HIP焼結Si_3N_4における表面層の破壊じん性評価

概要

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To clarify the validity of evaluation of the threshold value of fracture toughness K_<th> on the surface layer of ceramics by sphere indentation test, sphere indentation tests with indenters of various diameters 2R were performed using Si_3N_4 specimens made by HIP-sintering and the stress intensity factor K_I for surface crack under ball on plate contact loading was numerically obtained. The crack length c_i was estimated from experimental results using K_I, where c_i is the length of the crack leading to a ring crack and the conditions for ring crack initiation were assumed to be K_I>K_<th>. It was shown that the average values of c_i increased with increases in 2R in the case of small 2R, but the averages of c_i gradually approached a constant value in cases with a large 2R. The constant value of c_i was estimated as 8-9μm using K_<th>=5.3 MPa・m^<1/2> and was almost equivalent to the grain size of the test material.
2005-08-25