Ferromagnetic martensite phase

Keywords ferromagnetism, martensitic transformations, Heusler alloys, phase diagram. 

Figure 2. Temperatures of martensitic (Tm) and ferromagnetic (Tc) phase transitions determined from DSC and low-field magnetization measurements, as a function of Ni excess x in the studied Nig+zMni-zGa alloys.

Lakhani A, Dash S, Banerjee A, Chaddah P, Chen X, Ramanujan RV. Tuning the austenite and martensite phase fraction in ferromagnetic shape memory alloy ribbons of Ni45Co5Mn38Sn12. Applied Physics Letters. 2011 99 242503(l)-242503(3). DOI 10.1063/1.3669510. 

It is well known that paramagnetic phase in austenitic stainless steels, such as an Fe-18Cr-8Ni, transforms into ferromagnetic a martensite phase by plastic deformation at low temperature [4,5]. Since the amount of the deformation-induced martensite increases at a larger... 

Figure 3 shows the change in the saturation magnetization with strain in Type (A) specimens. It is clear that the saturation magnetization increases with increasing deformation (strain). This is because that the paramagnetic phase in austenitic stainless steels transforms into ferromagnetic a martensite phase by the plastic deformation. It is also found that the saturation... 

The base metal and HAZ compact specimen halves were relatively flat, showing no pronounced shear lips. The fracture surfaces formed at 76 and 4 K were ferromagnetic. Ferromagnetism is clear evidence that a body-centered cubic martensitic phase transformation occurred, since the original austenitic phase is... 

The name is derived from the analogous martensite phase in carbon steels. Martensite is produced by a shear-type phase transformation on cooling a steel rapidly (quenching) from the austenitic region of the phase diagram. These alloys are hardenable because of the phase transformation from body-centered cubic to body-centered tetragonal. As with the alloy steels, this transformation is thermally controlled. The martensitic stainless steels are normally 11-13% chromium and are ferromagnetic. 

A martensitic transformation occurs in austenitic stainless steels when they are strained and the amount of the ferromagnetic phase appearing is particularly important when the deformation is produced at low temperatures [1-3]. 

In some metals, an analogous behaviour is observed The stainless steel X5CrNil8-10, which is austenitic (face-centred cubic) at room temperature, is only metastable. Thus, the ferritic phase is thermodynamically stable, but the transformation does not occur because the driving force is too small. Under mechanical load, for instance during forming, a martensitic transformation can take place in parts of the component, easily detectable by the component becoming ferromagnetic locally. 

The relative stability of the austenite can be conveniently determined at lower temperatures with magnetic measurements, This is true because the transformed phase, martensite, is ferromagnetic, while austenite is paramagnetic, A determination of the relative amount of martensite present can be... 

Physical metallurgy is a rather wide field of applications of Mossbauer spectroscopy and it is possible to enumerate only the main topics phase analysis, order-disorder alloys, surfaces, alloying, interstitial alloys, steel, ferromagnetic alloys, precipitation, diffusion, oxidation, lattice defects etc. Alloys are well represented by the iron-carbon system, the mechanism of martensite transformation, high-manganese and iron-aluminium alloys, iron-silicon and Fe-Ni-X alloys. 

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