Effect of B4C reinforcement on microstructure, residual stress, toughening and scratch resistance of (Hf, Zr)B2 ceramics

Effect of B4C addition on the lower damage tolerance of spark plasma sintered (Hf, Zr)B-2 based ceramics has been elucidated. Increased densification (from 89% to 95%) with B4C addition has elicited hardness and elastic modulus increase from 25 GPa to 38 GPa (52%) and 439 GPa-635 GPa (45%), respectively. Systematic 3-9 vol% B4C addition resulted in an increased fracture toughness (from 2.2 MPa m(0.5) - 4.4 MPa M-0.5) and flexural strength (from 320 MPa to 357 MPa) compared to that of (Hf, Zr)B-2 due to synergistic effect of solid solutioning and compressive residual stresses generated around reinforcement. The decreased wear rate (from 0.163 mm(3)/N.m to 0.061 mm(3)/N.m) with optimal B4C addition, affirms enhanced damage tolerance of (Hf, Zr)B-2 composite. Enhanced cracking and fracture in (Hf, Zr)B-2 shifts to abrasion induced restricted micro-cracking as microscratch wear mechanism with B4C addition. Estimated elastic-modulus and extracted scratch-hardness are correlated with microstructural attributes of porosity, phase content and residual stress in (Hf, Zr)B-2 composites.