Since the time when a Ni-Mn-Ga alloy with composition near to the stoichiometric Heusler structure has been recognized as material revealing ferromagnetic shape memory effect, the number of experimental results and its practical application still increases. Especially, non-stoichiometric composition attracts its attention due to a course of martensitic transformation. Several types of martensite can be found such as non-modulated tetragonal martensite (T), five-layerd martensite (10M) as well as seven-layerd martensite (14M). Above the martensitic transformation, the parent phase undergoes ordering transformation from B2’ to the Heusler’s structure L2₁.

The purpose of presented work was to study the correlation between structure of the martensite type and ordering of the parent phase in the alloy with chemical composition: 51.2at%Ni, 27.6at%Mn and 21,1at% Ga. From the polycrystalline bulk material samples were cut and quenched after annealing at 700^oC, 800^oC and 900^oC for one hour. Increasing of quenching temperature results in lowering the characteristic temperatures of the martensitic transformation and simultaneously broadens its thermal hysteresis. The parent phase, in sample quenched from 900^oC, reveals the B2’ structure whereas in sample quenched from 700^oC - the Heusler’s structure L2₁. The ordering transformation was confirmed by the results obtained from high temperature DSC measurement. On a heating curve broad thermal peak appeared in the range between 750 and 850^oC.

Independently on the quenching temperature and the ordering of the parent phase the martensite shows the 10M structure type. However, in electron diffraction pattern additional effects of the diffusion electron scattering have been observed as a results of a short-range ordering caused by the Ni exceeding atoms.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/3690 must be provided.

1. Texture analysis of hot rolled Ni-Mn-Ga alloys
2. Structure and properties of high temperature nitrided/oxided surface of Ni-Ti alloy
3. Structure and shape memory effect in annealed Ni-Ti-Co strip produced by twin roll casting technique
4. Grains orientation and martensitic transformation in Ni-Ti strip produced by twin roll casting technique
5. Effect of deformation on structure and mechanical behavior of plycrystalline Ni-Mn-Ga alloys
6. Martensitic transformation and shape memory effect in NiTiCu strip covered by nanocrystalline platinum layer
7. Martensitic transformation in melt-spun NiMnGa ribbons