The influence of post-bond heat treatment on microstructural development in martensite-forming NiAl–NiTi transient liquid phase bonds employing copper interlayers


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Abstract

An investigation is presented of the influence of post-bond heat treatment on microstructural development in transient liquid phase bonds between L10 martensite-forming Ni–24 at% Al–16 at% Cr and nominally stoichiometric NiTi which transforms to monoclinic (distorted B19 type) martensite. The joints discussed in this article were prepared using 50 μm thick commercial purity copper (99.8 wt% Cu) interlayers and were bonded at 1150°C for 1 h. The resulting bonds were post-bond heat treated at 1000°C for times varying between 4 and 12 h and then characterized by edge-on transmission electron microscopy.The article discusses the formation of Ni2AlTi (with the L21 structure) at the bond-line and considers differences in the mode of Ni2AlTi precipitation between bonding and post-bond heat treatment. Changes in the nature of Ni3(Al, Ti) precipitation in the NiTi substrate from DO24 to L12 type are examined, as is the homogenization of the matrix of the NiTi substrate adjacent to the joint. Precipitation of Ni3Al in the NiAl substrate is also considered.

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