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Martensitic transformation, magnetic entropy, and direct adiabatic temperature changes in Ni48Mn39.5Sn12.5−xInx (x = 2, 4, 6) metamagnetic Heusler bulk and grain-constrained ribbon alloys were studied. All alloys showed a typical L21 structure in austenite and the 4O structure in martensite. Their relative volume contributions changed depending on In content. With increasing In concentration, the martensitic transformation temperature increased, whereas the Curie temperature of austenite decreased. The magnetic entropy change under magnetic field of 5 T attained maximum of 20 J/kgK in the bulk and 14.4 J/kgK in the ribbon alloys with the Ni48Mn39.5Sn8.5In4 nominal composition. The corresponding adiabatic temperature change under 1.7 T yielded 1.3 K for the Ni48Mn39.5Sn8.5In4 bulk alloy. Despite grain confinement, melt spinning was found to stabilize martensite phase. Changes observed were discussed with relation to strengthened covalency imposed by In substitution. Graphic abstract

KOBO type extrusion and following cyclic forging in two perpendicular directions at temperatures 150–200 °C were applied to new Mg–9Li–2Al–0.5Sc alloy to study its effect on strength and microstructure evolution. KOBO extrusion of as cast ingot caused significant grain refinement of (α + β) dual phase Mg–9Li–2Al–0.5Sc alloys down to range 1–10 μm for hcp α phase and 1–5 μm for the β phase as resulted from EBSD studies. At that stage ultimate tensile strength UTS of 168 MPa and elongation of 36% were attained. Additional deformation by cyclic forging alternatively from 2 perpendicular directions caused formation of much finer grains of average size of few hundred nm observed using TEM and close to 1 μm applying EBSD technique. Tensile strength increased after that operation above 200 MPa and elongation above 40%, which were the highest observed in the dual phase Mg–Li based alloys. Deformation by cyclic forging induced formation of strong texture with 0001 plane parallel to forging directions. Additional precipitates of size below 1 μm at α/β interfaces or within β phase were identified as hcp AlSc2 phase. Fine particles of hcp α phase were observed after severe plastic deformation SPD within β phase grains, as effect of diffusion assisted deformation. The amount of hcp α phase increased after SPD up to 70% from initial 40%. High density of defects at α/β interfaces on 0001 planes observed in HRTEM mode was responsible for promotion of hcp phase formation during SPD.

The quaternary Mg–9Li–2Al–0.5Sc alloy (in wt%) was prepared from pure components. After homogenization, the alloy was subjected to severe plastic deformation by KoBo extrusion and cyclic forging leading to grain refinement in the range of 0.5–2 µm of hexagonal close-packed (HCP) α phase. Deformed alloys showed high ultimate tensile strength near 200 MPa and good elongation in the range 30–40% at room temperature (RT). Large elongations close to 200% were obtained during the tensile test at a temperature of 200 °C. Deformed samples showed the presence of multiple voids confirming grain boundary sliding mechanism of deformation. Twins on {10$$\overline{1}$$ 1 ¯ 2} planes were identified using electron backscatter diffraction analysis, being in a good agreement with the earlier observation of Mg–Li and Mg–Sc alloys. Intermetallic phases such as cubic MgSc were identified in deformed alloys mostly within HCP α phase, whereas HCP MgSc2 particles were observed within body-centered cubic (BCC) β phase. Intermetallic phases were responsible for RT strengthening of alloys and slightly lower tensile elongation during superplastic deformation. Formation of the HCP α phase was observed within the BCC β phase in tensile deformed alloys. Atomic-level nucleation of HCP phase within the β phase was identified by the use of high-resolution transmission electron microscopy technique.

The dependences of the macro- and microstructures as well as the hardness of local TiC-Fe-type reinforcements (LR) fabricated in situ in steel casting using compacts containing different contents of TiC reactants and the addition of an Fe moderator have been investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Vickers hardness (HV) tests. Five powder mixtures were selected for compact preparation; one of them contains only TiC reactants, while the other four contain TiC reactants as well as 10, 30, 50, and 70 wt pct Fe moderator additions, respectively. Next, the ready compacts were introduced to the mold cavity and poured by cast steel for the in situ LR fabrication. This is the first time, through this study, that the fragmentation phenomena was revealed by macrostructural observations of the LR produced with only the TiC reactants. The increasing Fe content gradually limited the fragmentation and infiltration processes and stabilized the dimensions of the LR. With the increasing contents of the Fe moderator, the refinement of the TiC particles in the LR was observed. Due to the limited infiltration process and high surface content of the TiC, the LR produced with 30 wt pct Fe exhibited the greatest hardness.

