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84 MeV C-ions irradiation effects on Zr–45Ti–5Al–3V alloy
Nuclear Instruments and Methods in Physics Research B 334 (2014) 96–100
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
84 MeV C-ions irradiation effects on Zr–45Ti–5Al–3V alloy Weipeng Wang a, Zhengcao Li a, Zhengjun Zhang a,⇑, Chonghong Zhang b a b
School of Materials Science and Engineering, Tsinghua University, 100084 Beijing, PR China Institute of Modern Physics, Chinese Academy of Sciences, 730000 Lanzhou, PR China
a r t i c l e
i n f o
Article history: Received 2 January 2014 Received in revised form 4 April 2014 Accepted 21 May 2014
Keywords: High energy ions Carbon ions irradiation effects Carbide dispersion strengthening Superlattice
a b s t r a c t Newly developed Zr–45Ti–5Al–3V alloy were irradiated by 84 MeV carbon ions with doses of 4 1015 ions/cm2 and 12 1015 ions/cm2, respectively. XRD, SEM, TEM, SAD and tensile tests were performed to study the microstructural evolution and mechanical properties modification upon high energy carbon ion irradiation. XRD patterns show no phase change while the diffraction peak position and intensity vary with irradiation doses. Tensile tests verify monotonic change of alloy strengths and elongations upon irradiation. Microstructure observations of the irradiated samples reveal the irradiation-induced precipitation of (Zr,Ti)3C2, which was believed contributing to the alloy hardening. Superlattice was discovered by the SAD patterns of original and irradiated samples and the high energy C-ions implantation was demonstrated to promote the disorder–order transition by introducing lattice defects. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction With the development of nuclear power and aerospace industry, irradiation of high energy particles such as electron, proton, neutron and other particles on materials have drawn great attention both on scientific and application approach [1,2]. Upon irradiation, materials will present microstructure modification such as point defects formation, colloids interaction, etc. The structure evolution brought by the high energy particles to the materials will introduce physical properties modification [3,4]. Among the materials studied, zirconium/titanium alloys have always been a research focus as their unique properties [5–7]. Recently, a new designated alloy with the nominal composition of Zr–45Ti–5Al–3V (ZrTiAlV) have been developed by Liu et al. to meet the requirement of application under extreme environments [8,9]. Based on the idea of two-phase strengthening, they have established a successful processing to improve the strength of the alloy to be about 1500 MPa while maintaining excellent ductility, and declared the mechanical properties comparable to those of bulk metallic glass. Considering zirconium’s unique character of good resistance against irradiation and corrosion, this alloy are supposed to find applications in nuclear power plant and aerospace shuttle [10]. Upon application, the confident design of nuclear power plants requires knowledge in structural components and mechanical properties during their service in radiation environments. ⇑ Corresponding author. Tel.: +86 10 62797033; fax: +86 10 62771160. E-mail address: [email protected] (Z. Zhang). http://dx.doi.org/10.1016/j.nimb.2014.05.017 0168-583X/Ó 2014 Elsevier B.V. All rights reserved.
Swift heavy ions, among which accelerated carbon ions with energy of MeV, have been widely used as the irradiation source because of the relatively larger stopping range and chemicalactivation to transition metal [11–15]. Transition metal carbide was found to have great influence on mechanical properties of transition metal alloys [16] and it is also reported that the titanium carbide can be trapping sites for the He bubbles to release the He-swelling [17]. Inspired by these ideas, irradiation effects of high energy carbon particle on ZrTiAlV alloy was believed to be of great interest and importance for their potential applications in nuclear industry. In this letter, we report the irradiation effects of 84 MeV Carbon ions on two-phase strengthened ZrTiAlV alloy by focusing on the effects of irradiation on microstructure evolution and mechanical properties modification. Attempts have been put forward to clarify the relationship between the micro- and macro-effects. 2. Experimental procedure Newly developed ZrTiAlV was supplied by Liu et al. from Yanshan University. Alloy composition and processing method are reported elsewhere [10]. For mechanical property studies, sheet tensile specimens of 200 lm in thickness were prepared by fine polishing process to highlight the irradiation effects of C-ions. The gauge length of the sample is set to be 10 mm 3 mm 0.2 mm. Samples of 3 mm in diameter were thinned to about 100 lm for TEM observations. Finally, electropolishing was performed to remove the top oxide surface introduced by mechanical polishing.
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7% HClO4+93% ethanol at about 50 °C by using a liquid nitrogen/ethanol solution. The temperature variation during the polishing was put forward to highlight different phenomena, i.e., those at 0 °C were aimed to highlight precipitations introduce by C-ions while those at 50 °C aimed to highlight the superlattice transition upon irradiation. TEM (SAD) & HRTEM observations were performed by JEOL G20 & 2011 at operating voltage of 200 KeV. 3. Result
Fig. 1. XRD patterns of original and irradiated ZrTiAlV alloy. Inset was illustrated to highlight the peak evolution upon irradiation.
