Component interaction and thermal damage evolution of HTPB/AP/HMX/Al composite propellant under slow heating conditions

The thermal decomposition behavior and damage evolution of HTPB/AP/HMX/Al composite propellant under slow heating were investigated to clarify component interactions before ignition. Individual oxidizers, stepwise mixtures, and the four-component propellant were analyzed using SEM, XRD, TG-FTIR, and DSC. HMX showed thermally induced phase transformation, probably involving α-HMX formation, accompanied by surface defects and earlier decomposition. AP exhibited two-stage decomposition and progressive pore development extending into the particle interior. Introducing HTPB shifted HMX decomposition from about 280 °C to 260 °C, suggesting that binder pyrolysis products facilitate HMX decomposition. Al further affected gaseous product distribution, likely through heat-transfer enhancement and secondary reactions with oxygen-containing products. The four-component propellant showed three mass-loss stages assigned to HMX decomposition, low-temperature AP decomposition, and high-temperature AP decomposition, indicating progressive interfacial debonding and porous thermal-damage formation.