The effect of boron and alpha grain size on the massive transformation in Ti–46Al–8Nb–xB alloys

Hu, D.; Huang, Aijun; Novovic, Donka; Wu, Xinhua

doi:10.1016/j.intermet.2005.12.003

Cited by 33 publications

(28 citation statements)

References 14 publications

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“…Saage et al [8] noted that the cooling rates required for initiating massive transformation apparently depend on the compositions, and the element Ta can increase the tendency of massive γ formation because of its lower diffusion rate than Nb, which is also supported by the results from Imayev et al [11]. However, the addition of B suppresses the formation of the massive γ phase and increases the tendency of lamellar structure formation by the refinement of the high-temperature α phase, whereas the cooling rated needed for the onset of massive γ formation is hardly changed [18]. The massive γ phase is commonly reported to nucleate at the grain boundaries during cooling [9,19,20], which means that a fine-grained initial microstructure can facilitate the massive γ formation.…”

Section: Introductionsupporting

confidence: 56%

“…The cooling rate of oil-quenching should be lower than water-quenching; thus, more massive structures were expected in this sample [11]. This result might be related to the fact that boron has an effect on the kinetics of massive transformation [18]. The cooling rate with the same method will of course change for different specimen sizes.…”

Section: Effects Of Heat Treatment Parameters On the Massive Transformentioning

confidence: 91%

“…It can be seen from the images that when quenched from 1340 • C, a large volume fraction of massive γ phase, i.e., approximately 80%, is obtained. The remaining α 2 phase is a known result for higher cooling rates in literature because of the restricted range of the cooling rate for the massive transformation [7,18]. Beside the remaining α 2 phase, a tiny amount of β o phase is observed mostly at the boundaries of the α 2 phase.…”

Section: Effects Of Heat Treatment Parameters On the Massive Transformentioning

confidence: 98%

“…It seems that the borides at the boundary of α grains may have some effects on the nucleation of massive γ grains, which is beyond the scope of this article and needs further investigation. rate range of massive transformation [18], the prolonged heat treatment time may lead to enhanced aluminium depletion or oxidation. The increased amount of α grain boundaries also serve as the nucleation sites of massive γ, as implied by Figure 1c, in which most borides are in the center of the massive γ grains.…”

Section: Effects Of Heat Treatment Parameters On the Massive Transformentioning

confidence: 99%

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Microstructure Evolution of a Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y Alloy during Massive Transformation and Subsequent Annealing

Song

Wang

Xue

et al. 2018

Metals

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It has been widely reported that the microstructure refinement of TiAl alloys can be achieved by massive transformation and subsequent annealing in α 2 + γ two phase field. To achieve this goal, several heat treatment parameters must be adjusted, including the heat treatment temperature around single α phase field, the annealing temperature, and the annealing time for the precipitation of α 2 phase. Thus, a systematic study is needed for each alloy with different compositions. In this study, the heat treatment parameters for grain refinement via massive transformation of a high Nb-containing TiAl are investigated. Precipitation of α 2 phase during annealing is observed by transmission electron microscopy. It is found that 30 min at single α phase field is appropriate for the massive transformation; a full, massively transformed microstructure cannot be obtained by oil or water quenching. A short annealing time can result in a refined microstructure, whereas the sizes of the precipitated α 2 phase increases with the increase of annealing time. The α 2 phase can form at the interface of twin boundaries of the γ phase, following the Blackburn orientation relationship with both sides. The Vickers hardness is measured for the annealed samples, which remains relatively stable for different annealing times.

