Irreversible processes during martensitic transformation in Zr-based shape memory alloys

The purpose of this paper is to explain the thermodynamical and shape memory behaviour in comparison with structural parameters for Zr-based intermetallics - a new class of potential shape memory alloys (SMA) for high-temperature applications [1]. Electrical resistivity, structural, shape memory and calorimetric measurements were carried out for the Zr2CuNi - Zr2CuCo quasibinary cross-section. It was shown that the martensitic transformation (MT) of the high -temperature B2 phase resulted in the simultaneous formation of the two martensitic phases belonging to the P2(1)/m (B19' type) and Cm space groups in the case of Zr2CuNi similar to ZrCu [2]. Co for Ni substitution causes the changes in the martensite volume fractions up to formation of only B19' type martensite in Zr2CuCo compound without significant changes in lattice parameters for both martensites. Such substitution also decreases generally the transformation heats and energy dissipated during the full cycle of MT. The non-thermoelastic behaviour that was observed in [1] for Zr2CuNi changes to a thermoelastic one in the case of MT in Zr2CuCo. Shape memory effect (SME) is nearly complete for alloys with high Ni content (not less than 85% of shape recovery ratio (K-sme)). It becomes complete at Co additions. The effect of the interaction between two martensites on the non-thermoelastic MT behaviour and SME in Zr-based intermetallics is discussed in the present paper.status: publishe

Comparison of high temperature shape memory behaviour for ZrCu-based, Ti-Ni-Zr and Ti-Ni-Hf alloys

New ZrCu-based high temperature shape memory alloys with M-s close to 500 K are under development. The shape memory behaviour of this material is compared to those of Ti-Ni-Zr and Ti-Ni-Hf alloys. The optimal compositions show a shape recovery of not less than 3% at temperatures above 470 K. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.status: publishe

High temperature shape memory alloys: problems and prospects

In this article, a review of the existing high temperature shape memory alloy (HTSMA) systems is given. Certain crucial disadvantages general to all HTSMAs and related to structural mechanisms of the martensitic transformation (MT) taking place at elevated temperatures are described. The perspectives of the HTSMA's application are also discussed.status: publishe

Thermal characteristics of phase transformations in Fe-Pt alloy

The effect of ordering on the thermal characteristics of the magnetic and martensite transitions in the Fe-Pt alloy with a composition close to stoichiometric Fe₃Pt composition is analyzed. It is found that a transition to a partly ordered state reduces the specific heat variation and thermal effect of the material due to the magnetic transition.status: publishe

Martensitic transformation and shape memory effect in Ni₃Ta: A novel high-temperature shape memory alloy

This paper is dedicated to the first observations of the martensitic transformation (MT) and shape memory effect in Ni₃Ta intermetallic compound. It was found that Ni₃Ta undergoes MT with 50 K temperature hysteresis at elevated temperatures (Ms = 530 K, Mf = 500 K, As = 550 K, Af = 580 K). Thermal cycling over the temperature interval of MT does not affect MT temperatures except for a slight shift of the reverse MT temperatures during the first cycle. The crystal structure parameters of the austenite and martensite are determined. The volume change during forward MT deduced from the austenite and martensite lattice parameters relation is -0.45%. The shape recovery after 10% compression at room temperature is almost complete although it takes place in a wide temperature interval—about 300 K. This alloy might open new perspectives for the application of high-temperature shape memory alloys (HTSMA).status: publishe

Phase stability during martensitic transformation in ZrCu intermetallics: crystal and electronic structure aspects

This article is dedicated to the estimation of the relative stability for B2, B19` and Cm phase in ZrCu intermetallic compound through the ab-initio electronic structure calculations and subsequent crystal structure Rietveld refinement. The information about electronic and crystal structure of phases in ZrCu will allow selecting for this high temperature shape memory alloy such alloying elements that will significantly improve shape memory behavior through definite structural changes.status: publishe