Impact of β-phase in TiAl alloys on mechanical properties after high temperature air exposure

Abstract

In this paper, the influence of high temperature air exposure on the tensile properties at room temperature and on the fatigue strength at high temperature of two TiAl alloys, is studied. The alloys, Ti-48Al-2Cr-2Nb (Ti-48-2-2), and Ti-44Al-4Nb-1Mo-0.1B (TNM-B1), both exhibit near- microstructures, but the TNM-B1 alloy contains significant amounts of  phase. Air exposure at high temperature (650-700°C, 500 h) induces significant loss of ductility, and decrease of fatigue strength at high temperature, in the case of the -containing TNM-B1 alloy, but not for the -Ti-48-2-2 alloy. This indicates a potential influence of the presence of  phase for embrittleme nt. Because embrittlement is believed to be the consequence of microstructure modifications in the sub-surface, first attempts have been performed to investigate these local phenomena. For this purpose, SEM, FIB, STEM-EDX and ACOM techniques have been employed. Destablilization of  and, to a lesser extent, of , into 2, has been observed in the sub-surface of the TNM-B1 alloy. We interpret this as a consequence of oxygen diffusion during the high temperature air exposure, which would promote formation of 2 phase in which oxygen solubility is high, at the expenses of the  and  phases of lower oxygen solubility.

Interactions of oxygen with intrinsic defects in L10 γ-TiAl in presence of substitutional solutes: Influence on diffusion kinetics

“…The other phenomenon that causes a reduction in ductility is when the alloys are submitted to heat treatments in air at high temperature (300-800°C), for 10-100 h. In that case, a significant decrease in ductility at room temperature is observed [10][11][12][13][14][15][16][17]. To account for this phenomenon, the formation of a brittle surface layer [10,12,15], was proposed, but the underlying mechanisms remain largely obscure.…”

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

“…The gamma-TiAl (γ-TiAl) alloy is a novel type of lightweight material [ 53 ]. γ-TiAl-based alloys are potential substitutes for nickel (Ni) based superalloys especially in applications that require considerable weight saving and minimal redesigning [ 15 , 28 , 48 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 ]. According to Ding et al.…”

“…Thus, titanium aluminide has found application in making seal supports, cases and frames of aircraft engines where clearances are crucial [ 54 ]. Also, it is applied in turbocharger wheels and turbine blades of automobile and aero engines respectively [ 5 , 7 , 21 , 43 , 50 , 58 , 73 , 79 , 80 , 81 , 87 , 88 , 90 , 91 ]. Considerable decrease in fuel consumption and greenhouse gases have been achieved due to the lightweight of rotating components.…”

“…The gamma-TiAl (γ-TiAl) alloy is a novel type of lightweight material [53]. γ-TiAl-based alloys are potential substitutes for nickel (Ni) based superalloys especially in applications that require considerable weight saving and minimal redesigning [15,28,48,54,55,56,57,58,59,60,61,62]. According to Ding et al [63], γ-TiAl alloys with FL microstructures creates decent stability in properties such as ductility, creep resistance and fatigue resistance which are often needed in several engineering applications.…”

“…Also, it is applied in turbocharger wheels and turbine blades of automobile and aero engines respectively [49,50]. [5,7,21,43,50,58,73,79,80,81,87,88,90,91]. Considerable decrease in fuel consumption and greenhouse gases have been achieved due to the lightweight of rotating components.…”