Ordering effects in the Ni49Co1Mn37.5Sn6.5In6 alloy were studied by subjecting the alloy to annealing at 1220 K followed by water quenching and to subsequent annealing at 1070 K followed by slow cooling. Martensitic transformation temperature increases by 10 K owing to the slow cooling process, which further invites a change in the martensite structure: 6M → 10M. Across the transformation, regardless of the heat treatment applied, austenite phase is paramagnetic and it transforms into a weakly magnetic martensite. Magnetic moment of martensite is boosted due to slow cooling ( $$ \Delta \mu_{\text{eff}}^{\text{M}} = 1 \mu_{\text{B}} $$ ). Observed behaviours are associated with the changes in the degree of atomic ordering. Irrespective of the magnetic state of martensite, ordering process mitigates the transformation temperature most likely through the interaction with the free energy difference and through the influence of antiphase domains on the twinning stress.

Magnetic properties and exchange bias of $$\hbox { Ni}_{45}\hbox {Co}_{5}\hbox {Mn}_{35.5}\hbox {In}_{14.5}$$ ribbons were investigated by vibrating sample magnetometry (VSM) and electron magnetic resonance (EMR). Curie temperatures determined by using VSM and EMR methods are equal to 374 K and 377 K, respectively. Additionally, the EMR measurements revealed the existence of a weak ferromagnetic resonance (FMR) line in the paramagnetic region. The upward deviation of the integral intensity from Curie–Weis low below temperature $$T^*$$ and above $$T_\mathrm{C}$$ confirms the existence of ferromagnetic phase in this temperature region. Below $$T_\mathrm{C},$$ the integral intensity does not saturate, which can suggest the coexistence of different magnetic phases at low temperature range. Additional confirmation on the coexistence of magnetic phases in the sample are asymmetric hysteresis loops associated with the spontaneous exchange bias effect. The dependence of EMR signal on cyclic repetition of measurement is also discussed.

In this work, results of structural studies, performed as a function of temperature (13–1073 K) of Na0.72CoO2 cathode material, are presented, together with microstructural measurements, including detailed transmission microscopy examination, as well as electrochemical studies, showing current rate-dependent charge/discharge characteristics and also voltammetry tests. It was found that thermal expansion of P2 type (P63/mmc) Na0.72CoO2 differs along a- and c-axes. Microstructural studies showed platelet-like grains of the synthesized sodium cobaltate, while detailed transmission microscopy measurements indicated coexistence of well-defined layered regions with regions having somewhat disturbed atomic arrangement. For higher current densities, characteristic plateaus observed on Na/Na+/NaxCoO2 charge/discharge curves diminish, and the voltage dependence on the sodium concentration is smoothed out. Results of the electrochemical tests, performed on cathodes without any carbon additives, indicated that in fact, such additives influence electrochemical behavior during first charge considerably. Additional voltammetry investigations confirmed presence of nine characteristic anodic and cathodic peaks, corresponding well with plateaus observed during charge/discharge of the cells.

Powder metallurgy technology was elaborated for consolidation of shape memory NiTi powders. The shape memory alloy was compacted from the prealloyed powder delivered by Memry SA. The powder shows Ms = 10°C and As = -34°C as results from DSC measurements. The samples were hot pressed in the as delivered spherical particle's state. The hot compaction was performed in a specially constructed vacuum press, at temperature of 680°C and pressure of 400 MPa. The alloy powder was encapsulated in copper capsules prior to hot pressing to avoid oxidation or carbides formation. The alloy after hot vacuum compaction at 680°C (i.e. within the B2 NiTi stability range) has shown similar transformation range as the powder. The porosity of samples compacted in the as delivered state was only 1%. The samples tested in compression up to e = 0.06 have shown partial superelastic effect due to martensitic reversible transform- ation which started at the stress above 300 MPa and returned back to e = 0.015 after unloading. They have shown also a high ultimate compression strength of 1600 MPa. Measurements of the samples temperature changes during the process allowed to detect the temperature increase above 12°C for the strain rate 10-2 s-1 accompanied the exothermic martensite transformation during loading and the temperature decrease related to the reverse endothermic transformation during unloading.

The microstructure of Co 35+x - Ni 40-x - Al 25 (x = 0, 2.5, 5.0) ferromagnetic shape memory alloys annealed at 1200°C and water quenched has been investigated by optical (OM) and analytical transmission electron microscopy (TEM). The microstructure consists of elongated grains of martensite and 7 phase. Annealing twins were found frequently in the 7 phase. The volume fraction of γ phase has been determined to be about 40%. TEM observations show twinned L1 0 martensite with {111}-type twinning plane and tetragonality c/a = 0.85 in all investigated alloys. Determination of the composition of β phase, allows to calculate Al/Co and e/a ratio in the range 7.68-8.40 in correlation with its Ms temperatures between 66 and 167 °C, respectively. An increase in the Al/Co ratio together with a decrease of Ni content in β phase causes a decrease of the e/a ratio, which promotes a decrease of martensitic transformation temperatures.