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Article

Experimental Investigation of Phase Equilibria in the Co-Ta-Si Ternary System

1
College of Materials and Fujian Provincial Key Laboratory of Materials Genome, Xiamen University, Xiamen 361005, China
2
Xiamen Key Laboratory of High Performance Metals and Materials, Xiamen University, Xiamen 361005, China
3
Department of Mechanical and Energy Engineering, Southern University of Science and Technology, Shenzhen 518055, China
4
School of Materials Science and Engineering, Institute of Materials Genome & Big Data, Harbin Institute of Technology, Shenzhen 518055, China
*
Authors to whom correspondence should be addressed.
Materials 2022, 15(9), 3097; https://doi.org/10.3390/ma15093097
Submission received: 27 March 2022 / Revised: 20 April 2022 / Accepted: 22 April 2022 / Published: 25 April 2022
(This article belongs to the Section Metals and Alloys)

Abstract

:
In this work, two isothermal sections of the Co-Ta-Si ternary system at 900 °C and 1100 °C are constructed in the whole composition range via phase equilibrium determination with the help of electron probe microanalysis (EPMA) and X-ray diffraction (XRD) techniques. Firstly, several reported ternary phases G (Co16Ta6Si7), G″ (Co4TaSi3), E (CoTaSi), L (Co3Ta2Si) and V (Co4Ta4Si7) are all re-confirmed again. The G″ phase is found to be a kind of high-temperature compound, which is unstable at less than 1100 °C. Additionally, the L phase with a large composition range (Co32–62Ta26–36Si10–30) crystallizes with a hexagonal crystal structure (space group: P63/mmc, C14), which is the same as that of the binary high-temperature λ1-Co2Ta phase. It can be reasonably speculated that the ternary L phase results from the stabilization toward low-temperature of the binary λ1-Co2Ta through adding Si. Secondly, the binary CoTa2 and SiTa2 phases are found to form a continuous solid solution phase (Co, Si)Ta2 with a body-centered tetragonal structure. Thirdly, the elemental Si shows a large solid solubility for Co-Ta binary compounds while the Ta and Co are hardly dissolved in Co-Si and Ta-Si binary phases, respectively.

