摘要
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.
传统陶瓷材料的刚性结构变形能力非常有限,通常在很小的应变下就发生断裂.具有层状原子结构的陶瓷,原子层间存在较弱的相互作用,因而具有大的变形潜力.我们以氮化硼(BN)为例,研究了该类陶瓷的室温压缩行为.分别以洋葱结构BN纳米颗粒和石墨状六方BN纳米片为原料,采用放电等离子烧结(SPS)技术分别制备了BN-I和BN-II陶瓷材料.在BN-I中,随机取向的BN纳米薄片构成三维互锁的结构,而在BN-II中,BN纳米薄片表现出垂直于SPS压缩方向的择优取向.BN-I的压缩强度为343 MPa,断裂应变为4.2%.相比之下,BN-II的强度和应变分别为112 MPa和2.2%.不同的微观组织结构导致了BN-I和BN-II压缩性能的差异.此外,这两种陶瓷材料均表现出1.1%的塑性变形.该研究表明,对于具有层状原子结构的陶瓷,其纳米片作为结构基元构筑成无(或低)择优取向的三维互锁结构,有望同时提高其强度和变形能力.
基金
supported by the National Natural Science Foundation of China(NSFC,91963203,51672238,51772260,51722209 and 51525205)
the 100 Talents Plan of Hebei Province(E2016100013)
the NSF for the Distinguished Young Scholars of Hebei Province(E2018203349)。
