The compositions of the synthesized Ti–Cu–Zr–Ni-based melt-spun ribbons are listed in Table 1, including Ti₅₀Cu₄₀Zr₅Ni₅ called T0, Ti₄₅Cu₃₅Zr₁₀Ni₅Al₅ called T1, and Ti₄₅Cu₃₅Zr₁₀Ni₅Sn₅ called T2. Figure 1 shows the typical Ti–Cu–Zr–Ni-based amorphous alloys DSC curves.^[8] A glass transition (T_g) accompanied by three exothermic peaks is shown in Fig. 1(a) during the heating process and the heating rate is 20 K/min. The liquidus temperature (T_l) is shown in the high-temperature region as shown in Fig. 1(b). The endothermic characteristic that represents T_g is inconspicuous, so it is difficult to separate a glass transition characteristic out of DSC curves. Because the small area of the supercooled liquid region, the crystallization signal always part or all cover the glass transition signals, and the same situation were observed in aluminum-based bulk metallic glasses.^[21] The thermodynamic parameters are listed in Table 2. In addition to T_g, T_x, and T_l, three other values

Fig. 1.

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	Fig. 1. Characterization of Ti–Cu–Zr–Ni-based alloys: (a) Low- and (b) high-temperature DSC results at a heating rate of 20 K/min, (c) XRD patterns of as-spun ribbons.

Table 1.

Table 1.

Table 1. Ti–Cu–Zr–Ni alloys with different components (at.%). . Alloys Ti Cu Zr Ni Al Sn T0 50 40 5 5 – – T1 45 35 10 5 5 – T2 45 35 10 5 – 5

Table 1. Ti–Cu–Zr–Ni alloys with different components (at.%). .

Table 2.

Table 2.

Table 2. Calorimetric properties of three different alloys. . Alloys Tg/K Tx/K Tl/K ΔTx/K Trg γm T0 643.4 691.6 1193.9 48.1 0.54 0.62 T1 644.5 686.1 1194.4 41.5 0.54 0.61 T2 671.6 699.3 1153.9 27.7 0.58 0.63

Table 2. Calorimetric properties of three different alloys. .

Due to the size effect of the atoms,^[22] the difference between the atomic radius of the Sn or Al atoms with the alloy system atoms increases the mismatch between the atoms, thereby delaying the long-range arrangement of the atoms required for crystallization, which in turn increases the glass forming ability of the alloy system.^[23] On the other hand, due to the negative mixed entropy between the addition elements and the alloy constituent elements,^[24] and the mixed entropy of Ti–Sn (-21), Zr–Sn (-43), Ti–Al (-30), and Zr–Al (-44). We know that if there is positive mixed entropy, liquid phase separation will occur. However, research has found that negative mixed entropy can cause nano-scale chemical fluctuations across the entire macro heterogeneity material in the solidification of liquid metal.^[25,26] Such fluctuations may enhance the local order of the supercooled liquid,^[27] thereby improving the amorphous properties.

The XRD patterns of the melt-spun ribbons are depicted in Fig. 1(c), revealing a typical amorphous feature. The patterns exhibit only a broad diffraction halo peak between 2θ values of 35° and 45°, meaning the formation of amorphous phase in all the ribbons. No visible sharp Bragg diffraction peaks can be found that correspond to the crystalline structure. However, there are some nanocrystals in the melt-spun ribbon that do not produce clear diffraction peaks, as XRD cannot verify the actual microstructure of nanocrystalline systems with amorphous substrates smaller than 5 nm.^[28] To demonstrate this possibility, TEM was used, as presented in Fig. 2, showing the coexistence of crystalline and amorphous states.

Fig. 2.

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	Fig. 2. Microstructures of quaternary Ti50Cu40Zr5Ni5 alloy: (a) TEM images, (b) SAED patterns, (c) details of nanocrystals.

