scholarly journals Effect of post-deformation annealing on the R-phase transformation temperatures in NiTi shape memory alloys

2015 ◽  
Vol 62 ◽  
pp. 43-49 ◽  
Author(s):  
Xiebin Wang ◽  
Bert Verlinden ◽  
Jan Van Humbeeck
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Transformation Temperatures ◽  
Niti Shape Memory 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.

Experimental and FEM Analysis of the Fracture Behavior in NiTi Shape Memory Alloys

2006 ◽  
Vol 324-325 ◽  
pp. 919-922 ◽  
Author(s):  
Xin Mei Wang ◽  
Zhu Feng Yue
Keyword(s):  
Fracture Toughness ◽  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Fracture Behavior ◽  
Micromechanical Model ◽  
Crack Tip ◽  
Fem Analysis ◽  
Transformation Behavior ◽  
Niti Shape Memory Alloys

In the present work, the fracture toughness of a NiTi pseudoelastic alloy has been obtained by experiments on CT specimens, which is KIC =39.38MPa·m1/2. Then the stress induced phase transformation behavior in front of the crack tip of the CT specimen is simulated by a micromechanical model considering the different elastic properties between martensite and austenite. The results show that the pre-crack promotes phase transformation at the crack tip. And the phase transformation is localised near the crack tip. It is also shown that phase transformation reduces the Mises stress around the crack tip.

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