The decomposition of the beta phase in Ti–44Al–8Nb and Ti–44Al–4Nb–4Zr–0.2Si alloys

Cheng, T. T.; Loretto, M. H.

doi:10.1016/s1359-6454(98)00113-x

Cited by 160 publications

(65 citation statements)

References 4 publications

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“…[5,13] The tweed structure also comprises of slabs of hexagonal stacking, which appear to be a 2 phase (Fig. 2(a)).…”

Section: Constitution and Microstructurementioning

confidence: 99%

“…Cheng and Loretto, [5] Kobayashi et al [6] and Takeyama and Kobayashi [7] have shown that by stabilizing the b phase, a multitude of solid-state transformations and resulting microstructural morphologies can be achieved. In particular, a fine dispersion of the b phase in the microstructure can be established, which leads to a significant strengthening and good high-temperature deformability.…”

Section: Introductionmentioning

confidence: 99%

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Nano‐Scale Design of TiAl Alloys Based on β‐Phase Decomposition

Appel¹,

Oehring²,

Paul³

2006

Adv Eng Mater

109

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Phase decomposition and ordering reactions in β/B2‐phase containing TiAl alloys were utilized to establish a novel, previously unreported, type of laminate microstructure. The characteristic constituent of this microstructure are laths with a nanometer‐scale substructure that are comprised of several stable and metastable phases. Microstructural control can be achieved by conventional thermomechanical processing and leads to a structurally and chemically very homogeneous material with excellent mechanical properties. The physical metallurgy of this novel type of alloy has been assessed by transmission electron microscope investigations and mechanical testing.

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“…[5,13] The tweed structure also comprises of slabs of hexagonal stacking, which appear to be a 2 phase (Fig. 2(a)).…”

Section: Constitution and Microstructurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Nano‐Scale Design of TiAl Alloys Based on β‐Phase Decomposition

Appel¹,

Oehring²,

Paul³

2006

Adv Eng Mater

109

View full text Add to dashboard Cite

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“…Thus, it may improve the deformability at elevated temperature, where, for example, processes such as rolling and forging are carried out. A number of authors [11,[14][15][16][17][18] have demonstrated that, by stabilizing the b-phase through alloying with Nb, Ta, Mo or other elements, an improvement in hot-workability can be achieved and novel types of microstructures can be adjusted by exploiting a multitude of solid-state transformations. However, it is known that the b-phase or its ordered Counterpart B2 can decompose into several product phases, for example into x, x' and x", which possess lower crystal symmetry and are extremely brittle.…”

mentioning

confidence: 99%

Design of Novel β‐Solidifying TiAl Alloys with Adjustable β/B2‐Phase Fraction and Excellent Hot‐Workability

et al. 2008

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The research and development of c-TiAl based alloys for aero-engine and automotive components have been the target of several R & D projects since more than 20 years. [1][2][3] Titanium aluminides are considered for future advanced aero-engines due to their potential of significant component weight savings. Although, remarkable progress has been made, today, titanium aluminides have not been applied for aeroengine parts. Both fundamental materials research and design as well as production technologies have achieved an advanced state of maturity. But overall, the limited tensile ductility, poor crack propagation resistance and detrimental effects of defects, damage and long term cycling loads as well as exposure to hot oxidizing atmospheres on the fatigue life are the mayor concerns in the area of aero-engine components reliability and lifetime issues. There are further needs of understanding the source and effect of the different relevant damages and defects on the life-prediction for a particular titanium aluminide alloy and aero engine component. The attempts of scaling up the production of ingot materials, castings and forgings, have not yet met the required targets of reproducibility and affordability. Large-scale production of titanium aluminides ingots and parts requires further alloy and process development to become a reliable technology. Current titanium and nickel alloys exhibit balanced properties and achieve all requirements of the current design practices.Intermetallic c-TiAl based alloys are certainly among the most promising candidates to fulfill the required thermal and mechanical specifications. Especially, TiAl alloys with high Nb-contents showing a baseline composition of Ti-(42-45)Al-(5-10)Nb-(0-0.5)B (all compositions are stated in at%), termed TNB alloys, have attracted much attention because of their high creep strength, good ductility at room temperature, good fatigue properties, and excellent oxidation resistance. [1][2][3][4][5][6][7] Nb reduces the stacking fault energy in c-TiAl, retards diffusion processes and modifies the structure of the oxidation layer. [4,6,8] Cast alloys based on Ti-(42-45)Al, which solidify via the body-centered cubic b-phase, exhibit an isotropic, equiaxed and texture-free microstructure with modest micro-segregation, whereas peritectic alloys (solidification via the hexagonal a-phase) show anisotropic microstructures as well as significant texture and segregation. [9] Alloy design concepts for c-TiAl based alloys showing refined cast microstructures were recently reported by Imayev et al. [10] An alloy design strategy to improve the hot-workability of TiAl alloys is to exploit a combination of thermo-mechanical processing and additional alloying elements to induce the disordered b-phase at elevated temperatures as ductile phase. [11][12][13][14][15][16][17] The disordered b-phase with bcc lattice provides a sufficient number of independent slip systems. Thus, it may improve the deformability at elevated temperature, where, for example, processes such as rollin...

