Publication: Thermal and mechanical treatment of shape memory alloy for two-way shape memory behaviour
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Date
2023-07-01
Authors
Muhammd Amirul Aiman Bin Anuar
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Abstract
Thermal and mechanical treatment processes play a crucial role in shaping the
properties and performance of Nickel-Titanium (NiTi) alloys. These alloys possess
exceptional qualities, such as shape memory effect and super-elasticity, making them
highly sought after in diverse industries including biomedical, aerospace, and robotics.
The objective of this study was to employ thermal and mechanical treatment techniques
to modify the microstructure of NiTi alloys and enhance their functional properties. The
focus was on investigating the effects of these treatments on phase transformations and
mechanical behaviour, specifically comparing annealed and as-received specimens of
NiTi alloy.
To analyse the impact of thermal and mechanical treatment, the study examined
the shape memory behaviour of the NiTi alloy using both two-way and one-way
analyses. The alloy's response to different temperatures was observed to understand its
behaviour. Furthermore, as part of the research methodology, the annealed specimens
were subjected to testing using Differential Scanning Calorimetry (DSC). This allowed
for the observation and analysis of the transformation temperature, enabling a
comparison between the annealed specimens and the as-received specimens. The DSC
analysis provided valuable insights into the thermal behaviour of the NiTi alloys and
helped evaluate the effectiveness of the annealing process in altering the transformation
characteristics of the material.
The analysis of the obtained data demonstrated that subjecting the NiTi alloy to
annealing at elevated temperatures (550 – 600 °C) had significant consequences on its
functional behaviour. It was observed that such high-temperature annealing led to a
considerable increase in residual strain, while concurrently resulting in a noteworthy
decrease in transformation stress during the initial cycles and indicated a degradation
of the alloy's functional behaviour.
This degradation exerted an influence on the transformation temperatures and
hysteresis of the NiTi alloy, potentially leading to a shift in phase transition
temperatures and alterations in both the shape memory effect and super-elastic
properties. It is recommended that annealing of the 50.6% NiTi alloy be carried out at
a temperature of 600 °C for a duration of 30 minutes. This specific annealing condition
was found to be optimal for effectively modifying the microstructure of the alloy. By subjecting the alloy to this annealing condition, the redistribution of atoms within the
NiTi alloy can be achieved without incurring oxidation, thus preserving the alloy's
desired properties.