Alloy design concepts for refined gamma titanium aluminide based alloys

Imayev, R. M.; Imayev, V. M.; Oehring, Michael; Appel, F.

doi:10.1016/j.intermet.2006.05.003

Cited by 311 publications

(160 citation statements)

References 25 publications

(46 reference statements)

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“…2a). Similar observations were also made for ternary and multicomponent alloys solidifying via primary α phase, which have been reported in studies for raw ascast specimens ranging from arc-melted buttons to large ingots [7,8] . Figure 2(b) shows equiaxed grains at the center of this ingot.…”

Section: Resultssupporting

confidence: 84%

A high-Nb TiAl alloy with highly refined microstructure and excellent mechanical properties fabricated by electromagnetic continuous casting

et al. 2016

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Male, born in 1968, Ph.D, Professor. His main research fields include solidification and microstructure control, investment casting technology of titanium-aluminum alloys and directionally solidified titanium-aluminum alloys. [1] .Therefore, the development of such a material system has important implications for aeronautics and astronautics fields. However, poor ductility at room temperature as well as low workability at elevated temperatures of the high-Nb TiAl alloys restricts their applications [2] . According to current knowledge, high mechanical properties can be achieved in these materials by attaining a finer fully lamellar microstructure [3] . Electromagnetic continuous casting (EMCC) is a technique which is in virtue of electromagnetic force to strengthen the movement of the metallic melt and improve heat transfer during solidification. When the EMCC is applied to the melt during solidification, the Abstract: In the present research, microstructure refinement of a high-Nb TiAl alloy (Ti-48Al-8Nb-0.15B ) was realized by means of the electromagnetic continuous casting (EMCC) technique. The microstructure of an ingot obtained by EMCC was analyzed using scanning electron microscopy (SEM). As compared with the raw as-cast alloy, the obtained EMCC alloy presented a much finer microstructure with lamellar colonies with a mean size of about 50-70 μm because the electromagnetic stirring broke initial dendrites and enhanced the heterogeneous nucleation. As the grains were refined, the properties of the TiAl alloy were improved significantly. This implies that the EMCC technique could offer the possibility of application for high-Nb TiAl alloys with a refined microstructure and excellent properties to be used as a structural material. microstructure would be refined and the distribution of compositions also could be homogenized [4][5][6] . EMCC technique has been applied to the production of many alloys such as aluminum alloys [4] , magnesium alloys [5] and alloyed steels [6] , but application to TiAl alloys has rarely been reported. Based on the above opinions, the EMCC technique was used in refining a high-Nb TiAl alloy with the composition of Ti-48Al-8Nb-0.15B in the present study, and the microstructure and mechanical properties of EMCCed samples were investigated.

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Section: Resultssupporting

confidence: 84%

A high-Nb TiAl alloy with highly refined microstructure and excellent mechanical properties fabricated by electromagnetic continuous casting

et al. 2016

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“…Объемная доля β(В2)-фазы не превосхо-дит 2 -3 %. Вытянутая форма колоний и маленькая тол-щина γ / α 2 пластин обусловлены относительно высокой скоростью охлаждения слитков в процессе их изготов-ления [5]. В микроструктуре слитка также наблюдаются бориды (моно-и дибориды титана [18,19]), имеющие в основном нитевидную форму.…”

Section: результаты и обсуждениеunclassified

Microstructure and mechanical properties of intermetallic γ-TiAl alloy alloyed with dysprosium

Nazarova¹,

Nazarov²,

Sergeev³

et al. 2017

LoM

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In the present work, the effect of alloying with dysprosium on microstructure and compression mechanical properties of a β-solidifying γ-TiAl alloy has been studied. For this, ingots of the alloys Ti-45Al-6(Nb,Mo)-0,2B-xDy (at.%) with various additions of dysprosium (x = 0, 0,1 and 1 at.%) were melted. The as-cast alloys were homogenized and then cooled in a furnace. These conditions of the alloys were assumed as the initial cast conditions. Microstructure examination showed that Ti-45Al-6(Nb,Mo)-0,2B and Ti-45Al-6(Nb,Mo)-0,2B-0,1Dy alloys had near lamellar microstructures in the initial conditions. Alloying with 1 at.% of dysprosium caused a change in the microstructure morphology from near lamellar to mixed lamellarglobular one. The appearance of globular γ and α 2 grains in the alloy alloyed with 1 at.% of dysprosium resulted in an appreciable refinement of the γ / α 2 colonies. It was revealed that the addition of 1 at.% of dysprosium to the Ti-45Al-6(Nb,Mo)-0,2B alloy led to changing the phase composition: along with the basic γ, α 2 and β(B2)-phases an additional DyAl 2 phase was detected. Also, oxide particles Dy 2 O 3 were revealed in both alloys containing dysprosium. The alloys under study were subjected to heat treatment, which included a three-stage anneal. As a result, near lamellar structure was obtained in all alloys. It has been established that the alloys containing dysprosium in the heat treated conditions demonstrated higher values of both the strength and ductility as compared to the alloy free of dysprosium. At T = 800°C, the compression mechanical properties of the alloys were found to be similar. В работе изучали влияние легирования диспрозием на микроструктуру и механические свойства на сжатие интерме-таллидного β-затвердевающего γ-TiAl сплава. Для этого были выплавлены слитки сплавов Ti-45Al-6(Nb,Mo)-0,2B-xDy (ат.%) с различным содержанием диспрозия (x = 0, 0,1 и 1 ат.%). Слитки сплавов подвергали гомогенизационному отжигу с последующим охлаждением в печи. Данное состояние было принято за исходное литое состояние. Выпол-ненные исследования показали, что микроструктура сплавов Ti-45Al-6(Nb,Mo)-0,2B и Ti-45Al-6(Nb,Mo)-0,2B-0,1Dy в исходном состоянии преимущественно пластинчатая. Введение в сплав 1 ат.% диспрозия приводит к изменению морфологии микроструктуры от преимущественно пластинчатой к пластинчато-глобулярной. Появление глобуляр-ных γ и α 2 -зерен в сплаве с 1 ат.% диспрозия сопровождается заметным уменьшением размера γ / α 2 колоний. Было показано, что введение 1 ат.% диспрозия в сплав Ti-45Al-6(Nb,Mo)-0,2B приводит к изменению фазового состава материала: кроме основных γ, α 2 и β(В2)-фаз в сплаве была обнаружена фаза DyAl 2 . Кроме того, в микроструктуре сплавов, содержащих диспрозий, также были обнаружены оксидные частицы Dy 2 O 3 . Для всех исследованных спла-вов была выполнена термическая обработка, включавшая в себя трехстадийный отжиг. В результате во всех сплавах была получена преимущественно пластинчатая микроструктура. Установлено, что сплавы, легированные диспрози-ем, в те...