The samples were irradiated at room temperature with 84 MeV C-ions delivered from the injector of Heavy Ion Research Facility in Lanzhou (HIRFL) to ion doses of 4 1015, 12 1015 ions/cm2 [18]. Damage events was simulated by SRIM 2008™ and declare dpa value of 0.65 and 2, respectively. After irradiation, the as-received specimens were stored at the vacuum chamber until reach the radiation background. XRD patterns of as-irradiated samples were derived from a Mo target with wavelength of 0.71 Å (Rigaku R-axis Spider). For tensile tests, sheet specimens was deformed at a rate of 3 mm/min until fracture by MTS-100 equipment. SEM observation of the fracture surface was performed at field-emission SEM equipped with EDS (JSM-7001F). TEM samples were divided into two sets for different concerns. One set was two-jet polished with 7% HClO4+93% ethanol at about 0 °C while the other set was two-jet polished with
Fig. 1 shows the XRD patterns of the specimens upon different doses of C-ions irradiation. As shown in the figure, all specimens present diffraction peaks corresponding to a phase (JSPDF 05– 0665). No phase transition can be observed upon irradiation. With the irradiation dose increases, the peak corresponding to matrix weaken to great extent monotonic as the lattice defects introduced by the high energy particle increase. Inset of the Fig. 1 show the magnified image of the XRD patterns, it is notable that the diffraction peak of the matrix shift to higher angle which verify that the lattice constant got shorten upon irradiation. This can be explained by the smaller atomic radius of carbon ion (0.91 Å) than those of zirconium (2.16 Å) and titanium (2.00 Å). Meticulous comparison between the patterns of irradiated specimens show shift to lower angle of the higher dose. Considering that the energy density transferred from the high energy particle was as high as 0.16 MJ/cm2, the beam-induced heating would have effects on the specimens which were supplied in the forged state [9] and introduce residual stress evolution and peak shift during irradiation. Tensile tests were performed to study the effects of the irradiation on mechanical properties of the ZrTiAlV. As shown in Fig. 2(a), the specimens go through plastic deformation until fracture. With irradiation doses increase, the tensile strength show a monotonic tendency of hardening upon irradiation. As highlighted in the inset of Fig. 2(a), the tensile strength increase from 693 MPa to 826 MPa, while the elongation decrease from 1.9% to 1.7%. Fracture morphology evolution observed by FE-SEM was illustrated in Fig 2(b, c, d),
Fig. 2. Tensile tests (a) and corresponding fracture morphology observations (b–d) of original and irradiated ZrTiAlV alloy. (b–d) Correspond to the fracture surface of the original, 4 1015 and 12 1015 carbon ions irradiated samples, respectively.
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respectively. Comparisons among these graphs reveal no obvious changes but more uneven morphology upon doses increase. The roughness increase of the fracture surface then confirm the hardening behavior upon irradiation in another way. TEM characterizations of the irradiated sample were performed to gain insights on the microstructure evolution upon irradiation, and the as-received results are illustrated in Figs. 3 and 4, respectively. As shown in Fig. 3(a), low magnification observation of the
as-irradiated sample under dose of 4 1015 ions/cm2 reveal black dots well dispersed across the matrix. SAD patterns of one single black dot was shown in Fig. 3(b), one can tell that there are two sets of diffraction patterns, which indicate that the single black dot was multi-grained. The diffraction patterns were indexed to well fit those of (Zr,Ti)3C2 with hexagonal structure. HRTEM and EDS of the black dot shown in Fig. 3(d), combined with the SAD patterns ultimately confirm the precipitation of (Zr,Ti)3C2.
Fig. 3. TEM characterization of ZrTiAlV alloy irradiated by C-ions at dose of 4 1015 ions/cm2. (a) Represents the low magnification of precipitations, while (b) and (c) show the SAD patterns of the precipitation and matrix, respectively. (d) give the HRTEM and EDS of the precipitation.
Fig. 4. TEM characterization of ZrTiAlV alloy irradiated by C-ions at dose of 12 1015 ions/cm2. (a) Represents the low magnification of precipitations, while (b) show the SAD pattern of the matrix. (c and d) reveal the bridge behavior between two isolated particles.
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detected. This indicate that upon irradiation, amorphization emerged. Statistic of the precipitations based on TEM observation of samples under different doses of C-ions irradiation was performed and illustrated in Fig 5. Gauss distribution of the particle size can be attained at one glance. One can tell that with the irradiation doses increase, the number of the precipitations increases. Moreover, as particles with diameter larger than 100 nm increase significantly, the precipitation size was supposed to be larger upon irradiation. Gaussian fitting was applied to get further insights of the size distribution based on the function of
y ¼ y0
Fig. 5. Statistic of precipitations from ZrTiAlV alloy upon C-ions irradiation.
