† Corresponding author. E-mail:
Project supported by the National Natural Science Foundation of China (Grant Nos. 51671161, U1806219, U1660108, and 51327901) and the Research Project of the Natural Science Foundation of Shanxi Province, China (Grant Nos. 2017JM5116 and 2020JZ-08).
Amorphous Ti–Cu–Zr–Ni alloys with minor addition of Sn and Al were prepared by melt spinning technique. The effects of Sn and Al additions on the microstructures and mechanical properties of glassy ribbons were investigated. The amorphous state of ribbons was confirmed by x-ray diffraction and transmission electron microscopy, where those ribbons with Sn addition exhibited a fully amorphous state. The characteristic temperature indicates that Ti45Cu35Zr10Ni5Sn5 alloy has a stronger glass-forming ability, as proven by differential scanning calorimetry. Ti45Cu35Zr10Ni5Al5 alloy showed a better hardness of 9.23 GPa and elastic modulus of 127.15 GPa and good wear resistance. Ti45Cu35Zr10Ni5Sn5 alloy displayed a pop-in event related to discrete plasticity according to nanoindentation. When the temperature is below 560 K, Ti45Cu35Zr10Ni5Sn5 alloy mainly exhibits elasticity. When the temperature rises between 717 K and 743 K, it shows a significant increase in elasticity but decrease in viscoelasticity after the ribbon experiences the main relaxation at 717 K. When the temperature is above 743 K, the ribbon shows viscoplasticity.
For their specific properties, bulk metallic glasses (BMGs) are fascinating metallic materials that are often not available with traditional crystalline materials.[1] Due to crystalline lattice deletions and defects, such as stacking faults, boundaries, dislocations,[2,3] and the absence of long-range order in the metallic glass, BMGs show a high pressure strength, excellent corrosion resistance behavior, and outstanding soft magnetic properties.[4] Because of their excellent performance, Ti–Cu-based metallic glasses have a broad application prospect in structure and function.[5,6] Nevertheless, metallic glasses are unevenly deformed and have poor plasticity in a narrow shear band.[7,8] To solve this problem, a lot of experiments have been made to enhance plasticity to balance the strength and ductility as required for a component or device.[2,5] It was demonstrated that BMG-based composite materials with different crystal-phase alloying agents could effectively improve the plasticity and processing hardening properties of BMG materials,[9] which blocks the fork or expansion of the shear banding, so that the plastic strains distribution is relatively homogeneous. The plasticity is conspicuously improved.[10]
It is well known that the addition of trace elements also has significant benefits for the mechanical properties and glass-forming ability[9,11] of both BMG composites.[11–13] The alloying elements Fe, Cu, Al, Ni, and Cr can all improve the thermal stability, while the supercooled liquid zone containing Ag and V is narrow in the Ti–Zr–Be ternary alloy.[14] Trace addition of Nb can effectively improve the corrosion resistance of Ti-based amorphous alloys.[15] 0.5-at% Si addition has an optimum glass-forming ability in the Ti42.5Cu42.5Ni7.5Zr7.5 alloy,[8] the plasticity increases with the addition of Si without sacrificing their yield strength. To avoid toxic elements such as Be, precious metal elements such as Pd, and brittleness in bulk form, alloying addition effectively crops glass-forming ability[9] and the toughness[16] of BMG-based composite materials. However, it is sporadic to explore the impact of alloying accretion on the mechanical properties and phase formation of BMG composites, although some preliminary experimental results revealed that the damage tolerance and plastic deformation capability of BMG amount of alloying additions.[9] In this research, we compared the glass-forming ability and the mechanical properties of Ti–Cu–Zr–Ni-based amorphous ribbons with Sn or Al element additions. The ribbons were made by a single-roller facility with a water-cooled copper wheel to form Ti–Cu–Zr–Ni amorphous composites with Sn and Al additions. The ribbons are approximately 4-mm wide and 40-μm thick. The thermodynamics and mechanical properties for different ribbons are tested and discussed.
