Structure and Properties of TiAl Alloys Doped with Niobium and Chromium

Abstract

Quaternary as-cast Ti_96–хNb₂Cr₂Al_х and Ti_93–хNb₅Cr₂Al_х alloys, where х = 44, 46, 48, and 50, melted from pure components (~99.9 wt.%) in a laboratory arc furnace, were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM/EDS), and differential thermal analysis (DTA). Bending testing and fracture toughness measurements were performed at room temperature, and compression testing was carried out in a range from room temperature to 750 °С. The alloys were found to consist mainly of a superfine lamellar structure formed during decomposition of high-temperature phases. In addition, the alloys with 50 at.% Al contain grains of the γ phase, and in all others there are precipitates of the β/β₀ cubic phase at interfaces of the high-temperature phases because of double enrichment of the last melt drops with Cr. The testing shows that the Ti_96–хNb₂Cr₂Al_х alloys with 46 and 48 at.% Al possess the most balanced properties.