Relationship between grain size and thermal hysteresis of martensitic transformations in Cu-based shape memory alloys

2017 ◽  
Vol 135 ◽  
pp. 5-9 ◽  
Author(s):  
P. La Roca ◽  
L. Isola ◽  
Ph. Vermaut ◽  
J. Malarría
Keyword(s):  
Grain Size ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Thermal Hysteresis ◽  
Martensitic Transformations

Martensitic Transformations and Functional Stability in Ultra-Fine Grained NiTi Shape Memory Alloys

2008 ◽  
Vol 584-586 ◽  
pp. 852-857 ◽  
Author(s):  
Juri Burow ◽  
Egor Prokofiev ◽  
Christoph Somsen ◽  
Jan Frenzel ◽  
Ruslan Valiev ◽  
...  
Keyword(s):  
Grain Size ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Thermomechanical Processing ◽  
High Pressure Torsion ◽  
Martensitic Transformations ◽  
Coarse Grained ◽  
Functional Stability ◽  
Fine Grained ◽  
Niti Shape Memory Alloys

Martensitic transformations in NiTi shape memory alloys (SMAs) strongly depend on the microstructure. In the present work, we investigate how martensitic transformations are affected by various types of ultra-fine grained (UFG) microstructures resulting from various processing routes. NiTi SMAs with UFG microstructures were obtained by equal channel angular pressing, high pressure torsion, wire drawing and subsequent annealing treatments. The resulting material states were characterized by transmission electron microscopy and differential scanning calorimetry (DSC). The three thermomechanical processing routes yield microstructures which significantly differ in terms of grain size and related DSC chart features. While the initial coarse grained material shows a well defined one-step martensitic transformation on cooling, two-step transformations were found for all UFG material states. The functional stability of the various UFG microstructures was evaluated by thermal cycling. It was found that UFG NiTi alloys show a significantly higher stability. In the present work, we also provide preliminary results on the effect of grain size on the undercooling required to transform the material into B19’ and on the related heat of transformation.

Functional Properties of Ti-Ni-Based Shape Memory Alloys

2008 ◽  
Vol 59 ◽  
pp. 156-161 ◽  
Author(s):  
I. Khmelevskaya ◽  
Sergey Prokoshkin ◽  
Vladimir Brailovski ◽  
K.E. Inaekyan ◽  
Vincent Demers ◽  
...  
Keyword(s):  
Grain Size ◽  
Cold Rolling ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Functional Properties ◽  
High Pressure Torsion ◽  
Martensitic Transformations ◽  
Critical Temperatures ◽  
Recoverable Strain ◽  
Ultrafine Grained

The main functional properties (FP) of Ti-Ni Shape Memory Alloys (SMA) are their critical temperatures of martensitic transformations, their maximum completely recoverable strain (er,1 max) and maximum recovery stress (sr max). Control of the Ti-Ni-based SMA FP develops by forming well-developed dislocation substructures or ultrafine-grained structures using various modes of thermomechanical treatment (TMT), including severe plastic deformation (SPD). The present work shows that TMT, including SPD, under conditions of high pressure torsion (HPT), equal-channel angular pressing (ECAP) or severe cold rolling followed by post-deformation annealing (PDA), which creates nanocrystalline or submicrocrystalline structures, is more beneficial from SMA FP point of view than does traditional TMT creating well-developed dislocation substructure. ECAP and low-temperature TMT by cold rolling followed by PDA allows formation of submicrocrystalline or nanocrystalline structures with grain size from 20 to 300 nm in bulk, and long-size samples of Ti-50.0; 50.6; 50.7%Ni and Ti-47%Ni-3%Fe alloys. The best combination of FP: sr max =1400 MPa and er,1 max=8%, is reached in Ti-Ni SMA after LTMT with e=1.9 followed by annealing at 400°C which results in nanocrystalline (grain size of 50 to 80 nm) structure formation. Application of ultrafine-grained SMA results in decrease in metal consumption for various medical implants and devices based on shape memory and superelastiсity effects.

