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Effect of deformation temperature on the microstructure of hard magnetic FeCr30Co8 alloy subjected to tension combined with torsion

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The development of new generation of high-speed electrical devices requires high strength characteristics of magnetic materials used. Most magnetic materials of today reveal high magnetic characteristics but are brittle and have low ultimate rupture strength. The highest level of mechanical properties is realized in magnetically hard alloys of Fe-Cr-Co system. Fe-Cr-Co based alloys belong to the deformable magnetic materials of the precipitation-hardening class. Due to their good ductility, excellent magnetic properties and low cost, they are used for the production of permanent magnets of various sizes and shapes, such as wire, tube, bar, strip magnets, etc [1ˇŇ3]. A high-coercive state is obtained by a magnetic treatment and multistage tempering. This leads to the decomposition of the solid solution into the isomorphous Ł\1 and Ł\2 phases, containing ordered and coherent precipitates [4, 5]. The formation of such structures, in which each precipitate of the Ł\1 phase is a single magnetic domain, provides superior magnetic properties. However, internal stress fields, which originate from the formation of coherent boundaries between the precipitates of the Ł\1 and Ł\2 phases, cause a reduction in ductility and strength. It is known, that the structure of material and its mechanical properties can be changed using severe deformation techniques [6, 7]. Complex loading by compression, strength and torsion at an elevated temperature is rather a new method of severe plastic deformation [8]. It ensures a substantially refined microstructure without changing the shape of the specimen. Depending on the mode of the deformation chosen, this method allows localizing strain in specific regions and ensures the formation of gradient microstructure with different combination of magnetic and mechanical properties [9, 10]. The aim of the present work is to present the results of the microstructure and hardness investigations of the FeCr30Co8 a[...]

Inhomogeneous microstructural evolution during the annealing of 6013 aluminum alloy

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The mechanisms of recrystallization structure and texture formation in alloys with the bimodal second phase particle distribution were investigated by means of electron microscopy and calorimetry on the example of aluminum alloy 6013. The alloy contains both large (>1 ￿m) and small (<<1 ￿m) particles. During deformation the laminar structure and zones of localized strain around [...]

The evolution of the gradient microstructure of the hard magnetic alloy FeCr30Co8 subjected to plastic deformation by tension combined with torsion

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The FeCr30Co8 alloy belongs to the hard magnetic materials of the Fe-Cr-Co system [1]. Due to its good ductility, the excellent magnetic properties and the low cost, it is used to produce permanent magnets of various sizes and shapes, as wires, tubes, bars, and strips [2, 3]. The high coercive state of the Fe-Cr-Co alloys can be obtained in the process of a magnetic treatment and multi-stage tempering, which resulted in a spinodal decomposition of an α solid solution into isomorphous, ordered and coherent phases: magnetic α1 and paramagnetic α2 [4]. The formation of such a structure, where each precipitate of the α1 phase (with sizes of about 50÷100 nm) appears as a single domain, provides high magnetic properties. On the other hand, the microstructure (α1 + α2) causes a reduction of the material’s plasticity and strength to the level of 200÷400 MPa. This is a serious technological problem, since the commonly used industrial magnets require strength greater than ~900 MPa. The brittleness and the low strength of hard magnetic alloys in a high-coercive (α1 + α2) state limit the possible range of their applications. It is known that the magnetic and mechanical properties are dependent on the microstructure: they are changing significantly with the decreasing of the grain size, to nano- or submicron scale, and with the alteration of the phase morphology or the phase transformation. All these modifications of the microstructure can be achieved by means of an intensive plastic deformation, which is considered as one of the methods improving the material properties [5, 6]. In order to achieve the refinement of microstructure with a gradient character, the FeCr30Co8 alloy was deformed by tension combined with torsion at 700, 750, 800 and 850°C. It is known that the gradient microstructure results in gradual changes of material properties. This can be beneficial in the case of magnets, which[...]

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