1. Introduction

The γ′-Co3(Al, W) phase was found to be highly coherent orientation with the γ-Co matrix in the Co-based superalloys similar to the Ni-based superalloys, thus making Co-based superalloys expected to become the next generation of high-temperature structural materials such as aero-engine blades and turbine disk [1,2]. However, the novel Co-based superalloys have severe problems, such as high density and poor stability of γ′ phase at high temperatures, which limit their further development [3,4,5]. Previous studies have shown that the addition of alloying elements such as Ni, Si, Cr, V, Ta, Nb, and Ru can effectively improve the above-mentioned problems and enhance the overall mechanical properties [6,7,8,9,10,11,12]. The addition of Ta can improve the stability, volume fraction and solution temperature of the γ′ phase, and increase the stress required for the internal slip of the γ′ phase to improve the high-temperature mechanical properties of the cobalt-based superalloys [6,9,12]. The addition of Si can improve the oxidation resistance and reduce the density of the Co-based superalloys while maintaining the stability of γ′-phase and high-temperature mechanical properties of the superalloys [10,11]. However, interactions between alloying elements may also cause negative effects. For instance, the excessive addition of Si and Ta in Co-based superalloys promotes the formation of detrimental topological close-packed (TCP) phases that reduce the strength and ductility [13]. Therefore, theoretical and experimental research on the sub-systems of Co-based superalloy is needed to understand the interrelationship between composition and crystal structure, the related work has achieved considerable achievements [14,15,16,17,18,19,20,21]. Among them, the phase diagram is the theoretical fundamental to guiding the composition design and microstructure control of Co-based superalloys [22,23]. In order to better understand the relationship between the composition and microstructure of the critical Co-based superalloy system Co-Ni-Al-W-Ta-Ti-Hf-Cr-Si [24,25], the phase equilibria of the related sub-system Co-Ta-Si is of great importance.
The Co-Ta-Si ternary system is constituted by three sub-binary systems: Co-Si [26], Co-Ta [27] and Ta-Si [28], as shown in Figure 1. The crystal structure information of each equilibrium phases in the Co-Ta-Si ternary system and three sub-binary systems are shown in Table 1. Firstly, there are five intermediate phases in the Co-Si binary system, namely Co3Si, αCo2Si, βCo2Si, CoSi and CoSi2 and six intermediate phases in the Co-Ta binary system: Co7Ta2, Co6Ta7, CoTa2, λ1-Co2Ta, λ2-Co2Ta and λ3-Co2Ta. Among them, the λ1-Co2Ta is a high-temperature MnZn2-type Laves phase, which decomposes into the CoTa and λ2-Co2Ta phases by an eutectic reaction at 1294 °C. Additionally, the λ2-Co2Ta and λ3-Co2Ta phases are the MnCu2- and MgNi2-type Laves phases, respectively. The CoTa2 Laves phase is a kind of Al2Cu-type, which is the same as that of the Ta2Si. Besides, there are six intermediate compounds in the Ta-Si binary system, namely Ta3Si, Ta2Si, αTa5Si3, βTa5Si3, γTa5Si3, and TaSi2. The conversion among αTa5Si3, βTa5Si3 and γTa5Si3 are completed through crystal transformation.
Previous studies have reported five ternary compounds in the Co-Ta-Si ternary system: G (Co16Ta6Si7) [29], G″ (Co4TaSi3) [30,31], L (Co3Ta2Si) [32,33], E (CoTaSi) [29,34] and V (Co4Ta4Si7) [34,35,36]. The G phase was first reported in 1956 by Beattie [37] in A-286 alloy. It is a kind of ternary silicide with a cubic crystal system (space group: Fm 3 ¯ m) [38], which was named because it is easy to precipitate at the grain boundaries. Later studies found that there is a special cube-on-cube orientation relationship between the G phase and ferrite, which results in low interfacial energy, and thus makes it a potential strengthening phase of ferritic steel [39]. Additionally, the L phase was detected as a ternary MnZn2-type Laves phase [32]. Mittal et al. [33] design an alloy with a composition of Co3Ta2Si, which detected L and an unknown phase. In addition, the E, G″ and V phases can be treated as stoichiometric compounds and these phases are also detected in Co-Ti-Si [40] and Co-Nb-Si [41] systems.
However, as far as we know, the phase equilibrium of the Co-Ta-Si ternary system has not been reported as far. To better understand the interaction between composition and crystal structure in Co-based superalloys, also to construct the thermodynamic database of the Co-V-Al-Ta-Ti-Ni-Cr-Si multisystem, we devote ourselves to systematically exploring the phase equilibrium relationships in ternary Co-Ta-Si alloys, a sub-system of Co-based superalloys.
Table 1. The stable solid phases in the Co-Ta-Si ternary systems.
Table 1. The stable solid phases in the Co-Ta-Si ternary systems.
SystemPhasePearson
Symbol
PrototypeSpace GroupStruktur-berichtRefs.
Co-Si(αCo)cF4CuFm-3mA1[26]
(εCo)hP2MgP63/mmcA3[26]
Co3SihP8Mg3CdP63/mmc-[26]
αCo2SioP12Co2SiPnmaC23[26]
βCo2Si----[26]
CoSicP8FeSiP213B20[26]
CoSi2cF12CaF2Fm-3mC1[26]
(Si)cF8C(diamond)Fd-3mA4[26]
Co-TaCo7Ta2hR36BaPb3R-3m-[27]
λ1-Co2TahP12Zn2MgP63/mmcC14[27]
λ2-Co2TacF24Cu2MgFd-3mC15[27]
λ3-Co2TahP24MgNi2P63/mmcC36[27]
Co6Ta7hR13Fe7W6R-3mD85[27]
CoTa2tI12Al2CuI4/mcmC16[27]
(Ta)cI2WIm-3mA2[27]
Ta-SiTa3SitP32Ti3PP63/mcm-[28]
Ta2SitI12Al2CuI4/mcmC16[28]
αTa5Si3tI32Cr5B3I4/mcmD81[28]
βTa5Si3hP16Mn5Si3P63/mcmD88[28]
γTa5Si3tI32W5Si3I4/mcmD8m[28]
TaSi2hP9CrSi2P6222C40[28]
(Si)cF8C(diamond)Fd-3mA4[28]
Co-Ta-SiCoTaSi (E)oP12TiNiSiPnmaC23[34]
Co16Ta6Si7 (G)cF116Mg6Cu16Si7Fm3mA1[29]
Co4TaSi3 (G″)hP168Y13Pd40Sn31P6/mmm-[30]
Co3Ta2Si (L)hP12MgZn2P63/mmcC14[32]
Co4Ta4Si7 (V)tI60Zr4Co4Ge7--[34]

