Phase Equilibria of the Co-Ti-Ta Ternary System
by
and
Cuiping Wang
1,*, 
Xianjie Zhang
1,
Lingling Li
1,
Yunwei Pan
1,
Yuechao Chen
1,
Shuiyuan Yang
1,
Yong Lu
1,
Jiajia Han
1 and
Xingjun Liu
1,2,* 1
College of Materials and Fujian Key Laboratory of Materials Genome, Xiamen University, Xiamen 361005, China
2
State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Shenzhen 518005, China
*
Authors to whom correspondence should be addressed.
Metals 2018, 8(11), 958; https://doi.org/10.3390/met8110958
Submission received: 29 October 2018
/
Revised: 13 November 2018
/
Accepted: 14 November 2018
/
Published: 16 November 2018
Abstract
:The phase equilibria of the Co-Ti-Ta ternary system at 1000 °C, 1100 °C, and 1200 °C were experimentally investigated using an electron probe microanalyzer and X-ray diffraction. Experimental results show that: (1) No ternary compound exists in the studied isothermal sections; (2) the β(Ti) and β(Ta) phases form the continuous solid solution β(Ti,Ta) in the Ti-Ta side; (3) the solubility of Ta in the (αCo) is less than 5%; (4) the phases of Co2Ti(h) and γ-Co2Ta, Co2Ti(c) and β-Co2Ta form the continuous solid solutions Co2(Ta,Ti)(h) and Co2(Ta,Ti)(c), respectively.
1. Introduction
Since Sato et al. [1] reported the metastable L12 structure Co3(Al,W) phase, Co-based superalloys strengthened by γ′-Co3X phase with an ordered L12 structure got researchers’ attention again. Some reports have confirmed that the γ′-Co3Ti phase has a stable L12 structure [2]. So researchers [3,4] have focused on the γ/γ′ in the Co-Ti-X system, and found that the addition of elements Cr and V can distinctly improve strength above 600 °C, surpassing that of Co-9Al-8W and conventional Co-based superalloys. Furthermore, Ta is an important alloying element in both Co-based and Ni-based superalloys, in which Ta can stabilize the γ′ phase [5,6]. Ta mainly substitutes Ti in the L12 type Co3Ti phase [6], which makes the Co3Ti phase more stable. Therefore, information on the phase equilibria in the Co-Ti-Ta system is important for Co-based superalloys. However, information on the phase equilibria of the Co-Ti-Ta system is very limited. Up to now, only Xu et al. [7] have studied the phase equilibria in the Co-Ti-Ta system at 950 °C, and Jiang et al. [8] reported knowledge of the Co-Ti-Ta and the phase relationship in the Co-rich region. These are not enough to understand the phase relationship in the Co-Ti-Ta system, especially phase equilibria at high temperatures. In the present work, phase equilibria of the Co-Ti-Ta ternary system at 1000 °C, 1100 °C, and 1200 °C, and the corresponding microstructure of Co-Ti-Ta alloys were investigated.
Three binary systems of Co-Ta [9,10,11,12,13,14], Co-Ti [15,16,17,18,19,20], and Ta-Ti [21] constituting the Co-Ta-Ti ternary system are shown in Figure 1. Six intermediate phases are known in the Co-Ta system, namely by μ-Co6Ta7, CoTa2, α-Co2Ta, β-Co2Ta, γ-Co2Ta, and Co7Ta2. The Co-Ti system has five intermediate phases, CoTi, CoTi2(c), CoTi2(h), Co3Ti, and CoTi2. The Ta-Ti system is a continuous solid solution, without any compounds. The stable solid phases and their crystal structures in all three binary systems are listed in Table 1.
2. Experimental Procedures
Raw materials were from pure elements of cobalt (99.9 wt.%), titanium (99.9 wt.%), and tantalum (99.9 wt.%). Bulk alloys were prepared using an arc furnace (DHL-1, SKY Technology Development Co., Ltd, Shenyang, China), with non-consumable tungsten electrode under high purity argon atmosphere. In order to improve the homogeneity of the sample, the buttons were remelted four times. The weight loss of the alloys after melting did not exceed 0.5%. The samples for heat treatment were cut using a wire-cutting machine.
