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Cold embrittlement is one of the primary concerns challenging the usage of steels in infrastructures like pipelines and ocean platforms. This challenge is also compounded by the limited selection of materials for application in a cold and corrosive environment. Inspired by recent progresses in developing gradient structured materials with extraordinary properties, here we report a class of stainless steels with gradient phase structures achieving a superb combination of strength (1753 MPa) and tensile ductility (>25%) at the cryogenic temperature of 77 K. A set of cylindrical steel samples acquire a graded mixture of hard martensitic and soft austenitic phases through pre-torsion, which results in an optimal stress partition in the material - the hard martensitic structures showing a positive density gradient from core to edge carry higher stress near the edge, while the soft austenitic phase showing a negative density gradient from core to edge serves to retain substantial tensile ductility. The phase-transformation at low temperature in gradient structures and the resulted work-hardening could be adopted to enhance the ductility and strength of widely used engineering materials for their applications in harsh environment. [ABSTRACT FROM AUTHOR]

A polycrystalline Ni 41 Co 9 Mn 40 Sn 10 (at. %) magnetic shape memory alloy was prepared by arc melting and characterized mainly by magnetic measurements, in-situ high-energy X-ray diffraction (HEXRD), and mechanical testing. A large magnetoresistance of 53.8% (under 5 T) and a large magnetic entropy change of 31.9 J/(kg K) (under 5 T) were simultaneously achieved. Both of these values are among the highest values reported so far in Ni–Mn–Sn-based Heusler alloys. The large magnetic entropy change, closely related to the structural entropy change, is attributed to the large unit cell volume change across martensitic transformation as revealed by our in-situ HEXRD experiment. Furthermore, good compressive properties were also obtained. The combination of large magnetoresistance, large magnetic entropy change, and good compressive properties, as well as low cost makes this alloy a promising candidate for multifunctional applications. [ABSTRACT FROM AUTHOR]

Abstract: In contrast to most nanostructured materials, outstanding mechanical property has been demonstrated in a nanostructured metastable austenitic steel, owing to the new characteristics of deformation-induced martensitic transformation. In this paper, by employing an in situ high-energy X-ray diffraction technique, we explore these characteristics by examining factors from the load partitioning, Lüders banding, to texture development. It was found that the martensitic transformation was mainly driven through Lüders band propagation. Marked load transfer takes place from austenite to martensite as Lüders band propagates, and continues into the homogeneous deformation regime. The texture development is mostly contributed by martensitic transformation, but dislocation-based plasticity also plays a role. The effective load partitioning along with the deformability of martensite promotes sample ductility. [Copyright &y& Elsevier]

The neutron diffraction method and the synchrotron high-energy X-ray diffraction technique provide global and local measurements of textures and residual stresses in both structural and functional materials under various environments. In this paper, we present the in situ measurements in ferromagnetic shape-memory alloys during phase transformation, which reveal the good 'memory' of textures and stresses. [ABSTRACT FROM AUTHOR]