単結晶LiFの破壊じん性(<小特集>セラミック材料小特集)

概要

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The fracture toughness(K_<Ic>) of LiF single crystal was evaluated by the indentation microfracture technique (IMT) and the indentation strength technique (IST) at room temperature. The indentation crack on the (001) of <100> specimen resulted in the lowest K_<Ic> of about 0.5MNm^<-1.5> in both IMT and IST because the {110} is the preferred cleavage plane of this crystal. The Vickers hardness (H_V) for the (001) was obtained to be about 0.9 GPa. A fairly smooth planar was provided by the crack-propagation originated from the initial crack on the (001) of <110> specimen. However, cracks in the <110> (11^-0) specimen became eventually angled at 45° to the original flaw. As the result, K_<Ic>≒0.7 MNm^<-1.5>, H_V≒0.9 GPa for the former and K_<Ic>≒0.8 MNm^<-1.5>, H_<V>≒1.2 GPa for the latter. The indentation crack on both the (11^-0) and (1^-1^-2) of <111> specimen didn't propagate along the extention of Vickers indentation diagonal and produced the rough surface after fracture. The K_<Ic> values for <111>(11^-0) and <111>(1^-1^-2) were determined to be 1.5 and 1.8 MNm^<-1.5>, respectively, while H_V≒1 GPa. These results indicate that the K_<Ic> of single crystals is affected by the cleavability of crystals and the geometric configuration between the cleavage plane and the direction of crack propagation.
社団法人日本材料学会の論文
1986-01-15