On the effect of aging on martensitic transformations in Ni-rich NiTi shape memory alloys

2005 ◽  
Vol 14 (5) ◽  
pp. S186-S191 ◽  
Author(s):  
Gunther Eggeler ◽  
Jafar Khalil-Allafi ◽  
Susanne Gollerthan ◽  
Christoph Somsen ◽  
Wolfgang Schmahl ◽  
...  
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensitic Transformations ◽  
Niti Shape Memory Alloys

Thermodynamic Analysis of Thermoelastic Martensitic Transformations

2004 ◽  
Vol 449-452 ◽  
pp. 1325-0 ◽  
Author(s):  
Yinong Liu
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Experimental Determination ◽  
Thermodynamic Parameters ◽  
Thermodynamic Analysis ◽  
Martensitic Transformations ◽  
Thermoelastic Martensitic Transformations ◽  
The Past ◽  
Concise Overview

This paper is concerned with the application of fundamental thermodynamic theories in the analysis of thermoelastic martensitic transformations in shape memory alloys, with a particular reference to polycrystalline NiTi. The discussion is delivered in two parts. The first part presents a concise overview of the fundamental theories of thermodynamics of thermoelastic martensitic transformations established in the past 30 years. The second part focuses on the principles governing the application of the theories, interpretation of the thermodynamic parameters defined in the theories, experimental determination of the parameters, and some common misperceptions and unjustified assumptions in practice concerning these parameters.

scholarly journals Role of grain size on the martensitic transformation and ultra-fast superelasticity in shape memory alloys

2015 ◽  
Vol 95 ◽  
pp. 37-43 ◽  
Author(s):  
Keith R. Morrison ◽  
Mathew J. Cherukara ◽  
Hojin Kim ◽  
Alejandro Strachan
Keyword(s):  
Grain Size ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory

Powder Metallurgical Processes for NiTi Shape Memory Alloys

2010 ◽  
Vol 636-637 ◽  
pp. 928-933
Author(s):  
Filipe Neves ◽  
Francisco Manuel Braz Fernandes ◽  
Isabel M. Martins ◽  
Jose Brito Correia ◽  
Manuela Oliveira ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensitic Transformations ◽  
Reactive Extrusion ◽  
Powder Mixtures ◽  
Heat Treated ◽  
Niti Shape Memory Alloys ◽  
Metallurgical Processes ◽  
Niti Matrix

Two promising powder metallurgy (PM) processes were used for the fabrication of NiTi shape memory alloys (SMA): Mechanically Activated Reactive FOrging Synthesis (MARFOS) and Mechanically Activated Reactive Extrusion Synthesis (MARES). In these two processes, equimolar powder mixtures of elemental Ni and Ti are first mechanically activated and then forged/extruded at relatively low temperature. Afterwards, heat treatments are used to promote homogenization and to adjust the composition of the NiTi matrix. When MARFOS and MARES processes are compared some differences have been observed but only in relation to the extent of phase transformation and to the degree of densification. The crystallite size was less than 100 nm for all the phases which indicates nanostructured materials and multi-step martensitic transformations could be observed in heat treated materials.

Fabrication of Fine Grain Size Shape Memory Alloys Through Crystallization of Amorphous Ribbon

1995 ◽  
Vol 400 ◽  
Author(s):  
J. D. Shi ◽  
J. L. Ma ◽  
Y. Gao ◽  
Z. J. Pu ◽  
K. H. Wu
Keyword(s):  
Grain Size ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Amorphous Materials ◽  
Crystallization Process ◽  
Amorphous Material ◽  
Continuous Heating ◽  
Fine Grain ◽  
Mean Grain Size ◽  
The Mean

AbstractThe objective of this work is to fabricate fine grain size NiTi-based shape memory alloys through crystallization of amorphous materials. An amorphous material with a composition of Ti50Ni25Cu25 was used as a sample for this study. First, a systematic investigation was conducted to understand the kinetics of the crystallization process of amorphous materials under an isothermal mode and under a continuous heating mode, respectively. The characteristic parameters associated with the crystallization process, such as the starting and finishing times for the isothermal crystallization process, the peak temperature for the continuous heating crystallization process, and the activation energy of the material were determined. Based on the results of the kinetic study, a series of isothermal annealing experiments were conducted to characterize the microstructure of the fully crystallized materials. The TEM micrographs indicate that the mean grain size of the fully crystallized Ti50Ni25Cu25 alloy is independ of isothermal temperature. The mean grain size is around 400-500nm, which is 1/10 of the grain size of usual NiTi based shape memory alloys. In addition, the crystallization micro-mechanism of the amorphous material is discussed based on TEM observations.

Ab initio modeling of martensitic transformations (MT) in magnetic shape memory alloys

2007 ◽  
Vol 310 (2) ◽  
pp. 2761-2763 ◽  
Author(s):  
P. Entel ◽  
M.E. Gruner ◽  
W.A. Adeagbo ◽  
C.-J. Eklund ◽  
A.T. Zayak ◽  
...  
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Ab Initio ◽  
Martensitic Transformations ◽  
Magnetic Shape Memory ◽  
Magnetic Shape Memory Alloys ◽  
Ab Initio Modeling
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