Vacuum in the quartz capsule containing alloys was pumped to 5 Pa, then filled with high purity argon at a certain pressure. To avoid oxidation of the samples, this process was repeated four times. The samples sealed in the quartz capsule were annealed at 1000 °C for 45 days, 1100 °C for 35 days or 8 h, and 1200 °C for 25 days or 8 h.
After annealing and metallographic preparation, the microstructure images of alloys and the equilibrium composition of each phase were observed and measured by an electron probe micro-analyzer (EPMA, JXA-8100R, JEOL, Tokyo, Japan). The measurements were taken at a voltage of 20 kV and a current of 1.0 × 10−8 A, with the measured results calibrated by ZAF (Z: Atomic number effect; A: Absorption effect; F: Fluorescence effect) correction. In order to reduce errors, the composition of each phase was determined by measuring five points, and then the final values were the average. Compositions of the liquid phase were determined via area analysis using the EDS (Energy Dispersive Spectroscopy) (INCA x-sight 7412, Oxford instruments, London, UK) at a voltage of 20 kV and a current of 2.0 × 10−9 A, with seven measurements. The constituent phases of the alloys were determined by XRD (X-ray diffraction) (Bruker Daltonic Inc., Billerica, MA, USA) on a Phillips Panalytical X-pert diffractometer using Cu Kα radiation at 40 kV and 40 mA. The data were collected in the range of 2θ from 20° to 90° at a step of 0.0167°.
3. Results and Discussion
3.1. Microstructure Morphology
BSE images of typical ternary Co-Ti-Ta alloys are presented in Figure 2a–j, and the XRD results of the typical ternary Co-Ti-Ta alloys are presented in Figure 3a–c.
Figure 2a presents the three-phase microstructure of the (αCo) + Co3Ti + Co7Ta2 in the Co80Ti9Ta11 (at.%) alloy annealed at 1000 °C for 45 days. Figure 2b shows the three-phase microstructure of the CoTi2 + CoTi + β(Ti,Ta) in the Co30Ti50Ta20 (at.%) alloy annealed at 1000 °C for 45 days. The crystal structures of three phases were identified by the XRD in Figure 3a, the characteristic peaks of three phases are marked by different symbols. The two-phase equilibrium of the Co3Ti + Co2(Ta,Ti)(h) was identified in the Co71Ti28Ta1 (at.%) alloy annealed at 1000 °C for 45 days, as shown in Figure 2c. Figure 2d presents the two-phase microstructure of the CoTi + Co2(Ta,Ti) (c) in the Co60Ti30Ta10 (at.%) alloy annealed at 1100 °C for 35 days. The two-phase microstructure of the CoTi + Liquid (L) in the Co40Ti58Ta2 (at.%) alloy annealed at 1100 °C for 8 h, shown in Figure 2e. Figure 2f presents the three-phase microstructure of the CoTi + β(Ti,Ta) + Liquid(L) in the Co30Ti50Ta20 (at.%) alloy annealed at 1100 °C for 8 h. After annealing at 1200 °C for 8 h of the Co85Ti13Ta2 (Figure 2g), the two-phase microstructure of the (αCo) + Liquid(L) was observed. The three-phase equilibrium of the CoTi + Co2(Ta,Ti)(c) + Co6Ta7 was identified in the Co55Ti15Ta30 (at.%) alloy annealed at 1200 °C for 25 days, as shown in Figure 2h. Figure 2i presents the three-phase microstructure of the CoTi + Co6Ta7 + CoTa2 in the Co45Ti15Ta40 (at.%) alloy annealed at 1200 °C for 25 days, its XRD result is shown in Figure 3b. Figure 2j shows the three-phase microstructure of the CoTa2 + CoTi + β(Ti,Ta) in the Co30Ti20Ta50 (at.%) alloy annealed at 1200 °C for 25 days, its XRD result is shown in Figure 3c.
3.2. Isothermal Sections
The equilibrium compositions of the Co-Ti-Ta ternary system in this study at 1000 °C, 1100 °C, and 1200 °C determined by EPMA are summarized in Table 2, Table 3 and Table 4. Based on the obtained experimental data mentioned above, the isothermal sections at 1000 °C, 1100 °C, and 1200 °C have been constructed in Figure 4a–c. Undetermined three-phase equilibria are labeled in the dashed lines.