2. Experimental Procedures

High-purity cobalt (>99.9 wt.%, bulk, Beijing Trillion Metals Co., Ltd., Beijing, China), tantalum (>99.9 wt.%, flake, Beijing Trillion Metals Co., Ltd., Beijing, China) and silicon (>99.9 wt.%, block, Beijing Trillion Metals Co., Ltd., Beijing, China) were adopted as starting materials. The samples were prepared by arc-melting using a water-cooled copper crucible with a non-consumable tungsten electrode under the high purity Ar atmosphere (DHL-1250, Sky Technology Development Co, Ltd., Shenyang, China). The weight of each sample was about 20 g and they were arc-melted at least five times to achieve the compositional uniformity. The overall weight loss after arc-melting was no more than 0.5 wt.%. Then, these samples were sealed in capsules via backfilling with Ar and annealed at 900 °C and 1100 °C, respectively. Considering the high melting point for the elemental Ta, the time of annealing was set as 90 days for 900 °C and 60 days for 1100 °C, respectively. To prevent contamination of samples, the capsules were inserted with Ti scrap and the samples were wrapped with a Ta sheet. After reaching the preset annealing time, the samples were quenched into ice water and prepared by standard metallographic methods.
The equilibrium composition of each phase was investigated by EPMA (electron probe microanalyzer) (JAX-8100R, JEOL, Tokyo, Japan) with WDS (wavelength dispersive X-ray spectroscopy) and BSE (backscattered electrons). Crystal structure analysis was carried out through XRD (X-ray diffractometer) (D8 Advance, Bruker, Karlsruhe, Germany) using Cu Kα radiation at 40.0 kV and 40 mA, and the data were collected in the range of 2θ from 10° to 90° at a step size of 0.0167°.

3. Results and Discussion

3.1. Microstructure and Phase Equilibrium

In Figure 1, the Co-Ta-Si ternary system is divided into four regions (zone 1–4), phase equilibrium from each region is carefully discussed below. The following composition of each phase and alloy is described by the atomic ratio (at.%). The representative micrograph images and corresponding XRD indexing results are given below to indicate the phase equilibria relationship of the alloy. The nominal composition, annealing time and equilibrium composition of each phase measured by WDS are all listed in Table 2 and Table 3.

3.1.1. Equilibria at Zone 1

Zone 1 mainly contains the phase equilibria at the Si-rich corner (Si > 50 at.%). For the Co34Ta26Si40 alloy that was annealed at 1100 °C, a distinct three-phase equilibrium of E + V + CoSi was observed in Figure 2a and their crystal structures could be confirmed by the corresponding XRD pattern in Figure 3a. As shown in Figure 2b, the Co26Ta7Si67 alloy is located in a three-phase equilibria region after being annealed at 1100 °C. The white and light gray phases correspond to the TaSi2 and CoSi2 phases, respectively, while the dark gray phase is presumed to be the solid solution phase of Si (signed as (Si)). The corresponding XRD pattern indexing result in Figure 3b further confirmed this speculation.

3.1.2. Equilibria at Zone 2

Zone 2 corresponds to the phase equilibria at the Ta-rich corner (Ta > 50 at.%). In Figure 4a, a two-phase equilibrium of (Co, Si)Ta2 (white) + λ1-Co2Ta (black) was confirmed in the Co30Ta43Si27 alloy quenching from 1100 °C based on the support of the corresponding X-ray diffraction pattern in Figure 5. As shown in Figure 4b, the Co11Ta75Si14 alloy formed a two-phase equilibrium microstructure of (Ta) + (Co, Si)Ta2 after being annealed at 900 °C. Figure 4c depicts the three-phase equilibrium of (Co, Si)Ta2 (white) + Co6Ta7 (grey) + λ1-Co2Ta (black) in Co41Ta47Si12 alloy after being annealed at 900 °C.
Compositional analysis of the Co30Ta43Si27, Co27Ta60Si13, Co36Ta54Si10, Co2Ta75Si23, Co11Ta75Si14, Co38Ta58Si4, Co10Ta59Si31, Co37Ta42Si21, Co41Ta47Si12, Co27Ta68Si5 and Co26Ta53Si21 alloys indicate that these alloys contain a phase with about 63 at.% Ta after being annealed at 900 °C and 1100 °C. The X-ray diffraction analysis results of these alloys strongly suggest that the binary Al2Cu-type CoTa2 and Ta2Si phases form a continuous solid solution phase (Co, Si)Ta2. As far as we know, it is the first time to discover the infinite mutual solubility between CoTa2 and Ta2Si phases. Similarly, the phenomenon of Ni and Si can be entirely substituted by each other in Al2Cu-type compounds was also found in the Ni-Ta-Si ternary system [42].

