The Martensite Structure and Aging Precipitates of a TiNiHf High Temperature Shape Memory Alloy
Department of Materials Science, Dalian University of Technology, Dalian 116024, P.R. China
2 Beijing Laboratory of Electron Microscopy, Chinese Academy of Sciences, P.R. China
3 Department of Physics, Wuhan University, P.R. China
4 Florida International University, Miami, Florida, U.S.A.
The martensite and precipitate’s structure in a Ti36.5Ni48.5Hf 15 alloy are studied using transmission electron microscopy (TEM). The crystal structure of the martensite is basically keep invariant compared, with TiNi binary alloys. The lattice structure of the martensite is monoclinic with a = 0.293nm, b = 0.411nm , c = o.473nm and β = 100.4°. The space group is still P21/m. But the substructure in a martensite variant is (001)B19’ compound twins. The orientation relationships between parent phase and martensite phase are different from TiNi binary alloys, they are: (001)B2|| (011)B19’( B2||B19’. The crystal structure of precipitate formed at 873K are determined to be face-centered orthorhombic structure with A = 1.287nm , B= 0.874nm , C=2.622nm. The space group is F2/d 2/d 2/d.
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