Kink Formation through Creep Deformation and Possibility of Kink Strengthening in Ti₃SiC₂ MAX Phase

Abstract

Kink formation and kink strengthening mechanisms were examined in the polycrystalline Ti₃SiC₂ MAX phase prepared by a reaction sintering process using a spark-plasma-sintering machine. The creep behavior tested by compression at 1200°C showed two deformation regions depending on the applied stresses; at stresses lower than 120 MPa, the stress exponent n exhibited ≈1.8, whereas at higher stresses, it exhibited n ≥ 6. The creep behavior can be ascribed to grain boundary sliding mechanisms for the lower stresses with n ≈ 1.8 and to dislocation-related creep mechanisms for the higher stresses with n ≥ 6. The kink bands were frequently observed to form in the grains deformed only at the higher stresses when its basal plane was inclined by about 10–20° against the compressive axis. This suggests that the kink bands might be formed only when two factors of the high stresses acting on the basal plane and the resultant dislocation activities were satisfied. Nanoindentation tests conducted around the formed kink bands showed that the nanohardness linearly changed with the distance from the kink bands and showed higher values around the kink bands. Since the kink bands blocked the slip line caused by the nanoindentation, those become obstacles against the dislocation motion caused by the indentation deformation. This suggests that the kink bands would contribute to improving the mechanical properties of the Ti₃SiC₂ MAX phase.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 439–448.

(a) Low magnification SPM image of nanoindentations #0–#9 tested at the kink-formed grain; the arrows indicate kink boundaries of KB① and KB②. (b) Enlarged SPM image of the nanoindentations #2 and #4. (c) Nanohardness H_n plotted as a function of the distance L from the nearest kink boundary (KB) along the basal plane.