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Article

Effect of Ag and Ti Addition on the Deformation and Tribological Behavior of Zr-Co-Al Bulk Metallic Glass

by
Siva Shankar Alla
1,
Mohammad Eskandari
1,
Shristy Jha
1,
Ziyu Pei
1,
S. Vincent
2,
Wook Ha Ryu
3,
Eun Soo Park
4 and
Sundeep Mukherjee
1,*
1
Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203, USA
2
Department of Mechanical Engineering, Birla Institute of Technology and Science Pilani (BITS Pilani), Dubai Campus, Dubai 345055, United Arab Emirates
3
School of Materials Science and Engineering, Kumoh National Institute of Technology, Gumi 39177, Gyeongbuk, Republic of Korea
4
Department of Materials Science and Engineering, Research Institute of Advanced Materials & Institute of Engineering Research, Seoul National University, Seoul 08826, Republic of Korea
*
Author to whom correspondence should be addressed.
Metals 2025, 15(2), 213; https://doi.org/10.3390/met15020213
Submission received: 30 January 2025 / Revised: 12 February 2025 / Accepted: 15 February 2025 / Published: 18 February 2025
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Abstract

:
The effects of a small addition of Ag and Ti on the thermal stability, mechanical properties, and tribological behavior of Zr-Co-Al bulk metallic glass (BMG) were investigated. A 5 at.% addition of Ag and Ti to the Zr-Co-Al base alloy improved the thermal stability and had no significant effect on the mechanical properties but considerably improved the wear behavior. The coefficient of friction decreased while the wear rate increased with increasing normal loads for all three alloys. Zr-Co-Al-Ti showed the best tribological performance among the studied alloys, with coefficient of friction and wear rate lower by a factor of four compared to Zr-Co-Al BMG. Predominantly oxidative wear was seen for the quaternary Zr-Co-Al-Ag and Zr-Co-Al-Ti BMGs at higher loads in contrast to abrasive and adhesive wear for the ternary Zr-Co-Al base alloy. These results highlight the potential of Ag and Ti micro-alloying for improving the mechanical and tribological properties of Zr-based amorphous alloys.

1. Introduction

Zr-based BMGs have attracted widespread attention due to their excellent glass-forming ability (GFA), favorable biocompatibility, exceptional mechanical properties, high wear, and corrosion and erosion resistance [1,2,3,4]. Compared to other Zr-based alloys, the ternary Zr-Co-Al system is free from toxic elements (such as Ni and Be), exhibits large plasticity, and high fracture strength [1,5,6,7,8]. These exceptional properties make Zr-Co-Al-based amorphous alloys well suited for load-bearing bioimplants and other structural applications by tuning their composition and resulting properties [9]. Adding Fe or altering the Al/Co concentration has been shown to significantly enhance the GFA and mechanical properties of Zr-Co-Al BMGs [1,10]. Small addition of other elements has been reported to improve GFA, plasticity, and corrosion resistance of Zr-Co-Al BMGs, including Ag [11], Y [12], and Ti [13,14,15,16]. However, there are few reports and a very limited understanding of the tribological performance of these exceptional amorphous alloys. Many structural applications, including load-bearing bioimplants, involve contact surfaces subject to a range of loads and repetitive movement. For Zr-based BMGs, the wear mechanisms have been shown to change with varying normal loads as well as reciprocating frequency due to changes in the generated frictional heat [17,18,19,20,21]. In addition, the nature of the surface passivation layer may be altered significantly with a slight change in alloy chemistry. However, there are no systematic studies on the tribological performance of the Zr-Co-Al BMGs, the nature of their surface oxide layers, and the effect of slight changes in alloy chemistry on their wear and friction characteristics.
In this study, we report on the mechanical and tribological behavior of Zr56Co28Al16 BMG with systematic variation in normal load as well as the effect of small addition of Ag and Ti. Zr56Co28Al16 was chosen as a model bulk-glass-former in the Zr-Co-Al ternary system. Replacing 5 at% of Co with Ti in one case and Ag in another gave the best combination of glass-forming ability and thermal stability for the corresponding quaternary alloy systems. The three amorphous alloys are characterized by nano-indentation, micropillar compression, and reciprocating wear test. The nature of the surface passivation layers is evaluated in detail and the underlying wear mechanisms are discussed.

