Transformation behaviour of a Ti50Ni47Fe3alloy I. Premartensitic phenomena and the incommensurate phase

Publisher Website
Google Scholar
Abstract
The transformation behaviour of TiNiFe alloys of nominal composition Ti50Ni47Fe3 has been studied by transmission electron microscopy and diffraction, and electrical resistance measurements between room temperature and −196°C. Based on the present results and complementary neutron and X-ray diffraction data, charge density wave (CDW) phenomena and associated phase transitions were found to be involved in the ‘premartensitic’ behaviour of the Ti50Ni47Fe3 alloys. The crystal structure of the high-temperature parent phase was confirmed to he the CsCl (B2) structure with a0, = 3·02 Å. On cooling from room temperature, 1/3(110) and 1/3(111) superlattice reflections appeared, coincident with the onset of the electrical resistance anomaly (increase). The ‘1/3’ superlattice reflections were observed to intensify with decreasing temperature, and close inspection showed that such reflections deviated slightly from the exact 1/3 positions relative to the parent CsCl structure, suggesting the formation of an incommensurate super-lattice over a 12°C temperature range. The appearance of the ‘1/3’ superlattice reflections is interpreted to be associated with the formation of CDWs. Antiphase-like microdomains ∼ 1500 Å in diameter were revealed in dark-field images obtained using the ‘1/3’ reflections, suggestive of discommensuration-type domains. The above behaviour is considered to correspond to a second-order ‘normal-to-incommensurate’ transition.