Figure 4a shows the isothermal section at 1000 °C, six three-phase regions were experimentally determined as follows: (αCo) + Co3Ti + Co7Ta2, Co3Ti + Co7Ta2 + Co2(Ta,Ti)(h), Co2(Ta,Ti)(c) + Co6Ta7 + CoTi, CoTa2 + Co6Ta7 + CoTi, CoTa2 + β(Ti,Ta) + CoTi, CoTi + CoTi2 + β(Ti,Ta). The results show that: (1) The solubilities of Ta in the CoTi, and Co3Ti were 21%, and 12%, respectively. (2) The solubility of Ti in the Co7Ta2 was 9%. (3) The phases of Co2Ti (h) and γ-Co2Ta, Co2Ti (c) and β-Co2Ta formed continuous solid solutions.
There are five three-phase regions in the isothermal section at 1100 °C in Figure 4b, including the (αCo) + Co3Ti + Co2(Ta,Ti)(h), Co2(Ta,Ti)(c) + Co6Ta7 + CoTi, CoTa2 + Co6Ta7 + CoTi, CoTa2 + β(Ti,Ta) + CoTi, and CoTi + Liquid + β(Ti,Ta). In the isothermal section at 1100 °C, the phases of Co7Ta2 and CoTi2 disappeared and the liquid phase presented.
In the isothermal section at 1200 °C shown in Figure 4c, five three-phase regions of (αCo) + Liquid + Co2(Ta,Ti)(h), Co2(Ta,Ti)(c) + Co6Ta7 + CoTi, CoTa2 + Co6Ta7 + CoTi, CoTa2 + β(Ti,Ta) + CoTi,CoTi + Liquid + β(Ti,Ta) were completely obtained. When the temperature increased from 1100 °C to 1200 °C, the Co3Ti phase decomposed while a liquid phase appeared. The solubility of Ta in the CoTi phase increased to 26%, and the solubility of Ti in the CoTa2 increased to 12%.
Compared with the previous phase equilibria information on Co-Ti-Ta [7,8], we find that the results are consistent with the experimental results conducted by Xu [7] and Jiang [8]. Combining phase equilibria information of Co-Ti-Ta at the isothermal section 950 °C, which were obtained by Xu [7] (Figure 5), it was found that: (1) The phases of β(Ti) and β(Ta) form the continuous solid solution β(Ti,Ta); (2) the phases of Co2Ti(h) and γ-Co2Ta, Co2Ti (c) and β-Co2Ta form the continuous solid solutions Co2(Ta,Ti)(h) and Co2(Ta,Ti) (c), respectively; (3) the solubility of Ta in the Co3Ti decreases from 950 °C to 1100 °C, but the Co3Ti phase is absent at 1200 °C; (4) the Co7Ta2 does not exist in 1100 °C and 1200 °C, but it exists at 1000 °C with about 9% of the solubility of Ta; (5) a liquid phase region arises near the Ti-rich corner at 1100 °C and 1200 °C.
4. Conclusions
In the present study, three isothermal sections of the Co-Ti-Ta ternary alloys at 1000 °C, 1100 °C, and 1200 °C were determined by EPMA and XRD. The results show: (1) No ternary compound exists in the isothermal sections at 1000–1200 °C; (2) the β(Ti) and β(Ta) phases form the continuous solid solution β(Ti,Ta) in the Ti-Ta side; (3) the solubility of Ta in the (αCo) is less than 5%; (4) the phases of Co2Ti(h) and γ-Co2Ta, Co2Ti (c) and β-Co2Ta form the continuous solid solutions Co2(Ta,Ti)(h) and Co2(Ta,Ti)(c), respectively.
Author Contributions
Conceptualization, C.W. and X.L.; investigation, X.Z. and Y.C.; writing and original draft preparation, X.Z., Y.L. and J.H.; writing, reviewing and editing, Y.P., L.L. and S.Y.; supervision, X.L. and C.W.; and funding acquisition, X.L. and C.W.
Funding
This work was supported by the National Key R&D Program of China (Grant No. 2016YFB0701401), and the Natural Science Foundation of China (Grant No. 51471138 and 51571168).
Conflicts of Interest
The authors declare no conflict of interest.
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Figure 2.
