MICROMECHANICAL TOUGHNESS TEST APPLIED TO NIAL

A microscratch technique for determining the fracture toughness of bri ttle intermetallics is presented. Advantages include very small sample sizes and multiple tests on a single, flat polished surface. The frac ture toughnesses of single-crystal NiAl in {001}[100], {001}[110], {11 0}[110], and {110}[100] crack orientations were evaluated using this t echnique. The results of the scratch testing are compared with measure ments on small compact tension samples. Also, transmission electron mi croscopy is used to help explain the dislocation character of the resu lting plastic zones in samples tested. Lastly, a model for determining the dislocation velocity during nanoindentation is presented to help understand the ductile-brittle transition temperature of semibrittle m aterials.