LOAD AND DIRECTIONAL EFFECTS ON MICROHARDNESS AND ESTIMATION OF TOUGHNESS AND BRITTLENESS FOR FLUX-GROWN LABO3 CRYSTALS

Results of microhardness measurements on (100) and (110) planes of flux-grown LaBO3 crystals, in the applied load range of 10-100 g, are presented. The microhardness was found to decrease with increasing load in a non-linear manner. By applying Hays and Kendall's law, the materials resistance pressure and other constants of the equation could be calculated. Hardness anisotropy, showing periodic variation of H(v) with the maxima and minima repeating at every 15-degrees change in orientation of the indentor, is described and discussed. H(max)/H(min) are estimated as 1.14 and 1.06 for (100) and (110) planes, respectively. The fracture toughness values, K(c), determined from measurements of crack lengths, are estimated to be 1.6, 1.7 MN M-3/2 (for (100) planes) and 1.2, 1.5 M N m-3/2 (for (110) planes) at 90 and 100 g loads, respectively. The brittleness index, B(i), is estimated as 4.6, 4.0 muM-1/2 (for (100) planes) 6.0, 4.6 mum-1/2 (for (110) planes) at 90 and 100 g, loads respectively.