Meanwhile, typical SAD pattern of the matrix shown in Fig. 3(c) confirm the a-phase with no amorphous halo detected. From Fig. 4(a), one can tell that with the irradiation dose increases to 12 1015 ions/cm2, the precipitation of (Zr,Ti)3C2 trend to congregate and grow. From the higher magnification observation shown in Fig. 4(c), bridging effects between two isolated particles can be illustrated. It can be cautious to assume that the precipitation executed conglobation by bridging effects. To validate the assumption, lattice fringe from the edge of one single particle was observed by HRTEM and shown in Fig. 4(d), and reveal a lattice fringe variations. The variations of the lattice parameter was supposed to be caused by the composition fluctuation during the bridging process as zirconium and titanium was completely solution to each other. Interesting phenomenon was disclosured by the SAD pattern of the matrix upon high dose irradiation in Fig. 4(b). One can tell the a-phase of the matrix while weak halo ring caused by amorphous structure can be
! x x 2 A c PI exp 2 w w sqrt 2
Upon fitting, the y0 from dose of 4 1015 ions/cm2 is 8.33 while 13.93 from 12 1015 ions/cm2 which demonstrate that the vertical location for higher dose is larger than those of lower dose, remarks on the increase of total PPT number and larger PPT size upon irradiation can be drawn. When considering the parameters determining the function shape, it turn out that xc from 12 1015 (xc1 = 21.56 nm) is slightly smaller than xc from 4 1015 (xc2 = 22.92 nm), while A1 (7535) larger than A2 (5715). Variations of xc and A suggest that though the location of maximum probability is lower upon higher dose, the particle size distribute in a wider range. Combined with TEM observations, conclusion that consumption of the smaller particle to form larger one can be proposed. Superlattice was observed on the ZrTiAlV alloy upon cryogenic process. With superlattice mechanism beyond the scope of this letter, we focus on the irradiation effects on the superlattice formation ability. SAD patterns of samples under different irradiation doses were observed along [0 0 0 1] diffraction direction and shown in Fig 6(a, b, c), respectively. All the patterns confirm the DO19 superlattice structure with additional diffraction dots detected. The degree of order was calculated based on the brightness of diffraction spot from normal (1 0 0) and ordered 1/2(1 0 0) [19]. It is
Fig. 6. Superlattice evolution of ZrTiAlV alloy upon irradiation. (a–c) correspond to the SAD patterns of the original, 4 1015 and 12 1015 C-ions irradiated samples, respectively. (d) show the calculated degree of order of ZrTiAlV alloy.
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obvious that the order degree of ZrTiAlV increases monotonic with irradiation dose.
4. Discussion According to the mechanical properties tests in Fig. 2, significant strengthening behavior of ZrTiAlV upon C-ions irradiation was revealed. Combined with the detection of the (Zr,Ti)3C2 precipitation well dispersed across the matrix with irradiation (Figs. 3 and 4), it is confident to propose the carbide dispersion strengthening (CDS) mechanism of ZrTiAlV upon C-ions irradiation. This is an interesting results as dispersion strengthening is normally realized by adding nano-sized second-phase to the matrix or by internal oxidation, mechanical alloying [16]. Another routine of C-ions irradiation induced CDS was put forward in this work to have the same influence in zirconium or titanium alloy as the traditional methods did. This will help scientists and engineers to better understand the serving behavior or make a wider choice of materials for potential candidates used in high energy irradiation environment. Nevertheless, a mathematical model to precisely describe the relationship between strengthening and carbide precipitations is different to established as the reinforce behavior is combined results between point defects and precipitations. The high energy C-ions irradiation will also introduce point defects of antisites and vacancies other than carbide precipitations. These defects are hard to detect quantitatively. Also, comparison between SAD patterns of matrix in Figs. 3 and 4 reveal the amorphization behavior of matrix upon irradiation. Consider that the defects of vacancy, interstitial atom and amorphous phase would also contribute to the mechanical properties modification, it is difficult to build a description of the relationship between mechanical properties and carbide concentration. The point defects introduced by the high energy particles, at the same time, would have great effects on the superlattice transition, as illustrated by Fig. 6. Since the disorder–order transition was induced by the cryogenic temperature during the two-jet polishing process, the point defects play dominate role as nucleus for the superstructure formation [20]. With the irradiation doses increase, more as-produced defects was introduced and will promote the transition degree of the superlattice. At the same time, the precipitations upon irradiation are quite isolated and have no phase relation with the matrix (Figs. 3 and 4), it was supposed to have little effects on the disorder–order transformation.
5. Conclusion Newly developed Zr–45Ti–5Al–3V alloy were irradiated by 84 MeV carbon ions with different doses. Significant strengthening behavior upon irradiation was revealed and the mechanism was discussed based on the idea of carbide dispersion strengthening (CDS). Irradiation induced point defects was believed contributing to the disorder–order transformation and lead to an increase of the degree of order while the matrix-isolated precipitations are supposed to have little effects on the transition.
