Shape memory response of ni2mnga and nimncoin magnetic shape memory alloys under compression

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Title: Shape memory response of ni2mnga and nimncoin magnetic shape memory alloys under compression
Author: Brewer, Andrew Lee
Abstract: In this study , the shape memory response of Ni2MnGa and NiMnCoIn magnetic shape memory alloys was observed under compressive stresses . Ni2MnGa is a magnetic shape memory alloy (MSMA ) that has been shown to exhibit fully reversible , stressassisted magnetic field induced phase transformation (MFIPT ) in the I X -phase transformation because of a large magnetostress of 7 MPa and small stress hysteresis . The X -phase is a recently discovered phase that is mechanically induced , however , the crystal structure is unknown . To better understand the transformation behavior of Ni2MnGa single crystal with [100] orientation , thermal cycling and pseudoelasticity tests were conducted with the goal of determining the Clausius -Clapeyron relationships for the various phase transformations . This information was then used to construct a stresstemperature phase diagram that illustrates the stress and temperature ranges where MFIPT is possible , as well as where the X -phase may be found . NiMnCoIn is a recently discovered meta -magnetic shape memory alloy (MMSMA ) that exhibits unique magnetic properties . The ferromagnetic parent phase and the paramagnetic martensite phase allow the exploitation of the Zeeman energy . To gain a better understanding of the transformation behavior of NiMnCoIn , thermal cycling and pseudoelasticity tests were conducted on single crystals from two different batches with crystallographic orientations along the [100] (011 ) , [087] , and [25 7 15] directions . A stress -temperature phase diagram was created that illustrates the Clausius - Clapeyron relationships for each orientation and batch . SQUID tests revealed the magnetic response of the alloy as well as the suppression of the martensite start temperature with increasing magnetic field . Pseudoelasticity experiments with and without magnetic field were conducted to experimentally quantify the magnetostress as a function of magnetic field . For the first time , it has been shown that NiMnCoIn is capable of exhibiting magnetostress levels of 18 -36 MPa depending upon orientation , as well as nearly 6 .5 % transformation strain in the [100] direction . The results of this study reveal increased actuation stress levels in NiMnCoIn , which is the main limitation in most MSMAs . With this increased blocking stress , NiMnCoIn is a strong candidate for MFIPT .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1341
Date: 2009-05-15

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Shape memory response of ni2mnga and nimncoin magnetic shape memory alloys under compression. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1341 .

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