Effects of microstructure and composition on constitutive response of high temperature shape memory alloys: Micromechanical modeling using 3-D reconstructions with experimental validation

NiTiHf alloys are high temperature Shape Memory Alloys (SMAs) suitable for actuation applications in a wide range of temperatures. Aging heat treatments SMAs cause the formation nano-sized, non-transforming and elastic precipitates, which modify phase transformation behavior. Experimental observations aged showed counterintuitive trend increasing strain with precipitation. In order to predict such microstructure effects on constitutive response precipitated SMAs, this work finite element based micromechanical modeling framework is developed. Two types representative volume elements considered: (i) exact 3-D reconstructions precipitates using transmission electron microscopy, (ii) less expensive ellipsoidal representation precipitates. The composition changes material modeled, their incorporated by considering dependency properties matrix. resulting model used responses different aging conditions Ni50.3Ti29.7Hf20 Ni50.3Ti34.7Hf15 SMAs. predictions good agreement experimental measurements, results presented confidence intervals from sample-to-sample variations. present constitutes first consideration real microstructures.