Processing-property-microstructure relationships in TiAl-based alloys

Abstract

The influence of thermomechanical processing on the microstructure of a range of TiAl-based alloys has been assessed using optical and electron microscopy, and the room-temperature mechanical properties have been determined. Long-term exposure at high temperatures has been used to assess the thermal stability of some of the structures generated through the different processing routes, and it has been found that the (gamma and alpha 2) lamellar structures, in some of the alloys, are unstable at 700 ЊC, a likely operating temperature. Addition of boron increases the stability of the lamellar structure. The influence of the difficulty of slip transfer between gamma and alpha 2 has been assessed as one of the factors limiting ductility in samples with this lamellar structure. In addition to the alloys produced via the ingot route, some atomized material has been produced and the microstructure and properties of hot-isostatically pressed ''hipped'' material assessed. Regions, high in titanium, are present in all atomized powders that have been examined, and these regions are found to initiate fracture at very low strains. These results are briefly discussed in terms of the factors that control the room-temperature strength and fracture behavior of TiAl-based alloys.

Development of a heat treatment strategy for the γ-TiAl based alloy TNM-B1 to increase the hot workability

“…Titanium aluminide (TiAl) alloys based on the ordered γ-TiAl phase have drawn much attention in recent years, due to their great potential in high temperature applications [1,2]. The main characteristics distinguishing this intermetallic material from other construction materials are high specific yield strength, low density (3.9-4.2 g/cm 3 ) high corrosion resistance and good creep properties at high temperatures [3][4][5]. The areas of application includes isothermally forged turbine blades for aircraft engines, as TiAl blades offer reduced weight and similar strength compared to the conventional nickel-based blades [6].…”

Microstructural characterization of the γ-TiAl alloy samples fabricated by direct laser fabrication rapid prototype technique

“…Metallurgical efforts such as ternary alloying and thermomechanical treatment have been made to improve the room temperature toughness (Loretto et al 1998). It is possible to improve the ductility and toughness of the TiAl (γ) alloys through the modification of microstructure (Hu et al 1998a;Kim 1998).…”