【作者】 吕鹏；

【导师】 茹红强；

【作者基本信息】 东北大学 ， 材料学， 2009， 博士

【摘要】 碳化硼（B₄C）陶瓷由于具有密度低、熔点高、硬度高、耐高温、耐腐蚀、耐磨损性及良好的中子吸收性能等特性,因而在航空航天、军工防护、陶瓷刀具、耐磨耐蚀部件等方面均具有广泛的用途。但是由于B₄C陶瓷断裂韧性低(＜2.2 MPa·m^1/2)和难以烧结的缺陷大大限制了B₄C陶瓷的推广和应用。本文以提高材料的断裂韧性为目标,通过无压预烧和真空渗铝相结合的方法分别制备了B₄C-Al、B₄C-Al₂O₃-Al、B₄C-TiB₂-Al和B₄C-ZrB₂-Al复合材料,对材料的制备工艺、力学性能、物相组成、微观结构和补强增韧机理进行了系统的研究。结果表明:（1）不同体系的复合材料,其制备工艺不同。B₄C-Al、B₄C-Al₂O₃-Al、B₄C-TiB₂-Al、B₄C-ZrB₂-Al等复合材料所对应的预烧体的烧结工艺分别为2000℃×30 min（真空）、1900℃×30 min（真空）、1200℃×60 min（真空）+2050℃×30 min（氩气）和1400℃×60 min（真空）+1950℃×30 min（氩气）。复合材料的渗铝工艺均为1100℃×120 min（真空）。（2）在渗铝过程中,B₄C和Al之间的反应产物为AlB₂和Al₃BC,直接添加Al₂O₃第二相并不能改变B₄C和Al之间的反应产物。但是利用原位反应引入第二相（TiB₂和ZrB₂）则能够有效地改变B₄C和Al之间的反应产物。原位引入TiB₂后B₄C和Al之间的反应产物只有Al₃BC;原位引入ZrB₂时,随着ZrB₂含量的增加,反应产物由Al₃BC、AlB₁₂C₂和Al₈B₄C₇逐渐转变为AlB₁₂C₂和Al₈B₄C₇,而当ZrB₂含量为35%（质量分数）时,B₄C和Al之间几乎没有发生反应。（3）各体系复合材料预烧体中均有较高的气孔率,这些开口的孔隙相互之间形成了相互贯通的三维网状结构,为真空渗铝时金属铝的渗入提供了通道。渗铝后所有复合材料的致密度均较高,当细颗粒B₄C或第二相的含量较高时,晶粒均有不同程度的细化。（4）对于颗粒配比的B₄C-Al复合材料,随着细颗粒B₄C含量的增加,复合材料的硬度逐渐降低,抗折强度逐渐增大,断裂韧性基本呈增大的趋势,当细颗粒B₄C含量为40%（质量分数）时,复合材料具有较好的综合性能,材料的气孔率、硬度HRA、抗折强度和断裂韧性分别为1.08%、71.7、506 MPa和6.4 MPa·m^1/2。对于B₄C-Al₂O₃-Al复合材料,随着Al₂O₃添加量的增加,复合材料的硬度呈现先增大后降低的变化规律,抗折强度和断裂韧性均呈现先减小后增大的变化规律,当Al₂O₃添加量为25%（质量分数）时,复合材料具有较好的综合性能,材料的气孔率、硬度HRA、抗折强度和断裂韧性分别为2.06%,84.4,440 MPa和6.6 MPa·m^1/2。对于B₄C-TiB₂-Al复合材料,随着TiB₂含量增加,复合材料的硬度逐渐降低,抗折强度逐渐增大,断裂韧性基本呈增大的趋势。当TiB₂含量为40%（质量分数）时,复合材料具有较好的综合性能,材料的气孔率、硬度HRA、抗折强度和断裂韧性分别为1.32%、80.3、560 MPa和7.8 MPa·m^1/2。对于B₄C-ZrB₂-Al复合材料,随着ZrB₂含量增加,复合材料的硬度先增大后降低,抗折强度和断裂韧性均呈现先降低后增大的趋势,当ZrB₂含量为35%（质量分数）时,复合材料具有较好的综合性能,材料的气孔率、硬度HRA、抗折强度和断裂韧性分别为1.06%、82.2、522 MPa和8.6 MPa·m^1/2。（5）延性铝的加入是材料断裂韧性提高的主要原因。此外,对于B₄C-Al复合材料,细颗粒B₄C含量的增加也是提高材料断裂韧性的有利因素;对于添加第二相的B₄C-Al复合材料,第二相粒子与B₄C基体的热膨胀的不匹配及晶粒的细化也能有效地提高材料的断裂韧性。（6）复合材料的断裂方式主要为穿晶和沿晶混合断裂,由于延性Al的渗入,复合材料的断口中存在金属撕裂棱的特征,且随着Al渗入量的增加,金属撕裂棱和韧窝的比例增加。更多还原

