Defect structures and room-temperature deformation of single crystals of the mu-phase compound Fe7Ta6 investigated by micropillar compression

The deformation behavior of single crystals of the mu-phase compound Fe₇Ta₆ has been investigated by micropillar compression at room temperature as a function of crystal orientation and specimen size. Grown-in planar defects have also been investigated to avoid the confusion of grown-in defects and those introduced by deformation. (0001)<2$\bar{1}$$\bar{1}$0> (basal a) slip is identified to be the dominant slip system operative at room temperature. The CRSS for basal a slip is as high as 1.24 GPa. Direct observation of the dislocation core indicates that basal a slip in Fe₇Ta₆ of the mu-phase occurs by a synchroshear mechanism exclusively within the triple layers of the MgCu₂ (Laves-phase) block layer, so that one form of the MgCu₂ block layer is transformed into another (twin-related) by the passage of the leading synchro-Shockley partial dislocation. In addition to planar faults on the (0001) basal plane formed when a different form of the MgCu₂ block layer is incorporated in the [0001] stacking sequence (stacking faults and twins) and when a block layer either of the MgCu₂ or Zr₄Al₃ type is inserted consecutively or deleted, planar faults on {1$\bar{1}$02} and {1$\bar{1}$0$\bar{1}$} pyramidal planes are identified. These {1$\bar{1}$02} and {1$\bar{1}$0$\bar{1}$} pyramidal faults are found, for the first time, to be introduced to accommodate lattice incompatibility generated by the introduction of an intergrowth fault on the (0001) basal plane.