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Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing
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Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing ˜ A. Hernández-Pérez ∗ , M. Eddahbi, M.A. Monge, A. Munoz, B. Savoini Departamento de Física, Universidad Carlos III, 28911 Leganés, Madrid, Spain
h i g h l i g h t s • An ITER-grade Cu–Cr–Zr alloy was subjected to equal channel angular pressing (ECAP). • Development of macro and micro shear bands were observed in the microstructure. • The mechanical properties were improved after the ECAP process.
a r t i c l e
i n f o
Article history: Received 17 September 2014 Received in revised form 23 June 2015 Accepted 29 June 2015 Available online xxx Keywords: Equal channel angular pressing (ECAP) CuCrZr Copper Shear band
a b s t r a c t An ITER-grade Cu–Cr–Zr alloy was subjected to equal channel angular pressing (ECAP) at 400 ◦ C via routes BC and C, i.e. rotated 90◦ or 180◦ around the extrusion axis before subsequent passes. The microstructure of ECAP deformed samples showed shear bands confining small recrystallized grains of about ∼0.2–1 m in size. The best mechanical properties were observed for sample ECAP processed via route BC for which the density of shear bands is high and the interaction among them is notable. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Due to their high strength up to ∼400 ◦ C, good ductility, high thermal and electrical conductivity along with their commercial availability, precipitation hardened Cu–Cr–Zr alloys have been selected as heat-sink materials for ITER (International Thermonuclear Experimental Reactor) high heat flux (HHF) components such as the divertor, limiter and first wall of the reactor vacuum vessel [1,2]. Moreover, they exhibit higher fracture toughness and high resistance to radiation damage, compared with the oxide dispersion strengthened copper alloys such as GlidCop® Al25, allowing them to be good candidates for heat sinks in HHF applications in the baseline design of the prototype power plant DEMO (DEMOnstration Power Plant) with a water-cooled divertor [3–5]. Such properties depend strongly on the precipitation, grain structure, crystallographic texture, stored energy, chemical composition of the alloy, etc. [6,7]. For example, it has been established that the optimum concentration of elements for the ITER-grade Cu–Cr–Zr alloys that predicts fine precipitation and improves the radiation
∗ Corresponding author. E-mail address: aarherna@fis.uc3m.es (A. Hernández-Pérez).
resistance should be in the range of 0.6–0.9 wt.% for chromium and 0.07–0.15 wt.% for zirconium. Equal channel angular pressing (ECAP) is among the potential processing methods which introduce a high-accumulated deformation and drastic changes in the microstructure without changes in dimensions or shape compared to the conventional thermomechanical processing such as rolling or extrusion [8–10]. Grain and phase particles refinement along with the change in the crystallographic texture are the main microstructural changes involving the ECAP deformation that influence the material properties [11]. Whereas most of the thermomechanical processing methods applied for the production of Cu–Cr–Zr alloys use mainly the conventional techniques, lack of attention has been paid to the effect of ECAP on the properties of Cu–Cr–Zr alloys [12]. In this communication, the microstructure and the mechanical properties at room temperature of an ITER-grade Cu–Cr–Zr alloy subjected to ECAP via routes BC and C have been studied. 2. Experimental procedure The starting material was an extruded bar with composition Cu–0.65Cr–0.08Zr (wt.%). This composition fulfils the ITER-grade requirements [13]. Billets of 10 × 10 × 150 mm3 were cut from the
http://dx.doi.org/10.1016/j.fusengdes.2015.06.180 0920-3796/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: A. Hernández-Pérez, et al., Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.06.180
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Fig. 1. Microstructure of as-received Cu–Cr–Zr. Optical microscopy images of: (a) longitudinal section (L), (b) long transverse section (LT) and (c) short transverse section (ST). (d) SEM image of an etched sample (LT) showing precipitates (white contrast).
