Microstructural Characterization of NiTi-based Beta2/Ni2TiAl-based Beta-prime Two Phase Alloys
- ABSTRACT -
H. Murakami, P. J. Warren, T. kumeta, Y. Koizumi and H. Harada
Published in Proceedings of
2nd Internat. Symp. on "Microstructural Intermetallics 1997"
held at Seven Spring Mt. Champion, Penn. U.S.A, Sep. 25,1997
Abstract
The microstructural evolution of beta2(NiTi-based) / beta-prime(Ni2TiAl-based) two phase alloys as a function of aging time has been investigated using transmission electron microscopy, atom probe field ion microscopy, and high-temperature X-ray diffractometry. The materials investigated were Ni49Ti41.7Al7.3Mo2 and Ni49Ti41.7Al7.3Cr2 quaternary alloys together with a Ni50Ti42.5Al7.5 ternary alloy as a reference. These materials all showed supersaturated beta2 single phase microstructures after homogenization heat treatment at 1200 deg. C for 2 hrs, and coherent cuboidal precipitation of beta-prime phase after the early stages of the aging treatment at 800 deg. C (0.2hrs). Further aging caused precipitate coarsening and alignment followed by loss of coherence and coalescence (after 10 hrs for Ni49Ti41.7Al7.3Mo2 and 100 hrs for Ni49Ti41.7Al7.3Cr2 at 800 deg. C). Atom probe analyses revealed that both Mo and Cr partition preferentially into beta2 phase matrices. The different rates of change in morphology between the alloys investigated is discussed in terms of the partitioning behavior of the alloying additions and the resultant changes in lattice misfits.
go to NiTi-base High Temp. Alloy
go to Hith Temperature Materials 21 Project Home Page