Investigation of Ageing Phenomena in CuAlNi Based Shape Memory Alloys

2007 ◽  
Vol 537-538 ◽  
pp. 129-136 ◽  
Author(s):  
Marton Benke ◽  
Valéria Mertinger ◽  
E. Nagy ◽  
Jan Van Humbeeck
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Ternary Alloy ◽  
Room Temperature ◽  
Beta Phase ◽  
Heat Treatments ◽  
Thermoelastic Martensitic Transformation ◽  
Transformation Temperatures ◽  
Exothermic Process

The ageing phenomena and its effect on the thermoelastic martensitic transformation was investigated in three Cu-base SMAs. The transformation temperatures shifted to higher temperatures due to aging in the beta-phase. To increase the alloy’s ductility, a definite amount of Mn (4 wt%) and Fe (2 wt%) were added to the ternary alloy. The thermoelastic martensitic transformation was found in the not-aged samples of the CuAlNiMn and CuAlNiMnFe alloys. This transformation was destroyed due to ageing heat treatments by a fairly unknown exothermic process. The thermoelastic martensitic transformation appeared again in the aged CuAlNiMn and CuAlNiMnFe samples after keeping them on room temperature for a few months. This phenomena was investigated by DSC, SEM, TEM, and XRD.

In situ TEM study of irradiation-induced transformation in TiNi shape memory alloys

2003 ◽  
Vol 792 ◽  
Author(s):  
X. T. Zu ◽  
F.R. Wan ◽  
S. Zhu ◽  
L. M. Wang
Keyword(s):  
Phase Transformation ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Electron Irradiation ◽  
Room Temperature ◽  
Critical Voltage ◽  
In Situ Tem ◽  
In Situ Observation

ABSTRACTTiNi shape memory alloy (SMA) has potential applications for nuclear reactors and its phase stability under irradiation is becoming an important topic. Some irradiation-induced diffusion-dependent phase transformations, such as amorphization, have been reported before. In the present work, the behavior of diffusion-independent phase transformation in TiNi SMA was studied by electron irradiation at room temperature. The effect of irradiation on the martensitic transformation of TiNi shape memory alloys was studied by Transmission Electron Microscopy (TEM) with in-situ observation and differential scanning calorimeter (DSC). The results of TEM and DSC measurements show that the microstructure of samples is R phase at room temperature. Electron irradiations were carried out using several different TEM with accelerating voltage of 200 kV, 300 kV, 400 kV and 1000 kV. Also the accelerating voltage in the same TEM was changed to investigate the critical voltage for the effect of irradiation on phase transformation. It was found that a phase transformation occurred under electron irradiation above 320 kV, but never appeared at 300 kV or lower accelerating voltage. Such phase transformation took place in a few seconds of irradiation and was independent of atom diffusion. The mechanism of Electron-irradiation-induced the martensitic transformation due to displacements of atoms from their lattice sites produced by the accelerated electrons.

Effect of L21 Ordering on the Martensitic and Intermartensitic Transformations in a Ni-Mn-Ga Shape Memory Alloy

2007 ◽  
Vol 130 ◽  
pp. 127-134
Author(s):  
Concepcio Seguí ◽  
Jaume Pons ◽  
Eduard Cesari
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloy ◽  
Single Crystal ◽  
Shape Memory ◽  
Parent Phase ◽  
Heat Treatments ◽  
Free Energies ◽  
Transformation Temperatures ◽  
Reverse Martensitic Transformation ◽  
Order Degree

The present work analyses the influence of austenite ordering on a single crystal Ni-Mn- Ga alloy which displays, on cooling, a sequence of martensitic (MT) and intermartensitic (IMT) transformations. The MT and IMT show distinct behaviour after ageing in austenite: while the MT temperatures are not affected by the performed heat treatments, the IMT shifts toward lower temperatures after quenching from increasing temperatures, progressive recovery occurring upon ageing in parent phase. Such evolution can be related to changes in the L21 order degree, in the sense that ordering favours the occurrence of the intermartensitic transformation, while it does not affect noticeably the forward and reverse martensitic transformation temperatures. The closeness of the free energies of the different martensite structures allows to explain this behaviour.

scholarly journals Effect of Stoichiometry on Shape Memory Properties and Functional Stability of Ti–Ni–Pd Alloys

Materials ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 798 ◽  
Author(s):  
Yuki Hattori ◽  
Takahiro Taguchi ◽  
Hee Kim ◽  
Shuichi Miyazaki
Keyword(s):  
High Temperature ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Thermal Cycling ◽  
Shape Memory ◽  
Stoichiometric Composition ◽  
Atomic Ratio ◽  
Transformation Temperatures ◽  
Shape Memory Properties ◽  
Ti Content

Ti–Ni–Pd shape memory alloys are promising candidates for high-temperature actuators operating at above 373 K. One of the key issues in developing high-temperature shape memory alloys is the degradation of shape memory properties and dimensional stabilities because plastic deformation becomes more pronounced at higher working temperature ranges. In this study, the effect of the Ti:(Ni + Pd) atomic ratio in TixNi70−xPd30 alloys with Ti content in the range from 49 at.% to 52 at.% on the martensitic transformation temperatures, microstructures and shape memory properties during thermal cycling under constant stresses were investigated. The martensitic transformation temperatures decreased with increasing or decreasing Ti content from the stoichiometric composition. In both Ti-rich and Ti-lean alloys, the transformation temperatures decreased during thermal cycling and the degree of decrease in the transformation temperatures became more pronounced as the composition of the alloy departed from the stoichiometric composition. Ti2Pd and P phases were formed during thermal cycling in Ti-rich and Ti-lean alloys, respectively. Both Ti-rich and Ti-lean alloys exhibited superior dimensional stabilities and excellent shape memory properties with higher recovery ratio and larger work output during thermal cycling under constant stresses when compared with the alloys with near-stoichiometric composition.

Self-Tension of Martensite during Constrained Transformation

2005 ◽  
Vol 475-479 ◽  
pp. 1937-1940 ◽  
Author(s):  
Li Shan Cui ◽  
Yan Jun Zheng
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
The Self ◽  
Experimental Results ◽  
Reverse Transformation ◽  
Transformation Temperatures ◽  
External Constraint

In a constrained martensitic transformation of shape memory alloys, a fraction of martensite is always retained in the materials. Experimental results showed that the remaining martensite could be plastically deformed by the generated recovery stresses. The self-tension process elevated the reverse transformation temperatures of the remaining martensite, and the external constraint conditions had no significant effect on the self-tension process of the remaining martensite.

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