Martensite structures in Ti-rich Ti-Ni thin films were investigated. It was found that the existence of GP zones with coherency or Ti_2Ni precipitates with semi-coherency produces the formation of (001) compound twins as internal twinning. The structure consists of three domains in different orientations, each of which contains the (001) twins. These domains are related to each other by a (111) twinning orientation relationship, but the boundaries between the domains are divided into three types: (111) type, (001)//(11(1-bar)) type and nearly ((1-bar)(1-bar)3)-type. The last type of boundary was defined as a mixture of (001)//(11(1-bar)) and (11(1-bar))//(001) boundaries. The martensite structures in specimens with GP zones and Ti_2Ni precipitates are basically the same, but the martensite domain of the former specimen is much larger than that of the latter one. This is because the domains grow and pass through the GP zones by elastic deformation of the GP zones, while they stop in front of the Ti_2Ni precipitates or nucleate at the matrix-precipitate interfaces.
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