Typical ternary BSE (Back scattered Electron) images obtained from: (a) Co80Ti9Ta11 alloy annealed at 1000 °C for 45 days; (b) Co30Ti50Ta20 alloy annealed at 1000 °C for 45 days; (c) Co71Ti28Ta1 alloy annealed at 1000 °C for 45 days; (d) Co60Ti30Ta10 alloy annealed at 1100 °C for 35 days; (e) Co40Ti58Ta2 alloy annealed at 1100 °C for 8 h; (f) Co30Ti50Ta20 alloy annealed at 1100 °C for 8 h; (g) Co85Ti13Ta2 alloy annealed at 1200 °C for 25 days; (h) Co55Ti15Ta30 alloy annealed at 1200 °C for 25 days; (i) Co45Ti15Ta40 alloy annealed at 1200 °C for 25 days; and (j) Co30Ti20Ta50 alloy annealed at 1200 °C for 25 days.
Figure 2.
Typical ternary BSE (Back scattered Electron) images obtained from: (a) Co80Ti9Ta11 alloy annealed at 1000 °C for 45 days; (b) Co30Ti50Ta20 alloy annealed at 1000 °C for 45 days; (c) Co71Ti28Ta1 alloy annealed at 1000 °C for 45 days; (d) Co60Ti30Ta10 alloy annealed at 1100 °C for 35 days; (e) Co40Ti58Ta2 alloy annealed at 1100 °C for 8 h; (f) Co30Ti50Ta20 alloy annealed at 1100 °C for 8 h; (g) Co85Ti13Ta2 alloy annealed at 1200 °C for 25 days; (h) Co55Ti15Ta30 alloy annealed at 1200 °C for 25 days; (i) Co45Ti15Ta40 alloy annealed at 1200 °C for 25 days; and (j) Co30Ti20Ta50 alloy annealed at 1200 °C for 25 days.
Figure 3.
X-ray diffraction patterns obtained from: (a) Co30Ti50Ta20 alloy annealed at 1000 °C for 45 days; (b) Co45Ti15Ta40 alloy annealed at 1100 °C for 35 days; and (c) Co30Ti20Ta50 alloy annealed at 1100 °C for 35 days.
Figure 3.
X-ray diffraction patterns obtained from: (a) Co30Ti50Ta20 alloy annealed at 1000 °C for 45 days; (b) Co45Ti15Ta40 alloy annealed at 1100 °C for 35 days; and (c) Co30Ti20Ta50 alloy annealed at 1100 °C for 35 days.
Figure 4.
Experimentally determined isothermal sections of the Co-Ti-Ta system at: (a) 1000 °C; (b) 1100 °C; and (c) 1200 °C.
Figure 4.
Experimentally determined isothermal sections of the Co-Ti-Ta system at: (a) 1000 °C; (b) 1100 °C; and (c) 1200 °C.
Figure 5.
Experimentally determined isothermal sections of the Co-Ti-Ta system at 950 °C by Xu [7].
Figure 5.
Experimentally determined isothermal sections of the Co-Ti-Ta system at 950 °C by Xu [7].
Table 1.
The stable solid phases in the Co-Ti-Ta ternary system.
| System | Phase | Pearson’s Symbol | Space Group | Prototype | Strukturbericht | References |
|---|---|---|---|---|---|---|
| Co-Ti | (αTi) | hP2 | P63/mmc | Mg | A3 | [20] |
| (βTi) | cI2 | Im-3m | W | A2 | [20] | |
| CoTi2 | cF96 | Fd-3m | Fe3W3C | E93 | [20] | |
| CoTi | cP2 | Pm-3m | CsCl | B2 | [20] | |
| Co2Ti(c) | cF24 | Fd-3m | Cu2Mg | C15 | [20] | |
| Co2Ti(h) | hP24 | P63/mmc | MgNi2 | C36 | [20] | |
| Co3Ti | cP4 | Pm-3m | Au3Cu | L12 | [20] | |
| (εCo) | hP2 | P63/mmc | Mg | A3 | [20] | |
| (αCo) | cF4 | Fm-3m | Cu | A1 | [20] | |
| Co-Ta | Ta | cI2 | Im-3m | W | A2 | [14] |
| Co6Ta7 | hR13 | R-3m | Fe7W6 | D8b | [14] | |
| CoTa2 | tI12 | I4/mcm | Al2Cu | C16 | [14] | |
| α-Co2Ta | hP12 | P63/mmc | Zn2Mg | C14 | [14] | |
| β-Co2Ta | cF24 | Fd-3m | Cu2Mg | C15 | [14] | |
| γ-Co2Ta | hP24 | P63/mmc | MgNi2 | C36 | [14] | |
| Co7Ta2 | hR36 | R-3m | BaPb3 | -- | [14] | |
| (εCo) | hP2 | P63/mmc | Mg | A3 | [14] | |
| (αCo) | cF4 | Fm-3m | Cu | A1 | [14] | |
| Ti-Ta | β(Ti,Ta) | cI2 | Im-3m | W | A2 | [21] |
Table 2.
