Characterization and Toughening Mechanism of Crystallization of Canasite Glass-ceramics

doi:10.15541/jim20150063

Abstract

Abstract:

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.

Key words: R2O-CaO-SiO2-F glass-ceramics, canasite, crack propagation, toughening mechanism

CLC Number:

TQ174

LI Yao-Hui, WANG Jin-Zhen, HUANG You-Rong. Characterization and Toughening Mechanism of Crystallization of Canasite Glass-ceramics[J]. Journal of Inorganic Materials, 2015, 30(9): 977-983.

Figures/Tables 11

Fig. 1 Diagram of the heat treatment schedule

Fig. 2 DSC curves of different RCSF casting glasses

Fig. 3 XRD patterns of glass-ceramics after one-step heat treatment

Fig. 4 XRD patterns of glass-ceramics after two-step heat treatment

Fig. 5 SEM images of glass-ceramics after one-step (a) and two-step (b) heat treatment nsert is the enlarged image of the bladed morphology

Table 1 Mechanical properties of the RCSF glass and glass-ceramics (GC)

Sample	Hardness, H/GPa	Modulus, E/GPa	Flexural/MPa	Impact toughness / (kJ·m^-2)	Fracture toughness /(MPa·m^1/2)
Casting glass	7.48±0.21	73.66±1.78	64~69	1.32	0.77±0.06
GC-one-step	7.32±0.05	77.12±1.13	83~97	2.56	1.17±0.06
GC-two-step	7.52±0.31	77.82±3.23	109~119	6.70	1.72±0.45

Fig. 6 SEM images of crack propagation of RCSF casting glasses Insert shows the morphology of indentation

Fig. 7 SEM images of crack propagation of RCSF glass- ceramics after one-step heat treatment sert shows the morphology of indentation

Fig. 8 SEM images of indentation of RCSF canasite glass- ceramics after two-step heat treatment

Fig. 9 SEM images of crack propagation of RCSF canasite glass-ceramics after two-step heat treatment

Fig. 10 Thermal expansion curves of casting glass and canasite glass-ceramics

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