bar and ECAP processed at 400 ◦ C at a pressing rate of 1 mm/min. The ECAP die had an internal angle of 105◦ and an outer angle of 0◦ , which produced an effective strain of ∼1 by pass. The billets were subjected to a single pass (1p sample), and four passes via routes BC (4pBc sample) and C (4pC sample), i.e. before inserting in the die for the subsequent ECAP pass, the billets were rotated 90◦ (BC route) or 180◦ (C route) around the extrusion axis. Some test specimens obtained from the as-received and ECAP bars were annealed at 450 ◦ C for 1 h in vacuum (As-processed + 450 ◦ C/1 h sample) to study the effect of a stress-relief thermal treatment in the processed material. Metallographic analyses by optical microscopy (OM) and scanning electron microscopy (SEM) were performed on the as-received
bar, ECAP-processed and annealed materials. The specimens were mechanically polished using alumina and colloidal silica solution at the final stage. The microstructure was revealed by etching during 15 min in a solution of 20 ml of methanol and 80 ml of nitric acid. The mechanical properties of the materials were studied from tensile tests at room temperature at an initial true strain rate of 10−4 s−1 using an AG-I Shimadzu machine. Flat samples with gauge dimensions of 3 × 1 × 10 mm3 were spark machined from the billets, so the tensile axis of the ECAP deformed billets was parallel to the ED. The microstructure of tensile-strained samples in grip (non-deformed) and gauge (deformed) regions was also analyzed. Vickers microhardness measurements were conducted on the grip and gauge regions of tensile strained samples. A microhardness
Fig. 2. True stress–true strain curves of the Cu–Cr–Zr alloy for the as-received and ECAP processed samples (a) before and (b) after annealing 1 h at 450 ◦ C.
Please cite this article in press as: A. Hernández-Pérez, et al., Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.06.180
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Table 1 Mechanical properties at room temperature of as-received Cu–Cr–Zr ITER-grade alloy, after ECAP deformation and after subsequent annealing. The mechanical properties in the as-received condition are given. As-processed + 450 ◦ C/1 h
As-processed
As-received 1p 4pBc 4pC
y (MPa)
UTS (MPa)
εf
HV grip
HV gauge
y (MPa)
UTS (MPa)
εf
HV (grip)
HV (gauge)
436 443 485 461
524 508 542 522
0.14 0.18 0.17 0.17
170 178 185 183
186 183 188 188
442 428 470 450
533 507 529 522
0.11 0.19 0.18 0.18
176 176 181 178
183 177 188 185
test equipment Future-Tech-Corp-Model FM-100e applying a load of 500 g during 10 s was employed for these measurements.
Cu–Cr–Zr alloys, and they are attributed to stable intermetallic Cu–Zr compounds that do not dissolve during the homogenization treatment [14–16].
3. Results and discussion 3.2. Mechanical tests 3.1. Initial microstructure The microstructure of the as-received Cu–0.65Cr–0.08Zr alloy before ECAP deformation is shown in Fig. 1. It consists of grains elongated along the ED with ∼57 m in length and ∼36 m in width. Most of the grains are twinned, as the microstructure on the transverse section (ST) reveals (Fig. 1(c)). Two types of precipitates are observed: spherical and rod-like (see Fig. 1(d)). Energy Dispersive X-ray spectroscopy (EDX) analysis shows that the spherical precipitates are Cr enriched oxides of ∼1 m diameter and the Cu–Cr rod-like precipitates of ∼4 m in length and ∼0.64 m in diameter are Zr enriched. The latter are preferentially oriented along the ED. Zr rich precipitates have been observed in other
The true stress–true strain curves of the as-received Cu–Cr–Zr alloy after ECAP deformation and after subsequent annealing are shown in Fig. 2(a) and (b), respectively. The tensile properties and the microhardness (HV) values of tensile deformed samples are summarized in Table 1. The stress–strain curve shows that the asreceived material experiments some hardening till the Ultimate Tensile Strength (UTS) is attained and then the flow stress decreases significantly due to necking. In contrast, the curves corresponding to ECAP processed materials show similar tendency without appreciated hardening. It is noticeable that the elongation to failure after ECAP deformation increases irrespective of the route and the number of passes compared to the as-received material. Nonetheless,
Fig. 3. Microstructure after tensile test testing at RT at 10−4 s−1 of ECAP deformed Cu–Cr–Zr for: 1 pass ECAP (a) grip region and (b) gauge, 4 passes via route BC (c) grip and (d) gauge, and 4 passes via route C (e) grip region and (f) gauge region. The tensile stress direction is indicated in (f).