Acknowledgement The authors are very grateful to the financial support by the National Basic Research Program (Grant No. 2010CB731601). This work is also supported by Tsinghua University Initiative Scientific Research Program. References [1] Z.G. Wang, Materials research with swift heavy ions at the IMP accelerators, Nucl. Instrum. Methods Phys. Res., Sect. B 245 (2006) 189–193. [2] C.H. Zhang, Y. Song, Y.M. Sun, H. Chen, Y.T. Yang, L.H. Zhou, Y.F. Jin, Damage accumulation in gallium nitride irradiated with various energetic heavy ions, Nucl. Instrum. Methods Phys. Res., Sect. B 256 (2007) 199–206. [3] M. Lang, F.X. Zhang, R.C. Ewing, J. Lian, C. Trautmann, Z.W. Wang, Structural modifications of Gd(2)Zr(2-x)Ti(x)O(7) pyrochlore induced by swift heavy ions: Disordering and amorphization, J. Mater. Res. 24 (2009) 1322–1334. [4] D. Simeone, C. Dodane-Thiriet, D. Gosset, P. Daniel, M. Beauvy, Order-disorder phase transition induced by swift ions in MgAl2O4 and ZnAl2O4 spinels, J. Nucl. Mater. 300 (2002) 151–160. [5] M.P. Carroll, K. Stephenson, K.O. Findley, Characterization of high energy ion implantation into Ti-6Al-4V, J. Nucl. Mater. 389 (2009) 248–253. [6] S.X. Liang, L.X. Yin, M.Z. Ma, R. Jing, P.F. Yu, Y.F. Zhang, B.A. Wang, R.P. Liu, A multi-component Zr alloy with comparable strength and higher plasticity than Zr-based bulk metallic glasses, Mater. Sci. Eng., A 561 (2013) 13–16. [7] L.M. Howe, D.P. Mccooeye, M.H. Rainvelle, J.D. Bonnett, D. Phillips, Ionbombardment of Zr3Fe, Nucl. Instrum. Methods Phys. Res., Sect. B 59 (1991) 884–888. [8] S.X. Liang, M.Z. Ma, R. Jing, X.Y. Zhang, R.P. Liu, Microstructure and mechanical properties of hot-rolled ZrTiAlV alloys, Mater. Sci. Eng., A 532 (2012) 1–5. [9] S.X. Liang, M.Z. Ma, R. Jing, C.L. Tan, R.P. Liu, Structural evolution and mechanical properties of Zr–45Ti–5Al–3V alloy by heat treatments, Mater. Sci. Eng., A 541 (2012) 67–72. [10] S.X. Liang, M.Z. Ma, R. Jing, Y.K. Zhou, Q. Jing, R.P. Liu, Preparation of the ZrTiAlV alloy with ultra-high strength and good ductility, Mater. Sci. Eng., A 539 (2012) 42–47. [11] N. Shukla, M. Sarkar, N. Banerji, A.K. Gupta, H.C. Verma, Inducing large ferromagnetic ordering in graphite by 100 MeV 12C+ ion irradiation, Carbon 50 (2012) 1817–1822. [12] J.O. Orwa, J.L. Peng, J.C. McCallum, D.N. Jamieson, S. Rubanov, S. Prawer, Microstructure evolution in carbon-ion implanted sapphire, J Appl. Phys. 107 (2010). [13] C. Agodi, F. Bellini, G.A.P. Cirrone, F. Collamati, G. Cuttone, E. De Lucia, M. De Napoli, A. Di Domenico, R. Faccini, F. Ferroni, S. Fiore, P. Gauzzi, E. Iarocci, M. Marafini, I. Mattei, A. Paoloni, V. Patera, L. Piersanti, F. Romano, A. Sarti, A. Sciubba, C. Voena, Study of the time and space distribution of emitters from carbon ion beam irradiation on PMMA, Nucl. Instrum. Methods Phys. Res., Sect. B 283 (2012) 1–8. [14] H.S. Virk, P.S. Chandi, A.K. Srivastava, Physical and chemical changes induced by 70 MeV carbon ions in polyvinylidene difluoride (PVDF) polymer, Nucl. Instrum. Methods Phys. Res., Sect. B 183 (2001) 329–336. [15] M. Seidl, H. Voit, S. Bouneau, A. Brunelle, S. Della-Negra, J. Depauw, D. Jacquet, Y. Le Beyec, M. Pautrat, MeV carbon cluster-induced pulse height defect in a surface barrier detector, Nucl. Instrum. Methods Phys. Res., Sect. B 183 (2001) 502–508. [16] C. Wang, B. Qi, Y. Bai, J. Wu, J. Yang, Dispersion strengthened alloy due to the precipitation of carbide during mechanical alloying, Mater. Sci. Eng., A 308 (2001) 292–294. [17] H. Shiraishi, N. Yamamoto, A. Hasegawa, Helium embrittlement in Fe-Ni-Cr austenitic alloys and ferritic MA 956 alloy, J. Nucl. Mater. 169 (1989) 198–205. [18] Z.G. Wang, K.Q. Chen, L.W. Li, C.H. Zhang, J.M. Quan, M.D. Hou, R.H. Xu, F. Ma, Y.F. Jin, C.L. Li, Y.M. Sun, Surface morphology and void formation in 316L stainless steel irradiated with high energy C-ions, J. Nucl. Mater. 271–272 (1999) 306–310. [19] K. Sato, A. Kovacs, Y. Hirotsu, Order-disorder transformation in Fe-Pd alloy nanoparticles studied by in situ transmission electron microscopy, Thin Solid Films 519 (2011) 3305–3311. [20] J. Lian, L. Wang, J. Chen, K. Sun, R.C. Ewing, J. MattFarmer, L.A. Boatner, The order–disorder transition in ion-irradiated pyrochlore, Acta Mater. 51 (2003) 1493–1502.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
84 MeV C-ions irradiation effects on Zr–45Ti–5Al–3V alloy Weipeng Wang a, Zhengcao Li a, Zhengjun Zhang a,⇑, Chonghong Zhang b a b
School of Materials Science and Engineering, Tsinghua University, 100084 Beijing, PR China Institute of Modern Physics, Chinese Academy of Sciences, 730000 Lanzhou, PR China
a r t i c l e
i n f o
Article history: Received 2 January 2014 Received in revised form 4 April 2014 Accepted 21 May 2014
Keywords: High energy ions Carbon ions irradiation effects Carbide dispersion strengthening Superlattice
