Effect of Subcritical Crack Growth on Mechanical Properties of Porcelain for Metal-ceramics

Abstract

Using three kinds of porcelain for metal ceramics(PFM), the effect of subcritical crack growth(SCG)on mechanical properties was investigated by measuring fracture toughness K_IC and four points bending strength in both dry and corrosive surroundings. The K_IC in corrosive solutions(water, 0.9wt% NaCl and 50wt% acetic acid solution)and the bending strength in distilled water were decreased remarkably compared with dry condition. From these facts, it was considered that the SCG of PFM would be promoted by water, and would also take place in oral conditions. Furthermore, in order to elucidate the relations between SCG and the PFM textures, the load-displacement curve in the midst of SCG was measured, and the polishedetched surfaces and the failure surfaces were observed. As a result, it was found that although the PFM with large lucite crystals had a low bending strength even when dry because of cracks generated around the crystals, the K_IC was greater than that of other PFM. This indicates that these cracks may provide resistance against SCG.