MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Diffusion Bonding Associated with Phase Transformation in (γ+β) Micro-duplex Titanium Aluminides
Naoya MasahashiShuji HanadaYouji Mizuhara
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2001 Volume 42 Issue 6 Pages 1028-1034

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Abstract

Microstructure and bonding strength of diffusion-bonded γ titanium aluminide alloys have been investigated focusing on phase transformation during diffusion bonding. High resolution scanning electron microscopy (SEM) observation revealed that lamellar grains are evolved near a jointed interface in (γ+β) micro-duplex alloys bonded at high temperatures, while not alloys bonded at low temperatures. This result is consistent with the proposed TTT diagram with the a lamellar nose. The transformation accompanied by the redistribution of Cr is evidenced by calculating Cr composition in each phase. Lamellar structure is also observed at a localized region in the (γ+β) micro-duplex ternary alloy bonded at high temperatures. It is speculated that this region is exposed to a stress high enough to accelerate the transformation, thereby shifting the lamellar nose to shorter time or lower temperature in the TTT diagram. The phase transformation in the (γ+β) micro-duplex ternary alloy is due to the low thermal stability of the β phase, enhancing atomic mass transport by Cr redistribution. Mechanical test revealed the high bonding strength in (γ+β) micro-duplex alloys, in which fracture was characterized by rugged fractography across lamellar boundaries in fracture surface. Thin layer is produced at the jointed interface uniformly in the micro-duplex alloy and inhomogeneously in the other two samples.

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© 2001 The Japan Institute of Metals and Materials
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