1. 研究目的与意义（文献综述）

boroncarbide (b₄c) has absorbed considerate attentions due to its lowdensity(2.52 g/cm³), high hardness(35 gpa), excellent wearstability, great chemical resisitance, high melting point (2450 ^oc)[1-3]. owing to these outstanding properties, boron carbide ceramics have beenused in many structural application such as aerospace craft, shield materials,abrasive, tools and polishing media for hard and wear resistance materialsubstance [4-5]. they are also currently used in neutron detectors for its highneutron absorption cross-section [4, 6]. however, the practical applications ofb₄c ceramics are severely restricted by their drawbacks such as lowfracture toughness and flexural strength, poor oxidation resistance beyond 1000 ^oc and poor sinterability due to low self-diffusion coefficient andstrong b-c bond.

toobtain high dense b₄c ceramics, three most commonly used methodswere applied to manufacture b₄c ceramics. the first method was toincrease the sintering temperature, the second was to apply high pressure (≥80mpa)and the third was the introduction of additives, usually including ti, al, fe,ni, cu, si, tio₂, cr₂o₃, crb₂, sic,hfb₂, cr₃c₂, zrb₂, w_xb_y,etc.[7-15]. however, high temperature will lead to excessive growth of b₄cgrain, which is detrimental to mechanical properties of b₄c ceramic.on the contrary, appling high pressure can reduce the sintering temperature(1700 ^oc) and hinder the grain growth of b₄c put forwardby wei ji and sahibzada shakir rehman[16]. they prepared fully dense(99.7%) b₄cceramic with hardness values of 37.8 gpa and fracture toughness of 5.94 mpa#8226;m^1/2,flexural strength of 445.3 mpa. the additives can reduce the sinteringtemperature below 2150 ^oc [17] and promote the sinterability, orenhance the mechanicality of the manufacturedceramic compared with the pure boron carbide ceramic by controlling graingrowth and forming weak interface. suzuya [18] has successfully prepared b₄c-ti₂bcomposites with a fracture toughness of 3.2 mpa#8226;m^1/2 and a flexuralstrength of 866 mpa by reaction hot-pressing sintering of b₄cpowder, mean particle size of 0.5 μm, with 14.5 mol% nanometer tio₂ and 21.5 mol% c at 2000 ^oc. the addition of 5wt% al-tiintermetallics have greatly improved the sintering ability, and b₄cbased ceramics with hardness of 33.5 gpa, a flextural strength of 506 mpa and afracture toughness of 5.5 mpa#8226;m^1/2 are obtained at 1700 ^oc[19].

the objectives of recentreports are mainly to improve flextural strength and fracture toughness of b₄cceramics. some carbon materials such as carbon nanotubes (cnts) and grapheneplatelets (gpls) have attracted great attention as efficient reinforcement materials for b₄cceramics with outstanding mechanical properties, such as light weight, highaspect ratio and tensile strength [20-22]. fan zhang et al. [23] fabricated b₄c/cntsceramics usingthe spark-plasma sintering. the fracture toughness ofcomposite is improved by cnts addition to 4 mpa#8226;m^1/2. in contrast tocnts, graphene platelets have a larger specific surface area, two dimensionalhigher aspect ratio geometry [24]. therefore, they have a lager interfacialarea in contact with matrix, which can remarkably improve the mechanicalproperties of b₄c. yongqiang tan et al. [25] present improved fracture toughness of b₄cbased ceramics with 2 vol% gnps, which is attributed to nanoplatelets pull-out,bridging and deflecting. in their report, the fracture toughness of gnps/b₄ccomposite is about 5.26 mpa#8226;m^1/2. however, the application of cntsand gpls is limited mainly due to their difficulty in synthesis and high price,but also due to their poor high-temperature stability. cnts and gpls can beeasily oxidized at about 450-500 ^oc in air and are inappropriate forhigh-temperature application[26]. in addition, the black color and unknownpoisonous also restrict the use of the cnts and gpls as reinforcement materialsfor ceramic matrix composites. in order to avoid above-mentioned drawbacks ofgpls-reinforced ceramics material, boron nitride platelets (bnpls), astructural analogue of gpls is usually used as a reinforcement for ceramics atpresent [27-29]. bnpls also have two dimensional high aspect ratio like gplsand the mechanical properties of bnpls are also comparable to these of gpls.the elastic modulus of bnpls is about from 700-900 gpa, and that of gpls isabout 1tpa [31]. moreover, unlike gpls based materials, bnpls based materialsare allowed for application at high-temperature condition, which possessoutstanding high-temperature stability until 950 ^oc [32]. thesefindings indicate that bnpls have excellent potential to reinforce b₄cceramics.

2. 研究的基本内容与方案

(1)研究目标

利用立方氮化硼（cbn）在高温下可以经过相变转化为六方氮化硼(hbn)的特性，以及武汉理工大学shs课题组已经相对成熟的放电等离子体烧结技术(sps)，原位合成碳化硼(b₄c)/六方氮化硼(hbn)复相陶瓷，同时优化b₄c基陶瓷的最佳烧结参数；通过对碳化硼陶瓷体系设计，获得原位形成六方氮化硼最佳成分组成。

(2)本研究的基本内容

3. 研究计划与安排

第1-3周：查阅相关文献资料，明确研究内容，确定实验方案，了解试验仪器和设备，完成开题报告。

第4-5周：学习使用实验仪器和设备，并逐步开始制备样品。

第6-8周：采用sps技术烧结纯的立方氮化硼粉末，研究cbn的相变过程。

4. 参考文献（12篇以上）

[1] b. niu, f. zhang, j.y.zhang, w. ji, w.m. wang, z.y. fu, ultra-fast densification ofboron carbide by flash spark plasma sintering, scripta mater.116(2016)127-130.

[2] k.h. kim, j.h. chae,j.s. park, j.p. ahn, k.b. shim, sintering behavior and mechanical properties ofb₄c ceramics fabricated by spark plasma sintering,j.ceram.process.res. 10 (2009) 716–720.

[3] a.k. suri, c.subramanian, j.k. sonber, t.s.r.c. murthy, synthesis and consolidation of boroncarbide: a review, int. mater. rev. 55 (2010) 4–40.