RESUMO
The plastic deformation behavior of single crystals of α-Nb5Si3 with the tetragonal D8 l structure has been investigated by micropillar compression at room temperature as a function of crystal orientation and specimen size. Three slip systems, (001)<010>, {110}<1 1 - 0> and {0 1 - 1}<111>, 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.
RESUMO
Micropillar compression tests of Ti5Si3 single crystals were conducted at room temperature as a function of loading axis orientation and specimen size in order to investigate their room temperature plastic deformation behavior. Plastic flow by the operation of three deformation modes, {1[Formula: see text]00}[0001], {2[Formula: see text][Formula: see text]2} < 2[Formula: see text][Formula: see text][Formula: see text] > and {1[Formula: see text]01} < 2[Formula: see text][Formula: see text][Formula: see text] > slip were observed in [2[Formula: see text]05]-, [0001]- and [4[Formula: see text][Formula: see text]0]-oriented micropillar specimens deformed at room temperature, respectively. The CRSS values were evaluated to be very high above 2.7 GPa and were confirmed to increase up to about 6 GPa with the decrease in the specimen size. The fracture toughness values are evaluated to be 0.45 MPa m1/2 (notch plane // (0001)) and 0.73 MPa m1/2 (notch plane //(1[Formula: see text]00)) based on the results of micro-cantilever bend tests of chevron-notched specimens. The fracture toughness values are considerably lower than those for D8l-Mo5SiB2 and D8l-Nb5Si3 evaluated by the same method, indicating the inherent brittleness of binary Ti5Si3 compared to the other transition-metal silicides of the TM5Si3 type (TM: transition-metal).