2. Materials and Methods

2.1. Alloy Synthesis and Microstructure Characterization

Alloys with a nominal composition of Zr56Co28Al16, Zr56Co23Al16Ag5, and Zr56Co23Al16Ti5 were synthesized by arc-melting the mixture of high-purity constituent elements. They were re-melted six times under a Ti-gettered Ar atmosphere to ensure uniformity in composition. The actual composition measured by energy dispersive X-ray spectroscopy (EDS) analysis as an average over 10 different locations on the sample was within ±0.2 at% of the nominal composition, suggesting uniform elemental distribution. Three-millimeter-wide square plate samples of 1 mm thickness were made by suction casting in a copper mold. All three Zr-based BMGs were metallographically prepared for scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), mechanical characterization, and tribology testing. Microstructural characterization was performed using scanning electron microscopy (FEI Quanta-ESEM 200, FEI Company, Hillsboro, OR, USA) equipped with EDS. The amorphous nature of the plate samples was confirmed by XRD measurement with a Cu-Kα source (Rigaku III Ultima X-ray diffractometer, XRD Rigaku Corporation, Tokyo, Japan). DSC analysis was performed with a Discovery SDT 650 (TA Instruments- Waters LLC, New Castle, DE, USA) at a constant heating rate of 20 K/min to assess the transition temperatures from the heat flow.

2.2. Mechanical Characterization

Nano-indentation tests were conducted at room temperature to measure the hardness and modulus using TI-Premier nano-indenter (Bruker, Minneapolis, MN, USA) with a diamond Berkovich tip. A maximum load of 1 N was used, and a grid of 4 × 4 indents with 100 µm spacing was used to determine the mean and standard deviation. During each indentation, the load was linearly increased to 1 N for a duration of 5 s, held constant for 2 s, and unloaded in 5 s. For pillar compression, micropillars were made with a diameter (D) of ~2.5 µm and an aspect ratio of 2 through Ga ion milling at a voltage of 30 keV. This was conducted using the FEI Nova Nano Lab 200 focused ion beam SEM (FIB-SEM, FEI Company, Hillsboro, OR, USA) with an initial current of 5 nA, which was gradually decreased to 50 pA for the final finishing step. The micropillars had a taper of ~2 o. Micropillar compression was performed using Hysitron PI 88 Pico-indenter (Bruker, Minneapolis, MN, USA) using a 5 µm conical flat punch at a displacement rate of 30 nm/s. A minimum of three pillars were compressed for each alloy to determine the repeatability. The engineering stress (σ = F/((πD2)/4)) versus engineering strain (ε = Δh/H) was obtained from the load (F) versus displacement (h) curves, where D is the pillar diameter and H is the pillar height.

2.3. Wear Characterization

Reciprocating wear tests were performed using the RTEC Universal Tribometer (RTEC Instruments, San Jose, CA, USA). AISI 52100 chrome steel bearing ball with a 6.35 mm diameter was used as the counter-body. Tribology tests were performed at loads (L) of 1 N, 5 N, and 10 N, with a reciprocating frequency of 5 Hz and a stroke length of 3 mm. Each test was run for a duration of 30 min and performed under ambient conditions (~55% relative humidity). The coefficient of friction was continuously recorded during all the wear tests by the RTEC Instruments, MFT 17 software, and white light interferometry (WLI) at 10× magnification was used to capture the images of the wear tracks. Wear volume loss (mm3) was calculated using Gwyddion software version 2.30 for each condition, and the wear rate was calculated by using the relationship wear rate [mm3/N·m] = wear volume loss [mm3]/(applied load [N] × sliding distance [m]). Detailed characterization of the wear tracks and wear debris was conducted using SEM (FEI Quanta-ESEM 200) equipped with EDS. Raman spectroscopy was utilized to probe the nature of the tribo-films after the wear tests. Raman mapping from some sections of the wear tracks was created using a Renishaw Confocal Raman Spectrometer (Renishaw, Dundee, IL, USA) equipped with a green laser at 532 nm wavelength.