a b s t r a c t Newly developed Zr–45Ti–5Al–3V alloy were irradiated by 84 MeV carbon ions with doses of 4 1015 ions/cm2 and 12 1015 ions/cm2, respectively. XRD, SEM, TEM, SAD and tensile tests were performed to study the microstructural evolution and mechanical properties modification upon high energy carbon ion irradiation. XRD patterns show no phase change while the diffraction peak position and intensity vary with irradiation doses. Tensile tests verify monotonic change of alloy strengths and elongations upon irradiation. Microstructure observations of the irradiated samples reveal the irradiation-induced precipitation of (Zr,Ti)3C2, which was believed contributing to the alloy hardening. Superlattice was discovered by the SAD patterns of original and irradiated samples and the high energy C-ions implantation was demonstrated to promote the disorder–order transition by introducing lattice defects. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction With the development of nuclear power and aerospace industry, irradiation of high energy particles such as electron, proton, neutron and other particles on materials have drawn great attention both on scientific and application approach [1,2]. Upon irradiation, materials will present microstructure modification such as point defects formation, colloids interaction, etc. The structure evolution brought by the high energy particles to the materials will introduce physical properties modification [3,4]. Among the materials studied, zirconium/titanium alloys have always been a research focus as their unique properties [5–7]. Recently, a new designated alloy with the nominal composition of Zr–45Ti–5Al–3V (ZrTiAlV) have been developed by Liu et al. to meet the requirement of application under extreme environments [8,9]. Based on the idea of two-phase strengthening, they have established a successful processing to improve the strength of the alloy to be about 1500 MPa while maintaining excellent ductility, and declared the mechanical properties comparable to those of bulk metallic glass. Considering zirconium’s unique character of good resistance against irradiation and corrosion, this alloy are supposed to find applications in nuclear power plant and aerospace shuttle [10]. Upon application, the confident design of nuclear power plants requires knowledge in structural components and mechanical properties during their service in radiation environments. ⇑ Corresponding author. Tel.: +86 10 62797033; fax: +86 10 62771160. E-mail address: [email protected] (Z. Zhang). http://dx.doi.org/10.1016/j.nimb.2014.05.017 0168-583X/Ó 2014 Elsevier B.V. All rights reserved.
Swift heavy ions, among which accelerated carbon ions with energy of MeV, have been widely used as the irradiation source because of the relatively larger stopping range and chemicalactivation to transition metal [11–15]. Transition metal carbide was found to have great influence on mechanical properties of transition metal alloys [16] and it is also reported that the titanium carbide can be trapping sites for the He bubbles to release the He-swelling [17]. Inspired by these ideas, irradiation effects of high energy carbon particle on ZrTiAlV alloy was believed to be of great interest and importance for their potential applications in nuclear industry. In this letter, we report the irradiation effects of 84 MeV Carbon ions on two-phase strengthened ZrTiAlV alloy by focusing on the effects of irradiation on microstructure evolution and mechanical properties modification. Attempts have been put forward to clarify the relationship between the micro- and macro-effects. 2. Experimental procedure Newly developed ZrTiAlV was supplied by Liu et al. from Yanshan University. Alloy composition and processing method are reported elsewhere [10]. For mechanical property studies, sheet tensile specimens of 200 lm in thickness were prepared by fine polishing process to highlight the irradiation effects of C-ions. The gauge length of the sample is set to be 10 mm 3 mm 0.2 mm. Samples of 3 mm in diameter were thinned to about 100 lm for TEM observations. Finally, electropolishing was performed to remove the top oxide surface introduced by mechanical polishing.
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7% HClO4+93% ethanol at about 50 °C by using a liquid nitrogen/ethanol solution. The temperature variation during the polishing was put forward to highlight different phenomena, i.e., those at 0 °C were aimed to highlight precipitations introduce by C-ions while those at 50 °C aimed to highlight the superlattice transition upon irradiation. TEM (SAD) & HRTEM observations were performed by JEOL G20 & 2011 at operating voltage of 200 KeV. 3. Result
Fig. 1. XRD patterns of original and irradiated ZrTiAlV alloy. Inset was illustrated to highlight the peak evolution upon irradiation.
