Room-temperature deformation of single crystals of the sigma-phase compound FeCr with the tetragonal D8b structure investigated by micropillar compression

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.