3.1.3. Equilibria at Zone 3

Zone 3 mainly discusses the phase equilibria around G″ phase. The alloy Co46Ta13Si41, Co58Ta10Si32 and Co48Ta22Si30 were designed to explore the existence of the G″ phase. For Co46Ta13Si41 and Co58Ta10Si32 alloys that being annealed at 1100 °C, two three-phase equilibrium CoSi + E + G″ and αCo2Si + G + G″ were detected as shown in Figure 6a,b. The corresponding XRD patterns in Figure 7a,b indicate that the diffraction peaks belonging to the phases (CoSi, E, αCo2Si and G) are in good agreement with the standard patterns. However, the diffraction peak of the G″ phase was not interpreted due to the lack of crystallographic information. For the Co48Ta22Si30 alloy annealed at 1100 °C, a clearly three-phase equilibria E (white) + G (light gray) + G″ (dark gray) was detected, as shown in Figure 6c. However, the EMPA micrographs and WDS analysis of the same alloy (see Figure 6d) quenching from 900 °C show that it is a three-phase of E + G + CoSi. This result implies that the G″ phase is a high-temperature compound, which is not stable at 900 °C.

3.1.4. Equilibria at Zone 4

Zone 4 describes the phase equilibria of other ternary phases including G and L. As shown in Figure 8a, the dark grey G phase was observed at the grain boundaries of the light grey λ1-Co2Ta phase for the Co54Ta28Si18 alloy after being annealed at 1100 °C. This morphology is extremely similar to that of the G phase precipitation on the C14 Laves phase [42].
The alloy with a nominal composition of Co59Ta31Si10 was designed to detect the L phase as shown in Figure 8b. The interpretation of the corresponding XRD pattern in Figure 9a indicates that this ternary L phase crystalizes the same as the Zn2Mg-type compounds (P63/mmc, C14) like the binary λ1-Co2Ta phase. Additionally, the λ1-Co2Ta phase is a high-temperature phase that only exists above 1294 °C [27]. However, the detected ternary L phase is stable at 900 °C and 1100 °C, suggesting that the addition of Si stabilizes the λ1-Co2Ta phase toward low temperature. Besides, this Co-Ta-Si ternary L phase shows an extremely similar compositional range compared with the Ni-Nb-Si system [43]. The alloy Co65Ta27Si8 was designed to determine the phase equilibria of the G and three Laves phases (λ1-Co2Ta, λ2-Co2Ta and λ3-Co2Ta). A single λ3-Co2Ta phase was detected in Co65Ta27Si8 alloy annealed at 1100 °C (Figure 8c), while the λ3-Co2Ta + G was observed for the same alloy being annealed at 900 °C (Figure 8d). The corresponding XRD patterns in Figure 9b,c confirm the above equilibrium relationship.

3.2. Isothermal Sections

Based on the phase equilibrium information discussed in Section 3.1, the isothermal sections of the Co-Ta-Si ternary system at 900 °C and 1100 °C are constructed in the whole composition range (see Figure 10). Nineteen and twenty-one three-phase regions were observed at 900 °C and 1100 °C, respectively. Few undetected three-phase regions are indicated by the dashed line.
The solid solubilities of Ta in the Co-Si binary phases (CoSi2, CoSi and αCo2Si) are negligible. The maximum solubility of Co in the TaSi2 phase is 1.7 at.% at 1100 °C, and it increases to 3.4 at.% at 900 °C. When the temperature decreases from 1100 °C to 900 °C, the solid solubility of Co in the αTa5Si3 phase increases from 3.5 at.% to 5.3 at.%. In addition, the maximum solubility of Si in the λ3-Co2Ta phase was measured to be 15.3 at.% at 1100 °C and decreased to 11.5 at.% at 900 °C. At least 8.5 at.% of Si can be dissolved in the λ2-Co2Ta phase at 900 °C. However, the solid solubility of Si in Co6Ta7 hardly varies with temperature, maintaining 12 at.% at both 900 °C and 1100 °C.
In the Co-Ta-Si ternary system, there are four ternary compound phases G, G″, E and V and a binary high-temperature phase λ1-Co2Ta (L) stabilized by Si. The G, E, V and G″ phases are stoichiometric compounds exhibiting only small homogeneity ranges. Meanwhile, the G, E, V and L phases exist at 900 °C and 1100 °C. The G″ phase has also been reported in similar ternary systems like the Co-Nb-Si [41] and Co-Ti-Si [40]. The G″ phase was detected in the Co46Ta13Si41, Co58Ta10Si32 and Co48Ta22Si30 alloys after being annealed at 1100 °C, but it disappears at 900 °C.

