Structure and Properties of TiAl-Based Alloys Doped with Niobium and Chromium

Quaternary as-cast Ti (96-x) Nb (2) Cr (2) Al (x) and Ti (93-x) Nb (5) Cr (2) Al (x) alloys, where x = 44, 46, 48, and 50, melted from pure components (similar to 99.9 wt.%) in a laboratory arc furnace, were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM/EDX), 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 750A degrees C. The alloys were found to consist mainly of a superfine lamellar structure formed during decomposition of hightemperature phases. In addition, the alloys with 50 at.% Al contain grains of the gamma phase, and all others have precipitates of the cubic beta/beta (0) phase at boundaries of the high-temperature phases because of double enrichment of the last melt drops with Cr. The tests show that the Ti (96-x) Nb (2) Cr (2) Al (x) alloys with 46 and 48 at.% Al possess the most balanced properties.