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“…11) Hence, in the Ti-40Al-10Nb alloy, the high-temperature /B2 phase can be retained at the room temperature during solidification, yielding the microstructure in Fig. 1(a).…”

Section: )mentioning

confidence: 99%

Effects of High Niobium Addition on the Microstructure and High-Temperature Properties of Ti-40Al-<I>x</I>Nb Alloy

Zhan

Koo

2006

Mater. Trans.

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The effect of Nb content on the microstructure and high-temperature properties of the TiAl alloy with low Al content has been investigated. The as-cast Ti-40Al-10Nb alloy consists of a Widmanstätten lath and a phase in a B2 matrix. The increased addition of Nb to the alloy inhibits the solidification path ! þ . Therefore, the as-cast Ti-40Al-xNb (x ¼ 15; 16) alloys are composed of primary /B2 phases as the major constituent. Following heat treatment, the microstructure of the heat-treated Ti-40Al-10Nb alloy resembles that of the as-cast Ti-40Al-10Nb alloy. The homogenized Ti-40Al-15Nb alloy has a two-phase microstructure of B2 þ , while the homogenized Ti-40Al-16Nb alloy has a fourphase microstructure of B2 þ þ þ . The creep response of the studied TiAl-Nb alloy is correlated closely with the tertiary creep, and is affected strongly by its microstructure. The creep resistance of the alloy depends on the resistance to the propagation of the cracks in the B2 matrix. In the Ti-40Al-15Nb alloy, the resistance to the extending of cracks is the most apparent among these three alloys. Therefore, the Ti40Al-15Nb alloy has the highest creep life of the three tested alloys. The oxidation resistance of the investigated TiAl-Nb alloy is independent of the addition of Nb. The differences among the oxidation resistances of these three alloys arise from their various microstructures. The oxide scales of the Ti-40Al-10Nb alloy are composed mainly of TiO 2 , while the oxide scales formed on the Ti-40Al-15Nb alloy are dense Al 2 O 3 -rich oxides. The Ti-40Al-15Nb alloy has the lowest mass gain among these three alloys due to the existence of the Al 2 O 3 -rich oxides. The formation of Al 2 O 3 -rich oxides appears to be related to the high Nb content of the alloy. The fact that the Ti-40Al-16Nb alloy has the largest weight gain of these three alloys is attributed to the formation of oxide scales of phase.

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The decomposition of the beta phase in Ti–44Al–8Nb and Ti–44Al–4Nb–4Zr–0.2Si alloys

Cited by 160 publications

References 4 publications

Nano‐Scale Design of TiAl Alloys Based on β‐Phase Decomposition

Nano‐Scale Design of TiAl Alloys Based on β‐Phase Decomposition

Design of Novel β‐Solidifying TiAl Alloys with Adjustable β/B2‐Phase Fraction and Excellent Hot‐Workability

Effects of High Niobium Addition on the Microstructure and High-Temperature Properties of Ti-40Al-<I>x</I>Nb Alloy

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