3. Results and Discussion

Figure 1 summarizes the structural characterization results, calorimetry, and mechanical behavior of the studied alloys. Figure 1a shows the XRD patterns of the three BMGs, with broad diffraction peaks indicating their fully amorphous nature and absence of any crystalline phases. Figure 1b shows the DSC curves of the three BMGs measured at a heating rate of 20 K/min. All the alloys exhibited an endothermic peak associated with glass transition (Tg) and exothermic peaks associated with crystallization (Tx). The width of the supercooled liquid region (ΔT) was calculated, and the results are summarized in Table 1, along with the glass transition and crystallization temperatures.
The Tg decreased with the addition of Ag and Ti, as reported earlier for Ag addition to Zr-Cu-Al BMG [22] and Ti addition to Zr-Al-Ni-Cu BMG [23]. The width of the supercooled liquid region increased from 48 K in the case of the ternary BMG to 74 K and 54 K with the addition of Ag and Ti, respectively, indicating improvement in thermal stability and processing window of the amorphous alloys with the addition of the fourth element. The increased ΔT for the four component alloys suggests improved manufacturability via thermoplastic processing as well as the potential for utilizing these alloys in larger or more diverse shapes and applications. Figure 1c shows the average hardness and modulus of the three BMGs. With the addition of Ag and Ti, the hardness reduced on average by 2.4% and 4.3%, while the modulus reduced by 3.6% and 2.7%, respectively. The decrease in hardness and modulus with Ag and Ti addition may be attributed to increased heterogeneity in the system with the addition of a small amount of the fourth element and a corresponding increase in the diversity of the alloy constituents [24]. Figure 1d–f shows the engineering stress–strain curves during micropillar compression tests for the three BMGs, with insets showing in situ video snapshots of the micropillars at the yield point and a plastic strain of ~0.06 for the three alloys. The deformation is characterized by stress drops attributed to shear band formation in the amorphous alloys. The yield strength was calculated from the first appearance of a shear band observed in situ during micropillar compression. This was in line with the first major stress drop in the loading curve, with a yield strength value of 2257 ± 40 MPa for the ternary Zr-Co-Al BMG, 2104 ± 42 MPa for the Zr-Co-Al-Ag BMG, and 2010 ± 14 MPa for the Zr-Co-Al-Ti BMG. The yield strengths for the four component alloys are slightly lower than the ternary Zr-Co-Al BMG, similar to the trend in hardness. The micropillars for all three BMGs showed primary shear bands along with some secondary shear bands on the surface accommodating the plastic strain, but there were no significant differences between the failure modes of the three amorphous alloys.
The variations in the coefficient of friction (COF) as a function of time and representative cross-section depth profiles of the BMGs at each of the three loads of 1 N, 5 N, and 10 N are shown in Figure 2. The average COF and wear rate are summarized in Table 2. At 1 N load, all three BMGs showed an average COF in the range of ~0.7–0.8, with fluctuations of similar magnitude. At 5 N and 10 N loads, the Zr-Co-Al and Zr-Co-Al-Ag BMGs showed similar average COF values in the range of ~0.6–0.7, with relatively larger fluctuations for the ternary alloy compared to the quaternary alloy. However, the Zr-Co-Al-Ti BMG showed a significant drop in COF, with an average value of ~0.2, a reduction by a factor of three at the higher loads of 5 N and 10 N. A running-in stage was observed for the ternary alloy under all the normal loads. In contrast, the running-in stage for the quaternary alloys decreased with increasing normal load. This running-in stage may be associated with the formation of an oxide layer induced by friction [25] rather than the removal of asperities from the sliding surfaces [26]. The decrease in the running-in stage for the quaternary alloys may be due to enhanced plastic deformation of the BMG under high applied loads [27]. Compared to the two quaternary alloys, the ternary alloy exhibited relatively large fluctuations in COF. This indicates that the addition of 5 at% Ag or 5 at% Ti may help in the formation of a stable tribo-film on their surface.