4. Conclusions

The phase equilibrium of the Co-Ta-Si ternary system at 900 °C and 1100 °C is systematically studied by equilibrated alloy and the following conclusions can be drawn:
  • The four known ternary phases, G (Co16Ta6Si7), E (CoTaSi), G″ (Co4TaSi3) and V (Co4Ta4Si7) have almost no ternary solid solubilities, which could be treated as stoichiometric compounds.
  • The high-temperature phase G″ (Co4TaSi3) is only stable at 1100 °C and it disappears when the temperature decreases to 900 °C.
  • The addition of Si increases the thermal stability of the binary λ1-Co2Ta (C14 Laves) phase, resulting in the formation of the ternary L phase with the composition of Co32.3–58.8Ta28.2–36.8Si13.0–30.9 at 900 °C and Co39.3–62.3Ta26.8–33.9Si10.9–26.8 at 1100 °C.
  • Both the binary CoTa2 and SiTa2 phases crystallize with the same body-centered tetragonal structure (space group: I4/mcm, C16) and they form a continuous solid solution phase (Co, Si)Ta2.
  • The maximum solid solubility of Si for the λ3-Co2Ta phase is ~15.3 at.% at 1100 °C and it slightly decreases to be ~11.5 at.% at 900 °C. The solid solubility of Si for the Co6Ta7 phase is always ~12 at.% and does not change with temperature.
  • The elemental Ta is hardly dissolved in the CoSi2, CoSi and α-Co2Si phases. Similarly, the elemental Co has negligible solubilities in the TaSi2 and α-Ta5Si3 phases.
The results obtained from the present work make up the phase diagram information of the Co-Ta-Si ternary system, also provide the key experimental data for the establishment of Co-based superalloys thermodynamic database.

