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

N Thiyaneshwaran,B Ravisankar,K Sivaprasad

doi:10.1038/s41598-018-35247-0

N Thiyaneshwaran, B Ravisankar + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-35247-0

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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.

Highlights

20 times higher than Ti with the formation of Kirkendall pores near the Al/TiAl3 interface
On discussing the TiAl3 growth phenomenon in Ti/Al couple, diffusion kinetics plays an important role in determining the interface where the faster growth of TiAl3 takes place, as the individual Ti and Al atoms diffuse across the intermetallic layer to react with the respective interfaces
It is expected that Ti(Al) and Al(Ti) solid solution formation precedes the TiAl3 nucleation at both Ti/TiAl3 and Al/TiAl3 interfaces

Summary

Introduction

20 times higher than Ti with the formation of Kirkendall pores near the Al/TiAl3 interface. Ti/TiAl3/Al metal intermetallic laminates (MILs) are considered to be one of the promising materials for defense and aerospace applications due to its combined properties such as lower density, high specific strength and relatively good oxidation and corrosion resistance[1,2,3,4] In these MILs, TiAl3 is the only intermetallic phase that formed between Ti and Al at relatively lower temperatures (below Al melting point) as other intermetallic phases such as Ti3Al, TiAl and TiAl2 are expected to form either at higher temperatures or after the consumption of Al5. The studies conducted on Ti/Al system depicts, Al to be the dominant diffusing species at temperatures below Al melting point while Ti was considered to diffuse faster at higher temperatures especially above Al melting temperature[6,7,8,9] This led to the conclusion that TiAl3 nucleates due to the high diffusion of Al towards Ti and the nucleation of TiAl3 phase should be concentrated mostly at Ti/TiAl3 interface. The present work is mainly focused on calculating interdiffusion co-efficient of Ti and Al and thereby to clarify the contradictions in nucleation and growth phenomenon of TiAl3 intermetallic phase in multi-laminated Ti/Al diffusion couple

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Conclusion