Figure 2d–f shows the cross-section of wear tracks for the three amorphous alloys at different loads. The wear tracks became wider and deeper with increasing load from 1 N to 10 N. Compared to the ternary alloy, the Zr-Co-Al-Ag BMG showed wear depth reduction by 64% and 25% at 5 N and 10 N loads, respectively, while the Zr-Co-Al-Ti BMG showed wear depth reduction by 87% and 63% at 5 N and 10 N loads, respectively. The wear rate increased with increasing applied load for all the three BMGs. Compared to the ternary alloy, the wear rate of the two quaternary BMGs dropped sharply at the higher loads, indicating the beneficial effect of a small addition of Ag and Ti to the ternary Zr-Co-Al BMG. In summary, the Zr-Co-Al-Ti and Zr-Co-Al-Ag BMGs exhibited four times higher wear resistance compared to the ternary Zr-Co-Al BMG at the higher loads of 5 N and 10 N, while all three amorphous alloys showed similar wear resistance at the low load of 1 N.
SEM images of the wear tracks for the three alloys under different loads are shown in Figure 3. Areas of darker and lighter shades are clearly seen in the wear tracks. EDS analysis was performed on the dark grey regions, marked as (1–9) in Figure 3a–i. The chemical composition (at.%) of spots 1–9 on the worn surfaces is listed in Figure 3j. The EDS results indicate that the dark grey region has high oxygen content, suggesting the formation of oxides during the wear process. In contrast, the areas with the lighter shade (spots 4 and 7 in Figure 3) have a composition close to the nominal composition of the alloy, suggesting that a fresh BMG surface is exposed after delamination of the oxide films [17,28,29]. At 1 N load, the wear tracks for all three alloys show similar characteristics in the form of parallel grooves with minimal wear debris, indicating a mild abrasive wear mechanism. At 5 N load, the wear track for the ternary alloy (Figure 3d) indicates abrasive wear and plastic deformation. In contrast, the quaternary BMGs (Figure 3e,f) exhibit dark scales of tribo-layers on the surface. The tribo-layers provide a lubricating effect, consistent with findings in previous studies [30,31], and explain the reduced COF and lower wear rates of the quaternary BMGs under this loading condition. At 10 N load, the ternary alloy (Figure 3g) exhibits deep grooves indicative of abrasive wear, as well as debris suggesting adhesive wear. In comparison, the quaternary Zr-Co-Al-Ag BMG (Figure 3h) shows a compacted tribo-layer (marked by point 8 in Figure 3h, with the chemical composition listed in Figure 3j), indicating a combination of abrasive, adhesive, and oxidative wear mechanisms. The Zr-Co-Al-Ti BMG (Figure 3i) shows the shallowest wear tracks, demonstrating its superior wear resistance. The presence of a tribo-layer (marked by point 9 in Figure 3i) and peel-off zones for the Zr-Co-Al-Ti BMG surface suggests that abrasive, adhesive, and oxidative wear mechanisms are dominant.
Figure 4 shows the SEM images of the wear debris for the three BMGs studied at 10 N load. Figure 4a shows that the wear debris from Zr-Co-Al primarily consists of relatively small and dispersed particles. The fine debris suggests material removal due to direct metal–metal contact. In contrast, Figure 4b,c show the wear debris for Zr-Co-Al-Ag and Zr-Co-Al-Ti, which exhibit more clustered and compacted debris. This morphology is characteristic of oxidative wear, where wear debris aggregates due to the formation of a protective oxide layer. The presence of oxygen-rich debris suggests that Ag and Ti promote the formation of a tribo-layer, which reduces severe material removal by acting as a solid lubricant. The ternary Zr-Co-Al alloy, lacking a stable oxide layer, experiences severe wear, leading to deeper wear tracks and higher material loss. In contrast, the quaternary alloys form protective tribo-layers that enhance wear resistance and reduce direct metal-to-metal contact between the alloy surface and the counter-body, significantly improving their tribological performance.
Figure 5 illustrates the worn surface of the AISI 52100 chrome steel counter-bodies after the wear tests against the three amorphous alloys at 10 N load. The optical images of Figure 5a–c reveal that the chrome steel ball has the smallest wear scar, with a diameter of 0.57 mm, when rubbed against the ternary base alloy. The wear scar diameter increases to 0.88 mm when tested against the Zr-Co-Al-Ag BMG and further to 1.17 mm after being tested against the Zr-Co-Al-Ti BMG. The 3D surface profile of the chrome steel ball tested against Zr-Co-Al (Figure 5d) shows minimal wear, which is seen solely in the form of discoloration. Zr-Co-Al-Ag BMG produced mild wear on the counter-body, and some scratches are seen in the interferometry image in Figure 5e. Severe wear is evident in the counter-body after the wear test of Zr-Co-Al-Ti BMG, as seen in Figure 5f. The greater wear on the chrome steel ball when tested with the quaternary alloys, especially the alloy containing titanium, is likely due to the rubbing action against the protective oxide layers formed on the surface of the quaternary BMGs. These oxide layers act as protective coatings, preventing direct contact between the BMG and the chrome steel ball [32,33,34]. The formation of straight grooves may be attributed to delaminated oxide particles, which plow into the fresh BMG surface. This also explains the lower wear loss observed for the Zr-Co-Al-Ti amorphous alloy: the formed oxide layers protect the surface of Zr-Co-Al-Ti BMG, leading to greater deformation of the chrome steel counter-body instead.
