Room temperature stress-strain hysteresis in Ti₂AlC revisited

Room temperature cyclic compressive testing of high purity fine (FG) and coarse (CG) grained Ti₂AlC were carried out in combination with Resonant Ultrasound Spectroscopy (RUS) tests and post mortem Electron-backscatter Diffraction (EBSD). The results show that the room temperature mechanical response of Ti₂AlC can be divided in four stress regions with distinct underlying mechanisms: (a) Region I (FG: 0 to ≈ 175 MPa; CG: 0 to ≈ 100 MPa) characterized by a linear elastic behavior; (b) Region II (FG: from ≈175 to ≈ 350 MPa; CG from ≈100 to ≈ 200 MPa) in which stress strain hysteric behavior due to reversible dislocation flow in the soft grains; (c) Region III (FG: from ≈350 to ≈ 1100 MPa; CG from ≈200 to ≈650 MPa) accumulation of dislocation walls (DWs) results in cyclic hardening and contribute to larger hysteretic loops and thus a larger energy dissipation per loading cycle than in Region II; (d) Region IV (FG: from ≈1100 MPa to failure, CG from ≈600 MPa to failure) characterized by the occurrence of microcracking that, in addition to the other aforementioned deformation mechanisms, contributes to the energy dissipated in each loading cycle.