Mechanical properties degradation mechanism in melt-cast explosives under thermal cycling: Interfacial dissolution and recrystallization

2,4-Dinitroanisole (DNAN)-based melt-cast explosives, particularly the DNAN/Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)/3-Nitro-1,2,4-triazol-5-one (NTO) composite, exhibit excellent high-overload performance. However, thermal cycling near the melting point of DNAN induces interfacial micro-damage, deteriorating mechanical properties. Dynamic Mechanical Analysis and Split Hopkinson Pressure Bar experiments revealed that after thermal cycling at 75 °C, the storage modulus decreased by 12.8% and dynamic compressive strength declined by 7.99%, indicating irreversible damage. Micro-Computed Tomography and Scanning Electron Microscope characterizations showed the micro-defect volume fraction doubled (from 0.81% to 1.63%) alongside the formation of numerous needle-like crystals, linking interfacial damage to sharp defects. In-situ X-ray Diffraction and optical microscopy revealed that NTO undergoes significant dissolution within molten DNAN (22 wt%) and recrystallizes into needle-like structures upon cooling, whereas HMX dissolution is minor (8 wt%). Density Functional Theory-based molecular dynamics simulations elucidated the molecular origin: NTO's planar structure forms a stable bidirectional hydrogen bond network with DNAN. Compared to HMX, NTO exhibits a 34.8% lower dissolution barrier, higher interfacial binding energy (−2.09 eV), and significant electron transfer (356.68 e), explaining its preferential dissolution and needle growth. This study links macroscopic degradation to mesoscopic structural evolution and molecular mechanisms, providing a theoretical basis for designing high-overload-resistant explosives.