The wear behavior of the Zr-Co-Al-Ti alloy is significantly influenced by the presence of titanium. Due to the high oxygen affinity of elements like Zr, Ti, and Co in the alloy, surface oxidation occurs rapidly, leading to the spontaneous formation of a thin oxide layer during the initial stages [29]. As the test progresses, debris generated from wear is flattened by the reciprocating chrome steel ball under load, resulting in the formation of non-compacted tribo-layers that cover the worn surface. These tribo-layers, visible in Figure 3, are crucial for enhancing the wear resistance of the alloy. The Zr-Co-Al-Ti BMG shows the best tribological performance among the studied alloys because of the formation of a protective tribo-layer that prevents direct contact between the BMG and the counter-body [32,33,34]. The glazed tribo-layer acts as a solid lubricant [30,35], leading to the lowest COF and wear rate among the studied alloys, particularly at higher loads.
Raman mappings taken from a section of the wear tracks under 10 N load are shown in Figure 6. A representative Raman spectrum from inside the wear track (shown by a dot) is compared with the spectrum of a spot outside of the wear scar (shown by a star). For all three BMGs, the Raman spectra from outside the wear tracks are very similar to a broad peak in the middle of the wavenumber range studied attributed to naturally occurring oxides of zirconium, cobalt, and aluminum [36,37,38]. In the case of the Zr-Co-Al-Ti BMG (Figure 6e), the broad peak in the middle of the spectrum is skewed towards the left, which is attributed to titanium oxide, which also has a strong peak at this wavenumber range [39]. Figure 6c demonstrates the formation of combined zirconium and cobalt oxides after the wear test for the ternary alloy, where the cobalt oxide is in the form of Co3O4 with spinel structure as suggested from the peaks at 480, 520, 620, and 690 cm−1, as annotated on the graph [36]. These wavenumbers are from the phonon modes: Eg, F2g, F2g, and A1g [40]. The zirconium oxide formed is in a monoclinic crystal structure, with the main peaks at 181–190 (the doublet), 335, 376, and 559 cm−1 [37], which correspond to the phonon modes of Ag, Bg, and Ag [37]. Raman mapping from this wear track in Figure 6a shows that these two oxides are formed in similar areas of the wear track.
For Zr-Co-Al-Ti BMG, the Raman peaks at 410 and 630 cm−1 (Figure 6f) suggest the formation of a rutile phase of TiO2 [39,41], consistent with the results obtained from EDS analysis. The vibrational mode of the 630 cm−1 peak is A1g and that of the 410 cm−1 peak is Eg [42]. While the 630 cm−1 peak shows some overlap with the peaks from cobalt oxide, the other peak at 410 cm−1 occurs solely because of rutile formation, as suggested by similar intensities of the two titanium oxide peaks. Raman mapping in Figure 6d demonstrates the regions inside the wear track where these protective lubricious oxide layers are formed. In the case of Zr56Co23Al16Ag5 BMG, the main Raman peaks of silver oxide are not present, but this may be because of the photo-activation of silver oxide. Considering the ~550 nm band gap, the silver oxide formed during wear tests may have photo-dissociated into silver nanostructures and oxygen upon exposure to the green laser (532 nm) used in this study [43]. Short exposure of silver oxide to laser, especially green and shorter wavelengths, leads to the disappearance of oxide peaks and the appearance of new peaks at around 992 cm−1, 1336 cm−1, and 1596 cm−1 [44]; the last two are attributed to D and G Raman modes of carbon layers, which are formed on silver nanostructures [45,46]. The D peak results from disorder in graphite, the G peak forms because of in-plane stretching of the sp2-hybridized carbon–carbon bonds [47], while the 992 cm−1 peak is attributed to carbonates [44]. The areas with these species in the Raman mapping of Figure 6g strongly support the presence of silver oxide before photo-dissociation.

