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

Abstract

ABSTRACTSolution treatment is an important process parameter in the context of thermomechanical processing of shape memory alloys. It is one of the preliminary steps thatis required to obtain martensite in the alloys. As far as martensite is concerned, itforms the basis of shape memory effect as shape memory alloys are usedcapitalizing on their unique properties of shape memory effect and superelasticeffect. It is well known that the grain size of austenite in the solutionized conditiondepends on the austenitizing/solutionizing temperature. Moreover, the solutiontreatment temperature influences the transformation temperatures of SMAS. It hasbeen found by researchers that solutionizing temperature brings about modification inthe grain size, the grain boundary angles, and the annealing twins. The majorobjective of the present work is to assess the influence of modifications in themicrostructural features brought about increasing/decreasing the solution treatmenttemperature. Optical microscopic and back scattered electron diffraction studiesreveal the microstructural changes brought about by changing the solutionizingtemperature. The X-ray diffraction experiments reveal the increase in SIEM in thealloy that was solution treated at 800, 900, 1000°C.The TEM studies reveal the formation of stacking faults and their interaction with oneanother and also with the grain boundaries. The results indicate that solutionizing atan optimal temperature of 1000°C leads to increased shape recovery strain as wellas shape recovery stress. The results are presented and discussed in the paper.