Abstract:
In the present work, a comparative study of the shape memory and thermomechanical
behavior of four alloys containing different amount of samarium have been carried out at
a strain rate of 0.08x10 -6 s -1 . After hot rolling, annealing and solution treatment, the alloy
samples were tensile deformed at room temperature from 1% to 5% and were then
recovered at 600 ̊C for 20 minutes repeatedly for six times to complete six training
cycles.
It has been found that the addition of samarium strengthens the austenitic matrix,
increases the c/a ratio and reduces the grain size. It has been noticed that the addition of
samarium (0.64 wt. %) improves the shape memory effect when the alloys were strained
from 1% to 5%. This improvement in shape memory effect presumably can be regarded
as the increase in strength, increase in c/a ratio and absence of ά (martensite). It has been
further noticed that when samarium contents are gradually reduced from 0.64 % to 0.21%
the shape memory effect decreases. The decrease in shape memory effect by the decrease
in samarium contents can be attributed to decrease in strength, decrease in c/a ratio and
formation of ά (martensite). It has been further noticed that the shape memory effect
decreases with the increase in amount of strain.
It is found that thermomechanical treatment (training) results in improvement of shape
memory effect and has a significant influence on mechanical parameters like proof stress
(σ
0.002 ),
critical stress (σ 0.0008 ) and strain hardening exponent. The improvement in shape
memory effect by thermomechanical treatment can be regarded as the effect of reduction
in the values of proof stress and critical stress during training which facilitates the
formation of ε (martensite). It has also been noticed that excessive training may result in
the formation of ά (martensite) due to continuous softening of the alloy during training,
thus degrading the shape memory effect. Finally, it has also been noticed that the addition
of samarium increases the values of proof stress, critical stress and strain hardening
exponent. Although the addition of samarium increases the values of proof stress, critical
stress and strain hardening exponent yet it has not an adverse effect on shape memory
effect.
