The characteristics of magnetostructural coupling play a crucial role in the magnetic field-driven behaviour of magnetofunctional alloys. The availability of magnetostructural coupling over a broad temperature range is of great significance for scientific and technological purposes. This work demonstrates that strong magnetostrucural coupling can be achieved over a wide temperature range (222 to 355 K) in Co-doped high Mn-content Mn₅₀Ni_42−x Co _x Sn₈ (0 ≤ x ≤ 10) melt-spun ribbons. It is shown that, over a wide composition range with Co content from 3 to 9 at.%, the paramagnetic austenite first transforms into ferromagnetic austenite at T _C on cooling, then the ferromagnetic austenite further transforms into a weakly magnetic martensite at T _M. Such strong magnetostructural coupling enables the ribbons to exhibit field-induced inverse martensitic transformation behaviour and a large magnetocaloric effect. Under a field change of 5 T, a maximum magnetic entropy change ΔS _M of 18.6 J kg⁻¹ K⁻¹ and an effective refrigerant capacity RC _eff of up to 178 J kg⁻¹ can be achieved, which are comparable with or even superior to those of Ni-rich Ni–Mn-based polycrystalline bulk alloys. The combination of high performance and low cost makes Mn–Ni–Co–Sn ribbons of great interest as potential candidates for magnetic refrigeration.

Exploring novel materials with large magnetocaloric effect and excellent mechanical properties near room temperature (RT) are highly desired for Ni-Mn based Heusler alloys. In this work, the martensitic transformation, magnetic properties, and mechanical properties of Ni_50-xCo_xMn_50-yTi_y (x = 13–15, y = 13–16) alloys were systematically investigated by tuning Co or Ti contents. The magnetism of austenite was enhanced with an increase in Co or Ti content. 5M and 6M martensites were observed in Ni-Co-Mn-Ti alloys by transmission electron microscopy. The Ni₃₆Co₁₄Mn₃₅Ti₁₅ alloy with a large magnetocaloric effect was found near room temperature by tuning composition. The largest magnetization change (ΔM) and magnetic entropy change (ΔS_m) in the Ni₃₆Co₁₄Mn₃₅Ti₁₅ non-textured polycrystalline alloy obtained during martensitic transformation under the magnetic field of 5 T were about 106 emu/g and 19.3 J kg⁻¹ K⁻¹, respectively. Furthermore, the maximum compressive strength and ductility for the Ni₃₆Co₁₄Mn₃₅Ti₁₅ as-cast alloy can exceed 1220 MPa and 15%, respectively. The fracture mechanism and bonding interaction were analyzed by a scanning electron microscope and first-principles calculations.

For the β phase of Ti-5553-type metastable β-Ti alloys, striations in transmission electron microscopy (TEM) bright- and dark-field images have been frequently observed but their origin has not been sufficiently investigated. In the present work, this phenomenon is studied in depth from the macroscopic scale by neutron diffraction to the atomic scale by high-resolution TEM. The results reveal that the β phase contains homogeneously distributed modulated structures, intermediate between that of the β phase (cubic) and that of the α phase or the ω phase (hexagonal), giving rise to the appearance of additional diffraction spots at 1/2, 1/3 and 2/3 β diffraction positions. The intermediate structure between β and α is formed by the atomic displacements on each second {110}_βplane in the \langle 1{\overline 1}0\rangle_{\beta} direction, whereas that between β and ω is formed by atomic displacements on each second and third {112}_βplane in the opposite \langle 11{\overline 1}\rangle_{\beta } direction. Because of these atomic displacements, the {110}_βand {112}_βplanes become faulted, resulting in the streaking of β diffraction spots and the formation of extinction fringes in TEM bright- and dark-field images, the commonly observed striations. The present work reveals the origin of the striations and the intrinsic correlation with the additional electron reflections of the β phase.