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Abstract Here, the compressive deformation behaviors of a CuZr-based bulk metallic glass composite (BMGC) has been studied under both unconfined and confined conditions. The threshold strain for the martensitic transformation (MT) is experimentally determined to be 0.8%, and 1.9% for the unconfined and confined compression, respectively. The complicated stress state in the confined compression postpones MT of the B2 phase, which has been verified by both experiments and molecular dynamic simulation. The yielding of the B2 phase is dominated by the uniaxial compressive stress. It is expected that the obtained results can provide more insights into the deformation mechanism of BMGCs. Graphical abstract Image 1 Highlights • The threshold strain for the martensitic transformation is quantitatively determined. • The complicated stress state in the confined compression postpones martensitic transformation. • The yielding of the B2 phase is dominated by the uniaxial compressive stress. [ABSTRACT FROM AUTHOR]

The longitude magnetic field annealing on the soft magnetic properties of Fe-based Fe 78 Si 9 B 13 amorphous powder cores were investigated. The magnetic properties of powder core greatly change when annealed under longitude magnetic field. With the increase of magnetic field intensity, the permeability of annealed powder core further increase. The core shows an enhanced effective magnetic permeability of 66 after longitude magnetic field annealing at an applied field of 30 Oe and temperature of 400 °C, which is attributed to the relief of internal stress and the variation of atomic structure. The permeability was improved by 8% and the frequency stability of FeSiB amorphous powder core is up to 2 MHz. The core loss decreases obviously and DC bias property stays at a same level compared with zero field treatment with the increase of magnetic field intensity. For the powder cores, the core loss ranges from 90 to 180 W/kg at 50 mT and 100 kHz, and DC bias property reaches over 70% at 100 Oe. This work provides a novel approach to improve permeability for Fe 78 Si 9 B 13 powder cores and also validates the application prospect of powder core in the work condition of different ripple currents, different loads and a wide frequency range (10 kHz–2 MHz). [ABSTRACT FROM AUTHOR]

• The cooling induced structural evolution of CuZr-based BMGC is in-situ studied. • The hydrostatic pressure exerts a crucial role on the martensitic transformation of B2 CuZr phase. • The thermodynamics mechanism of the phase transformation of CuZr phase is clarified. [Display omitted] In - situ high-energy X-ray diffraction and molecular dynamic simulation were employed to study the structural evolution of a B2 phase reinforced CuZr-based bulk metallic glass composite in different structural states during cryogenic treatment between 300 K and 100 K. No phase transformation occurs in the as-cast sample during cryogenic treatment, while the pre-strained sample undergoes martensitic transformation and reverse martensitic transformation. The ambient temperature, uniaxial stress, and hydrostatic pressure on the B2 CuZr phase are closely related to the phase transformation behavior of the CuZr phase in the pre-strained composite sample. Molecular dynamic simulation confirms the experimental results. The findings in this work will help to clarify the mechanism of the martensitic transformation in the B2 CuZr phase, and finely tune the structure and mechanical behaviors of CuZr-based bulk metallic glass composites. [ABSTRACT FROM AUTHOR]

In this work, a long-term room-temperature aging treatment of the order of years is applied to a B2 phase-reinforced CuZr-based bulk metallic glass composite (BMGC). Presumably governed by residual stress, B19' CuZr martensitic phase gradually precipitates in the crystals after such long-term aging, while structural relaxation takes place in the glassy matrix, which finally induces precipitation of Cu 10 Zr 7 nanocrystals. Tensile tests prove that these time-dependent structural changes have a measurable effect on deformation behaviors of BMGC. The findings are helpful for understanding the thermodynamic stability and the kinetics of structural evolution of metastable alloys and have useful implications for tailoring the structure and mechanical behavior of BMGCs. Image 1 • Natural aging induces structure evolution in CuZr-based bulk metallic glass composite. • Structure stabilization occurs in both the B2 CuZr phase and the amorphous phase. • Hydrostatic pressure plays a crucial role in the structural transformation of phases. [ABSTRACT FROM AUTHOR]

Bulk metallic glass composites (BMGCs) containing an in-situ formed metastable β phase (β-type BMGCs) being capable of transforming to martensites, are a promising class of alloys. Nonetheless, the influence of the structural metastability of β phases on the deformation mechanisms of BMGCs remains largely unclear. This, however, is crucial for understanding and optimizing plastic deformability. In this study, three Ti-based β-type BMGCs with nominal compositions of (Ti 0.505 Zr 0.353 Fe 0.028 Be 0.114 ) 100− x Cu x ( x = 1, 5, 8) have been developed, in each of which the β-Ti phase has a different metastability. For x = 8, the β phase precipitates exclusively and does not transform martensitically during deformation. At the lowest Cu content ( x = 1), however, the β phase contains a high density of fine ω phase upon quenching, which hinders the deformation-induced martensitic transformation. β phases in both BMGCs deform plastically by dislocation glide. Only when x = 5 does the β phase undergo the martensitic transformation to α″-Ti due to an appropriate degree of metastability. The reversible phase transformation between β and α″ followed by twinning in α″ on continuing deformation leads to a “double yielding” behavior and results in strong work-hardening capability as well as superelasticity during compression (cyclic loading) tests. [ABSTRACT FROM AUTHOR]

• TNTZO alloy was processed by high-pressure torsion under different conditions. • The samples' phase volume fraction were investigated by Rietveld refinement. • β-phase stability increases relative to α"-phase after severe plastic deformation. • α" → β reverse martensitic transformation was clearly observed. • Significant hardening and grain refinement were obtained after HPT. ga1 In this work, the Ti-29Nb-13Ta-4.6Zr-0.07O (TNTZO) alloy was processed by high-pressure torsion (HPT), and its microstructure, phase stability, elastic behavior, mechanical properties and deformation mechanisms were determined for samples prepared under different conditions. An increase in β-phase stability relative to martensite and a significant hardening was observed after severe plastic deformation. The increase in β-phase stability is attributed to the sharp increase in the system's Gibbs free energy that occurs when the α"-laths reach a critical nanometer-size during the HPT processing. This system's Gibbs free energy increase triggers the occurrence of the α"→ β reverse martensitic transformation. The greater hardness can be related to three factors: microstructural refinement; high dislocation density and stress-induced formation of the ω-phase. Plastic deformation is based on conventional slip, detwinning, stress-induced martensite formation, as well as the reverse martensitic transformation. The reverse martensitic transformation observed during HPT corresponds to a recently discovered mechanism that has not been well addressed in the literature until now. In this paper, this new mechanism is clearly detected and detailed discussed based on a systematic Rietveld refinement, in-depth microscopy, and calorimetry. [ABSTRACT FROM AUTHOR]