Study on the microstructure, phase transition and hardness for the TiAl–Nb alloy design during directional solidification

Liu, Guohuai; Wang, Zhaodong; Fu, Tianliang; Li, Yong; Liu, Haitao; Li, Tianrui; Gong, Meina; Wang, Guodong

doi:10.1016/j.jallcom.2015.07.259

Cited by 48 publications

(10 citation statements)

References 31 publications

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“…1c. Furthermore, according toLiu et al,[19], the hardness values have a linear relationship with the yield stress in solidified TiAl alloys reflecting the material properties. The finer the grain size leads to high hardness, high strength and poor ductility.…”

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confidence: 95%

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

Mathabathe

Bolokang

Govender

et al. 2018

Vacuum

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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. ...

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confidence: 95%

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

Mathabathe

Bolokang

Govender

et al. 2018

Vacuum

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“…Clements et al [8] reported that solidification path via -phase is complimentary to obtaining a fine-grained casting microstructure without significant texture and segregation. Additions of Nb, Mo, Cr, W, Ta and V alloying elements enlarge and stabilises the -phase domain with a bcc crystal structure [9]. In the work done by Rajararn [10], the annealed Ti-46.6Al-2.3V-0.9Cr alloy yielded the  plates spheriodised by continuous and discontinuous coarsening, resulting in near- structure, which is affected by alloy composition and the morphology of the starting as-cast microstructure.…”

Section: Introductionmentioning

confidence: 99%

Phase transformation and microstructural control of the α-solidifying γ-Ti-45Al-2Nb-0.7Cr-0.3Si intermetallic alloy

Mathabathe

Govender

Bolokang

et al. 2018

Journal of Alloys and Compounds

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The -Ti-45Al-2Nb-0.7Cr-0.3Si based intermetallic alloy was developed. Microstructure evolution of the as-cast and heat-treated alloy yielded the spheriodised and Widmanstätten laths. High temperature differential thermal analysis (HTDTA) was performed on the as-cast Ti-45Al-2Nb-0.7Cr-0.3Si alloy in order to determine critical temperatures and provide insight into phase transformations prior heat treatment. The morphology of the alloy was analysed by the optical microscopy, scanning and transmission electron microscopy (SEM/TEM). The SEM was equipped with energy dispersion spectroscopy (EDS) for chemical composition. The EBSD mapping was employed to determine microstructural evolution. The results show that after heat-treatment the homogeneous microstructures were obtained, compared to the dendritic as-cast structure. The spheriodised laths were seen embedded inside the lamellar structure; whereas the Widmanstätten laths were observed as crossed/needle like ( 2 +) laths of small spacing, with a spatial orientation with respect to the lamellar structure. The structural development was determined by the X-ray diffraction (XRD).

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“…TiAl alloys are highly promising for high-temperature structural applications in aerospace with the potential to replace nickel-based superalloys because of their excellent properties [ 1 , 2 ], including being of low density, having high-temperature strength, high specific modulus and creep resistance, etc. Recently, TiAl alloys were studied from the perspective of using them for turbines of aircraft engines and gas-burning power-generation plants, which are believed to be on the verge of reaching the goal for industrial scale.…”

Section: Introductionmentioning

confidence: 99%

Flow Stress Prediction and Hot Deformation Mechanisms in Ti-44Al-5Nb-(Mo, V, B) Alloy

Liu

et al. 2018

Materials

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To elucidate the hot deformation characteristics of TiAl alloys, flow stress prediction, microstructural evolution and deformation mechanisms were investigated in Ti-44Al-5Nb-1Mo-2V-0.2B alloy by isothermal compression tests. A constitutive relationship using the Arrhenius model involving strain compensation and back propagation artificial neural network (BP-ANN) model were developed. A comparison of two models suggested that the BP-ANN model had excellent capabilities and was more accurate in predicting flow stress. Based on the microstructural analysis, bending and elongation of colonies, γ and B2 grains were the main microstructural constituents at low temperature and high strain rate. Dynamic recrystallization (DRX) of γ and dynamic recovery (DRY) of β/B2 were the main deformation mechanisms. With the increase of temperature and decrease of strain rate, phase transformation played an important role. The flake-like γ precipitates in B2 grains, and a coarsening of γ lamellae via α lath dissolution during compression were observed. Additionally, the flow softening process commenced with dislocation pile-up and formation of sub-grain boundaries, followed by grain refinement, twins and nano-lamellar nucleation. Continuous DRX and phase transformation promoted the formability of Ti-44Al-5Nb-1Mo-2V-0.2B alloy.

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Study on the microstructure, phase transition and hardness for the TiAl–Nb alloy design during directional solidification

Cited by 48 publications

References 31 publications

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

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

Phase transformation and microstructural control of the α-solidifying γ-Ti-45Al-2Nb-0.7Cr-0.3Si intermetallic alloy

Flow Stress Prediction and Hot Deformation Mechanisms in Ti-44Al-5Nb-(Mo, V, B) Alloy

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