Please cite this article in press as: A. Hernández-Pérez, et al., Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.06.180
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the best mechanical properties, yield stress ( y ) and UTS, are observed for sample 4pBc. No significant differences are observed for annealed samples, as the comparison of Fig. 2(a) and (b) reveals. This result should be attributed to the stability of the microstructure under the imposed annealing conditions. 3.3. Deformed microstructure The microstructure of 1p, 4pBc and 4pC samples after tensile testing at RT at 10−4 s−1 are shown in Fig. 3. Fig. 3(a), (c) and (e) correspond to grip regions and Fig. 3(b), (d) and (f) to gauge regions. In the grip region, it is observed that the grain after one pass is somewhat elongated towards the shear direction with a deviation of about 10◦ with respect to the pressing direction. However, the most important feature arising from Fig. 3 is the formation of shear bands (SB), microshear bands (MB) and/or deformed twins inside the grains, oriented at 40◦ –45◦ with respect to the pressing direction, (see white arrows in Fig. 3(a)). Similar results have been observed in previous studies of polycrystalline Cu and Cu alloys [17,18]. These SB confine fine recrystallized grains of ∼0.2–1 m in size, as shown in the inset of Fig. 3(a). Additionally, small recrystallized grains of similar size are also developed along the original grain boundaries aligned with the pressing direction, as indicated for 4pBc and 4pC samples in Fig. 3(c) and (e), respectively. The volume fractions of both SB and recrystallized grains are significant higher in 4pBc sample compared to 1p and 4pC samples. No major differences in the microstructure of the processed materials were observed after the stress relief thermal treatment. Furthermore, interaction between SB in different directions for 4pBc sample is pronounced due the complex strain path attributed to route BC (Fig. 3c). Nevertheless, the width of SB in 4pC sample is somewhat larger and no significant SB interaction is observed (Fig. 3e). Similar observations are found in the corresponding gauge regions, albeit the microstructure is slightly elongated along the tensile stress direction and the width of SB is slightly lower compared to the one observed in the unstrained regions. These results are in good agreement with those reported for pure Cu and Cu–0.44Cr–0.2Zr processed by route BC [19–21]. In parallel, the rod-like precipitates manifest fragmentation during ECAP deformation and deviation from the initial orientation. From the above-mentioned data, it becomes apparent that ECAP deformation up to four passes produces only a partial grain refinement. It is expected that further ECAP deformation up to 8 or even 12 passes via route BC should produce a total recrystallization of Cu–0.65Cr–0.08Zr with ultrafine-grained microstructure. Further works are needed to reveal the microstructural and mechanical characteristics of samples ECAP processed for more than four passes. 4. Conclusions The microstructure and mechanical properties of an ITER-grade Cu–0.65Cr–0.08Zr ECAP processed at 400 ◦ C via route BC and C have been studied and the following conclusions can be drawn:
1. For one ECAP pass the deformation is governed by the formation of SB oriented at 40◦ –45◦ with respect to the pressing direction. 2. New small recrystallized grains of ∼0.2–1 m in size have been developed inside SB and along the original grain boundaries. The second phase particles were further fragmented and rearranged during ECAP deformation. 3. The mechanical properties were improved in the ECAP deformed sample up to four passes via route BC . The microstructure showed high density of SB interacting in different directions compared to the ECAP processed samples for one pass and for four passes via route C. 4. No significant differences were observed in the mechanical properties of the annealed ECAP processed samples. Acknowledgements This research has been supported by Ministerio de Economía y Competitividad of Spain (ENE2012-39787-C06-05). The financial support from the Comunidad de Madrid, through the programs S2013/MAE-2745 TECHNOFUSION(II)-CM and S2013/MIT-2862MULTIMAT-CHALLENGE and the additional subvention from EURATOM/CIEMAT association through contract EFDA (WP12MAT-HHFMAM-02) are also gratefully acknowledged. References [1] S.A. Fabritsiev, S.J. Zinkle, B.N. Singh, J. Nucl. Mater. 233–237 (1996) 127–137. [2] V.R. Barabash, G.M. Kalinin, S.A. Fabritsiev, S.J. Zinkle, J. Nucl. Mater. 417 (2011) 904–907. [3] D. Stork, P. Agostini, J.-L. Boutard, et al., Fusion Eng. Des. (2014), http://dx.doi. org/10.1016/j.fusengdes.2013.11.007 (in press). [4] S.A. Fabritsiev, A.S. Pokrovsky, A. Peacock, M. Roedig, J. Linke, A.A. Gervash, V.R. Barabash, J. Nucl. Mater. 386–388 (2009) 824–829. [5] M. Li, M.A. Sokolov, S.J. Zinkle, J. Nucl. Mater. 393 (2009) 36–46. [6] A. Vinogradov, Y. Suzuki, T. Ishida, K. Kitagawa, V.I. Kopylov, Mater. Trans. 45 (2004) 2187–2191. [7] U. Holzwarth, H. Stamm, J. Nucl. Mater. 279 (2000) 31–45. [8] V.M. Segal, Mater. Sci. Eng. A: Struct. Mater. A197 (1995) 157–164. [9] I. Kopylov, in: T.C. Lowe, R.Z. Valiev (Eds.), Investigations and Applications of Severe Plastic Deformation, NATO ASI Series 3, vol. 80, Netherlands, Kluwer, 2000, pp. 23–27. [10] R.Z. Valiev, R.K. Islamgaliev, I.V. Alexandrov, Prog. Mater. Sci. 45 (2000) 103–189. [11] R.Z. Valiev, T.G. Langdon, Prog. Mater. Sci. 51 (2006) 881–981. ˜ [12] M.A. Munoz-Morris, K. Valdés León, F.G. Caballero, D.G. Morris, Scr. Mater. 67 (2012) 806–809. [13] Materials Assessment Report (MAR), ITER Doc.G AO FDR 1 01-a07-13 R1.0, July 2013. [14] T.B. Massalski, Binary Alloy Phase Diagrams, 2nd ed., ASM, Metals Park, OH, 1987, pp. 982. [15] M. Apello, P. Fenici, Mater. Sci. Eng. A: Struct. Mater. 102 (1988) 69–75. [16] A. Chbihi, X. Sauvage, D. Blavette, Acta Mater. 60 (2012) 4575–4585. [17] C.X. Huang, K. Wang, S.D. Wu, Z.F. Zhang, G.Y. Li, S.X. Li, Acta Mater. 54 (2006) 655–665. [18] S. Qu, X.H. An, H.J. Yang, C.X. Huang, G. Yang, Q.S. Zang, Z.G. Wang, S.D. Wu, Z.F. Zhang, Acta Mater. 57 (2009) 1586–1601. [19] F. Dalla Torre, R. Lapovok, J. Sandlin, P.F. Thomson, C.H.J. Davies, E.V. Pereloma, Acta Mater. 52 (2004) 4819–4832. [20] A. Mishra, B.K. Kad, F. Gregori, M.A. Meyers, Acta Mater. 55 (2007) 13–28. [21] P.K. Jayakumar, K. Balasubramanian, G. Rabindranath Tagore, Mater. Sci. Eng. A: Struct. Mater. A538 (2012) 7–13.
