EFFECT OF AGING ON THE MARTENSITIC TRANSFORMATION CHARACTERISTICS OF A <font>Ni</font>-RICH <font>NiTiHf</font> HIGH TEMPERATURE SHAPE MEMORY ALLOY

Abstract

The effect of aging on the microstructure and transformation temperatures of Ni 50.3 Ti 34.7 Hf 15 was studied. Small interparticle spacing induced by the precipitation of very fine particles, 4–5 nm in size, decreases M s after short term aging at 450°C and 500°C. The precipitate size and volume fraction increase with aging at longer times and higher temperatures, and as a consequence, M s increases due to Ni -depletion of the matrix. In general, thermal stability is improved due to precipitation hardening.