The T0 ribbons corresponding TEM graphs and selected area diffraction (SAED) patterns are shown in Figs. 2(a) and 2(b). For T0, heterogeneously distributed nanocrystallites exist in the amorphous matrix. In parallel, amorphous and crystalline phases coexist in the T0 alloy, as evidenced by the diffraction points and diffuse halo rings in the SAED pattern (b). More details of the image in Fig. 2(c) are given with a higher resolution. The lattice fringes area indicates that the crystalline structure can be observed clearly in the circled area.

For T1 as shown in Fig. 3, we can still see the coexistence of crystalline and amorphous phases according to the SAED pattern in Fig. 3(b). Nevertheless, the TEM image of T2 (Fig. 4) display more homogeneously distributed nanocrystallites than T1. In contrast, the featureless contrast and wide halo ring indicate a fully amorphous structure, as shown in Fig. 4(b). Simultaneously, the elemental allocation in the T1 and T2 ribbons was investigated by EDX and present the homogeneity of the T1 and T2 ribbons, their chemical composition was determined by EDX analysis, as shown in Figs. 3(c)–3(g) and 4(c)–4(g).

Fig. 3.

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	Fig. 3. Microstructures of quinary Ti45Cu35Zr10Ni5Al5 alloy: (a) STEM image, (b) SAED patterns, and EDX mappings (c)–(g).

Fig. 4.

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	Fig. 4. Microstructures of quinary Ti45Cu35Zr10Ni5Sn5 alloy: (a) STEM image, (b) SAED patterns, and EDX mappings (c)–(g).

Additionally, theb atomic segregation has not been found,^[1] and the as-spun ribbons displayed a uniform atomic allocation in the mappings. It is worth while noting that the chemical homogeneity is identical for both T1 and T2 ribbons. On the other hand, the concentrations of Ti and Cu are higher than those of other elements due to the compositions of the ribbon.

Nanoindentation is an applicable apparatus to characterize the mechanical properties of the ribbons. In this work, the indentation function, a total of 12 s, the loading process is 5 s to 5 mN, maximum force is maintained at 2 s, and 5 s are finally unloaded as depicted in Fig. 5(a). The representative load versus displacement curves, which is so called P–h curves, got from the Berkovich indentations on the alloys are illustrated in Figs. 5(b)–5(d) under the same experimental conditions corresponding to T0, T1, and T2, respectively. For the T2 curve (Fig. 5(d)), the typical pop-in event, which is a symbol of discrete plasticity,^[29] can be conspicuously observed in the insets, showing the enlargements of the circled area. As widely reported in metallic glass materials, the pop-in events are related to the shaping and expansion of shear bands.^[30] This phenomenon was also detected in Ti-rich^[31] and Al-rich^[21] metallic glasses. The pop-in events in T0 insets Fig. 5(b) and T1 insets Fig. 5(c) indicate that shear band activity is not as remarkable as that of T2 in alloy plastic deformation.

Fig. 5.

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	Fig. 5. Nanoindentation properties of three amorphous alloys: (a) the load–time curve, (b) Ti50Cu40Zr5Ni5, (c) Ti45Cu35Zr10Ni5Al5, and (d) Ti45Cu35Zr10Ni5Sn5. The circled insert corresponds to the typical pop-in event.

The hardness (H) and reduced elastic (Young’s) modulus (E_r) values were counted based on the Oliver and Pharr method^[17] from the P–h curves and are summarized in Fig. 6(a). According to the indentation curves unloading portion gradient, E_r was determined. As a result, the hardness increased linearly with the addition of Sn and Al to the T0 matrix, which showed the hardness of 9.23 GPa was observed for T1. T2 exhibits a moderate hardness of 8.84 GPa. The Young’s modulus demonstrates the same regularity with hardness, with the values of 101.59 GPa, 127.15 GPa, and 119.76 GPa corresponding to T0, T1, and T2, respectively. Generally, an increase in the reduced elastic modulus E_r was accompanied by an increase in the hardness H. Hence, the consequence suggested that T1 exhibits the best performance in hardness and Young’s modulus characteristics.

