High Temperature Oxidation Behavior Of Quasi-continuous Network Ti₅Si₃/TiAl Composites

Due to the low density, relatively high specific stiffness, high specific strength and high specific modulus, Ti Al based alloy has become very promising applied as high- temperature structural materials. To enhance the strength, toughness and oxidation resistance, second phase is introduced into the Ti A l matrix. In this article, quasi-continuous network distributed Ti5Si3/Ti A l composites with a volume content of 4.5vol.% and 9vol.% respective ly were manufactured by pressure infiltration and hot-pressure sintering. Then the composites were treated to be lamellar and the oxidation behavior at high temperature was investigated.Analysis methods like O M, XRD and SEM were utilized to observe and analyze the microstructure of the composites.The matrix of the fabricated composites was duplex Ti A l alloy with Ti3 Al, and the reinforcement Ti5Si3 was network distributed. Especially, the matrix of 9vol.%Ti5Si3/duplex Ti Al contained high- content Si. The results of the oxidation experiments at the temperature range of 750℃ to 850℃ indicated that with the volume fraction of Ti5Si3 increasing, the oxidation mass gain decreased and the oxidation index factor n increased, meanwhile, the oxidation activation energy enhanced by 90 k J·mol-1. The difference of the oxidation between Ti A l and Ti3 Al reduced and network distributed oxide film tended to be more evident. Besides, the grain size of at the oxidation surface decreased and the bonding of the oxide film and the matrix become better. It was also found that Ti5Si3 oxidation did not occur and the oxidation products of the composites were Ti O2 and Al2O3. The ult imate oxide films were Ti O2 layer, mixed layer of Al2O3 with small amount of Ti O2 and mixed layer of Ti O2 with small amount of Al2O3 from outside to inside respectively.After 4.5vol.%Ti5Si3/duplex Ti Al composites were treated to be lamellar, the microstructure become more uniform, while the reinforcements were still network distributed. The oxidation experiments after the lamellar treatment revealed that the oxidation mass gain decreased while the oxidation index factor n increased. And the oxidation activation energy was 271.54 k J·mol-1, elevated by 43.66 k J·mol-1 compared to the untreated composites. Meanwhile, it was seen that the grain size of the oxidation products was refined and the thickness of the oxide film was reduced after the lamellar treatment. The ultimate oxide films included two layers: the inside one was the mixed layer of Al2O3 and Ti O2, and the outside one was the loose Ti O2 layer. And the transition layer contained large content of Al2O3.