Oxidation Behavior And Mechanical Properties Of Ti Alloys And Ti-based Composites

The TiAl intermetallic compound is an attractive material for high-temperature structuralapplications. High-Nb TiAl based alloy represents the latest trend of the development of TiAlintemetallic compound. From recent studies, the simplex intermetallic composite has notmany kinds of properties such as good high temperature strength, good creep resistance orexcellent endurant property at the same time. However, if these intermetallic compounds areenforeced by particles or whiskers to be composites, they will have not only their ownproperties, but also excellent synthetical properties. In this paper, a series of High-NbTiAl-based alloys and their composites were made by smelting or hot pressing sintering. Thentheir mechanical properties and oxidation resistance at 900℃or 1000℃/100h in air werestudied. The phase composition of the alloys and the character of the oxidation at hightemperature were analyzed by XRD,SEM (equipped with EDS) and EPMA.Based on the researches above, the conclusions of this paper are as follows:1. Three alloys with different microstructure were made using smelting method by addingdifferent amount of Nb into TiAl alloys, that was Ti-47.5Al-5Nb, Ti-42.85Al-14.3Nb andTi-40Al-20Nb (at%). From mechanical properties test, it's seen that Ti-42.85Al-14.3Nb withsandwich structure is made up ofγ-TiAl andα₂-Ti₃Al, and it has higher yield strength incompressive test, and high ductile fractures at 1373K in tensile property test.2. ZrC particles reinforced Ti-47.5Al-5Nb,Ti-42.85Al-14.3Nb,Ti-40Al-20Nb andTi-30Al-40Nb based composites were made by smelting. The results of oxidation at hightemperature are as follows: ZrC particles don't change the oxidation mechanism of thematrix. And because of the good high-temperature stability, no interface reactions occur. Butaddition of the ZrC makes the surface having many channels good to oxidation diffusion andreduces the oxidation resistance. The oxidation resistance of the TiAl-based intermetalliccomposites is generally worse than their parent material.3. Ti-47.5Al-5Nb and Ti-42.85Al-14.3Nb were made by hot pressing sintering. SiCwhiskers reinforced Ti-47.5Al-5Nb and Ti-42.85Al-14.3Nb were also made by the same way.High temperature oxidation test tells, SiC whisker is good for Al₂O₃ forming at the surfaceand improves the oxidation resistance of the TiAl alloys.