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“…The first approach can include: i) adding strong b-stabilizers (such as Re) and boron, [3,4] ii) adding boron in a level of about 1 at%, [4,5] iii) the use of b-solidifying alloys doped with b-stabilizing elements (such as Nb, Mo) and small boron additions. [6] The second approach is often associated with the use of the "massive transformation technique", which includes quenching from the single a phase field, followed by ageing in the temperature range of the (a+c)/a phase field. The most attractive advantages of this treatment are its simplicity and excluding boron as a grain refining agent necessary in the case of the first approach.…”

mentioning

confidence: 99%

Grain Refinement in Cast Ti‐46Al‐8Nb AND Ti‐46Al‐8Ta Alloys via Massive Transformation

Imayev¹,

Khismatullin

Oleneva

et al. 2008

Adv Eng Mater

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TiAl alloys are of increasing technical importance for high temperature applications in automotive and aerospace industries due to their low density combined with attractive high temperature properties. However, cast TiAl-based alloys usually suffer from poor room temperature ductility and a large scatter in other mechanical properties that impedes their wide industrial application. It is associated not only with intrinsic brittleness caused by directed type of interatomic bonding in the c-TiAl phase but also with a coarse columnar structure and a sharp casting texture which often evolves in castings during freezing and cooling. To overcome these deficiencies hot working (canned extrusion or forging) is usually applied in order to breakdown the ingot structure and to reach refined microstructure. However, this way is very laborious taking into account very high extrusion/forging temperatures. [1,2] Two approaches are now considered in the literature to refine the microstructures in cast TiAl alloys without involving any hot working: it is through solidification (during freezing and cooling) and through various heat treatments. The first approach can include: i) adding strong b-stabilizers (such as Re) and boron, [3,4] ii) adding boron in a level of about 1 at%, [4,5] iii) the use of b-solidifying alloys doped with b-stabilizing elements (such as Nb, Mo) and small boron additions. [6] The second approach is often associated with the use of the "massive transformation technique", which includes quenching from the single a phase field, followed by ageing in the temperature range of the (a+c)/a phase field. The most attractive advantages of this treatment are its simplicity and excluding boron as a grain refining agent necessary in the case of the first approach. The latter should be beneficial for ductility taking into account that coarse borides reduce the tensile ductility in cast TiAl alloys. [7] Quenching can lead to the massive a 7 ! c m phase transformation, where c m is the massive c phase, and subsequent ageing in the (a+c)/a phase field can provide a desirable refined (convoluted) lamellar structure, which is preferable from the viewpoint of the room temperature ductility and is expected to yield well balanced mechanical properties. [8][9][10][11][12][13] The main problem in developing the massive transformation as a useful processing route for c-TiAl alloys relates to the fact that high cooling rates and a very narrow cooling rate window are commonly required for the massive transformation. High cooling rates can lead to crack formation and is moreover hard to achieve in thick sections. Another problem is to know the temperature range at which c m transforms into a convoluted structure avoiding the re-transformation to a grains because this can lead to coarse lamellar c+a 2 structure during final cooling. Therefore, to utilize the massive transformation as a method of microstructural refinement in c-TiAl alloys special alloying additions such as niobium or tantalum are requested: they reduce the diffusivit...

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Alloy design concepts for refined gamma titanium aluminide based alloys

Cited by 311 publications

References 25 publications

A high-Nb TiAl alloy with highly refined microstructure and excellent mechanical properties fabricated by electromagnetic continuous casting

A high-Nb TiAl alloy with highly refined microstructure and excellent mechanical properties fabricated by electromagnetic continuous casting

Microstructure and mechanical properties of intermetallic γ-TiAl alloy alloyed with dysprosium

Grain Refinement in Cast Ti‐46Al‐8Nb AND Ti‐46Al‐8Ta Alloys via Massive Transformation

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