4. Conclusions

The addition of a small fraction of Ag and Ti to Zr-Co-Al amorphous alloys improved their thermal stability, wear resistance, and tribological performance. Protective tribo-layer formation was seen for the four-component Zr-Co-Al-Ag and Zr-Co-Al-Ti amorphous alloys, which enhanced their wear resistance and reduced the coefficient of friction. At higher loads, Zr-Co-Al-Ti exhibited the best wear resistance, followed by Zr-Co-Al-Ag, while the ternary Zr-Co-Al BMG showed a significantly higher wear rate and friction coefficient. Specifically, Zr56Co23Al16Ti5 BMG showed a friction coefficient of ~0.2 and a wear rate of ~15 × 10−5 mm3/N·m. Under high loads of 5 N and 10 N, frictional heat causes the high oxygen affinity of Ti in Zr56Co23Al16Ti5 BMG to form a TiO2-containing complex oxide layer on the surface. This oxide layer acts as a protective barrier, reducing metal-to-metal contact and lowering both the friction coefficient and wear rate. The oxide layer, even when worn off, is continuously regenerated, leading to a wear-resistant oxidative wear mechanism that dominates under these conditions.

Author Contributions

S.S.A.: Conceptualization, Validation, Formal analysis, Investigation, Writing—original draft; M.E.: Validation, Formal analysis, Investigation, Writing—review and editing; S.J.: Validation, Formal analysis, Investigation, Writing—review and editing; Z.P.: Validation, Formal analysis, Investigation, Writing—review and editing; S.V.: Validation, Formal analysis, Investigation, Writing—review and editing; W.H.R.: Validation, Formal analysis, Investigation, Writing—review and editing; E.S.P.: Validation, Formal analysis, Investigation, Writing—review and editing; S.M.: Conceptualization, Formal analysis, Investigation, Supervision, Project administration, Writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (no. NRF-2019M3D1A1079215).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors thank the Materials Research Facility (MRF) at the University of North Texas for access to the characterization equipment used in this study.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Metals 15 00213 g001
Figure 1. (a) XRD patterns, (b) DSC curves, (c) hardness and modulus, and (d–f) engineering stress-strain curves of the three BMGs studied.
Figure 1. (a) XRD patterns, (b) DSC curves, (c) hardness and modulus, and (d–f) engineering stress-strain curves of the three BMGs studied.
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Metals 15 00213 g002
Figure 2. (a–c) Coefficient of friction and (d–f) cross-sectional wear track profiles under varying loads for the three BMGs studied.
Figure 2. (a–c) Coefficient of friction and (d–f) cross-sectional wear track profiles under varying loads for the three BMGs studied.
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Metals 15 00213 g003
Figure 3. SEM micrographs of worn surfaces under normal loads: (a–c) 1 N, (d–f) 5 N, and (g–i) 10 N for the three BMGs; (j) distribution of elements on the worn surface of the three BMGs studied. The compacted tribo-layers are marked by dashed oval symbols and peel-off zones are marked by dashed rectangular symbols in (h,i).