Please cite this article in press as: A. Hernández-Pérez, et al., Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.06.180
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FUSION-8212; No. of Pages 4
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Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing ˜ A. Hernández-Pérez ∗ , M. Eddahbi, M.A. Monge, A. Munoz, B. Savoini Departamento de Física, Universidad Carlos III, 28911 Leganés, Madrid, Spain
h i g h l i g h t s • An ITER-grade Cu–Cr–Zr alloy was subjected to equal channel angular pressing (ECAP). • Development of macro and micro shear bands were observed in the microstructure. • The mechanical properties were improved after the ECAP process.
a r t i c l e
i n f o
Article history: Received 17 September 2014 Received in revised form 23 June 2015 Accepted 29 June 2015 Available online xxx Keywords: Equal channel angular pressing (ECAP) CuCrZr Copper Shear band
a b s t r a c t An ITER-grade Cu–Cr–Zr alloy was subjected to equal channel angular pressing (ECAP) at 400 ◦ C via routes BC and C, i.e. rotated 90◦ or 180◦ around the extrusion axis before subsequent passes. The microstructure of ECAP deformed samples showed shear bands confining small recrystallized grains of about ∼0.2–1 m in size. The best mechanical properties were observed for sample ECAP processed via route BC for which the density of shear bands is high and the interaction among them is notable. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Due to their high strength up to ∼400 ◦ C, good ductility, high thermal and electrical conductivity along with their commercial availability, precipitation hardened Cu–Cr–Zr alloys have been selected as heat-sink materials for ITER (International Thermonuclear Experimental Reactor) high heat flux (HHF) components such as the divertor, limiter and first wall of the reactor vacuum vessel [1,2]. Moreover, they exhibit higher fracture toughness and high resistance to radiation damage, compared with the oxide dispersion strengthened copper alloys such as GlidCop® Al25, allowing them to be good candidates for heat sinks in HHF applications in the baseline design of the prototype power plant DEMO (DEMOnstration Power Plant) with a water-cooled divertor [3–5]. Such properties depend strongly on the precipitation, grain structure, crystallographic texture, stored energy, chemical composition of the alloy, etc. [6,7]. For example, it has been established that the optimum concentration of elements for the ITER-grade Cu–Cr–Zr alloys that predicts fine precipitation and improves the radiation
∗ Corresponding author. E-mail address: aarherna@fis.uc3m.es (A. Hernández-Pérez).
resistance should be in the range of 0.6–0.9 wt.% for chromium and 0.07–0.15 wt.% for zirconium. Equal channel angular pressing (ECAP) is among the potential processing methods which introduce a high-accumulated deformation and drastic changes in the microstructure without changes in dimensions or shape compared to the conventional thermomechanical processing such as rolling or extrusion [8–10]. Grain and phase particles refinement along with the change in the crystallographic texture are the main microstructural changes involving the ECAP deformation that influence the material properties [11]. Whereas most of the thermomechanical processing methods applied for the production of Cu–Cr–Zr alloys use mainly the conventional techniques, lack of attention has been paid to the effect of ECAP on the properties of Cu–Cr–Zr alloys [12]. In this communication, the microstructure and the mechanical properties at room temperature of an ITER-grade Cu–Cr–Zr alloy subjected to ECAP via routes BC and C have been studied. 2. Experimental procedure The starting material was an extruded bar with composition Cu–0.65Cr–0.08Zr (wt.%). This composition fulfils the ITER-grade requirements [13]. Billets of 10 × 10 × 150 mm3 were cut from the
http://dx.doi.org/10.1016/j.fusengdes.2015.06.180 0920-3796/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: A. Hernández-Pérez, et al., Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.06.180
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Fig. 1. Microstructure of as-received Cu–Cr–Zr. Optical microscopy images of: (a) longitudinal section (L), (b) long transverse section (LT) and (c) short transverse section (ST). (d) SEM image of an etched sample (LT) showing precipitates (white contrast).