Author Contributions

Conceptualization, C.W. and X.L.; data curation, L.H. and P.Y., methodology, C.W., X.L. and M.Y.; investigation, X.H., L.H. and J.Z; writing—original draft preparation, X.H. and L.H.; writing—review and editing, L.H., M.Y., Y.C., S.Y. and J.Z.; supervision, C.W. and X.L.; funding acquisition, C.W., M.Y. and X.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Nature Science Foundation of China, grant number 51971082, 51831007 and the National Post-doctoral Program for Innovative Talents, grant number BX20200103.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data sharing not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The sub-binary phase diagrams of Co-Si [26], Co-Ta [27] and Ta-Si [28] systems.
Figure 1. The sub-binary phase diagrams of Co-Si [26], Co-Ta [27] and Ta-Si [28] systems.
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Figure 2. Typical ternary micrograph images obtained of (a) Co34Ta26Si40 alloy annealed at 1100 °C for 60 days and (b) Co26Ta7Si67 alloy annealed at 1100 °C for 60 days.
Figure 2. Typical ternary micrograph images obtained of (a) Co34Ta26Si40 alloy annealed at 1100 °C for 60 days and (b) Co26Ta7Si67 alloy annealed at 1100 °C for 60 days.
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Figure 3. XRD patterns obtained of (a) Co34Ta26Si40 alloy annealed at 1100 °C for 60 days and (b) Co26Ta7Si67 alloy annealed at 1100 °C for 60 days.
Figure 3. XRD patterns obtained of (a) Co34Ta26Si40 alloy annealed at 1100 °C for 60 days and (b) Co26Ta7Si67 alloy annealed at 1100 °C for 60 days.
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Figure 4. Typical ternary micrograph images obtained of (a) Co30Ta43Si27 alloy annealed at 1100 °C for 60 days; (b) Co11Ta75Si14 alloy annealed at 900 °C for 90 days and (c) Co41Ta47Si12 alloy annealed at 900 °C for 90 days.
Figure 4. Typical ternary micrograph images obtained of (a) Co30Ta43Si27 alloy annealed at 1100 °C for 60 days; (b) Co11Ta75Si14 alloy annealed at 900 °C for 90 days and (c) Co41Ta47Si12 alloy annealed at 900 °C for 90 days.
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Figure 5. XRD patterns obtained of Co30Ta43Si27 alloy annealed at 1100 °C for 60 days.
Figure 5. XRD patterns obtained of Co30Ta43Si27 alloy annealed at 1100 °C for 60 days.
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Figure 6. Typical ternary micrograph images obtained of (a) Co46Ta13Si41 alloy annealed at 1100 °C for 60 days; (b) Co58Ta10Si32 alloy annealed at 1100 °C for 60 days; (c) Co48Ta22Si30 alloy annealed at 1100 °C for 60 days and (d) Co48Ta22Si30 alloy annealed at 900 °C for 90 days.
Figure 6. Typical ternary micrograph images obtained of (a) Co46Ta13Si41 alloy annealed at 1100 °C for 60 days; (b) Co58Ta10Si32 alloy annealed at 1100 °C for 60 days; (c) Co48Ta22Si30 alloy annealed at 1100 °C for 60 days and (d) Co48Ta22Si30 alloy annealed at 900 °C for 90 days.
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Figure 7. XRD patterns obtained of (a) Co46Ta13Si41 alloy annealed at 1100 °C for 60 days and (b) Co58Ta10Si32 alloy annealed at 1100 °C for 60 days.
Figure 7. XRD patterns obtained of (a) Co46Ta13Si41 alloy annealed at 1100 °C for 60 days and (b) Co58Ta10Si32 alloy annealed at 1100 °C for 60 days.
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Figure 8. Typical ternary micrograph images obtained of (a) Co54Ta28Si18 alloy annealed at 1100 °C for 60 days; (b) Co59Ta31Si10 alloy annealed at 1100 °C for 60 days; (c) Co65Ta27Si8 alloy annealed at 1100 °C for 60 days and (d) Co65Ta27Si8 alloy annealed at 900 °C for 90 days.
