OPTIMIZATION OF SHAPE MEMORY EFFECT IN FE-BASED SHAPE MEMORY ALLOYS BY MODIFICATION OF SOLUTION TREATMENT TEMPERATURE

Document Type : Original Article

Authors

1 Central Metallurgical and Research and Development Institute (CMRDI), Cairo, Egypt.+

2 corresponding author.

3 Department of Metallurgical and Materials Engineering, Indian Institute of

4 Central Metallurgical and Research and Development Institute (CMRDI), Cairo, Egypt.

Abstract

ABSTRACT
Solution treatment is an important process parameter in the context of thermo
mechanical processing of shape memory alloys. It is one of the preliminary steps that
is required to obtain martensite in the alloys. As far as martensite is concerned, it
forms the basis of shape memory effect as shape memory alloys are used
capitalizing on their unique properties of shape memory effect and superelastic
effect. It is well known that the grain size of austenite in the solutionized condition
depends on the austenitizing/solutionizing temperature. Moreover, the solution
treatment temperature influences the transformation temperatures of SMAS. It has
been found by researchers that solutionizing temperature brings about modification in
the grain size, the grain boundary angles, and the annealing twins. The major
objective of the present work is to assess the influence of modifications in the
microstructural features brought about increasing/decreasing the solution treatment
temperature. Optical microscopic and back scattered electron diffraction studies
reveal the microstructural changes brought about by changing the solutionizing
temperature. The X-ray diffraction experiments reveal the increase in SIEM in the
alloy that was solution treated at 800, 900, 1000°C.
The TEM studies reveal the formation of stacking faults and their interaction with one
another and also with the grain boundaries. The results indicate that solutionizing at
an optimal temperature of 1000°C leads to increased shape recovery strain as well
as shape recovery stress. The results are presented and discussed in the paper.

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