The influence of α/β phase constitution on the combustion behavior of TC25G alloy under oxygen-enriched atmosphere

Although the phase constitution significantly influences mechanical properties in α + β titanium alloys, however its role in the combustion behavior remains poorly understood. Herein, the influence of α-phase content, which controlled by annealing treatment, on the critical ignition conditions and combustion velocity of TC25G alloy was investigated by using promoted ignition-combustion (PIC) tests. Results indicate that while the critical ignition pressure and temperature show minimal variation but the combustion rate increases markedly by 132.6% from 9.38 mm/s to 21.82 mm/s as the α-phase content rises from 69.1% to 94.6%. Microstructural analysis reveals that dissolved oxygen in the melting zone increases from 20 to 35 at % and Mo segregation at melting/heat-affected zone interface is significantly suppressed with higher α-phase content. A combustion kinetic model containing α and β phases is proposed and shows excellent agreement with the experimental data (R 2 =97.8%). The accelerated combustion rate is attributed to the reduced elemental segregation at solid-liquid interface and increased heat release from the melting pool. This work brings to a new insight into the material design and selection of titanium alloy for high-temperature services.