【Abstract】 Boron carbide（B₄C） ceramics possesses excellent physical and mechanical properties of high melting point and hardness,good impact and wear resistance,excellent resistance to chemical agents as well as high capability for neutron absorption.It has shown the potential for use in various industrial fields,such as aerospace,military,engineering and nuclear energy.However,the widespread application of B₄C ceramics has been restricted because of the low fracture toughness(＜2.2 MPa·m^1/2) and the poor sinterability due to a low self-diffusion coefficient.In order to improve the fracture toughness,B₄C-Al,B₄C-Al₂O₃-Al, B₄C-TiB₂-Al and B₄C-ZrB₂-Al composites were synthesized using pressureless presintering and aluminium infiltration in vacuum.In this paper,the preparation processing,mechanical properties,phase composition,microstructure and toughening mechanism of the composites were investigated.The experimental results were shown as the following.（1） The presintering processes for B₄C,B₄C-Al₂O₃,B₄C-TiB₂ and B₄C-ZrB₂ preforms were 2000℃×30 min（in vacuum）,1900℃×30 min（in vacuum）,1200℃×60 min（in vacuum）+2050℃×30 min（in argon） and 1400℃×60 min（in vacuum）+1950℃×30 min （in argon）,respectively.The infiltration processing was 1100℃×120 min（in vacuum） for B₄C-Al,B₄C-Al₂O₃-Al,B₄C-TiB₂-Al and B₄C-ZrB₂-Al composites.（2） The reaction products between B₄C and Al were AlB₂ and Al₃BC during the aluminum infiltration.The Al₂O₃ addition did not change the reaction products.However,the reaction products between B₄C and Al were effectively affected by the different in situ synthesized second phases,such as TiB₂ and ZrB₂.In situ synthesized TiB₂ could change the products from AlB₂ and Al₃BC into single Al₃BC.With increasing the ZrB₂ content,the reaction products of Al₃BC,AlB₁₂C₂ and Al₈B₄C₇ changed into AlB₁₂C₂ and Al₈B₄C₇. Furthermore,there was almost no reaction happened between B₄C and Al when the ZrB₂ content increased to 35 mass%.（3） There were plentiful interconnected pores in the preforms of B₄C-Al,B₄C-Al₂O₃-Al, B₄C-TiB₂-Al and B₄C-ZrB₂-Al systems.Consequently,a three-dimensional network of interconnected capillaries was formed as the path for liquid aluminum to obtain the compact composites after aluminum infiltration.After aluminum infiltration,the densifications of the composites obtained were high.With high content of the fine B₄C particle and the second-phase particles（Al₂O₃,TiB₂ and ZrB₂）,the grain sizes of the composites were decrased.（4） In B₄C-Al system,with increasing the fine B₄C particle content,hardness decreased while bending strength increased,and fracture toughness showed an increasing trend approximately.The composite with 40 mass%fine B₄C particle showed the optimized properties.Porosity,hardness HRA,bending strength and fracture toughness of that were 1.08 %,71.7,506 MPa and 6.4 MPa·m^1/2,respectively.In B₄C-Al₂O₃-Al system,with increasing the Al₂O₃ addition,hardness increased first and then decreased,bending strength and fracture toughness decreased first and then increased.The composite with 25 mass%Al₂O₃ addition showed the optimized properties.Porosity,hardness HRA,bending strength and fracture toughness of that were 2.06%,84.4,440 MPa and 6.6 MPa·m^1/2,respectively.In B₄C-TiB₂-Al system,with increasing the TiB₂ content,hardness decreased while bending strength increased gradually,and fracture toughness showed a trend of increase approximately. The composite with 40 mass%TiB₂ showed the optimized properties.Porosity,hardness HRA,bending strength and fracture toughness of that were 1.32%,80.3,560 MPa and 7.8 MPa·m^1/2,respectively.In B₄C-ZrB₂-Al system,with increasing the ZrB₂ content,hardness first increased and then decreased while the flexural strength and fracture toughness first decreased and then increased.The composite with 35 mass%ZrB₂ showed the optimized properties.Porosity,hardness HRA,bending strength and fracture toughness of that were 1.06 %,82.2,522 MPa and 8.6 MPa·m^1/2,respectively.（5） The ductile aluminum addition was the leading reason for the fracture toughness improvement of the composites.Furthermore,the increase of fine B₄C particles could contribute to the increased fracture toughness of the B₄C-Al composite.For the other three systems,both the fine grain and the difference in thermal expansion coefficients between the B₄C matrix and second-phase particles could effectively enhance the fracture toughness of the composites.（6） It was found that the fracture was mainly in mixed mode of intergranular and transgranular forms.The amounts of tear ridge and dimple on the fracture surface increased with increasing the infiltrated aluminum content.更多还原