Equilibrium composition of the Co-Ti-Ta ternary system at 1000 °C determined in the present work.
Table 2.
Equilibrium composition of the Co-Ti-Ta ternary system at 1000 °C determined in the present work.
| Alloys (at.%) | Annealed Time | Equilibria | Composition (at.%) | |||||
|---|---|---|---|---|---|---|---|---|
| Phase 1/Phase 2/Phase 3 | Phase 1 | Phase 2 | Phase 3 | |||||
| Ta | Ti | Ta | Ti | Ta | Ti | |||
| Co85Ti13Ta2 | 45 days | (αCo)/Co3Ti | 1.0 | 10.8 | 3.0 | 17.1 | — | — |
| Co85Ti2Ta13 | 45 days | (αCo)/Co7Ta2 | 0.9 | 2.3 | 1.0 | 22.5 | — | — |
| Co80Ti9Ta11 | 45 days | (αCo)/Co3Ti/Co7Ta2 | 2.1 | 5.3 | 11.5 | 10.3 | 16.4 | 7.7 |
| Co71Ti28Ta1 | 45 days | Co3Ti/Co2(Ti,Ta)(h) | 0.8 | 24.1 | 1.3 | 28.7 | — | — |
| Co74Ti16Ta10 | 45 days | Co3Ti/Co7Ta2/Co2(Ti,Ta)(h) | 7.0 | 15.8 | 8.4 | 15.3 | 10.5 | 15.4 |
| Co74Ti10Ta16 | 45 days | (αCo)/Co7Ta2 | 2.1 | 4.2 | 19.2 | 5.1 | — | — |
| Co75Ti1Ta14 | 45 days | Co2(Ti,Ta)(h) | 23.1 | 0.6 | — | — | — | — |
| Co60Ti2Ta38 | 45 days | Co2(Ti,Ta)(c)/Co6Ta7 | 31.5 | 2.1 | 43.2 | 1.8 | — | — |
| Co55Ti15Ta30 | 45 days | Co2(Ti,Ta)(c)/Co6Ta7/CoTi | 28.4 | 8.1 | 39.9 | 6.0 | 20.8 | 27.6 |
| Co60Ti30Ta10 | 45 days | Co2(Ti,Ta)(c)/CoTi | 10.8 | 19.4 | 4.5 | 41.6 | — | — |
| Co45Ti15Ta40 | 45 days | CoTi/Co6Ta7/CoTa2 | 19.8 | 30.3 | 47.1 | 7.9 | 53.2 | 7.9 |
| Co30Ti20Ta50 | 45 days | CoTi/CoTa2/β(Ti,Ta) | 8.1 | 43.7 | 55.6 | 9.8 | 86.0 | 8.3 |
| Co30Ti50Ta20 | 45 days | CoTi/CoTi2/β(Ti,Ta) | 2.1 | 43.3 | 6.3 | 61.4 | 51.3 | 42.5 |
| Co40Ti58Ta2 | 45 days | CoTi/CoTi2 | 1.1 | 51.1 | 3.5 | 64.1 | — | — |
| Co80Ti15Ta5 | 45 days | (αCo)/Co3Ti | 1.0 | 9.5 | 5.7 | 16.1 | — | — |
| Co62Ti20Ta18 | 45 days | Co2(Ti,Ta)(c)/CoTi | 22.3 | 11.9 | 11.3 | 35.7 | — | — |
| Co20Ti75Ta5 | 45 days | CoTi2/β(Ti,Ta) | 2.0 | 65.0 | 6.2 | 78.8 | — | — |
| Co42Ti3Ta55 | 45 days | Co6Ta7/CoTa2 | 52.0 | 3.0 | 57.5 | 3.5 | — | — |
| Co30Ti40Ta30 | 45 days | CoTi/β(Ti,Ta) | 3.1 | 46.2 | 71.2 | 22.9 | — | — |
Table 3.
