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Nucleation and growth of TiAl₃ intermetallic phase in diffusion bonded Ti/Al Metal Intermetallic Laminate.

ABSTRACT: A novel nucleation and growth phenomenon for TiAl₃ intermetallic phase in Ti/Al diffusion couple is proposed based on diffusion kinetics. The interdiffusion and intrinsic diffusion co-efficients are calculated to make evident of dominant diffusion of Al towards Ti in Ti/Al diffusion couple obtained by solid state diffusion bonding. It was surprising to observe that the diffusion rate of Al was around 20 times higher than Ti with the formation of Kirkendall pores near the Al/TiAl₃ interface. With such dominant diffusion of Al towards Ti, the nucleation and growth of TiAl₃ intermetallic phase in Ti/Al couple happens mainly at the Ti/TiAl₃ interface rather than Al/TiAl₃ interface which is evident by the presence of very fine nearly nano-sized TiAl₃ nuclei/grains near the Ti/TiAl₃ interface. Even though the intermetallic phase is expected to nucleate at Al/TiAl₃ interface, the relatively larger TiAl₃ grains near that interface depicts grain growth with minimal nucleation. The theoretical calculations on diffusion parameters are in accordance with experimental observations of TiAl₃ intermetallic growth phenomenon in Ti/Al system.

SUBMITTER: Thiyaneshwaran N

PROVIDER: S-EPMC6235842 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Nucleation and growth of TiAl3 intermetallic phase in diffusion bonded Ti/Al Metal Intermetallic Laminate.

Thiyaneshwaran N N Sivaprasad K K Ravisankar B B

Scientific reports 20181114 1

A novel nucleation and growth phenomenon for TiAl3 intermetallic phase in Ti/Al diffusion couple is proposed based on diffusion kinetics. The interdiffusion and intrinsic diffusion co-efficients are calculated to make evident of dominant diffusion of Al towards Ti in Ti/Al diffusion couple obtained by solid state diffusion bonding. It was surprising to observe that the diffusion rate of Al was around 20 times higher than Ti with the formation of Kirkendall pores near the Al/TiAl3 ...[more]

PMID: 30429519

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Project description:Coating system(s) will be required for Nb-silicide based alloys. Alumina forming alloys that are chemically compatible with the Nb-silicide based alloy substrate could be components of such systems. The intermetallic alloys Nb1.45Si2.7Ti2.25Al3.25Hf0.35 (MG5) and Nb1.35Si2.3Ti2.3Al3.7Hf0.35 (MG6) were studied in the cast, heat treated and isothermally oxidised conditions at 800 and 1200 °C to find out if they are αAl₂O₃ scale formers. A (Al/Si)alloy versus Nb/(Ti + Hf)alloy map, which can be considered to be a map for Multi-Principle Element or Complex Concentrated Nb-Ti-Si-Al-Hf alloys, and a [Nb/(Ti + Hf)]Nb5Si3 versus [Nb/(Ti + Hf)]alloy map were constructed making use of the alloy design methodology NICE and data from a previously studied alloy, and were used to select the alloys MG5 and MG6 that were expected (i) not to pest, (ii) to form αAl₂O₃ scale at 1200 °C, (iii) to have no solid solution, (iv) to form only hexagonal Nb₅Si₃ and (v) to have microstructures consisting of hexagonal Nb₅Si₃, Ti₅Si₃, Ti₅Si₄, TiSi silicides, and tri-aluminides and Al rich TiAl. Both alloys met the requirements (i) to (v). The alumina scale was able to self-heal at 1200 °C. Liquation in the alloy MG6 at 1200 °C was linked with the formation of a eutectic like structure and the TiAl aluminide in the cast alloy. Key to the oxidation of the alloys was the formation (i) of "composite" silicide grains in which the Nb₅Si₃ core was surrounded by the Ti₅Si₄ and TiSi silicides, and (ii) of tri-aluminides with high Al/Si ratio, particularly at 1200 °C and very low Nb/Ti ratio forming in-between the "composite" silicide grains. Both alloys met the "standard definition" of high entropy alloys (HEAs). Compared with HEAs with bcc solid solution and intermetallics, the VEC values of both the alloys were outside the range of reported values. The parameters VEC,  and  of Nb-Ti-Si-Al-Hf coating alloys and non-pesting Nb-silicide based alloys were compared and trends were established. Selection of coating alloys with possible "layered" structures was discussed and alloy compositions were proposed.

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Nucleation and growth of TiAl₃ intermetallic phase in diffusion bonded Ti/Al Metal Intermetallic Laminate.

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Nucleation and growth of TiAl<sub>3</sub> intermetallic phase in diffusion bonded Ti/Al Metal Intermetallic Laminate.

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