Room-temperature deformation of single crystals of the sigma-phase compound FeCr with the tetragonal D8b structure investigated by micropillar compression
Kyosuke Kishida, Masaomi Okutani, Hirotaka Suzuki, Haruyuki Inui, Martin Heilmaier, Dierk Raabe
Abstract
The deformation behavior of single crystals of the sigma-phase compound FeCr with the tetragonal D8b structure has been investigated by micropillar compression at room temperature as a function of crystal orientation and specimen size. In spite of the repeatedly reported brittleness, plastic flow is observed at room temperature for all loading axis orientations tested. Three slip systems, {100}[001], {100}<010> and {111}<01¯1> are newly identified to be operative at room temperature depending on the loading axis, in addition to {110}[001] slip we previously identified. The CRSS values for all the identified slip systems are very high exceeding 1.3 GPa and decrease with increasing specimen size, following an inverse power-law relationship with a very small power-law exponent. Similarly to {110}[001] slip, {100}[001] slip is confirmed to be carried by the motion of [001] zonal dislocations through atomic-resolution scanning transmission electron microscopy imaging of their core structures. <010> dislocations gliding on {100} are confirmed to dissociate into two collinear partial dislocations, while <01¯1> dislocations gliding on {111} to dissociate into three collinear partial dislocations. The fracture toughness values estimated by micro-cantilever bend tests of chevron-notched micro beam specimens are indeed very low, 1.6∼1.8 MPa·m1/2 (notch plane // (001) and (100)), indicating significant brittleness of sigma FeCr.