硅碱钙石微晶玻璃的析晶特性及其增韧机理研究

Characterization and Toughening Mechanism of Crystallization of Canasite Glass-ceramics

通过调整热处理工艺制备了不同结构的R2O-CaO-SiO2-F系硅碱钙石微晶玻璃,分析了析晶特性和力学性能,重点研究以硅碱钙石为主晶微晶玻璃的裂纹扩展机制及增韧机理。结果表明,基础玻璃在低温处理时首先析出CaF2微晶作为异质晶核,一步法处理后得到岛屿状硬硅钙石/硅碱钙石复相微晶玻璃,两步法处理后得到了力学性能优异、具有板条交错结构的硅碱钙石微晶玻璃。研究发现,硅碱钙石微晶玻璃的裂纹扩展受到周围板条晶体取向及晶界影响,存在穿晶断裂和沿晶断裂两种模式扩展,呈现出随机取向的折线或台阶状裂纹路径。其中具有一定长径比的板条状硅碱钙石具有较好的桥联作用,承载补强效果显著,此外硅碱钙石晶体与玻璃相之间存在的残余应力,有利于缓解裂纹应力集中以及增加裂纹扩展能。即,硅碱钙石微晶玻璃优异的力学性能是各种增强和增韧机制综合作用的结果。

The R2O-CaO-SiO2-F system glass-ceramics were prepared through different heat treatment schedules. The crystallization, microstructure and mechanical properties, especially the crack propagation and toughening mechanism of the canasite-based glass-ceramics, were studied. The results show that CaF2 crystallites precipitate firstly during heat treatment at low temperature. After one-step heat treatment block-like xonotlite/canasite complex phases can be obtained. And after two-step heat treatment, the canasite-based glass-ceramics, composed of particularly interlocking blade-like crystals, are obtained with excellent mechanical properties. The micrographs suggest the orientation and interface of canasite crystals radically change the crack propagation, showing intercrystalline and transcrystalline cracks forming random-step or fold-like line. Based on these results, the blade-like canasite crystals at certain slenderness ratios, display favorable anti-cracking effect because of their bridging toughen mechanism. In addition, the residual stress between matrix and crystals also benefits relaxation of stress and deflection of crack. So, the excellent mechanical properties of the as-prepared glass-ceramics are resulting from multiple toughening mechanisms.