The intrinsically low toughness and high brittleness of diboride ceramics are major limitations restricting their widespread application. Toughness can be enhanced through increased configurational entropy; however, the physical mechanisms underpinning this entropy-induced toughening remain poorly understood. In this study, a comprehensive approach from element screening to mechanistic elucidation and experimental validation is undertaken to address these gaps. First, a theory-guided element screening strategy is employed. Starting from dilute solid-solution models and integrating calculation of phase diagrams (CALPHAD) composition–property fitting, Ta, Nb, Mo, Hf, and V are identified for their synergistic optimization of hardness and toughness. Subsequently, the evolution of toughness with increasing configurational entropy is assessed using bulk modulus/shear modulus (B/G), fracture toughness (K_IC), and related metrics. The calculations are validated against available experimental data, revealing an almost monotonic trend, with the six-component system exhibiting a K_IC exceeding 5.8 MPa·m^1/2—approximately double that of the single-component counterpart. A systematic analysis of the lattice distortion and crystal orbital Hamilton population is performed for diborides containing two to six alloying elements. From a bond-strength perspective, the toughening mechanism originates from increased thermodynamic disorder, which broadens and flattens the bond-strength distribution, giving rise to a “bond-strength trap”. Experimental validation is conducted on the (TiTa)B₂ and (TiNb)B₂ systems with pronounced bond-strength contrast, as well as the ternary (TiTaNb)B₂ system. The results corroborate the predicted electronic bonding evolution, while further analysis of phonon force constants and stacking fault energies indicates that the synergy between strengthened M–B bonds and reduced dislocation slip barriers underpins the enhanced toughness.

The generation and evaluation of severely high thermal stress (σ) is known to be responsible for failure of thermal barrier coatings (TBCs) during thermal cycling. It is crucial and challenging to capture fluctuations in σ caused by the phase transition, which has motivated us to develop a high-throughput multiscale evaluation method for σ in TBCs that considers the phase transition of the top ceramic materials by coupling first-principles calculations with finite element simulations. The method quantitatively evaluates and visualizes σ of the real TBC structure under thermal cycling by multifield coupling. Additionally, the thermophysical properties calculated by the first-principles calculations consider the effects of temperature and phase transition, which not only reduces the cost of obtaining data but also has a more physical connotation. In this work, rare earth tantalites (RETaO₄) are introduced as ceramic layers, and the results demonstrate that σ undergoes a rapid escalation near the phase transition temperature (T_t), particularly in the TBCs_GdTaO₄ system, where it rises from 224 to 435 MPa. This discontinuity in σ may originate from the significant alterations in Young’s modulus (increase by 27%–78%) and thermal conductivity (increase by 53%–146%) near T_t. The TBCs_NdTaO₄ and TBCs_SmTaO₄ systems exhibit noteworthy temperature drop gradients and minimal σ fluctuations, which are beneficial for extending service lifetime of TBCs. This approach facilitates the prediction of failure mechanisms and provides theoretical guidance for the reverse design of TBC materials to obtain low thermal stress systems.