Load-biased martensitic transformation strain of Ni-Ti-Co strip obtained by Twin-Roll Casting technique.

ISOLA, LUCIO M.; LA ROCA, PAULO; ROATTA, ANALIA; MALARRÍA, JORGE A.

Paris

Simposio; Oral presentation (Laboratoire de Métallurgie Structurale); 2013

Laboratoire de Métallurgie Structurale-Ecole Nationale Superieure de Chimie de Paris

Mechanical properties of the Ti−47Ni−3Co (at.%) strips produced by twin-roll casting are analyzed, focusing on the maximum recoverable strain obtained by inducing the martensitic transformation under constant tensile load. The recoverable strain achieves a value close to 5.5 % for a load of ∼120 MPa. The microstructure shows a typical cellular solidification structure, where the austenite grains tend to a columnar array morphology with strong 100 B2 fiber texture aligned with ND (perpendicular to the strip surface). On the basis of the measured texture, the maximum B2 → B19′transformation strain was estimated at 5.6%, using a Sachs-type upper bound model, which averages the most favorable martensite variants in each grain, disregarding interactions between them. The agreement between the measured maximum recoverable strain and the model?s outcome is ascribed to special properties of Ni-T i alloys which allow it to overcome imcompatibilities in shape changes of transforming grains in this particular Polycrystalline environment.