Figure 8. Typical ternary micrograph images obtained of (a) Co54Ta28Si18 alloy annealed at 1100 °C for 60 days; (b) Co59Ta31Si10 alloy annealed at 1100 °C for 60 days; (c) Co65Ta27Si8 alloy annealed at 1100 °C for 60 days and (d) Co65Ta27Si8 alloy annealed at 900 °C for 90 days.
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Figure 9. XRD patterns obtained of (a) Co59Ta31Si10 alloy annealed at 1100 °C for 60 days; (b) Co65Ta27Si8 alloy annealed at 1100 °C for 60 days and (c) Co65Ta27Si8 alloy annealed at 900 °C for 90 days.
Figure 9. XRD patterns obtained of (a) Co59Ta31Si10 alloy annealed at 1100 °C for 60 days; (b) Co65Ta27Si8 alloy annealed at 1100 °C for 60 days and (c) Co65Ta27Si8 alloy annealed at 900 °C for 90 days.
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Figure 10. Experimental determined isothermal sections of the Co-Ta-Si system at (a) 900 °C and (b) 1100 °C.
Figure 10. Experimental determined isothermal sections of the Co-Ta-Si system at (a) 900 °C and (b) 1100 °C.
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Table 2. Equilibrium compositions of the Co-Ta-Si ternary system at 900 °C determined in the present work.
Table 2. Equilibrium compositions of the Co-Ta-Si ternary system at 900 °C determined in the present work.
Alloy
(at.%)
Annealed TimePhase EquilibriaComposition (at.%)
Phase 1/Phase 2/Phase 3Phase 1Phase 2Phase 3
TaSiTaSiTaSi
Co10Ta10Si8090 daysTaSi2 / CoSi2 / (Si)30.368.60.170.30.199.7
Co33Ta14Si5390 daysV / CoSi24.848.40.151.6
Co30Ta43Si2790 days(Co, Si)Ta2 / λ1-Co2Ta62.630.832.229.5
Co54Ta28Si1890 daysλ1-Co2Ta / G28.218.919.225.1
Co16Ta18Si6690 daysTaSi2 / CoSi / CoSi230.467.80.251.80.267.2
Co22Ta27Si5190 daysTaSi2 / V / CoSi30.667.825.348.20.551.6
Co27Ta60Si1390 days(Co, Si)Ta2 / Co6Ta763.722.849.66.7
Co34Ta26Si4090 daysE / V / CoSi31.634.822.746.50.250.5
Co25Ta38Si3790 daysαTa5Si3 / E / V58.439.032.135.225.248.1
Co64.5Ta22.5Si1390 daysλ3-Co2Ta / G23.511.519.925.4
Co36Ta54Si1090 days(Co, Si)Ta2 / Co6Ta764.020.649.79.2
Co2Ta75Si2390 days(Ta) / (Co, Si)Ta2 / Ta3Si92.35.463.828.671.028.6
Co26Ta7Si6790 daysCoSi2 / TaSi20.167.529.567.1
Co46Ta13Si4190 daysG / CoSi18.225.80.151.2
Co58Ta10Si3290 daysCo2Si / CoSi / G0.134.60.150.618.026.2
Co48Ta22Si3090 daysE / G / CoSi30.235.118.326.10.151.1
Co36Ta33Si3190 daysE / λ1-Co2Ta30.935.231.130.9
Co59.5Ta22.5Si1890 daysλ3-Co2Ta / G22.111.018.624.6
Co59Ta31Si1090 daysλ1-Co2Ta / λ2-Co2Ta29.713.028.88.5
Co11Ta75Si1490 days(Ta) / (Co, Si)Ta291.23.063.728.1
Co38Ta58Si490 daysCo6Ta7 / (Co, Si)Ta263.312.452.15.9
Co25Ta33Si4290 daysαTa5Si3 / E / V57.239.632.435.624.448.9
Co24Ta44Si3190 daysαTa5Si3 / E58.139.431.634.8
Co65Ta27Si890 daysG / λ3-Co2Ta19.124.125.39.2
Co56Ta9Si3590 daysG / αCo2Si / CoSi19.025.00.433.60.349.2
Co44Ta25Si3190 daysE / G / CoSi30.733.619.324.60.747.4
Co10Ta59Si3190 daysαTa5Si3 / E / (Co, Si)Ta258.839.432.029.763.433.2
Co61Ta11Si2890 daysG / αCo2Si17.724.80.132.6
Co70Ta9Si2190 daysG / (εCo) / αCo2Si57.724.30.114.40.229.7
Co37Ta42Si2190 days(Co, Si)Ta2 / λ1-Co2Ta62.024.744.322.2
Co71Ta13Si1690 daysG / (αCo)18.824.40.56.7
Co78Ta10Si1290 daysλ3-Co2Ta / G / (αCo)20.68.518.723.70.74.0
Co51Ta37Si1290 daysCo6Ta7 / λ1-Co2Ta46.56.232.416.2
Co41Ta47Si1290 days(Co, Si)Ta2 / Co6Ta7 / λ1-Co2Ta62.922.347.68.936.813.5
Co78Ta17Si590 daysλ3-Co2Ta / (αCo)21.06.40.91.9
Co57Ta38Si590 daysCo6Ta7 / λ2-Co2Ta43.24.135.56.1
Co27Ta68Si590 days(Ta) / (Co, Si)Ta291.72.963.56.2