Equilibrium composition of the Co-Ti-Ta ternary system at 1100 °C determined in the present work.
Table 3.
Equilibrium composition of the Co-Ti-Ta ternary system at 1100 °C determined in the present work.
| Alloys (at.%) | Annealed Time | Equilibria | Composition (at.%) | |||||
|---|---|---|---|---|---|---|---|---|
| Phase 1/Phase 2/Phase 3 | Phase 1 | Phase 2 | Phase 3 | |||||
| Ta | Ti | Ta | Ti | Ta | Ti | |||
| Co85Ti13Ta2 | 35 days | (αCo)/Co3Ti | 1.6 | 11.5 | 5.9 | 11.6 | — | — |
| Co80Ti5Ta15 | 35 days | (αCo)/Co2(Ti,Ta)(h) | 2.7 | 5.6 | 18.7 | 6.7 | — | — |
| Co85Ti2Ta13 | 35 days | (αCo)/Co2(Ti,Ta)(h) | 3.6 | 1.3 | 22.4 | 1.2 | — | — |
| Co71Ti28Ta1 | 35 days | Co3Ti/Co2(Ti,Ta)(h) | 0.6 | 23.8 | 1.0 | 28.7 | — | — |
| Co74Ti16Ta10 | 35 days | (αCo)/Co3Ti/Co2(Ti,Ta)(h) | 1.7 | 10.5 | 6.9 | 16.2 | 10.8 | 15.9 |
| Co74Ti10Ta16 | 35 days | (αCo)/Co2(Ti,Ta)(h) | 2.4 | 8.3 | 15.2 | 10.9 | — | — |
| Co75Ti1Ta24 | 35 days | Co2(Ti,Ta)(h) | 23.2 | 0.9 | — | — | — | — |
| Co60Ti2Ta38 | 35 days | Co2(Ti,Ta)(c)/Co6Ta7 | 31.4 | 2.2 | 44.7 | 1.9 | — | — |
| Co55Ti15Ta30 | 35 days | Co2(Ti,Ta)(c)/Co6Ta7/CoTi | 29.6 | 8.0 | 41.1 | 6.3 | 23.3 | 26.3 |
| Co60Ti30Ta10 | 35 days | Co2(Ti,Ta)(c)/CoTi | 11.6 | 22.7 | 5.5 | 41.1 | — | — |
| Co45Ti15Ta40 | 35 days | CoTi/Co6Ta7/CoTa2 | 21.4 | 29.6 | 46.4 | 8.3 | 61.3 | 3.7 |
| Co30Ti20Ta50 | 35 days | CoTi/CoTa2/β(Ti,Ta) | 16.8 | 38.5 | 56.6 | 9.9 | 86.1 | 9.9 |
| Co30Ti50Ta20 | 8 h | CoTi/Liquid/β(Ti,Ta) | 2.9 | 50.0 | 4.5 | 68.3 | 45.9 | 48.8 |
| Co40Ti58Ta2 | 8 h | CoTi/Liquid | 1.0 | 51.7 | 2.7 | 69.2 | — | — |
| Co15Ti84Ta1 | 8 h | Liquid/β(Ti,Ta) | 0.7 | 78.8 | 2.0 | 88.0 | — | — |
| Co62Ti20Ta18 | 35 days | Co2(Ti,Ta)(c)/CoTi | 20.6 | 12.8 | 12.3 | 34.0 | — | — |
| Co20Ti75Ta5 | 8 h | Liquid/β(Ti,Ta) | 4.0 | 73.9 | 7.3 | 82.7 | — | — |
| Co42Ti3Ta55 | 35 days | Co6Ta7/CoTa2 | 52.9 | 3.0 | 63.1 | 1.6 | — | — |
| Co30Ti40Ta30 | 35 days | CoTi/β(Ti,Ta) | 3.9 | 48.5 | 66.7 | 28.9 | — | — |
Table 4.
Equilibrium composition of the Co-Ti-Ta ternary system at 1200 °C determined in the present work.
Table 4.