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Section: Introductionsupporting

confidence: 56%

Section: Effects Of Heat Treatment Parameters On the Massive Transformentioning

confidence: 91%

Section: Effects Of Heat Treatment Parameters On the Massive Transformentioning

confidence: 98%

Section: Effects Of Heat Treatment Parameters On the Massive Transformentioning

confidence: 99%

See 2 more Smart Citations

Microstructure Evolution of a Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y Alloy during Massive Transformation and Subsequent Annealing

Song

Wang

Xue

et al. 2018

Metals

View full text Add to dashboard Cite

show abstract

“…It has been observed that the a grain size has an important effect on the overall kinetics of the lamellar transformation and the critical cooling rate of the massive to lamellar transition [23]. This is explained by the fact that g lamellae preferentially nucleate on grain boundaries due to lattice defects and possible segregation of alloying elements.…”

Section: Introductionmentioning

confidence: 99%

A numerical model for the description of the lamellar and massive phase transformations in TiAl alloys

Rostamian

Jacot

2008

Intermetallics

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a b s t r a c tA phenomenological modelling approach has been developed to describe the massive transformation and the formation of lamellar microstructures during cooling in binary g titanium aluminides. The modelling approach is based on a combination of nucleation and growth laws which take into account the specific mechanisms of each phase transformation. Nucleation of massive and lamellar g is described with classical nucleation theory, accounting for the fact that nuclei are formed predominantly at a/ a grain boundaries. Growth of the massive g grains is based on theory for interface-controlled reactions. A modified Zener model is used to calculate the thickening rate of the g lamellar precipitates. The model incorporates the effect of particle impingement and coverage of the nucleation sites by the growing phase. The driving pressures of the phase transformations are obtained from Thermo-Calc based on the actual temperature and matrix composition. CCT diagrams and lamellar spacings calculated with the model are in good agreement with experimental data obtained from dedicated heat treatment experiments and from the literature. The model permitted investigating the influence of cooling rate, alloy chemistry and average a grain size upon the amount of massive g and the average thickness and spacing of the lamellae. In particular it indicates that the Al depletion of the a phase during lamellar precipitation seems to play an important role in the suppression of the massive transformation at moderate cooling rate and in the large lamellar spacings observed at low cooling rate.

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Alloy Design

2011

Gamma Titanium Aluminide Alloys

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In the TiAl literature, alloy and suitable processing technology development has played a signifi cant role for at least the last 20 years. Advances have been made, so that the strength levels achieved in technical alloys over the last few years are around double those of 20 years ago, while maintaining the same levels of roomtemperature ductility. Improvement of other properties such as creep and oxidation resistance has been achieved through alloying and the use of halogens, although improvement of other properties, such as toughness, through composition rather than microstructure has met with less success. It now seems well acknowledged that there is no universal alloy composition that is suitable for all applications; rather alloy composition must be tailored together with processing to achieve the required properties for specifi c components.Accurate information concerning the phase relationships in both binary Ti -Al and in multicomponent systems is very important in designing alloys and suitable heat treatments. This is because for a given alloy, properties are very dependent on microstructure, and microstructure is highly sensitive to composition. The high microstructure/composition sensitivity is perhaps one of the most challenging aspects in producing components from industrially produced ingot stock; as compositional variation within ingots can lead to fi nished components with a range of microstructures and thus properties. This is obviously unacceptable, especially for safety -relevant aerospace parts. A good overview concerning the infl uence of different alloying elements was published in 1993 [1] . This chapter will briefl y outline how alloys have developed over the last 20 years and discuss the different alloydesign philosophies. Effect of Aluminum ContentIn binary alloys, the aluminum level determines the initial phase to precipitate and the subsequent phase transformations that occur on solidifi cation. According to Huang and Hall [2] who published work in 1991 on binary alloys within the range Ti -(46 -60)Al made via rapid -solidifi cation processing, ductility is highest for duplex microstructures where the heat treatment is roughly in the middle of the 13 Gamma Titanium Aluminide Alloys: Science and Technology, First Edition.

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The effect of boron and alpha grain size on the massive transformation in Ti–46Al–8Nb–xB alloys

Cited by 33 publications

References 14 publications

Microstructure Evolution of a Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y Alloy during Massive Transformation and Subsequent Annealing

Microstructure Evolution of a Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y Alloy during Massive Transformation and Subsequent Annealing

A numerical model for the description of the lamellar and massive phase transformations in TiAl alloys

Alloy Design

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