Master alloy ingots were prepared by arc melting under the atmosphere of Ti-gettered argon, the constituent elements with a higher purity than 99.9%. The master alloy ingots were melted more than three times to ensure uniformity of the composition. The rapidly solidified melt-spun ribbons were produced by melt spinning technique, in which the master alloy ingots were induction-melted in a quartz tube and then through a nozzle ejected onto a rotating copper wheel surface with high speed in argon atmosphere. The single roller rotation speed is 40 m/s and was cooled internally to ensure amorphous formation. The melt-spun ribbons were about 40-μm thick and 4-mm wide in this work.
The amorphous state of ribbons was verified by x-ray diffractometer (XRD, Rigaku D/max2500 V) using Cu-Kα radiation with 2θ angular scanning between 30° and 80° at the sweep speed of 4 °/min. Differential scanning calorimetry (DSC, Netzsch DSC 404C) was carried out to measure the curves of endothermic versus temperature from room temperature to 1200 K with a heating rate of 20 K/min in argon atmosphere. According to the endothermic peaks we can get amorphous characteristic temperature, for example the crystallization temperature (Tx) and the glass transition temperature (Tg), etc.
The microstructure of the melt-spun ribbons was confirmed by transition electron microscopy (TEM, FEI Talos F200X). TEM is equipped with scanning transmission electron microscopy (STEM) and energy dispersive x-ray spectroscopy (EDX). TEM samples were thinned by ion milling (Gatan 695 PIPS COOL) to make them electron transparent.
Nanoindentation technology has become an effective measuring technique for exploring mechanical characteristics of ribbons under micro-Newton loads, for example the elastic modulus and hardness.[17] To evaluate the mechanical properties, the cross-section of the ribbons was detected by nanoindentation (Hysitron TI980). To ensure accuracy, at least five indents were measured, with the results as the average severity of these tests. Nanoindentation in the load-control mode was made using the Berkovich diamond tip, the maximum applied load is 5 mN, and the loading rate is 1 mN/s. Before the nanoindentation test, samples inlaid with epoxy resin were polished manually using diamond paste. Scanning probe microscopy (SPM, attached by Hysitron TI980) was carried out to observe the surface deformation behavior after nanoindentation.
The dynamic mechanical analysis (DMA) is another extensively used method for investigating mechanical properties.[18,19] Dynamic relaxation processes are related to the mechanical behavior and internal atomic structure of metallic glassy materials,[20] and the procedures were caused by the metastable texture of the amorphous structure. The main relaxation, α relaxation, in glassy materials is interrelated with the viscous flow and the appearance of the glass transition. The mechanical reaction of materials is the sum of three different factors: elasticity, viscoelasticity, and viscoplasticity.[18] Applied periodic stress to the materials,
The compositions of the synthesized Ti–Cu–Zr–Ni-based melt-spun ribbons are listed in Table
![]() | 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. Ti–Cu–Zr–Ni alloys with different components (at.%). . |
![]() | 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.
![]() | 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.
For T1 as shown in Fig.
![]() | Fig. 3. Microstructures of quinary Ti45Cu35Zr10Ni5Al5 alloy: (a) STEM image, (b) SAED patterns, and EDX mappings (c)–(g). |
![]() | 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.
The hardness (H) and reduced elastic (Young’s) modulus (Er) values were counted based on the Oliver and Pharr method[17] from the P–h curves and are summarized in Fig.
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/Er ratio, which has been widely reported.[32,34,35] Generally, our results reveal the nearly identical wear resistance according to the H/Er ratio, as shown in Table
![]() | Table 3. The H/Er and |
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
The comparative study of the thermodynamics and mechanical properties of Ti–Cu–Zr–Ni melt-spun ribbons with Sn and Al addition were investigated in this paper. Our results reveal that the addition of Sn can improved the amorphous formation ability of the Ti–Cu–Zr–Ni ribbons more than that of Al. With the addition of Sn, the homogeneous distribution of characterless contrast in the microstructure of Ti45Cu35Zr10Ni5Sn5 reveals the totally amorphous state. On the other hand, there is a conspicuous enhancement in the mechanical properties upon trace addition of Sn and Al. Furthermore, the addition of Al results in a higher hardness, elasticity and excellent wear resistance. Ti45Cu35Zr10Ni5Sn5 shows the discrete plasticity by the pop-in event in nanoindentation. The ribbons display strong elasticity at a low temperature and experience a noticeable increase in elasticity but a decrease in viscoelasticity after α relaxation. The viscoplasticity plays a main role after 743 K.
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