Study On Microstructure And Property Of Multi-component TiAl Based Alloy With High Nb Content

The as-cast and heat treated microstructure as well as high temperature oxidation resistance of TiAl based alloy with high Nb content was investigated by changing relative amount of Mo or Nb alloying elements. Heat treatment processing was given as1325℃/4h/FC+900℃/30min/ AC, high temperature oxidation of these alloys were studied by the cyclic oxidation behaviors at 900℃ in static air. Observation and analysis of phase,oxidation surface and oxide scale was investigated by the optical microscope(OM), scanning electronic microscope(SEM), X-ray diffraction(XRD).Studies show that the as-cast microstructure of two kinds of alloys of Ti-45Al-xNb-1Mo-0.2B(x = 6, 7, 8)(at.%) and Ti-45Al-7Nb- yMo-0.2B-0.1Y(y=0,1,2)(at.%), which are near lamellar microstructure. After homogenization treatment of1325℃/4h/FC+900℃/30min/AC, the heat treated microstructure of Ti-45Al-xNb-1Mo-0.2B(x = 6, 7, 8) is full lamellar microstructure and the heat treated microstructure of Ti-45Al-7Nb- yMo-0.2B-0.1Y(y=0,1,2) is still near lamellar microstructure.In addition, with Nb alloying element added amount increasing, the lamellar colonies size of the kind of alloy had become a little larger, the size of lamellar colonies is larger. The addition of Mo refine(α2+γ) lamellar colonies to some degree, and lamellar colonies became thicker with the increased amount of Mo addition.The addition of Nb alloying element had a great influence on high temperature oxidation resistance of TiAl based alloy with high Nb content and reduced high temperature oxidation rate. With added amount increasing, Nb alloying element made oxide film structure becomes compact, enhanced adhesion between oxide film and substrate and oxide film fell off for a relative long time. Due to the addition of Nb element, the mutual transmission between the metal elements in the alloy substrate and the external oxygen elements are hindered to some degree, which made the amount of oxygen element within the matrix reduced greatly and improved the high temperature oxidation resistance of the alloy.High temperature oxidation weight of the alloy adding 2Mo increased slowly,but oxide scale fell off more, compared tothe alloy without Mo added, with the oxidation time increased, the oxidation resistance at high temperature had not improved obviously.