【作者】 张福平；

【导师】 贺红亮；

【作者基本信息】 中国工程物理研究院 ， 凝聚态物理， 2013， 博士

【摘要】 利用铁电陶瓷在冲击波压缩作用下相变快速放电的过程,可以用作高功率脉冲电源,有着广阔的应用前景。同时,铁电陶瓷作为脆性材料,易于发生冲击压缩损伤,继而对铁电陶瓷的电学行为造成影响,因此铁电陶瓷的失效问题是一个典型的力-电失效问题。对于铁电陶瓷在冲击条件下的力-电失效问题,目前除了Sandia实验室的Setchell等人报道了多孔PZT95/5陶瓷的屈服效应(对应于多孔陶瓷的孔洞塌缩)外,特别是针对国产致密PZT95/5陶瓷的力-电失效问题,还未见公开报道。本论文以国产致密PZT95/5陶瓷为研究对象,采用实验研究为主、理论分析为辅的方法,系统地研究了PZT95/5陶瓷在多场作用下的失效机理。研究结果证实了致密PZT95/5陶瓷具有与多孔PZT95/5陶瓷不同的压缩损伤模式,确定了国产高密度PZT95/5的冲击压缩损伤应力范围,得到了压缩损伤演化规律的定量认识,该压缩损伤演化规律很好地揭示了不同应力下的放电波形变化的内在原因,对指导PZT95/5陶瓷应用、优化脉冲电源设计具有重要意义,也为其它脆性电介质材料的冲击失效研究提供参考。论文研究的主要内容和创新点归纳如下：1.开展了PZT95/5陶瓷自由面粒子速度波剖面测试,结果表明：在2.0GPa下的波剖面为典型的弹性响应;当应力增加到2.4GPa时,首次在铁电陶瓷波剖面中观察到与二次压缩信号类似的再加载信号；应力进一步增加到4.0GPa及以上时,再加载信号消失,自由面粒子速度出现一个缓爬坡过程。2.针对传统测量层裂强度无法区分破坏波与孔洞塌陷的问题,本文通过增加高阻抗蓝宝石窗口这一独特实验设计,证实和确认了2.4GPa下PZT95/5陶瓷存在有低阻抗的破坏区,即存在有破坏波,排除了该应力下孔洞塌缩、相变造成自由面粒子速度二次上升的可能性。同时,本文对自由面粒子速度剖面观测到的多次上升现象,进行了分析解读,也从一个侧面确认了破坏波的存在性。上述实验结果表明致密PZT95/5陶瓷的冲击压缩失效模式以破坏波为主,与Setchell等人报道的多孔PZT95/5陶瓷冲击压缩失效模式明显不同,后者为孔洞塌缩模式。3.通过测量和分析不同厚度下样品的破坏波特征参数,获得了PZT95/5陶瓷破坏波的形成、传播和演化规律。结果表明：PZT95/5陶瓷的破坏波形成与材料内部缺陷有关,同时破坏波速度与冲击波速度一致,并且破坏波弛豫时间随应力增加而减小,最终破坏波与冲击波重合,导致在4.0GPa及以上压力,自由面粒子速度无二次压缩信号,解释了实验中观察到的缓爬坡信号。这种二次压缩信号的消失并不说明材料的压缩损伤消失或减轻；相反,随着冲击应力的增加,材料内部的损伤应该是更严重,只是由于破坏区伴随冲击波扩展,无法有效区分破坏波与冲击波而已,因此表现为弥散波行为。上述现象与Grady等人在玻璃中观察到的压缩损伤信号一致,即应力低于破坏波阈值时为典型的弹性响应；冲击应力高于某一应力时,由于裂纹分布均匀化,表现为明显的弥散波行为；只有在一定应力范围内,粒子速度剖面才会出现明显的破坏波特征。4.对于极化PZT95/5陶瓷,当冲击应力达到2.4GPa及以上时,发现有破坏波的特征。比较极化陶瓷与未极化陶瓷的破坏波传播特性,发现极化陶瓷的破坏波驰豫时间大于未极化陶瓷驰豫时间,基于“相变增韧”的物理机制,论文解释了极化陶瓷中破坏波驰豫时间增大的原因。5.基于理论计算,论文分析了在外加脉冲和直流电场作用下PZT95/5陶瓷的电学失效机制,并与不同冲击应力下PZT95/5陶瓷的放电波形进行了比较,指出在低应力下(1.5GPa),PZT95/5陶瓷失效以电学失效为主；而在高冲击应力下(3.0GPa或4.3GPa),电学参数的变化规律揭示了PZT95/5陶瓷失效以力学失效为主,破坏波即裂纹的萌生、扩展行为主导了PZT95/5陶瓷的放电行为。PZT95/5陶瓷力学损伤演化规律很好地解释了在冲击波作用下电学参数变化的原因,是本文对冲击波压缩下铁电陶瓷力-电失效研究的重要认识。更多还原

