Structure-property orientation relationship of a γ/α2/Ti5Si3 in as-cast Ti-45Al-2Nb-0.7Cr-0.3Si intermetallic alloy

Abstract

Structure-property orientation relationship of a γ/α 2 /Ti 5 Si 3 in as-cast Ti-45Al-2Nb-0.7Cr-0.3Si intermetallic alloy, Journal of Alloys and Compounds (2018), Abstract Structure-property relationship of the as-cast γ-Ti-45Al-2Nb-0.7Cr-0.3Si based intermetallic alloy was examined. The phases stable at room temperature in the alloy were γ/α 2 /Ti 5 Si 3 , respectively; while their crystal structures were described by means of chemical formulas, Pearson's number, space groups, lattice parameters, atomic positions and occupancy numbers using a Vienna ab initio simulation package (VASP) software for materials design. Moreover, high resolution electron backscatter diffraction (HSEBSD) was used to analyse the orientation relationship of both the ascast (β-solidifying) and heat-treated (α-solidifying) microstructural phases. The results showed that the formation of γ/α 2 /Ti 5 Si 3 follows the Blackburn orientation relationship (BOR): (β-solidifying) {110} β // {0001} α and <111> β // <2110> α , and for (α-solidifying) = (111)γ || (0001)α and <110]γ || <1120>α.

Characteristic effects of alloying elements on β solidifying titanium aluminides: A review

“…Figure 3 indicates β-phase located at the layers of lamellae boundary colonies ( Figure 3 a) and significant coarsening of lamellae width shown in Figure 3 b. Beta (β) stabilizers like Mo, Nb, W and Cr do also contribute to refining microstructure grains by stabilizing the metastable B2-phase (ordered β-phase) at low temperatures, thereby, enhancing high-temperature deformability [ 9 , 51 ]. Lately, the Ti–44Al–7Mo ternary alloy has drawn attention, with research works demonstrating that heat treatment procedure resulted in a considerable microstructural refinement with a substantial increase in hardness.…”

“…However, only the prior β 0 -phase that decomposed into γ-platelets and ω 0 -particles with few undissolved β 0 -phases during annealing could be resolved by SEM. The γ-lamellar formed from the transformation of α 2 -grains tend to align parallel through the mechanism known as the BOR [ 37 ]; that has been explained by several authors [ 51 , 76 , 81 ]. Also, it was observed by Klein et al.…”

“…It has been reported by various authors [ 1 , 3 , 51 ] that Si dissolves by substituting for Al as determined by ab initio calculations. This leads to Al deficiencies in Si-containing TiAl-based alloys, but strong β-stabilizers like Mo if present would substitute for Ti which relocates to the Al-sites.…”

“…Four possible microstructures are usually formed by TiAl-based intermetallic alloys are shown in Figure 1 . It is reported that the nearly fully lamellar and/or fully lamellar microstructures could provide the much-needed combination of mechanical properties using a viable production method and provide structural integrity during the components’ lifetime [ 5 , 7 , 14 , 16 , 22 , 30 , 46 , 51 , 52 ]. The duplex or equiaxed microstructure (γ+α 2 ) provides adequate ductility and fatigue but it exhibits low creep resistant and fracture toughness; while the microstructure with fully lamellar (with alternating plates of γ and α 2 phases) demonstrates superior fracture toughness and creep resistant but demonstrates poor ductility [ 30 , 31 , 52 ].…”

“…Moreover, fracture toughness and limited ductility at RT hampers the widespread applications of TiAl-based alloys in fabricating functional parts [ 8 , 15 , 26 , 73 ]. This could be overcome by micro-alloying elements additions [ 15 , 51 ]. Also, crack initiation and propagation, inferior performance in hot oxidizing atmospheres (above 750 °C) and low fatigue life are the main problems hindering its wider adaptability as aero-engine components [ 18 ].…”