高温高性能Bi4Ti3O12基陶瓷在循环压缩载荷下的铁弹行为及压电疲劳研究

This project caters to the urgent need for high-temperature piezoelectric materials proposed by the technological development of weapon equipments and experimental test, to further investigate their ferroelastic behavior and piezoelectric fatigue as mechanical problems, based on the development of bismuth layer structured ferroelectric/piezoelectric ceramics as new materials. The experiment choosed Bi4Ti3O12-based ceramics with high temperature and performance as the research target, with applying a cyclic compressive load on the material by DMA, dertemining the accumulation value of ferroelastic strain, observing the orientation state of ferroelastic domains on their compressed surfaces by EBSD, characterizing the evolution of their crystalline structures, mechanical and electrical properties, establishing the life-prediction model of piezoceramics by fitting the curve of piezoelectric constant-cyclic number. The research will illuminate the influencing mechanisms of the polorization state, load condition and surrounding temperature on the accumulating process of ferroelastic strain for materials, establish the theoretical mode of ferroelastic domain switching and analyze the corresponding frequency and temperature effect, obtain the evolution rule of structures and properties of materials, reveal the fatigue mechanism of piezoelectric property for the material subjected to cyclic compressive load. This project is located in the cross research filed between material science and solid mechanics, whose results could tamp the base for the engineering application of high-temperature piezoceramics, as well as broaden the fatigue research of functional materials.

本项目面向武器装备及实验测试技术发展对高温压电材料的迫切需求，在铋层状结构铁电/压电陶瓷这一新材料研制的基础上，进一步研究其在循环压缩载荷下的铁弹行为及压电疲劳等相关力学问题。实验选取高温高性能Bi4Ti3O12基陶瓷为对象，通过DMA对材料加载循环压缩载荷；依靠XRD确定材料铁弹应变的累积值大小；利用EBSD观察材料压缩表面上铁弹畴的取向状态；表征材料在应力疲劳过程中晶体结构及力学、电学性能的变化；拟合压电常数-循环周次曲线建立压电陶瓷的寿命预测模型。研究将阐明极化状态、载荷条件以及环境温度对材料铁弹应变累积过程的影响机制；建立铁弹畴转向的理论模型并分析其频率温度效应；获取材料在铁弹畴转向过程中结构和性能的演变规律；揭示材料在循环压缩载荷下压电性能的疲劳机理。本项目立足材料学与固体力学的交叉研究领域，研究成果既可以为高温压电陶瓷的工程应用夯实基础，也可以为功能材料的疲劳研究拓展方向。

本项目面向重大技术装备高温振动测量器件的研发对高温压电材料的迫切需求，在铋层状结构铁电陶瓷这一新材料研制的基础上，进一步研究了其在循环压缩载荷下的铁弹行为及压电疲劳等相关力学问题。项目首先通过W/Cr离子共掺杂和氧化物固相反应成功制备出一种兼具高居里温度和高力、电性能的Bi4Ti3O12基铁电陶瓷（以下简称BTWC陶瓷），然后分别针对BTWC陶瓷在循环应力下的疲劳断裂行为、在热冲击下的裂纹扩展行为、在压缩载荷下的铁电畴90o翻转（即“铁弹”）行为以及陶瓷的三维电畴结构特征等方面展开了深入研究。一些重要数据和关键结论如下：（1）通过烧结温度调控成功制备得到一种BTWC陶瓷样品，其力、电性能表现优异：Tc=640 oC；d33=28 pC/N；kp=8.97%；Y=69 GPa；KIC=1.94 MPa•m1/2；σc=365 MPa。（2）在循环应力作用下，BTWC陶瓷内部的固有缺陷（微裂纹、孔洞、杂相颗粒等）引发疲劳裂纹失稳扩展、从而导致其快速断裂呈现低周疲劳行为。（3）受热冲击后，BTWC陶瓷的剩余强度在300~400 ℃温差区间内下降接近50%。根据TSR模型计算得到其临界热冲击温度为356 ℃，正好位于该区间范围内，并通过SEM观测到了宏观热裂纹的出现。（4）在单轴压缩载荷下，BTWC陶瓷的压缩应力-应变曲线存在由铁弹变形引起的非线性区域。铁弹变形主要由压缩载荷作用下的铁电畴90o翻转行为所主导，新畴萌生与畴壁移动的数量越多，铁弹变形程度越大，产生的宏观应变也越大。（5）BTWC陶瓷晶粒存在条状或针状的91o畴壁与90o畴壁，也存在少量的不规则9o畴壁与180o畴壁以及带电的171o畴壁。本项目立足材料学与固体力学的交叉研究领域，研究成果不仅为重大技术装备高温振动测量器件的研发提供了一种高温压电陶瓷材料，也为电子功能材料的细观力学和断裂力学研究拓展了新方向。