Development and elemental powder metallurgy of a Y-containing two-phase TiAl alloy

Abstract

The Y modification of a two-phase (␥ ϩ ␣ 2 ) TiAl-(Mn,Mo,C) alloy was studied with an aim to improve, mainly, the oxidation resistance and the mechanical properties in a high-temperature air environment. The experimental alloy was prepared by the elemental powder metallurgy (EPM) method. The addition of up to 0.6 at. pct Y resulted in a significant improvement in tensile properties and compressive yield strength and an anomalous yielding phenomenon withal. Two structural characteristics were identified: first, microstructural refinement in terms of the grain size as well as the interlamellar spacing, and second, precipitation of fine oxides that might scavenge harmful oxygen. Deformation was found to be mainly provided by 1/2͗110] ordinary dislocations and a much lesser amount of ͗011] superdislocations as compared to what has been reported in other (␥ ϩ ␣ 2 ) TiAl alloys. The oxidation resistance of the experimental alloy was evaluated by air-exposure tests at 800°C, from which the oxidation kinetics and the morphological and phase characteristics of the oxide scales were analyzed. With a Y addition, the constituents of the oxide scale changed from those of the Y-free alloy. In the case of the Y-free alloy, the oxide scale which formed upon extended air exposure (350 hours) at 800°C consisted of a mixture of TiO 2 and ␣-Al 2 O 3 . In the case of the alloy modified with Y (0.6 at. pct), however, the oxide scale formed in an identical environment was considerably different: it consisted of a complex mixture of

Hot deformation behavior of TiAl alloys prepared by blended elemental powders

“…Meanwhile, some problems, such as poor ductility and low fracture toughness, caused by inhomogeneities and segregations in the solidification microstructure, also make the IM TiAl alloys restricted in application [3]. PM technique, especially the blended elemental PM technique appears to be more economical because of cheap raw material and preparation process [4]. Recently, significant progresses have been made in lowering the cost of raw powder, such as titanium and aluminide powders [5,6], that leads to further lower the cost of PM TiAl alloys.…”

Isothermal oxidation behavior of two-phase TiAl–Mn–Mo–C–Y alloys fabricated by different processes

“…As same as the extruded alloy, the surface of the melted sample was covered by dense and fine oxide except for a slight growth of oxide in the latter (Figs. [6][7][8], and a thinner oxide scale was observed during oxidation at 800 8C for 24 and 350 h, as shown in Figs. 11(b) and 12(a), respectively.…”

“…Elements such as Mn and V improve the room temperature ductility due to activation of mechanical twinning [1][2][3], while Mo, C and Y are known to improve the high temperature strength [4][5][6]. The oxidation resistance can be improved by addition of the minor elements such as Mo, Nb, Cl and Y [7][8][9][10][11][12][13].…”

“…In previous studies [6,7], the microstructural development, mechanical properties and creep behavior of EPM extruded TiAl-based rods with fully lamellar microstructure were examined and the high temperature oxidation behavior of the extruded alloys was evaluated. The present alloy has strong application potential due to its convenient fabrication processing and excellent high-temperature mechanical properties.…”

High-temperature oxidation behavior of TiAl-based alloys fabricated by spark plasma sintering

“…The minor amount of Y is reported to have a favorable effect, while the addition of W and B into the high Nb-containing TiAl alloys is deleterious to the oxidation resistance [25][26][27][28]. However, from the obtained results it is hard to draw definitive conclusions about the exact role of the presence of Y, W and B in the oxidation behavior.…”