Effects of niobium on phase composition and improving mechanical properties in TiAl alloy reinforced by Ti2AlC

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

“…In β-solidifying γ-TiAl-based alloys, alloying elements aimed at improving the mechanical properties include Nb, Mo, V, Cr and Mn for increasing ductility and stabilizing β-phase in the microstructure [ 45 , 57 , 95 ]. Others include Ta, Mo and W that are meant to improve oxidation resistance [ 45 ]; while B, C and Si are for microstructural refinement [ 45 , 93 ]. Among these alloying elements, effective hardening is caused by C when finely dispersed precipitates of carbides are formed in TiAl-based alloys.…”

“…Niobium (Nb) addition in γ-TiAl-based alloys stands out when compared to most alloying elements in providing a balance elevated temperature and RT properties [ 14 ]. These mechanical properties enhancement is ascribed to the combined influence of precipitation strengthening, solid solution strengthening, increase in γ-phase content and grain boundary strengthening [ 45 ]. It is well reported in literature that Nb plays a vital role in oxidation resistance and high-temperature strength improvements in TiAl-based alloys [ 15 , 18 , 25 , 97 ].…”

“…These positive effects of Nb manifest through increased propensity of the α 2 -phase basal slip, ductile β-phase stabilization, and oxidation resistance improvement [ 35 , 55 ]. This is related to the Nb solid solubility which increases within the γ-phase and lesser diffusion in α 2 -phase; while segregation of Nb results in B2-phase formation [ 45 ]. The B2-phase is formed through a β-phase transformation and α-grains nucleation in the β-grains.…”

“…This section discusses the influence of well-known alloying elements effects that are characteristically used in developing superior titanium aluminide intermetallic alloys. According to Fang et al [45], the benefits of alloying are to (i) cause relaxation of slip modes restriction; (ii) reduce the ordering kinetics or alter long-range ordering degrees; (iii) modify the alloy structure by introducing β-phase as a ductile phase to mitigate microcrack growths formed in α 2 /γ phases; (iv) adjust transformation behaviour when processing or heat treating to facilitate the control of microstructural refinement. It is understood that Al contents are central to manipulating the microstructural transformations, phase evolution and lamellar content (α 2 þγ phases) in TiAl-based alloys.…”

“…Titanium aluminides are problematic to process due to their brittle nature, hence, limiting its widespread production. The intrinsic brittleness at RT and poor hot-deformability limit its application in manufacturing complex-shaped structural components [ 14 , 31 , 39 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ]. Consequently, conventional processing of TiAl-based alloys such as forging and extrusion are restricted; while casting is known to always produce coarse microstructure and arbitrary defects resulting in inhomogeneous mechanical properties [ 20 , 47 ].…”