The samples were irradiated at room temperature with 84 MeV C-ions delivered from the injector of Heavy Ion Research Facility in Lanzhou (HIRFL) to ion doses of 4 1015, 12 1015 ions/cm2 [18]. Damage events was simulated by SRIM 2008™ and declare dpa value of 0.65 and 2, respectively. After irradiation, the as-received specimens were stored at the vacuum chamber until reach the radiation background. XRD patterns of as-irradiated samples were derived from a Mo target with wavelength of 0.71 Å (Rigaku R-axis Spider). For tensile tests, sheet specimens was deformed at a rate of 3 mm/min until fracture by MTS-100 equipment. SEM observation of the fracture surface was performed at field-emission SEM equipped with EDS (JSM-7001F). TEM samples were divided into two sets for different concerns. One set was two-jet polished with 7% HClO4+93% ethanol at about 0 °C while the other set was two-jet polished with
Fig. 1 shows the XRD patterns of the specimens upon different doses of C-ions irradiation. As shown in the figure, all specimens present diffraction peaks corresponding to a phase (JSPDF 05– 0665). No phase transition can be observed upon irradiation. With the irradiation dose increases, the peak corresponding to matrix weaken to great extent monotonic as the lattice defects introduced by the high energy particle increase. Inset of the Fig. 1 show the magnified image of the XRD patterns, it is notable that the diffraction peak of the matrix shift to higher angle which verify that the lattice constant got shorten upon irradiation. This can be explained by the smaller atomic radius of carbon ion (0.91 Å) than those of zirconium (2.16 Å) and titanium (2.00 Å). Meticulous comparison between the patterns of irradiated specimens show shift to lower angle of the higher dose. Considering that the energy density transferred from the high energy particle was as high as 0.16 MJ/cm2, the beam-induced heating would have effects on the specimens which were supplied in the forged state [9] and introduce residual stress evolution and peak shift during irradiation. Tensile tests were performed to study the effects of the irradiation on mechanical properties of the ZrTiAlV. As shown in Fig. 2(a), the specimens go through plastic deformation until fracture. With irradiation doses increase, the tensile strength show a monotonic tendency of hardening upon irradiation. As highlighted in the inset of Fig. 2(a), the tensile strength increase from 693 MPa to 826 MPa, while the elongation decrease from 1.9% to 1.7%. Fracture morphology evolution observed by FE-SEM was illustrated in Fig 2(b, c, d),
Fig. 2. Tensile tests (a) and corresponding fracture morphology observations (b–d) of original and irradiated ZrTiAlV alloy. (b–d) Correspond to the fracture surface of the original, 4 1015 and 12 1015 carbon ions irradiated samples, respectively.
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respectively. Comparisons among these graphs reveal no obvious changes but more uneven morphology upon doses increase. The roughness increase of the fracture surface then confirm the hardening behavior upon irradiation in another way. TEM characterizations of the irradiated sample were performed to gain insights on the microstructure evolution upon irradiation, and the as-received results are illustrated in Figs. 3 and 4, respectively. As shown in Fig. 3(a), low magnification observation of the
as-irradiated sample under dose of 4 1015 ions/cm2 reveal black dots well dispersed across the matrix. SAD patterns of one single black dot was shown in Fig. 3(b), one can tell that there are two sets of diffraction patterns, which indicate that the single black dot was multi-grained. The diffraction patterns were indexed to well fit those of (Zr,Ti)3C2 with hexagonal structure. HRTEM and EDS of the black dot shown in Fig. 3(d), combined with the SAD patterns ultimately confirm the precipitation of (Zr,Ti)3C2.
Fig. 3. TEM characterization of ZrTiAlV alloy irradiated by C-ions at dose of 4 1015 ions/cm2. (a) Represents the low magnification of precipitations, while (b) and (c) show the SAD patterns of the precipitation and matrix, respectively. (d) give the HRTEM and EDS of the precipitation.
Fig. 4. TEM characterization of ZrTiAlV alloy irradiated by C-ions at dose of 12 1015 ions/cm2. (a) Represents the low magnification of precipitations, while (b) show the SAD pattern of the matrix. (c and d) reveal the bridge behavior between two isolated particles.
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detected. This indicate that upon irradiation, amorphization emerged. Statistic of the precipitations based on TEM observation of samples under different doses of C-ions irradiation was performed and illustrated in Fig 5. Gauss distribution of the particle size can be attained at one glance. One can tell that with the irradiation doses increase, the number of the precipitations increases. Moreover, as particles with diameter larger than 100 nm increase significantly, the precipitation size was supposed to be larger upon irradiation. Gaussian fitting was applied to get further insights of the size distribution based on the function of
y ¼ y0
Fig. 5. Statistic of precipitations from ZrTiAlV alloy upon C-ions irradiation.