Figure 3. SEM micrographs of worn surfaces under normal loads: (a–c) 1 N, (d–f) 5 N, and (g–i) 10 N for the three BMGs; (j) distribution of elements on the worn surface of the three BMGs studied. The compacted tribo-layers are marked by dashed oval symbols and peel-off zones are marked by dashed rectangular symbols in (h,i).
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Metals 15 00213 g004
Figure 4. SEM images of the wear debris from (a) Zr-Co-Al, (b) Zr-Co-Al-Ag, and (c) Zr-Co-Al-Ti BMGs at 10 N load.
Figure 4. SEM images of the wear debris from (a) Zr-Co-Al, (b) Zr-Co-Al-Ag, and (c) Zr-Co-Al-Ti BMGs at 10 N load.
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Metals 15 00213 g005
Figure 5. Optical images and 3D surface profiles showing the wear morphology of steel counter-body rubbed against (a,d) Zr-Co-Al BMG, (b,e) Zr-Co-Al-Ag BMG, and (c,f) Zr-Co-Al-Ti BMG.
Figure 5. Optical images and 3D surface profiles showing the wear morphology of steel counter-body rubbed against (a,d) Zr-Co-Al BMG, (b,e) Zr-Co-Al-Ag BMG, and (c,f) Zr-Co-Al-Ti BMG.
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Figure 6. Raman spectroscopy analyses for (a–c) Zr-Co-Al BMG, (d–f) Zr-Co-Al-Ti BMG, and (g–i) Zr-Co-Al-Ag BMG, where Metals 15 00213 i001 indicates outside the wear track and Metals 15 00213 i002 indicates inside the wear track for the three BMGs studied.
Figure 6. Raman spectroscopy analyses for (a–c) Zr-Co-Al BMG, (d–f) Zr-Co-Al-Ti BMG, and (g–i) Zr-Co-Al-Ag BMG, where Metals 15 00213 i001 indicates outside the wear track and Metals 15 00213 i002 indicates inside the wear track for the three BMGs studied.
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Table 1. Thermal properties of the three BMGs studied.
Table 1. Thermal properties of the three BMGs studied.
BMGTg (K)Tx (K)ΔT = Tx − Tg (K)
Zr-Co-Al73978748
Zr-Co-Al-Ag68876274
Zr-Co-Al-Ti70976354
Table 2. Coefficient of friction and wear rate of the three BMGs studied.
Table 2. Coefficient of friction and wear rate of the three BMGs studied.
AlloyCOFWear rate [10−5 mm3/N·m]
1 N5 N10 N1 N5 N10 N
Zr-Co-Al0.73 ± 0.20.63 ± 0.20.64 ± 0.23 ± 0.125 ± 0.260 ± 0.1
Zr-Co-Al-Ag0.73 ± 0.20.71 ± 0.10.53 ± 0.16 ± 0.17 ± 0.117 ± 0.5
Zr-Co-Al-Ti0.77 ± 0.20.14 ± 0.10.2 ± 0.14 ± 0.56 ± 0.415 ± 0.5
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Alla, S.S.; Eskandari, M.; Jha, S.; Pei, Z.; Vincent, S.; Ryu, W.H.; Park, E.S.; Mukherjee, S. Effect of Ag and Ti Addition on the Deformation and Tribological Behavior of Zr-Co-Al Bulk Metallic Glass. Metals 2025, 15, 213. https://doi.org/10.3390/met15020213

AMA Style

Alla SS, Eskandari M, Jha S, Pei Z, Vincent S, Ryu WH, Park ES, Mukherjee S. Effect of Ag and Ti Addition on the Deformation and Tribological Behavior of Zr-Co-Al Bulk Metallic Glass. Metals. 2025; 15(2):213. https://doi.org/10.3390/met15020213

Chicago/Turabian Style

Alla, Siva Shankar, Mohammad Eskandari, Shristy Jha, Ziyu Pei, S. Vincent, Wook Ha Ryu, Eun Soo Park, and Sundeep Mukherjee. 2025. "Effect of Ag and Ti Addition on the Deformation and Tribological Behavior of Zr-Co-Al Bulk Metallic Glass" Metals 15, no. 2: 213. https://doi.org/10.3390/met15020213

APA Style

Alla, S. S., Eskandari, M., Jha, S., Pei, Z., Vincent, S., Ryu, W. H., Park, E. S., & Mukherjee, S. (2025). Effect of Ag and Ti Addition on the Deformation and Tribological Behavior of Zr-Co-Al Bulk Metallic Glass. Metals, 15(2), 213. https://doi.org/10.3390/met15020213

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