MEASUREMENT OF THE FRACTURE-TOUGHNESS OF NI3GE USING SMALL DISK-SHAPED SPECIMENS

The fracture toughness of the ordered intermetallic compound Ni3Ge (L1(2)) was measured using the controlled-flaw method in conjunction with the miniaturized disk-bend test. The specimens used in these experiments were 3 mm in diameter and varied in thickness from 150 to 450 mu m. They were indented using a Vickers pyramid indenter to indention loads varying from 9.8 to 88.2 N. Ni3Ge does not experience indentation cracking at any indentation load, but postmortem examination of the fractured specimens indicated that fracture generally started at the indentation for indentation loads exceeding 38.2 N. The fracture toughness was determined using a straightforward graphical procedure involving an empirical R-curve equation and established fracture-mechanics equations, in conjunction with a few measurements of critical crack lengths to obtain values of several important constants required for the analysis. The fracture toughness is 7.9 +/- 1.0 MPa m(1/2). The significance of this value is discussed in the context of data on other Lit ordered intermetallic compounds. It is demonstrated that the influence of the residual stress produced by indentation is crucial to the success of the method.