PHASE-FRACTION EVOLUTION DURING INCOMPLETE CYCLIC TRANSFORMATION IN TINI - CORRELATION OF ANALYTICAL MODELS WITH MAGNETIC-SUSCEPTIBILITY MEASUREMENTS

The response of titanium-nickel, and other alloys exhibiting thermoela stic martensite transformations, display phase-coexistence and hystere sis over a wide range of temperature, arising from the fourfold splitt ing of a single transformation temperature into M(f), M(s), A(s), and A(f). Attempts to precisely characterize the evolution of phase-fracti on during temperature reversals that involve incomplete transformation has led to the formulation of various hysteresis descriptions. We exa mine a description based on the Duhem-Madelung framework, which takes complete transformation behavior as constitutive input, and on this ba sis formally predicts the hysteresis associated with transformation ar rest and reversal. In conjunction with this effort, a series of magnet ic susceptibility measurements on TiNi has been conducted using a SQUI D susceptometer. The measured hysteresis in the temperature/susceptibi lity curves are qualitatively described by the Duhem-Madelung model.