A small-specimen investigation of the fracture toughness of Ti<Subscript>5</Subscript>Si<Subscript>3</Subscript>

The fracture toughness of the refractory hardmetal TisSi3, with a grain size between 5 and 6 lam, was measured using the controlled-flaw method in conjunction with the miniaturized disc-bend test. The specimens used in these experiments were 3 mm diameter and varied in thickness from 150-450 lam. They were indented using a Vickers pyramid indentor to indention loads varying from 2.9-79.2 N. Indentation cracking was experienced at all indentation loads, and R-curve behaviour was exhibited. The fracture toughness was determined to be 2.69 + 0.21 MPam 1/2 using a straightforward graphical procedure involving an empirical R-curve equation. This value is almost 30% higher than that of similar material (2.1 MPam 1/2) with a larger grain size, suggesting that the fracture toughness of this material, which fractures intergranularly, might be grain-size dependent.