Meanwhile, typical SAD pattern of the matrix shown in Fig. 3(c) confirm the a-phase with no amorphous halo detected. From Fig. 4(a), one can tell that with the irradiation dose increases to 12 1015 ions/cm2, the precipitation of (Zr,Ti)3C2 trend to congregate and grow. From the higher magnification observation shown in Fig. 4(c), bridging effects between two isolated particles can be illustrated. It can be cautious to assume that the precipitation executed conglobation by bridging effects. To validate the assumption, lattice fringe from the edge of one single particle was observed by HRTEM and shown in Fig. 4(d), and reveal a lattice fringe variations. The variations of the lattice parameter was supposed to be caused by the composition fluctuation during the bridging process as zirconium and titanium was completely solution to each other. Interesting phenomenon was disclosured by the SAD pattern of the matrix upon high dose irradiation in Fig. 4(b). One can tell the a-phase of the matrix while weak halo ring caused by amorphous structure can be
! x x 2 A c PI exp 2 w w sqrt 2
Upon fitting, the y0 from dose of 4 1015 ions/cm2 is 8.33 while 13.93 from 12 1015 ions/cm2 which demonstrate that the vertical location for higher dose is larger than those of lower dose, remarks on the increase of total PPT number and larger PPT size upon irradiation can be drawn. When considering the parameters determining the function shape, it turn out that xc from 12 1015 (xc1 = 21.56 nm) is slightly smaller than xc from 4 1015 (xc2 = 22.92 nm), while A1 (7535) larger than A2 (5715). Variations of xc and A suggest that though the location of maximum probability is lower upon higher dose, the particle size distribute in a wider range. Combined with TEM observations, conclusion that consumption of the smaller particle to form larger one can be proposed. Superlattice was observed on the ZrTiAlV alloy upon cryogenic process. With superlattice mechanism beyond the scope of this letter, we focus on the irradiation effects on the superlattice formation ability. SAD patterns of samples under different irradiation doses were observed along [0 0 0 1] diffraction direction and shown in Fig 6(a, b, c), respectively. All the patterns confirm the DO19 superlattice structure with additional diffraction dots detected. The degree of order was calculated based on the brightness of diffraction spot from normal (1 0 0) and ordered 1/2(1 0 0) [19]. It is
Fig. 6. Superlattice evolution of ZrTiAlV alloy upon irradiation. (a–c) correspond to the SAD patterns of the original, 4 1015 and 12 1015 C-ions irradiated samples, respectively. (d) show the calculated degree of order of ZrTiAlV alloy.
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obvious that the order degree of ZrTiAlV increases monotonic with irradiation dose.
4. Discussion According to the mechanical properties tests in Fig. 2, significant strengthening behavior of ZrTiAlV upon C-ions irradiation was revealed. Combined with the detection of the (Zr,Ti)3C2 precipitation well dispersed across the matrix with irradiation (Figs. 3 and 4), it is confident to propose the carbide dispersion strengthening (CDS) mechanism of ZrTiAlV upon C-ions irradiation. This is an interesting results as dispersion strengthening is normally realized by adding nano-sized second-phase to the matrix or by internal oxidation, mechanical alloying [16]. Another routine of C-ions irradiation induced CDS was put forward in this work to have the same influence in zirconium or titanium alloy as the traditional methods did. This will help scientists and engineers to better understand the serving behavior or make a wider choice of materials for potential candidates used in high energy irradiation environment. Nevertheless, a mathematical model to precisely describe the relationship between strengthening and carbide precipitations is different to established as the reinforce behavior is combined results between point defects and precipitations. The high energy C-ions irradiation will also introduce point defects of antisites and vacancies other than carbide precipitations. These defects are hard to detect quantitatively. Also, comparison between SAD patterns of matrix in Figs. 3 and 4 reveal the amorphization behavior of matrix upon irradiation. Consider that the defects of vacancy, interstitial atom and amorphous phase would also contribute to the mechanical properties modification, it is difficult to build a description of the relationship between mechanical properties and carbide concentration. The point defects introduced by the high energy particles, at the same time, would have great effects on the superlattice transition, as illustrated by Fig. 6. Since the disorder–order transition was induced by the cryogenic temperature during the two-jet polishing process, the point defects play dominate role as nucleus for the superstructure formation [20]. With the irradiation doses increase, more as-produced defects was introduced and will promote the transition degree of the superlattice. At the same time, the precipitations upon irradiation are quite isolated and have no phase relation with the matrix (Figs. 3 and 4), it was supposed to have little effects on the disorder–order transformation.
5. Conclusion Newly developed Zr–45Ti–5Al–3V alloy were irradiated by 84 MeV carbon ions with different doses. Significant strengthening behavior upon irradiation was revealed and the mechanism was discussed based on the idea of carbide dispersion strengthening (CDS). Irradiation induced point defects was believed contributing to the disorder–order transformation and lead to an increase of the degree of order while the matrix-isolated precipitations are supposed to have little effects on the transition.