Table 3. Equilibrium compositions of the Co-Ta-Si ternary system at 1100 °C determined in the present work.
Table 3. Equilibrium compositions of the Co-Ta-Si ternary system at 1100 °C determined in the present work.
Alloy
(at.%)
Annealed TimePhase EquilibriaComposition (at.%)
Phase 1/Phase 2/Phase 3Phase 1Phase 2Phase 3
TaSiTaSiTaSi
Co10Ta10Si8060 daysTaSi2 / CoSi2 / (Si)31.067.30.768.00.199.0
Co33Ta14Si5360 daysV / CoSi25.448.20.150.9
Co10Ta38Si5260 daysTaSi2 / αTa5Si3 / V31.468.158.539.325.648.8
Co46Ta28Si2660 daysE / G30.834.819.725.5
Co30Ta43Si2760 days(Co, Si)Ta2 / λ1-Co2Ta63.630.332.926.4
Co54Ta28Si1860 daysλ1-Co2Ta / G28.219.520.125.4
Co16Ta18Si6660 daysCoSi / TaSi2 / V30.867.60.151.824.548.4
Co22Ta27Si5160 daysTaSi2 / V31.468.425.348.9
Co27Ta60Si1360 days(Co, Si)Ta2 / Co6Ta763.821.150.77.5
Co35Ta5Si6060 daysV / CoSi23.848.60.151.2
Co34Ta26Si4060 daysE / V / CoSi31.835.425.246.80.151.9
Co25Ta38Si3760 daysE / αTa5Si3 / V57.739.632.035.625.748.3
Co64.5Ta22.5Si1360 daysλ3-Co2Ta / G22.112.619.523.8
Co2Ta75Si2360 daysTa / (Co, Si)Ta2 / Ta3Si94.84.064.030.027.971.6
Co26Ta7Si6760 daysTaSi2 / CoSi2 / (Si)30.468.10.167.80.199.5
Co46Ta13Si4160 daysE / G″ / CoSi30.235.013.037.40.150.5
Co58Ta10Si3260 daysαCo2Si / G / G″0.134.718.625.813.637.1
Co48Ta22Si3060 daysG / G″ / E18.725.913.437.330.734.8
Co36Ta33Si3160 daysE / λ1-Co2Ta30.735.430.526.8
Co59.5Ta22.5Si1860 daysG / λ3-Co2Ta18.825.124.215.3
Co59Ta31Si1060 daysλ1-Co2Ta28.711.3
Co11Ta75Si1460 days(Ta) / (Co, Si)Ta295.03.163.327.9
Co38Ta58Si460 daysCo6Ta7 / (Co, Si)Ta263.512.052.13.4
Co25Ta33Si4260 daysE / V31.435.924.648.8
Co24Ta44Si3160 daysαTa5Si3 / E58.639.430.835.5
Co65Ta27Si860 daysλ3-Co2Ta25.19.1
Co42Ta15Si4360 daysCoSi / E0.350.830.035.0
Co26Ta33Si4160 daysV / E24.948.531.335.1
Co56Ta9Si3560 daysG" / αCo2Si / CoSi13.636.50.133.90.149.3
Co44Ta25Si3160 daysG / G"18.925.613.936.4
Co10Ta59Si3160 daysαTa5Si3 / Ta2Si / E58.739.163.434.132.934.4
Co61Ta11Si2860 daysG / αCo2Si18.124.90.232.7
Co70Ta9Si2160 daysG / (εCo) / αCo2Si17.924.60.217.40.132.0
Co54Ta25Si2160 daysλ1-Co2Ta / G26.818.519.225.6
Co54Ta25Si2160 daysλ1-Co2Ta31.224.1
Co37Ta42Si2160 days(Co, Si)Ta2 / λ1-Co2Ta62.426.632.523.5
Co26Ta53Si2160 days(Co, Si)Ta2 / λ1-Co2Ta62.726.933.919.9
Co60Ta24Si1660 daysλ3-Co2Ta / G21.313.918.924.5
Co78Ta10Si1260 daysλ3-Co2Ta / G / (αCo)20.613.818.824.21.38.9
Co51Ta37Si1260 daysCo6Ta7 / λ1-Co2Ta45.85.532.610.9
Co41Ta47Si1260 days(Co, Si)Ta2 / Co6Ta7 / λ1-Co2Ta62.621.545.910.133.616.5
Co21Ta67Si1260 days(Co, Si)Ta2 / (Ta)94.13.063.624.5
Co78Ta17Si560 daysλ3-Co2Ta / (αCo)22.47.12.63.5
Co57Ta38Si560 daysCo6Ta7 / λ2-Co2Ta45.33.632.56.8
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Wang, C.; Huang, X.; Huang, L.; Yang, M.; Yang, P.; Cui, Y.; Zhang, J.; Yang, S.; Liu, X. Experimental Investigation of Phase Equilibria in the Co-Ta-Si Ternary System. Materials 2022, 15, 3097. https://doi.org/10.3390/ma15093097

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Wang C, Huang X, Huang L, Yang M, Yang P, Cui Y, Zhang J, Yang S, Liu X. Experimental Investigation of Phase Equilibria in the Co-Ta-Si Ternary System. Materials. 2022; 15(9):3097. https://doi.org/10.3390/ma15093097

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Wang, Cuiping, Xiang Huang, Liangfeng Huang, Mujin Yang, Peng Yang, Yunrui Cui, Jinbin Zhang, Shuiyuan Yang, and Xingjun Liu. 2022. "Experimental Investigation of Phase Equilibria in the Co-Ta-Si Ternary System" Materials 15, no. 9: 3097. https://doi.org/10.3390/ma15093097

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