Abstract
In this report, we present findings of systematic research on NiCoMnAl alloys, with the purpose of acquiring a higher thermal transformation arrest temperature (TA). By systematic research, TA in the NiCoMnAl alloy systems was raised up to 190 K, compared to the highest TA of 130 K in NiCoMnIn. For a selected alloy of Ni40Co10Mn33Al17, magnetization measurements were performed under a pulsed high magnetic field, and the critical magnetic field-temperature phase diagram was determined. The magnetic phase diagram for Ni50-xCoxMn50-yAly was also established. Moreover, from the discussion that the formerly called “kinetic arrest phenomenon” has both thermodynamic and kinetic factors, we suggest a terminology change to the “thermal transformation arrest phenomenon”.
Highlights
Kinetic Arrest Phenomenon and Thermal Transformation Arrest PhenomenonIt has been reported in Ni(Co)MnIn alloys that the martensitic transformation is interrupted during the cooling process, and the coexisting martensite and parent phases stay “stable” at low temperatures, even when the magnetic field is removed [1,2]
We suggest and will on neutrally call this phenomenon the “thermal transformation arrest (TTA) phenomenon” and the corresponding temperature, at which the forward martensitic transformation stops, to be the “thermal transformation arrest temperature (TA )”
The magnetic properties of the Ni50−x Cox Mn50−y Aly alloy system were systematically investigated with the purpose of raising the thermal transformation arrest temperature (TA )
Summary
It has been reported in Ni(Co)MnIn alloys that the martensitic transformation is interrupted during the cooling process, and the coexisting martensite and parent phases stay “stable” at low temperatures, even when the magnetic field is removed [1,2]. The arrested parent phase during field cooling can be considered to be a thermodynamic phenomenon, while when the magnetic field is removed, it does not transform to the martensite phase, mainly because of kinetic reasons. Since the process of magnetic field-induced reverse martensitic transformation is used for actuators, the consideration only focuses on the heating process, and the temperature range available for practical application is very limited, as shown by ∆T0p. (b) By adjusting the composition of the alloy, the flat portion of the thermal transformation arrest phenomenon is utilized to obtain a wider temperature window for application. This process has been shown to be easy to realize by former studies. Approaches for modification of the shape of the H0 –T diagram have not been reported to date
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