In-situ crack propagation dynamics in multicomponent ultra-high temperature carbides

Solid-solutioning in multicomponent ultra-high temperature ceramics (MC-UHTCs) has been shown to improve their thermo-mechanical properties unattainable by conventional UHTCs. Herein, MC-UHTCs are synthesized by varying the components from binary up to quaternary in (Ta,Nb,Hf,Ti)C system using spark plasma sintering (SPS). The present work identifies real-time quantitative failure events such as cracking, crack propagation and fracture using a high-speed camera during 4-point flexural testing in MC-UHTCs. Quaternary UHTCs showed the highest flexural strength of 726 MPa, representing an improvement of ∼166 % over binary and ∼ 24 % over ternary UHTCs. This has been attributed to processing-induced solid solutions and sub-micron feature defects, such as dislocations, intergrain twisting, and plasticity, revealed from the high-resolution microscopy. Crack-propagation rate significantly depreciated over 37 times in quaternary UHTC. An improvement in crack shielding is observed in quaternary UHTC, showcasing the highest fracture toughness at 4.7 MPa·m^0.5, surpassing binary and ternary UHTCs by ∼270 % and ∼ 166 %, respectively. The lower mechanical properties in binary UHTCs are also attributed to high porosity. Post-fracture microstructural analysis supports this finding due to the presence of river patterns contrived by crack-arrest at grain boundary or crack re-initiation in different orientations. The study reveals the exceptional damage tolerance of quaternary UHTCs over other compositions, making them a potential structural material for hypersonic applications.