Laser ignited burning behavior and mechanism of TiAl alloy

The ignition and combustion behaviors of titanium aluminide (TiAl alloy) were studied by using laser oxygen concentration experimental method combined with ultra-high temperature infrared thermometer, high-speed camera in-situ observation, scanning electron microscopy and X-ray diffraction. The formation and movement laws of the molten body, types and structural characteristics during the combustion process were revealed, and the molten body mechanism was further explored. The results show that the critical conditions of laser power and oxgyen concentration for the ignition and sustained burning of TiAl alloy follow parabolic and parabolic+linear laws, respectively, which are significantly higher than those of near α high temperature titanium alloy, indicating the better flame retardant properties of TiAl alloy. The ignition temperature of TiAl alloy is higher than the melting point. During the ignition period, the partial melting of the matrix causes the transition of Al element from internal oxidation to external oxidation. The oxides formed during the sustained burning stage are characterized as Al2O3, Al2Ti7O15, Al2TiO5, and Al6Ti2O13 phases from the inner side to the burning surface. The continuous network Al2O3 layer formed in the fusion zone can hinder the movement of the melt. The Ti-Al-O ternary phase formed in the combustion zone can improve the stability of the Al2O3 protective layer by reducing the decomposition pressure of Al2O3, thus leading to the better flame retardant performance of TiAl alloy.