**2. Materials and Methods**

In the first case, the Fe53.3Ni26.5 B20.2 and Co28.2Fe38.9Cr15.4Si0.3 B17.2 (at. %) melt quenched AA ribbons 25 μm thick were taken as objects of the study and composite constituents (Figure 1b). The total thickness of the initial sample (before HPT), consisting of 4 alternating layers of ribbons of AA, was 100 μm, respectively.

In this case, SPD was performed by HPT ( *P* = 6 GPa, ν = 1 rpm) in a Bridgman chamber to di fferent degrees of deformation preset by varying the number of revolutions ( *N*) of rotating anvil from 1/2 to 9. Before HPT, the AA ribbons were cut into fragments 1 cm × 1 cm in size, and then the fragments were piled in groups of four and deformed in the Bridgman chamber to a given number of revolutions. Ethanol was applied to the degreasing of the ribbons surface before the HPT. In such a way, the deformation-induced disk samples were formed from each alloy and similar composite samples were formed from alternating Fe53.3Ni26.5 B20.2 and Co28.2Fe38.9Cr15.4Si0.3 B17.2 AA layers. The amorphous and crystalline phases in the alloys and composites were identified by transmission electron microscopy (TEM) with a JEM 1400 microscope (Jeol Ltd., Tokyo, Japan) at an accelerating voltage of 120 kV and by X-ray di ffraction (XRD) analysis with an Ultima IV multifunctional di ffractometer (Rigaku Corp, Tokyo, Japan) with CoKα radiation. The microhardness of the disk samples was measured at 1/2 radius by indentation with a Vickers pyramid using a MHT-3M microhardness tester (Lomo, St. Petersburg, Russia) at a load of 0.40 N by a standard technique. *K*1*c* values were calculated by the formula:

$$\mathbb{K}\_{\mathbb{L}} = A(\mathbb{E}/HV)^{1/2} \mathbb{P}/\mathbb{C}^{3/2} \tag{1}$$

where *A* = 0.016 is the calibration coe fficient of proportionality for thin ribbons of amorphous alloys; *E* is Young's modulus measured by dynamic indentation methods; *HV* is Vickers microhardness; *P* is the critical load for the appearance of radial cracks in the process of local loading of samples of amorphous alloys; *C* is the average length of cracks [32,33]. The indentation of amorphous alloys was carried out only in the plane of the sample.

The magnetic properties were measured at room temperature in fields of up to 20 kOe with a VSM 250 vibrating-sample magnetometer (Xiamen Dexing Magnet Tech. Co., Ltd., Xiamen, China). Measured hysteresis loops were used to determine the saturation magnetization (<sup>σ</sup>*s*) and the coercive force ( *Hc*).

In the second case, the initial Cu-Nb nanolaminates (Figure 1c) were produced by a series of the following sequential operations making up technological cycle of the MPR process [34,35]: assembling a pack with a given number of layers, rolling of the pack in vacuum at a temperature of 750–800 ◦C, and then cold rolling in air to a thickness equal to that of a single initial layer of the composite. This procedure is more e fficient than that reported in [36,37]. In addition, the holding time of the compacted pack at high temperature within this technological scheme is much shorter than that is in the case of di ffusion welding. The initial plates of 50 mm × 100 mm in area and 0.35 mm thick were assembled into a pack of 32 alternating copper and niobium layers. The total degrees of reduction were 40% upon vacuum rolling and 10% upon cold rolling.

The prepared nanolaminates were subjected to HPT in Bridgman anvils at *P* = 4 GPa to 1/2–4 revolutions. Before HPT, the samples were cut to fragments of 1 cm × 1 cm in area. The thickness of the Cu-Nb laminate samples (before HPT) was 200 μm (Figure 1c).

The structure changes in the samples were examined by the methods of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with a JEM 2100 microscope (Jeol Ltd., Tokyo, Japan) equipped with a BSE detector. The chemical composition of the elements and their distribution in the specimens subjected to SPD were determined by the methods of bright-field and dark-field scanning transmission electron microscopy (BF-STEM/DF-STEM) and energy dispersive

X-ray spectroscopy (EDS) with a JEM ARM-200F cold-emission microscope (Jeol Ltd., Tokyo, Japan) equipped with a CENTURIO EDX E-Max EDS detector (Jeol Ltd., Tokyo, Japan). The foils for the high-resolution electron-microscopic examinations were prepared from cross-section samples by a standard procedure [38]. The XRD spectra were obtained with an Ultima IV multifunction di ffractometer (Rigaku Corp, Tokyo, Japan), using copper emission and a *<sup>K</sup>*β filter (Ni). The Vickers hardness was measured in the half-radius region of consolidated disk-shaped specimens using a standard procedure with a microhardness tester in three dimensions (3D). For this purpose, the disk-shaped nanocomposite samples were cut in four equal segments, and their flat surfaces and two orthogonally related butt-ends after polishing were subjected to indentation.