Fig. 6.

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	Fig. 6. Mechanical properties of amorphous alloys: (a) the hardness (H) and reduced Young’s modulus (Er) curves, (b) the the storage modulus (G′), loss modulus (G″), and internal friction (tan δ) of Ti45Cu35Zr10Ni5Sn5.

In addition to hardness and Young’s modulus, nanoindentation contributes to the acquisition of other significant indicators to forecast the working life of devices or equipment.^[32] In principle, metallic glasses are supposed to display excellent wear resistance as a result of high strength and grain boundaries missing.^[33] According to the measurement results of nanoindentation, it is widely reported that that the wear resistance of the alloy is positively correlated with the H/E_r ratio, which has been widely reported.^[32,34,35] Generally, our results reveal the nearly identical wear resistance according to the H/E_r ratio, as shown in Table 3. Another indicator connected with the wear property is . When in loaded contact, is proportional to the impedance of the materials to plastic deformation.^[36] This substantially stands for the grater the impedance to plastic deformation is, the ratio higher is. The value of ratio displayed a prominent regularity, which reveals that T1 and T2 have better resistance to plastic deformation than T0 without element addition. Overall, the trace addition of Sn and Al elements exhibited optimized performance in wear resistance, as seen by comprehensively evaluating the two parameters. Currently, nanoindentation is increasingly used to detect the metallic glassy materials deformation behavior. The further plastic deformation is limited to a few amounts of material near the indentation.^[37] To further describe the typical surface deformation features, SPM observations around the indents were investigated in T0. Figure 6(a) insets show the 3D morphology of the usual impression marks of T0 after a maximum load of 5 mN, the standard pileup was observed in topographic profile after nanoindentation. The cooling rate during ribbon fabrication has a significant infection on the pileup, and the cooling rate is related to the material flow during plastic deformation of the ribbons.^[31]

Table 3.

Table 3.

Table 3. The H/Er and values of three amorphous alloys. . Alloys H/Er T0 7.56 × 10−2 4.38 × 10−2 T1 7.26 × 10−2 4.86 × 10−2 T2 7.38 × 10−2 4.82 × 10−2

Table 3. The H/Er and values of three amorphous alloys. .

Besides, T2 exhibited fascinating properties in the above mentioned investigation. Furthermore, DMA is a widely used method to explore the mechanical properties of T2. Figure 6(b) exhibits the temperature versus the loss modulus (G″), the storage modulus (G′), and the phase lag δ of T2, the loading frequency is ω = 1 Hz and the heating rate is 5 K/min. Consequently, the typical dynamic mechanical behavior of T2 can be segmented into three areas. Area (I): When the temperature is inferior to 560 K, G′ is nearly constant 36 GPa, whereas G″ is constant at approximately 0.5 GPa, which indicates the amorphous state of the ribbon. Therefore, the ribbon exhibits strongly elastic properties, but the viscoelasticity nature is negligible at low temperatures. With the temperature increased to 685 K, the G′ reached the highest value of 46.7 GPa, and G″ begin to raising, indicating the increase of viscoelasticity. Area (II): G″ arrived a maximum amount of 10 GPa at a temperature of 717 K, which is called T_α and is associated with the main relaxation, α relaxation, meaning the appearance of the dynamic glass transition.^[38] The outright increase in G″ and the decrease in G′ in Area (II) indicate a marked rise in elasticity but decrease in viscoelasticity after the ribbon experiences α relaxation. Area (III): In contrast, the storage modulus decreases, nevertheless the loss modulus increases after 743 K as a result of crystallization, the ribbon indicates viscoplasticity. The internal friction (tan δ) displays a similar tendency to loss modulus during the whole process; nevertheless, a small difference is observed in T_α because of the dramatically reduced G′ in this area.