Acknowledgement The authors are very grateful to the financial support by the National Basic Research Program (Grant No. 2010CB731601). This work is also supported by Tsinghua University Initiative Scientific Research Program. References [1] Z.G. Wang, Materials research with swift heavy ions at the IMP accelerators, Nucl. Instrum. Methods Phys. Res., Sect. B 245 (2006) 189–193. [2] C.H. Zhang, Y. Song, Y.M. Sun, H. Chen, Y.T. Yang, L.H. Zhou, Y.F. Jin, Damage accumulation in gallium nitride irradiated with various energetic heavy ions, Nucl. Instrum. Methods Phys. Res., Sect. B 256 (2007) 199–206. [3] M. Lang, F.X. Zhang, R.C. Ewing, J. Lian, C. Trautmann, Z.W. Wang, Structural modifications of Gd(2)Zr(2-x)Ti(x)O(7) pyrochlore induced by swift heavy ions: Disordering and amorphization, J. Mater. Res. 24 (2009) 1322–1334. [4] D. Simeone, C. Dodane-Thiriet, D. Gosset, P. Daniel, M. Beauvy, Order-disorder phase transition induced by swift ions in MgAl2O4 and ZnAl2O4 spinels, J. Nucl. Mater. 300 (2002) 151–160. [5] M.P. Carroll, K. Stephenson, K.O. Findley, Characterization of high energy ion implantation into Ti-6Al-4V, J. Nucl. Mater. 389 (2009) 248–253. [6] S.X. Liang, L.X. Yin, M.Z. Ma, R. Jing, P.F. Yu, Y.F. Zhang, B.A. Wang, R.P. Liu, A multi-component Zr alloy with comparable strength and higher plasticity than Zr-based bulk metallic glasses, Mater. Sci. Eng., A 561 (2013) 13–16. [7] L.M. Howe, D.P. Mccooeye, M.H. Rainvelle, J.D. Bonnett, D. Phillips, Ionbombardment of Zr3Fe, Nucl. Instrum. Methods Phys. Res., Sect. B 59 (1991) 884–888. [8] S.X. Liang, M.Z. Ma, R. Jing, X.Y. Zhang, R.P. Liu, Microstructure and mechanical properties of hot-rolled ZrTiAlV alloys, Mater. Sci. Eng., A 532 (2012) 1–5. [9] S.X. Liang, M.Z. Ma, R. Jing, C.L. Tan, R.P. Liu, Structural evolution and mechanical properties of Zr–45Ti–5Al–3V alloy by heat treatments, Mater. Sci. Eng., A 541 (2012) 67–72. [10] S.X. Liang, M.Z. Ma, R. Jing, Y.K. Zhou, Q. Jing, R.P. Liu, Preparation of the ZrTiAlV alloy with ultra-high strength and good ductility, Mater. Sci. Eng., A 539 (2012) 42–47. [11] N. Shukla, M. Sarkar, N. Banerji, A.K. Gupta, H.C. Verma, Inducing large ferromagnetic ordering in graphite by 100 MeV 12C+ ion irradiation, Carbon 50 (2012) 1817–1822. [12] J.O. Orwa, J.L. Peng, J.C. McCallum, D.N. Jamieson, S. Rubanov, S. Prawer, Microstructure evolution in carbon-ion implanted sapphire, J Appl. Phys. 107 (2010). [13] C. Agodi, F. Bellini, G.A.P. Cirrone, F. Collamati, G. Cuttone, E. De Lucia, M. De Napoli, A. Di Domenico, R. Faccini, F. Ferroni, S. Fiore, P. Gauzzi, E. Iarocci, M. Marafini, I. Mattei, A. Paoloni, V. Patera, L. Piersanti, F. Romano, A. Sarti, A. Sciubba, C. Voena, Study of the time and space distribution of emitters from carbon ion beam irradiation on PMMA, Nucl. Instrum. Methods Phys. Res., Sect. B 283 (2012) 1–8. [14] H.S. Virk, P.S. Chandi, A.K. Srivastava, Physical and chemical changes induced by 70 MeV carbon ions in polyvinylidene difluoride (PVDF) polymer, Nucl. Instrum. Methods Phys. Res., Sect. B 183 (2001) 329–336. [15] M. Seidl, H. Voit, S. Bouneau, A. Brunelle, S. Della-Negra, J. Depauw, D. Jacquet, Y. Le Beyec, M. Pautrat, MeV carbon cluster-induced pulse height defect in a surface barrier detector, Nucl. Instrum. Methods Phys. Res., Sect. B 183 (2001) 502–508. [16] C. Wang, B. Qi, Y. Bai, J. Wu, J. Yang, Dispersion strengthened alloy due to the precipitation of carbide during mechanical alloying, Mater. Sci. Eng., A 308 (2001) 292–294. [17] H. Shiraishi, N. Yamamoto, A. Hasegawa, Helium embrittlement in Fe-Ni-Cr austenitic alloys and ferritic MA 956 alloy, J. Nucl. Mater. 169 (1989) 198–205. [18] Z.G. Wang, K.Q. Chen, L.W. Li, C.H. Zhang, J.M. Quan, M.D. Hou, R.H. Xu, F. Ma, Y.F. Jin, C.L. Li, Y.M. Sun, Surface morphology and void formation in 316L stainless steel irradiated with high energy C-ions, J. Nucl. Mater. 271–272 (1999) 306–310. [19] K. Sato, A. Kovacs, Y. Hirotsu, Order-disorder transformation in Fe-Pd alloy nanoparticles studied by in situ transmission electron microscopy, Thin Solid Films 519 (2011) 3305–3311. [20] J. Lian, L. Wang, J. Chen, K. Sun, R.C. Ewing, J. MattFarmer, L.A. Boatner, The order–disorder transition in ion-irradiated pyrochlore, Acta Mater. 51 (2003) 1493–1502.