The rise of plastic deformation in boron nitride ceramics
The rise of plastic deformation in boron nitride ceramics
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氮化硼陶瓷塑性变形的增加
DOI：
10.1007/s40843-020-1466-0
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发表时间：
2020
影响因子：
8.1
通讯作者：
Tian Yongjun
中科院分区：
文献类型：
--
作者：
Wu Yingju;Zhang Yang;Zhang Shuangshuang;Wang Xiaoyu;Liang Zitai;Hu Wentao;Zhao Zhisheng;He Julong;Yu Dongli;Xu Bo;Liu Zhongyuan;Tian Yongjun
陶瓷通过离子键或共价键结合，位错成核和移动的滑移系统非常有限[1]。陶瓷的主要缺点是变形性差和天然脆性，特别是与金属相比。在应力作用下，陶瓷在发生明显的塑性变形之前就趋于断裂。陶瓷在承受远低于理论强度的应力时会出现裂纹并迅速扩展[2]。因此，陶瓷只能承受非常小的应变（< 1%），吸收有限的机械能，并显示出较差的韧性[3]。此外，陶瓷中的微结构缺陷可能进一步降低韧性。由于陶瓷材料缺乏明显的塑性变形能力，在应力作用下容易发生毫无征兆的灾难性失效，严重增加了陶瓷材料在结构材料应用中的不可靠性。与具有刚性结构的传统陶瓷相比，具有层状原子结构和原子层之间相对较弱的相互作用的陶瓷可能具有更好的变形能力，其贡献来自一系列变形模式，例如基底滑移、扭结和剪切带变形以及晶粒分层[4-6]。这种类型的典型陶瓷包括石墨和MAX相[7，8]。多晶石墨的抗压强度高达100 MPa，断裂应变小于2.2%，残余塑性应变小于0.2%[9]。Max（具有通式Mn+ 1AXn（MAX）-的三元碳化物和氮化物，其中n= 1、2或3; M是前过渡金属; A是A族元素（第13-16族元素的子集）;和X是C和/或N）相陶瓷通常表现出脆性并在小的压缩应变下趋于断裂，例如，Ti 2AlC在1.2%的应变下断裂，最大残余应变为0.55%[10]。具有定向毫米级晶粒的Ti 3SiC 2显示出改善的压缩延展性[11]。然而，屈服强度（ca。200 MPa）显著降低，仅为细晶粒Ti 3SiC 2陶瓷的五分之一[11，12]。同时提高具有层状原子结构的陶瓷的变形性和强度是一个巨大的挑战。层状氮化硼（hBN）具有类似于石墨的层状原子结构[13]。它具有优异的化学和物理性能，如高导热性，抗热震性，耐烧蚀性以及热稳定性和化学稳定性，因此广泛用于冶金，汽车工业和航空航天等许多领域[14，15]。然而，hBN陶瓷表现出较差的机械性能，这引起了最近的许多研究工作[16-20]。用放电等离子烧结（SPS）制备的致密化hBN陶瓷的压缩强度被限制在约100 MPa [20]。同时，hBN陶瓷的变形行为基本上被忽略。在这项研究中，hBN陶瓷样品制备与SPS与两个前体，洋葱状BN（oBN）纳米粒子和hBN纳米片。由oBN纳米颗粒（BN-I）制成的陶瓷由互锁成三维（3D）结构的随机取向的纳米层片构成，表现出高达343 MPa的压缩强度和高达4.2%的断裂应变。相比之下，来自hBN纳米片（BN-II）的陶瓷由具有优选取向的微米级薄片制成，并且与BN-I相比显示出较差的机械性能。两个样本都显示出明显的
Ceramics are bonded by ionic or covalent bonds, with very limited slip systems for dislocation nucleation and movement [1]. The poor deformability and natural brittleness are the major drawbacks of ceramics, especially when compared with metals. Under stress, ceramics tend to fracture before noticeable plastic deformation takes place. Cracks occur and propagate rapidly in ceramics subjected to stress much lower than the theoretical strength [2]. As a result, ceramics can only endure very small strains (< 1%), absorb limited mechanical energy, and display poor toughness [3]. Moreover, microstructure imperfections in ceramics may decrease the toughness even further. Due to the lack of significant plastic deformation capacity for ceramic materials, the catastrophic failures without warning are easy to happen under stress which critically increases the unreliability of ceramics in the applications as structural materials. Compared with traditional ceramics with a rigid structure, ceramics with a layered atomic structure and relatively weak interactions between atomic layers might possess a promoted capability in deformation, with contributions from a range of deformation modes, such as basal slip, kink and shear band deformations, and grain delamination [4–6]. Typical ceramics of this type include graphite and MAX phases [7, 8]. Polycrystalline graphite shows a compressive strength up to 100 MPa and fracture strain less than 2.2%, with a residual plastic strain less than 0.2%[9]. MAX (the ternary carbides and nitrides with the general formula Mn+ 1AXn (MAX)—where n= 1, 2, or 3; M is an early transition metal; A is an A-group element (a subset of group 13–16 elements); and X is C and/or N) phase ceramics with fine grains usually show a brittle nature and tend to fracture under small compressive strains, eg, Ti2AlC fractures under strain of 1.2%, with a maximum residual strain of 0.55%[10]. Ti3SiC2 with oriented millimeter-sized grains displays improved compression ductility [11]. However, the yield strength (ca. 200 MPa) is significantly reduced, only onefifth of that of the fine-grained Ti3SiC2 ceramics [11, 12]. It is a great challenge to simultaneously improve the deformability and strength of ceramics with a layered atomic structure.Hexagonal boron nitride (hBN) possesses a layered atomic structure similar to graphite [13]. It has an excellent combination of chemical and physical properties, such as high thermal conductivity, thermal shock resistance, ablation resistance, and thermal and chemical stability, and thus it is widely used in many fields such as metallurgy, automotive industry and aerospace [14, 15]. However, hBN ceramics show inferior mechanical properties, which arouse numerous research efforts recently [16–20]. The compressive strength of the densified hBN ceramics prepared with spark plasma sintering (SPS) is limited to about 100MPa [20]. Meanwhile, the deformation behaviors of the hBN ceramics are essentially left out. In this study, the hBN ceramic samples were fabricated with SPS with two precursors, onion-like BN (oBN) nanoparticles and hBN nanoplates. The ceramic from oBN nanoparticles (BN-I) is constructed with randomly oriented nanolaminae interlocked into a threedimensional (3D) structure, exhibiting a compressive strength as high as 343 MPa and fracture strain up to 4.2%. In comparison, the ceramic from hBN nanoplates (BN-II) is made of micron-sized laminae with a preferred orientation, and shows inferior mechanical properties compared with BN-I. Both samples display an obvious