bar and ECAP processed at 400 ◦ C at a pressing rate of 1 mm/min. The ECAP die had an internal angle of 105◦ and an outer angle of 0◦ , which produced an effective strain of ∼1 by pass. The billets were subjected to a single pass (1p sample), and four passes via routes BC (4pBc sample) and C (4pC sample), i.e. before inserting in the die for the subsequent ECAP pass, the billets were rotated 90◦ (BC route) or 180◦ (C route) around the extrusion axis. Some test specimens obtained from the as-received and ECAP bars were annealed at 450 ◦ C for 1 h in vacuum (As-processed + 450 ◦ C/1 h sample) to study the effect of a stress-relief thermal treatment in the processed material. Metallographic analyses by optical microscopy (OM) and scanning electron microscopy (SEM) were performed on the as-received
bar, ECAP-processed and annealed materials. The specimens were mechanically polished using alumina and colloidal silica solution at the final stage. The microstructure was revealed by etching during 15 min in a solution of 20 ml of methanol and 80 ml of nitric acid. The mechanical properties of the materials were studied from tensile tests at room temperature at an initial true strain rate of 10−4 s−1 using an AG-I Shimadzu machine. Flat samples with gauge dimensions of 3 × 1 × 10 mm3 were spark machined from the billets, so the tensile axis of the ECAP deformed billets was parallel to the ED. The microstructure of tensile-strained samples in grip (non-deformed) and gauge (deformed) regions was also analyzed. Vickers microhardness measurements were conducted on the grip and gauge regions of tensile strained samples. A microhardness
Fig. 2. True stress–true strain curves of the Cu–Cr–Zr alloy for the as-received and ECAP processed samples (a) before and (b) after annealing 1 h at 450 ◦ C.
Please cite this article in press as: A. Hernández-Pérez, et al., Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.06.180
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Table 1 Mechanical properties at room temperature of as-received Cu–Cr–Zr ITER-grade alloy, after ECAP deformation and after subsequent annealing. The mechanical properties in the as-received condition are given. As-processed + 450 ◦ C/1 h
As-processed
As-received 1p 4pBc 4pC
y (MPa)
UTS (MPa)
εf
HV grip
HV gauge
y (MPa)
UTS (MPa)
εf
HV (grip)
HV (gauge)
436 443 485 461
524 508 542 522
0.14 0.18 0.17 0.17
170 178 185 183
186 183 188 188
442 428 470 450
533 507 529 522
0.11 0.19 0.18 0.18
176 176 181 178
183 177 188 185
test equipment Future-Tech-Corp-Model FM-100e applying a load of 500 g during 10 s was employed for these measurements.
Cu–Cr–Zr alloys, and they are attributed to stable intermetallic Cu–Zr compounds that do not dissolve during the homogenization treatment [14–16].
3. Results and discussion 3.2. Mechanical tests 3.1. Initial microstructure The microstructure of the as-received Cu–0.65Cr–0.08Zr alloy before ECAP deformation is shown in Fig. 1. It consists of grains elongated along the ED with ∼57 m in length and ∼36 m in width. Most of the grains are twinned, as the microstructure on the transverse section (ST) reveals (Fig. 1(c)). Two types of precipitates are observed: spherical and rod-like (see Fig. 1(d)). Energy Dispersive X-ray spectroscopy (EDX) analysis shows that the spherical precipitates are Cr enriched oxides of ∼1 m diameter and the Cu–Cr rod-like precipitates of ∼4 m in length and ∼0.64 m in diameter are Zr enriched. The latter are preferentially oriented along the ED. Zr rich precipitates have been observed in other
The true stress–true strain curves of the as-received Cu–Cr–Zr alloy after ECAP deformation and after subsequent annealing are shown in Fig. 2(a) and (b), respectively. The tensile properties and the microhardness (HV) values of tensile deformed samples are summarized in Table 1. The stress–strain curve shows that the asreceived material experiments some hardening till the Ultimate Tensile Strength (UTS) is attained and then the flow stress decreases significantly due to necking. In contrast, the curves corresponding to ECAP processed materials show similar tendency without appreciated hardening. It is noticeable that the elongation to failure after ECAP deformation increases irrespective of the route and the number of passes compared to the as-received material. Nonetheless,
Fig. 3. Microstructure after tensile test testing at RT at 10−4 s−1 of ECAP deformed Cu–Cr–Zr for: 1 pass ECAP (a) grip region and (b) gauge, 4 passes via route BC (c) grip and (d) gauge, and 4 passes via route C (e) grip region and (f) gauge region. The tensile stress direction is indicated in (f).
