Kink Formation through Creep Deformation and Possibility of Kink Strengthening in Ti<sub>3</sub>SiC<sub>2</sub>-MAX Phase

Abstract

Kink formation and kink strengthening mechanisms were examined in the polycrystalline Ti3SiC2-MAX phase prepared by a spark-plasma-sintering technique. The creep behavior tested by compression at 1200℃ showed two deformation regions depending on the applied stresses; at lower stresses of <120 MPa, the stress exponent n exhibited ≈1.8, whereas at higher stresses, it exhibited n ≥ 6.0. The creep behavior can be ascribed to grain boundary sliding mechanism for the lower stresses with n ≈ 1.8 and dislocation-related creep mechanisms for the higher stresses with n ≥ 6.0. The kink bands were frequently observed to form in the grains deformed only at the higher stresses when its basal plane inclined by about 10-20° against the compressive axis. This suggests that the kink bands might be formed only when two factors of the large stresses acting on the basal plane and the resultant dislocation activities were satisfied. Nanoindentation tests conducted around the formed kink boundaries showed that the hardness increased linearly with decreasing in the distance from the kink boundaries and showed higher values around the kink boundaries. Since the kink boundaries blocked the slip line caused by the nanoindentation, those become a resistance against the dislocation motion caused by the indentation deformation. This suggests that the kink boundaries would be contributed to improve the mechanical properties of the Ti3SiC2-MAX phase.