Fig. 1. SEM micrographs (a-d) and CT reconstructions (e-h) of the BMG composites with different volume fractions of NiTi: (a, e) 10-BMGC, (b, f) 20-BMGC, (c, g) 40-BMGC and (d, h) 60-BMGC. The dark contrast in the SEM micrographs and the yellow phase in the CT reconstructions correspond to the NiTi particles. (i) XRD patterns of the monolithic BMG, BMG composites and NiTi alloy. (j) Bright-field TEM image of the 40-BMGC; the inset in (j) shows the selected area diffraction pattern (SAED) of the glassy matrix (MG). (k) HRTEM image of the interface between the B2 phase and glassy matrix corresponding to the area marked e in (j).

Fig. 2. (a) Representative compressive stress-strain curves for the monolithic BMG, BMG composites and NiTi alloy and (inset) enlarged view of the curves delimited by the red dotted box corresponding to the first yield. SEM micrographs of the BMG composites after fracture: (b) 20-BMGC, (c) 40-BMGC and (d) 60-BMGC.

Fig. 3. (a) Cyclic loading-unloading stress-strain curves of 40-BMGC and (inset) schematic of the specimen shape; (b) XRD patterns and (c-h) SEM micrographs of the composite after different loading-unloading cycles: (c) before loading, (d, e) 2.0% strain ((e) is the enlarged view of the dotted area in (d); SBs = shear bands), (f) 4.0% strain, (g) 6.5% strain and (h) fractured (9.5% strain).

Fig. 4. (a) Cyclic loading-unloading stress-strain curves of 60-BMGC; (b) XRD patterns and (c-h) SEM micrographs of the composite after different loading-unloading cycles: (c) before loading, (d) 2.0% strain, (e) 4.0% strain (the inset shows the enlarged view of the dotted area; SBs = shear bands), (f) 6.5% strain, (g) 9.5% strain and (h) fractured (17.5% strain).

Fig. 5. (a) Macroscopic first yield strength of the BMG composites and (b) confining stress (i.e. the contribution of confinement to the first yield strength) as a function of NiTi content. (c) High-energy XRD patterns of the NiTi alloy, 40-BMGC and 60-BMGC at loading stress of 80 MPa. (d) Variation of the strain tensor of the B2 phase in the NiTi alloy and of the B2 and glassy phase (MG) in the 40-BMGC and 60-BMGC during the early stage of deformation. The yield strength of the B2 phase ($\sigma _{y}^{\text{XRD}}$) is marked by arrows. The strain components of the glassy phase are shown only up to the composite yield; beyond the yield, fitting was not possible because the progressively stronger overlap of the B19´ phase to the amorphous maximum. (e) Variation of the normalized B2 intensity in the NiTi alloy, 40-BMGC and 60-BMGC during loading, representing the evolution of the martensitic transformation. The inset shows an enlarged view of the area corresponding to the dashed box. (f) Confining stress ($\text{ }\!\!\Delta\!\!\text{ }{{\sigma }^{\text{XRD}}}$) parallel and perpendicular to the loading axis in the 40-BMGC and 60-BMGC evaluated by HEXRD.

Fig. 6. (a) Cyclic loading-unloading stress-strain curves, (b) XRD patterns after different loading-unloading cycles of the NiTi alloy. (c) DSC scans of NiTi alloy, 40-BMGC and 60-BMGC. The DSC scan exhibits a two-step martensitic transformation (B2 → R → B19΄) upon cooling. During heating, the transformation from martensite to austenite is apparently a single-step transformation because of the overlap of the peaks. The R phase start temperature (Rs) and austenite finish temperature (Af) are 312 ± 3 K and 315 ± 2 K, respectively, for both NiTi alloy and BMGCs. (d) Normalized residual strain after different loading-unloading cycles in NiTi alloy, 40-BMGC and 60-BMGC. (e) Normalized shear band (SB) density as a function of the loading strain and loading stress. (f) Relationship between the residual strain resulting from shear banding and normalized shear band density in the 40-BMGC and 60-BMGC specimens.

Fig. 7. Schematic illustration of shear band formation via the sequential activation of the shear transformation zones (STZ) in a shape memory BMGC with increasing load from (a) to (d). The non-activated STZs are represented by circles, whereas activated STZs are depicted as ellipses. The surface relief formed by the martensitic transformation from B2 to B19´ generates a stress field in the adjacent glassy matrix which activates a STZ. The stress field is then transmitted from one STZ to the following one, forming a shear band. The shear band formed in this way propagates through the glassy phase and, when impinging the B2 phase, the associated stress field locally triggers the martensitic transformation.

Fig. 8. (a) Common neighbor analysis (CNA) showing the martensitic transformation during loading. (b) Spatially-resolved maps obtained by MD simulations of the eigenvector ν1 representing the strain magnitude and direction along one of the principal strain axes (the second eigenvector is perpendicular to ν1). The magnitude of the eigenvector is represented by the length of the vectors. (c) Angle formed by the eigenvector ν1 with the x axis showing that the direction of the principal strain axis (i.e. the eigenvector ν1) is the same along the shear band and in the martensite.