【Abstract】 Ferroelectric ceramics is utilized for the use in shock-driven pulsed power supplies for many years. Not only the electric field, but also the shock stress is applied to the ferroelectric ceramics as shock-driven pulsed power supplies. The failure, induced by electric field or stress, is a key problem to the application of ferroelectric ceramics under shock compression.This paper is primarily devoted to study the failure behaviors of PZT95/5ferroelectric ceramics under shock compression through experimental study aided with theoretical analyses. Electric and mechanical failure behaviors of PZT95/5were systematically investigated. The results confirm that the failure mechanism of high density PZT95/5ceramics is different from that of porous PZT95/5ceramics, and the threshold of failure stress and the evolution rules of failure wave have been getted. This kind of failure behaviors are important to the application of PZT95/5or other dielectric materials under shock compression and the optimization of shock-driven pulsed power supplies.Following is the main content and conclusion of this study:To the unpoled PZT95/5, no obvious recompression signal is observed when the shock pressure is2.0GPa, whereas at2.5GPa, not only the free-surface particle velocity increases, but also a reload signal similar to the recompression signal appears. At a shock stress of4.0GPa or much higher, the reload signals disappear and the free-surface velocity increases slowly to the final state signifying a ramp-wave behavior.An innovative experimental method that using a high impendance window (sapphire) adheared to the back of the PZT95/5sample has been established to confirm the existence of failure wave in PZT95/5. The PZT/sapphire interface particle velocity profile indicates that a low impendence zone truelly exists in PZT95/5when the shock stress is2.4GPa and the reload signal is caused by the failure wave but not by pore collapse or pahse transition. In addition, the occurrence of a multi-reload signal in the rear free surface velocity also confirms the failure wave in PZT95/5.The delay time and velocity of the failure layer has been determined by measuring samples of varying thicknesses at fixed pressure. Results show that the velocity of failure wave is the same as the shock wave speed, and the delay time decreases with increasing shock stress. When the shock stress increases to4.0GPa, the delay time falls to zero, which means the failure layer and the shock wave will disperse synchronously, and the recompression signal disappears and a ramp wave appears. The disappearance of the recompression signal and the observation of the ramp wave mean the increasing of shock damaged in failure layer. Comparing with the failure signal of glass by Gadry, it finds the same points that when the stress is lower than the threshold of failure stress, the velocity profiles suggest nominal elastic response. The successively high stress will induce the behavior of failure wave. If further increasing the stress, a ramp wave will be formed.On the poled samples, the reload signal resulted by the the FE→AFE phase transition is observed at first. In addition to this reload signal, when the pressure increases to2.4GPa or much more, it still has the failure wave. Comparing the failure behaviors of the poled PZT95/5with that of unpoled PZT95/5, results show that the delay time in poled PZT95/5is greated than that of unpoled PZT95/5. This difference is resulted by phase transition (FE→AFE) reinforcement effect.Base on the theoretical calculation, the direct current or pulse electric field induced failure of PZT95/5is discussed in this paper, and the current waveforms of PZT95/5under different shock stress have been investigated. The results show that the electric failure dominates the failure behaviors of PZT95/5when the shock pressure is2.0GPa. As the shock stress reaches3.0GPa, which pressure means that the failure wave exists in PZT95/5, and its dielectric strength slightly decreases and equivalent internal resistant decreases to the order of kΩ due to the existence of failure wave in PZT95/5. When the pressure further increased to4.3GPa, not only the internal resistant but also the dielectric strength dramatically decreases. The evolution of the failure wave, such as expansion of microcracks, induces that the dielectric strength and internal resistant of PZT95/5decreases with increasing the shock stress. This point is important to understand the failure behaviors of PZT95/5ceramics under shock compression.更多还原