Effects of the Colony Size on the Fracture Toughness of TiAl-Mo-B Alloys

intermetallics, thermo-mechanical processing, microstructure, scanning electron microscopy (SEM), XRD spectra, micro-hardness test

“…One must have in view that for obtaining this kind of structure/morphology there has been selected a specific new chemical composition that, by nature and quantity of alloying elements, can assure the proposed main objective -the obtaining of a high quality cast material. The most important goal in selecting the alloying elements for the present case was the concept, according to which a high quality cast material can be obtained by means of solidification through beta phase, which allows avoiding significant chemical non--homogeneity induced by peritectic reactions [4,5,11]. For this reason, niobium is the most important alloying element in this case, because it is a beta stabilizing element and also has low diffusion mobility in the γ and α 2 phases, thus facilitating a decrease rate of grain growth [2,10,11,20].…”

“…One of the main conclusions of these studies refers to the necessity of achieving an important prerequisite for the commercialization of these alloys consisting in the production of high quality cast material, with a fine-grained microstructure, weak texture, and without chemical non--homogeneities [6], characteristics that can assure a subsequently efficient thermo-mechanical processing. These characteristics can be achieved via a rational selection of the alloy composition, by introducing proper alloying elements [4,5]. Adhering to this research direction, present paper reports some structural and mechanical properties for a new near gamma alloy composition concept, with high Nb concentration and small additions of Cr, Ta, Ni, Si, a cold crucible levitation melting technique being used for its elaboration.…”

“…Compared to Ti alloys, they offer better creep oxidation and burn resistance, and increased strength at elevated temperatures [1]. However, poor ductility and low fracture toughness, not only at room temperature but also at high temperatures, still represent the main obstacle against full utilization of these alloys [2][3][4][5][6]. Therefore, in the last years many studies have been performed to improve the structural and chemical homogeneity of near gamma TiAl-based alloys [2,4,7,8], especially for most technically interesting alloys based *Corresponding author: tel./fax: +40241606431; e-mail address: anocivin@univ-ovidius.ro on Ti-(44-49)at.%Al but with several other containing elements.…”