Shape memory alloys with high transformation temperatures

doi:10.1016/j.materresbull.2012.04.118

Materials Research Bulletin

Volume 47, Issue 10, October 2012, Pages 2966-2968

https://doi.org/10.1016/j.materresbull.2012.04.118 Get rights and content

Abstract

This papers summarizes the alloys systems in which a martensitic transformation at high transformation temperatures occurs with potentials for shape memory effect.

Introduction

In recent years, the interest for shape memory alloys with high transformation temperatures (HTSMA) has significantly increased not only due to pure academic interest but also due to a market push especially from transport (aerospace, automobile), oil industry and robotics.

However, so far a real break-through has not been realized yet because of several problems: (much) lower quality than NiTi-alloys, stabilization of martensite (shift of transformation temperatures), decomposition of the matrix phase, plasticity problems, brittleness, oxidation, etc. In spite of those problems encountered, steady progress has been made on specific systems and special thermo-mechanical treatments have been elaborated to reach optimal behavior.

This paper summarizes the different systems in a temperature range between 100 °C and 1000 °C with an extensive reference and patent list

Section snippets

Definition of HTSMA

Conventional shape memory alloys (SMA) are limited to maximal A_f-temperatures of 120 °C, M_s generally being below 100 °C [1].

In order to distinguish low temperatures SMA (LTSMA) from high temperature SMA (HTSMA), we define HTSMA as alloys of which the reverse transformation A_s starts only above 120 °C (390 K) in stress-free condition. This definition might include alloys that show a forward transformation (M_s, M_f) below 100 °C but excludes alloys that show a reverse transformation above 120 °C only

Overview of HTSMA

In fact many alloy systems fulfill that simple condition, which does not mean they are suitable for applications.

The extensive research on Co-, Fe–Mn–Si-, Cu–Al–Ni-, Ni–Mn-, Ni–Al-, Ti(Pt Pd, Au,)- and Ni–Ti-based HTSMA reviewed by Beyer and Mulder [2], Otsuka and Ren [3], Van Humbeeck [1], Koval [4] and recently by Ma et al. [5] has added significant new knowledge and experience during the last decade. The HTSMA list mentioned above was replenished with Zr-based quasibinary [6], [7], Ta–Ru and

Some common HTSMA problems and work to be done

Martensitic (diffusionless) transformations in HTSMA take place at elevated temperatures where diffusion controlled processes, such as decomposition, recrystallization, recovery, cannot be neglected. In addition, it is necessary to alloy binary systems in order to adjust high temperatures of the martensitic transformation properly and to improve the ductility of the alloys. Such multi-component alloy systems are prone to decomposition processes. Besides, the initial structure and microstructure

Some interesting patents about HTSMA

•
US Patent 4,865,663. September 12, 1989 “High Temperature Shape Memory Alloys” (Ti–Ni–Pd).
•
US Patent 5,114,504. May 19, 1992, “High Transformation Temperature Shape Memory Alloys” (Ti–Ni–(Zr,Hf)).
•
US Patent 5,641,364, June 24, 1997, “Method of Manufacturing High Temperature Shape memory Alloys” (Ti–Ni–(Pd, Hf, Zr))
•
US Patent 6,010,584, January 4, 2000 “High Temperature Shape Memory Effect in Ruthenium Alloys” (Ru–(Ta, Nb))
•
US Patent 7,501,032 B1, March 10, 2009 “High Work Output Ni–Ti–Pt High

Acknowledgement

The author acknowledges FWO (Flemish Foundation for Scientific Research) for financial support by project number G.0576.09N.

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