Abstract
Fracture behavior via a flexural test for a newly found CaO–Al2O3–SiO2 (CAS) glass-ceramic (GC) was compared with that of enstatite GC and mica GC, which are well-known GCs with high-fracture toughness and machinability, respectively. By focusing on the nonelastic load–displacement curves, CAS GC was characterized as a less brittle material similar to machinable mica GC, compared with enstatite GC, which showed higher fracture toughness, KIC. The microcrack toughening mechanism in CAS GC was supported by the nondestructive observation of microcracks around the Vickers indentation using the X-ray microcomputed tomography technique. The CAS GC also showed higher transparency than mica GC due to its low crystallinity. Moreover, the precursor glass had easy formability due to its low-liquidus temperature.
Highlights
After the discovery of toughened zirconia ceramics in the 1970s [1], studies to increase the toughness of ceramic materials have received a great deal of attention [2]
We recently studied the mechanical properties of GCs using metallic molybdenum and tungsten particles as the nucleating agents in the MgO–Al2O3–SiO2 (MAS) [21,22] and CaO–Al2O3–SiO2 (CAS) [23,24,25] systems to develop new GCs with superior mechanical properties
The crystalline phase was identified to be hexagonal metastable CaAl2Si2O8 crystals, its exact structure was slightly distorted as shown by detailed analysis using the Rietveld method [36]
Summary
After the discovery of toughened zirconia ceramics in the 1970s [1], studies to increase the toughness of ceramic materials have received a great deal of attention [2]. The so-called “resistant-curve (R-curve)” behavior, which indicates the increase of fracture resistance as the crack extends, is regarded as another important factor and inherent for understanding the toughness of ceramics [2]. One of the simple and easy methods to evaluate the toughness of ceramic materials is a flexural test using samples introducing various types of notches including chevron notch or a single notch. From load–displacement curves of the flexural test, R-curve behavior can be evaluated [8,9]. There is no mechanism to increase the resistance against the propagation of cracks; the R-curve is flat (Figure 1A). If the resistance increases as the crack extends, the load–displacement curve shows nonelastic behavior and the material gradually breaks (Figure 1B). One feels the material as “less brittle” or “tough”
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