TWO-WAY SHAPE MEMORY EFFICIENCY OF THE Ti-Ni 54.4 Wt. (%) ENHANCED BY THERMAL TREATMENTS

2013 ◽  
Vol 06 (06) ◽  
pp. 1350057 ◽  
Author(s):  
CRISTINA URBINA ◽  
SILVIA DE LA FLOR ◽  
FRANCESC GISPERT ◽  
FRANCESC FERRANDO
Keyword(s):  
Phase Transformation ◽  
Thermal Cycling ◽  
Shape Memory ◽  
The Other ◽  
Thermal Treatments ◽  
Transformation Behavior ◽  
Memory Efficiency ◽  
Heat Treated ◽  
Sample Set ◽  
Training Efficiency

This paper experimentally analyzes the influence of repeated thermal cycling at zero stress on the two-way training efficiency for developing the two-way shape memory effect in TiNi shape memory alloys. Four different sets of TiNi wire are used in the study: two sets have been heat-treated to ensure a transformation path with no R-phase, whereas the other two sets have had the same heat-treatment which is then followed by repeated thermal cycling at zero stress to stabilize their phase transformation behavior. Subsequently, thermal cycling under constant stress two-way training is performed on each sample set. The study then analyzes the training efficiency and the recoverable two-way memory strain for each sample set. The results suggest that to obtain the best two-way material performance, that is, to obtain a substantial two way memory strain together with an increase in the efficiency of the training, the TiNi wire should be thermally cycled at zero stress prior to training until the phase transformation is stabilized.

Phase Constitution and Transformation Behavior of Ni2MnGa-Cu2MnAl Pseudobinary Intermetallic Compounds

2005 ◽  
Vol 475-479 ◽  
pp. 841-844 ◽  
Author(s):  
Hideki Hosoda ◽  
Yuji Higaki ◽  
Shuichi Miyazaki
Keyword(s):  
Continuous Solid Solution ◽  
Lattice Parameter ◽  
The Other ◽  
Phase Decomposition ◽  
Martensitic Transformation Temperature ◽  
Transformation Behavior ◽  
Solution Hardening ◽  
Phase Constitution ◽  
Heat Treated ◽  
Curie Temperature Tc

The phase constitution, lattice parameter, martensitic and magnetic transformation behavior and hardness of the Ni2MnGa-Cu2MnAl pseudobinary alloys designed as (Ni2MnGa)x(Cu2MnAl)1-x were investigated in order to improve magnetic properties of Ni2MnGa. It was revealed that L21 Ni2MnGa and Cu2MnAl make a continuous solid solution of (Ni,Cu)2Mn(Ga,Al) when heat treated at 1073K, and that the lattice parameter of the L21 phase increases monotonously with increasing the compositional ratio x, that is, the amount of Cu2MnAl. Curie temperature TC also increases with increasing x. On the other hand, the martensitic transformation temperature of Ni2MnGa seems to decrease rapidly by adding Cu2MnAl. Hardness of the alloys heat-treated at 1073K ranges from HV200 to HV370, and solution hardening was recognized by mixing. When heat treated at 773K, a phase decomposition from L21 phase to Cu9Al4 and b-Mn was confirmed in the Cu2MnAl-rich alloys. The phase decomposition causes a decrease in the lattice parameter of L21 phase and TC and a significant increase in hardness.

scholarly journals Microstructure and Phase Transformation Analysis of Ni50−xTi50Lax Shape Memory Alloys

Crystals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 345 ◽  
Author(s):  
Weiya Li ◽  
Chunwang Zhao
Keyword(s):  
Phase Transformation ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensite Transformation ◽  
Transformation Behavior ◽  
Ni Content ◽  
Start Temperature

The microstructure and martensitic transformation behavior of Ni50−xTi50Lax (x = 0.1, 0.3, 0.5, 0.7) shape memory alloys were investigated experimentally. Results show that the microstructure of Ni50−xTi50Lax alloys consists of a near-equiatomic TiNi matrix, LaNi precipitates, and Ti2Ni precipitates. With increasing La content, the amounts of LaNi and Ti2Ni precipitates demonstrate an increasing tendency. The martensitic transformation start temperature increases gradually with increasing La content. The Ni content is mainly responsible for the change in martensite transformation behavior in Ni50−xTi50Lax alloys.

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.

Sign in / Sign up

Export Citation Format

Share Document