Please cite this article in press as: A. Hernández-Pérez, et al., Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.06.180
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the best mechanical properties, yield stress ( y ) and UTS, are observed for sample 4pBc. No significant differences are observed for annealed samples, as the comparison of Fig. 2(a) and (b) reveals. This result should be attributed to the stability of the microstructure under the imposed annealing conditions. 3.3. Deformed microstructure The microstructure of 1p, 4pBc and 4pC samples after tensile testing at RT at 10−4 s−1 are shown in Fig. 3. Fig. 3(a), (c) and (e) correspond to grip regions and Fig. 3(b), (d) and (f) to gauge regions. In the grip region, it is observed that the grain after one pass is somewhat elongated towards the shear direction with a deviation of about 10◦ with respect to the pressing direction. However, the most important feature arising from Fig. 3 is the formation of shear bands (SB), microshear bands (MB) and/or deformed twins inside the grains, oriented at 40◦ –45◦ with respect to the pressing direction, (see white arrows in Fig. 3(a)). Similar results have been observed in previous studies of polycrystalline Cu and Cu alloys [17,18]. These SB confine fine recrystallized grains of ∼0.2–1 m in size, as shown in the inset of Fig. 3(a). Additionally, small recrystallized grains of similar size are also developed along the original grain boundaries aligned with the pressing direction, as indicated for 4pBc and 4pC samples in Fig. 3(c) and (e), respectively. The volume fractions of both SB and recrystallized grains are significant higher in 4pBc sample compared to 1p and 4pC samples. No major differences in the microstructure of the processed materials were observed after the stress relief thermal treatment. Furthermore, interaction between SB in different directions for 4pBc sample is pronounced due the complex strain path attributed to route BC (Fig. 3c). Nevertheless, the width of SB in 4pC sample is somewhat larger and no significant SB interaction is observed (Fig. 3e). Similar observations are found in the corresponding gauge regions, albeit the microstructure is slightly elongated along the tensile stress direction and the width of SB is slightly lower compared to the one observed in the unstrained regions. These results are in good agreement with those reported for pure Cu and Cu–0.44Cr–0.2Zr processed by route BC [19–21]. In parallel, the rod-like precipitates manifest fragmentation during ECAP deformation and deviation from the initial orientation. From the above-mentioned data, it becomes apparent that ECAP deformation up to four passes produces only a partial grain refinement. It is expected that further ECAP deformation up to 8 or even 12 passes via route BC should produce a total recrystallization of Cu–0.65Cr–0.08Zr with ultrafine-grained microstructure. Further works are needed to reveal the microstructural and mechanical characteristics of samples ECAP processed for more than four passes. 4. Conclusions The microstructure and mechanical properties of an ITER-grade Cu–0.65Cr–0.08Zr ECAP processed at 400 ◦ C via route BC and C have been studied and the following conclusions can be drawn:
1. For one ECAP pass the deformation is governed by the formation of SB oriented at 40◦ –45◦ with respect to the pressing direction. 2. New small recrystallized grains of ∼0.2–1 m in size have been developed inside SB and along the original grain boundaries. The second phase particles were further fragmented and rearranged during ECAP deformation. 3. The mechanical properties were improved in the ECAP deformed sample up to four passes via route BC . The microstructure showed high density of SB interacting in different directions compared to the ECAP processed samples for one pass and for four passes via route C. 4. No significant differences were observed in the mechanical properties of the annealed ECAP processed samples. Acknowledgements This research has been supported by Ministerio de Economía y Competitividad of Spain (ENE2012-39787-C06-05). The financial support from the Comunidad de Madrid, through the programs S2013/MAE-2745 TECHNOFUSION(II)-CM and S2013/MIT-2862MULTIMAT-CHALLENGE and the additional subvention from EURATOM/CIEMAT association through contract EFDA (WP12MAT-HHFMAM-02) are also gratefully acknowledged. References [1] S.A. Fabritsiev, S.J. Zinkle, B.N. Singh, J. Nucl. Mater. 233–237 (1996) 127–137. [2] V.R. Barabash, G.M. Kalinin, S.A. Fabritsiev, S.J. Zinkle, J. Nucl. Mater. 417 (2011) 904–907. [3] D. Stork, P. Agostini, J.-L. Boutard, et al., Fusion Eng. Des. (2014), http://dx.doi. org/10.1016/j.fusengdes.2013.11.007 (in press). [4] S.A. Fabritsiev, A.S. Pokrovsky, A. Peacock, M. Roedig, J. Linke, A.A. Gervash, V.R. Barabash, J. Nucl. Mater. 386–388 (2009) 824–829. [5] M. Li, M.A. Sokolov, S.J. Zinkle, J. Nucl. Mater. 393 (2009) 36–46. [6] A. Vinogradov, Y. Suzuki, T. Ishida, K. Kitagawa, V.I. Kopylov, Mater. Trans. 45 (2004) 2187–2191. [7] U. Holzwarth, H. Stamm, J. Nucl. Mater. 279 (2000) 31–45. [8] V.M. Segal, Mater. Sci. Eng. A: Struct. Mater. A197 (1995) 157–164. [9] I. Kopylov, in: T.C. Lowe, R.Z. Valiev (Eds.), Investigations and Applications of Severe Plastic Deformation, NATO ASI Series 3, vol. 80, Netherlands, Kluwer, 2000, pp. 23–27. [10] R.Z. Valiev, R.K. Islamgaliev, I.V. Alexandrov, Prog. Mater. Sci. 45 (2000) 103–189. [11] R.Z. Valiev, T.G. Langdon, Prog. Mater. Sci. 51 (2006) 881–981. ˜ [12] M.A. Munoz-Morris, K. Valdés León, F.G. Caballero, D.G. Morris, Scr. Mater. 67 (2012) 806–809. [13] Materials Assessment Report (MAR), ITER Doc.G AO FDR 1 01-a07-13 R1.0, July 2013. [14] T.B. Massalski, Binary Alloy Phase Diagrams, 2nd ed., ASM, Metals Park, OH, 1987, pp. 982. [15] M. Apello, P. Fenici, Mater. Sci. Eng. A: Struct. Mater. 102 (1988) 69–75. [16] A. Chbihi, X. Sauvage, D. Blavette, Acta Mater. 60 (2012) 4575–4585. [17] C.X. Huang, K. Wang, S.D. Wu, Z.F. Zhang, G.Y. Li, S.X. Li, Acta Mater. 54 (2006) 655–665. [18] S. Qu, X.H. An, H.J. Yang, C.X. Huang, G. Yang, Q.S. Zang, Z.G. Wang, S.D. Wu, Z.F. Zhang, Acta Mater. 57 (2009) 1586–1601. [19] F. Dalla Torre, R. Lapovok, J. Sandlin, P.F. Thomson, C.H.J. Davies, E.V. Pereloma, Acta Mater. 52 (2004) 4819–4832. [20] A. Mishra, B.K. Kad, F. Gregori, M.A. Meyers, Acta Mater. 55 (2007) 13–28. [21] P.K. Jayakumar, K. Balasubramanian, G. Rabindranath Tagore, Mater. Sci. Eng. A: Struct. Mater. A538 (2012) 7–13.
Please cite this article in press as: A. Hernández-Pérez, et al., Microstructure and mechanical properties of an ITER-grade Cu–Cr–Zr alloy processed by equal channel angular pressing, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.06.180