Grain refinement mechanism in advanced γ-TiAl boron-alloyed structural intermetallics: The direct observation

Microstructure determined fracture behavior of a high Nb containing TiAl alloy

“…It has been reported that the fully lamellar and nearly lamellar microstructures consisting γ and α 2 have much higher fracture toughness and creep resistance than those of other kinds of microstructures [1]. At present, the thermo-mechanical processing and heat treatment have been received considerable attention in TiAl alloys [18,19]. However, based on the microstructure control, understanding the relationship between microstructure and properties is conducive to improve the performance of TiAl alloys.…”

Solidification and grain refinement in Ti(48–50)Al2Mn2Nb1B alloys

“…Guillard and Rack showed that in investment cast 16mm bars the microstructure of Ti48Al2Mn2Nb was changed from columnar to fine equiaxed lamellar when B concentration was at/over 0.69% [31] and the grain refinement was indeed caused by boron addition, as proven by many studies in the following years. [12]. In another solidifying alloy, Ti44Al8Nb1B, Bridgman sample, where coarse boride precipitates were found embedded in 2 grains, a specific orientation relationship between inoculating TiB particles and the inoculated 2 grains was revealed by EBSD analysis [17].…”

“…Alongside technological advance in manufacturing aero-engine components the demand for scientific understanding into grain refinement mechanisms has been increased and so have been the research activities in this field. The dedicated and unambiguously evidenced research relating grain refinement to alloys' solidification pathways was first published in 2007 and has been continued even since [10][11][12]. The findings so far are summarised here.…”

Advanced Heat-Resistant TiAl (Nb,Cr,Zr)-Based Intermetallics with the Stabilized β(Ti)-Phase

“…This particular boride-induced mechanism of phase-and structure-forming in a TNM-like alloy have been studied and published by us for the first time in papers [15,16]. [11,12]; c, d-Ti-44Al-5Nb-1Cr-1.5Zr-1B-0.17La (at.%), with LaB 6 [15] High-Gradient Float-Zone Processing Another fruitful approach in structure and properties engineering is using of controlling thermodynamic impact to the intermetallic system, i.e., solidification and cooling (annealing) of alloys in the strong directional fields-in magnetic or/and thermal ones. The directional solidification within thermal gradient is the most studied and therefore is most applicable.…”

“…3 Boride ribbons resolved in Ti-44Al-5Nb-2Cr-1.5Zr-0.4B-0.07La (a) and three consecutive stages of structure refining mechanism development: event of solid-state germination (seeding) of a 2 -Ti 3 Al phase on boride facet (b); morphological development of a 2 -laths and their growth through c-TiAl matrix (c); formation of new grain boundary by elongated curved boride surrounded by fine c + a 2 phase structure inside the delimited grains (d). The electron microscopy micrographs [15,16] Figure 4a displays the irregular microstructure of initial virgin ingot of Ti-44Al-5Nb-3Cr-1.5Zr, which was manufactured by semi-continuous electron-beam synthesis/casting technique from the pure metals [14]. Basic phase c-TiAl is imaged here by gray, a 2 -Ti 3 Al-by black and B2-as bright phase.…”