Micropillar compression deformation of single crystals of α-Nb5Si3 with the tetragonal D8l structure

The plastic deformation behavior of single crystals of α-Nb5Si3 with the tetragonal D8l structure has been investigated by micropillar compression at room temperature as a function of crystal orientation and specimen size. Three slip systems, (001), {110} and {0$$\bar 1$$1}, are found to be operative in micropillar specimens of α-Nb5Si3 single crystals at room temperature, as in the case of isostructural Mo5SiB2. The CRSS values obtained for the three slip systems are extremely high above 2.0 GPa and exhibit the ‘smaller is stronger’ trend, which can be approximated by the inverse power-law relationship. The fracture toughness evaluated by single-cantilever bend testing of a chevron-notched micro-beam specimen is 1.79 MPa m1/2, which is considerably lower than that (2.43 MPa m1/2) reported for isostructural Mo5SiB2. The selection for the dissociation schemes and possible glide planes for dislocations of the three slip systems is discussed based on generalized stacking fault energy (GSFE) curves theoretically calculated by first-principles calculations.