Transformation and Precipitation Processes in a Metal Substrate of Oxidized TiAl-Based Alloys

Małecka, J.

doi:10.1007/s11085-019-09886-1

Cited by 13 publications

(7 citation statements)

References 26 publications

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“…This means diffusion of O towards the bulk and of Al towards the surface. This observation is in agreement with the usual description of the phase sequence in the sub-surface of oxidized TiAl, namely: TiAl -Al depleted zone -TiO2+Al2O3 [3,4]. Concerning Al, an estimatio n of the diffusion length d can be carried out using the usual relation = 2√ (with D: self diffusion coefficient and t: time).…”

Section: Discussionsupporting

confidence: 86%

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

et al. 2020

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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.

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Section: Discussionsupporting

confidence: 86%

“…A review can be found for example in Appel's book [1]. Oxidation processes of TiAl give rise to the following phase sequence in the sub-surface: TiAl -Al depleted zone -TiO2+Al2O3 [3,4]. The Nb and Mo elements which are added to the TNM-B1 alloy have been found to improve oxidation resistance [5][6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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“…The observed rates indicate that the oxidation is mainly dominated by bulk diffusion. In particular, Maleka [18] has recently shown that the oxidation process takes place as a result of the outward diffusion of titanium and aluminium, as well as the inward diffusion of oxygen. Therefore, for a complete understanding of the oxidation mechanisms, the knowledge of the diffusion coefficients of all the species involved in the process is necessary.…”

Section: Introductionmentioning

confidence: 99%

First-principle study of the solubility and diffusion of oxygen and boron in γ-TiAl

Epifano

Hug

2020

Computational Materials Science

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Solubility and diffusion of boron and oxygen in the γ-TiAl intermetallic compound are herein investigated by firstprinciple calculations. On the basis of the space group of the γ phase, the accommodation of the light atoms in the various interstitial positions is studied by density functional theory. Diffusion coefficients are also obtained from ab initio calculations. Barrier energies for the boron and oxygen diffusion among the different stable interstitial sites are computed using the Nudged Elastic Band method and atomic jumping rates are obtained from the Transitional State Theory. Diffusion coefficients are obtained from the solution of the transport equation in the infinite time limit, using the analytical Multi-State Diffusion method. The methodology here applied is validated by the good agreement between the computed diffusion coefficient of boron and the experimental data available in the literature for this species.

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“…As compared to B characterized with a solubility of <1 at%, [ 49 ] the extensive solubility of N in the α‐phase (up to 23 at%) results in the formation of a solid solution via interstitial diffusion. [ 50 ] The diffusion of N atoms into the interstitial sites of Ti has been reported to result in the expansion of the α‐Ti crystal lattice, causing compressive strains. [ 51 ] Therefore, it is deduced that the induced lattice expansion is responsible for the peak shifts observed in Figure 2b.…”

Section: Resultsmentioning

confidence: 99%

Boron Nitride Nanotube–Reinforced Titanium Composite with Controlled Interfacial Reactions by Spark Plasma Sintering

Bustillos

Nautiyal

et al. 2020

Adv Eng Mater

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In this study, Boron Nitride Nanotube (BNNT) reinforced Titanium matrix composites are synthesized by Spark Plasma Sintering. Two main challenges directly affecting the mechanical performance of BNNT-metal matrix composites are addressed:(i) Homogenous dispersion of high surface energy BNNTs, and (ii) Controlling interfacial reactions at the metal/nanotube interface. High affinity of acetone with BNNTs and high energy ultrasonication induced the mechanical dispersion and stability of BNNTs in their dispersion. The sintering of Ti (99% relative density) was achieved at 50% less processing temperature than those used in conventional sintering to minimize interfacial reactions when reinforced with BNNTs. The reduction of temperatures in addition to the reduction (by 91%) in processing times was shown to control reaction phases. Bulk compressive yield strengths of Ti-BNNT sintered at low (750 o C) and high (950 o C) temperatures were improved by 21% and 50% respectively, as compared to Ti alloy without reinforcement. Twin boundaries, pinning of dislocations by BNNTs, and crack bridging were strengthening mechanisms identified in the composites. vi TABLE OF CONTENT CHAPTER

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Transformation and Precipitation Processes in a Metal Substrate of Oxidized TiAl-Based Alloys

Cited by 13 publications

References 26 publications

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

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

First-principle study of the solubility and diffusion of oxygen and boron in γ-TiAl

Boron Nitride Nanotube–Reinforced Titanium Composite with Controlled Interfacial Reactions by Spark Plasma Sintering

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