Equilibrium composition of the Co-Ti-Ta ternary system at 1200 °C determined in the present work.
| Alloys (at.%) | Annealed Time | Equilibria | Composition (at.%) | |||||
|---|---|---|---|---|---|---|---|---|
| Phase 1/Phase 2/Phase 3 | Phase 1 | Phase 2 | Phase 3 | |||||
| Ta | Ti | Ta | Ti | Ta | Ti | |||
| Co85Ti13Ta2 | 8 h | (αCo)/Liquid | 1.2 | 11.4 | 2.1 | 17.2 | — | — |
| Co85Ti2Ta13 | 25 days | (αCo)/Co2(Ti,Ta) (h) | 4.7 | 1.2 | 22.5 | 1.0 | — | — |
| Co80Ti9Ta11 | 25 days | (αCo)/Co2(Ti,Ta)(h) | 3.2 | 7.2 | 16.5 | 8.6 | — | — |
| Co71Ti28Ta1 | 8 h | Liquid/Co2(Ti,Ta)(h) | 0.1 | 23.2 | 0.9 | 30.2 | — | — |
| Co74Ti16Ta10 | 8 h | Liquid/Co2(Ti,Ta)(h) | 3.1 | 18.5 | 9.9 | 17.4 | — | — |
| Co60Ti2Ta38 | 25 days | Co2(Ti,Ta)(c)/Co6Ta7 | 32.5 | 1.0 | 44.4 | 0.8 | — | — |
| Co55Ti15Ta30 | 25 days | Co2(Ti,Ta)(c)/Co6Ta7/CoTi | 30.4 | 7.5 | 40.7 | 5.4 | 26.0 | 22.0 |
| Co60Ti32Ta8 | 25 days | Co2(Ti,Ta)(c)/CoTi | 10.3 | 20.3 | 5.9 | 37.7 | — | — |
| Co45Ti15Ta40 | 25 days | CoTi/Co6Ta7/CoTa2 | 25.2 | 24.1 | 45.1 | 7.0 | 60.3 | 3.8 |
| Co30Ti50Ta20 | 8 h | CoTi/Liquid/β(Ti,Ta) | 5.5 | 46.5 | 7.7 | 63.2 | 49.5 | 43.5 |
| Co40Ti58Ta2 | 8 h | CoTi/Liquid | 1.0 | 49.8 | 2.7 | 67.6 | — | — |
| Co14Ti84Ta2 | 8 h | Liquid/β(Ti,Ta) | 1.5 | 84.5 | 2.5 | 89.2 | — | — |
| Co80Ti15Ta5 | 8 h | (αCo)/Liquid/Co2(Ti,Ta)(h) | 2.1 | 11.7 | 3.8 | 16.0 | 10.0 | 16.2 |
| Co60Ti20Ta20 | 25 days | Co2(Ti,Ta)(c)/CoTi | 19.1 | 14.2 | 12.3 | 32.5 | — | — |
| Co75Ti6Ta19 | 25 days | (αCo)/Co2(Ti,Ta)(h) | 3.9 | 4.4 | 19.2 | 4.7 | — | — |
| Co42Ti3Ta55 | 25 days | Co6Ta7/CoTa2 | 52.9 | 3.0 | 63.1 | 1.6 | — | — |
| Co30Ti40Ta30 | 25 days | CoTi/β(Ti,Ta) | 6.6 | 44.7 | 74.2 | 23.2 | — | — |
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MDPI and ACS Style
Wang, C.; Zhang, X.; Li, L.; Pan, Y.; Chen, Y.; Yang, S.; Lu, Y.; Han, J.; Liu, X. Phase Equilibria of the Co-Ti-Ta Ternary System. Metals 2018, 8, 958. https://doi.org/10.3390/met8110958
AMA Style
Wang C, Zhang X, Li L, Pan Y, Chen Y, Yang S, Lu Y, Han J, Liu X. Phase Equilibria of the Co-Ti-Ta Ternary System. Metals. 2018; 8(11):958. https://doi.org/10.3390/met8110958
Chicago/Turabian StyleWang, Cuiping, Xianjie Zhang, Lingling Li, Yunwei Pan, Yuechao Chen, Shuiyuan Yang, Yong Lu, Jiajia Han, and Xingjun Liu. 2018. "Phase Equilibria of the Co-Ti-Ta Ternary System" Metals 8, no. 11: 958. https://doi.org/10.3390/met8110958
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