原位合成h-BN增强B4C陶瓷研究开题报告
2020-05-02 17:59:01
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, wxby,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;m1/2,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;m1/2 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;m1/2 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;m1/2. 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;m1/2. 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.