.1 实验原料 5

2.2 固相反应 5

2.2.1 工艺和设备 5

2.2.2 物相及微结构 6

2.3 晶须和纳米颗粒的引入 6

2.4 SPS放电等离子烧结 7

2.4.1 工艺和设备 7

2.4.2 块体物相 7

2.4.3 块体密度 8

2.4.4 微观结构 8

2.5 小结 10

第3章 晶须-纳米颗粒复合材料的力学性能 11

3.1 力学性能的表征方法和设备 11

3.1.1 弯曲实验 11

3.1.2 压缩实验 12

3.1.3 断裂实验 13

3.2 Co₄Sb_11.5Te_0.5/x vol%SiC_w y vol%SiC_p的力学性能 14

3.2.1 弯曲强度和弯曲模量 14

3.2.2 压缩强度和压缩模量 15

3.2.3 硬度和断裂韧性 16

3.3 退火处理后材料的密度和力学性能 17

3.3.1密度 18