The vacuum melted ɣ-TiAl (Nb, Cr, Si)-doped alloys and their cyclic oxidation properties

Abstract

The γ-TiAl intermetallic alloy doped with Nb, Cr, and Si metals has been developed.It has emerged that the ternary Ti-48Al-2Nb and quinary Ti-48Al-2Nb-0.7Cr-0.3Si alloys yielded the best mechanical and cyclic oxidation properties. In particular, the quinary Ti-48Al-2Nb-0.7Cr-0.3Si alloy rapidly developed the protective stable Al 2 O 3 oxide doped with nitrogen and titanium oxynitride during cyclic oxidation. This showed a lower hardness when compared to the other alloys after cyclic oxidation.The oxide layer proved to have a good adhesive relationship with the parent metal.The alloys microstructures were analysed with the scanning electron microscopy (SEM). The sample hardness test were conducted by Vickers hardness tester. Research Highlights• Ti-48Al, Ti-48Al-2Nb, Ti-48Al-2Nb-0.7Cr and Ti-48Al-2Nb-0.7Cr-0.3Si were developed.• Ti-48Al-2Nb and Ti-48Al-2Nb-0.7Cr-0.3Si has excellent mechanical properties• Ti-48Al-2Nb and Ti-48Al-2Nb-0.7Cr-0.3Si revealed best cyclic oxidation resistance.• Formation of oxynitrides mixed with Al 2 O 3 /TiO 2 was detected.for scientists and engineers aiming to minimise the effect of both oxidation and oxygen embrittlement when these materials are in applications. One of the γ-TiAl intermetallic competitive material for high temperature applications are NiAl alloys [1-3]. Different approaches have been adopted to resolve the high temperature oxidation, leading to the development of coatings to prevent detrimental environmental effect on these alloys [4-6].The heat and creep-resistant intermetallic substrates deposited with nanocrystalline γ-TiAl intermetallic TiAl-based coatings micro-alloyed with Cr atoms induced very good oxidation resistance at 1173 K [4]. Furthermore, TiAl 3 /Al 2 O 3 composite powders were prepared by high energy ball milling and subsequent heat-treatment. The TiAl 3 /Al 2 O 3 powders deposited on γ-TiAl intermetallic and decreased the oxidation rate of γ-TiAl substrate [7] and Cr 2 AlC coatings with better Al rich oxide scale [8]. The laser aided manufacturing of γ/β-Al 2 O 3 coating on NiCrAlY coatings proved to withstand the operating temperature of 1200°C for ten cycles [9]. Additionally, another method of improving the properties of γ-TiAl alloys is to modify their chemical composition with alloying elements. For example, doping of traditional high temperature alloys such as β-NiAl to improve cyclic oxidation have been investigated [10-12]. Also, attempts to improve the oxidation resistance of Ti-Al intermetallic phase based alloys showed positive results [13-17]. Ding et al, [18] further investigated Nb-doped TiAl for cyclic deformation and microstructure evolution of high Nb containing TiAl alloy during high temperature low cycle fatigue. Our current investigation focus on the innovative alloying elements to produce the binary, ternary, quaternary and quinary alloys by addition of the Nb, Cr and Si γ-Ti-Al alloys. The arc button melting performed under vacuum was employed to manufacture the four γ-TiAl based alloys of nominal composition binary Ti-48Al (at. ...

The Oxidation Behaviour and Notch Wear Formation of TiAlN Coated Tools Using Different Oxidation Techniques

“…On the other hand, in the case of Ti alloys oxidized in high temperature, the mixture of Al2O3 and Moreover, the highest mass increment was observed for the TiAlN+Ti6Al4V diffusion couple due to additional diffusion of Ti documented by appropriate EDS analysis (for instance, see the at.% for Ti in the estimated chemical composition below). On the other hand, in the case of Ti alloys oxidized in high temperature, the mixture of Al 2 O 3 and TiO 2 are produced, however the Al 2 O 3 oxide scale is thermodynamically more stable at 900 • C [15].The annealing time influences the oxidation effects in such a way that for the shortest time of 2.5 min the mass increment (bars 1 and 3 in sections for TiAlN and TiAlN + Ti6Al4V) increased by 70% and 130% in comparison to about 12% and 22% when the annealing was continued up to 30 min for diffusion couples including IN718 and Ti6-4 coupons, respectively. This is because the relation of mass increment versus oxidation time is not linear but fits a logarithmic function [13].…”

Microstructure Evolution and Mechanical Properties of PM-Ti43Al9V0.3Y Alloy

“…The precipitates required a ZAF calibration method to calibrate the EDS results. According to Criss and Birks [18], the Materials 2020, 13,198 3 of 13 EDS results require a threefold iteration to be calibrated to the appropriate accuracy. The iteration equation is as follows:…”

“…The high O content would degenerate plasticity [11]. Many methods, including micro-alloying and high-vacuum experimenting, have been used to reduce the O content of TiAl alloys [12,13]. TiAl powder needs to be degassed in a vacuum before HIP.…”

Microstructure evolution and its effect on mechanical properties of cast Ti48Al6NbxSi alloys

“…Nb can increase the high temperature strength, ductility, and toughness of TiAl alloys. The service temperature of high-Nb TiAl alloys can exceed 800 °C [16][17] .…”

“…Silicon is one of the most important alloying elements of TiAl alloys [16,[18][19][20] . Ti 5 Si 3 phases are formed during the solidification process of TiAl alloys when the addition of silicon reaches a certain level.…”