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The applications of Cu substrate in liquid metal cooling systems
Materials Letters 227 (2018) 116–119
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Featured Letter
The applications of Cu substrate in liquid metal cooling systems Tomasz Gancarz a,⇑, Katarzyna Berent b a b
Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 30-059 Krakow, Poland AGH University of Science and Technology, Academic Centre for Materials and Nanotechnology, 30-059 Krakow, Poland
a r t i c l e
i n f o
Article history: Received 4 May 2018 Received in revised form 10 May 2018 Accepted 11 May 2018
Keywords: Interface Wettability Intermetallic layer Chemical reaction Liquid metal Microstructure
a b s t r a c t Advances in electronics and nuclear energy have led to devices producing greater heat and therefore requiring more efficient cooling systems. The proposed liquid metal based on eutectic Ga-Sn-Zn meets such expectations. First, however, the materials which are used for storage and mostly applied in electronics, such as Cu, should be examined. The investigated liquid/Cu substrate couples were crosssectioned and subjected to scanning electron microscopy to observe interfacial microstructure changes. The created intermetallic Cu-Ga phase layer at the liquid/Cu substrate interface was identified by x-ray diffraction analysis, and the kinetics of the formation and growth of the IMC layer were determined. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction The application of liquid metals for cooling allow smaller and more efficient cooling systems. Various liquid metals are used as primary coolants in fast breeder reactors (LMFBR) in Gen-IV nuclear energy systems [1–3]. The advantage to using liquid metals in cooling systems is that it is easier to recycle spent fuels from nuclear power plant operations. So far, the mostly commonly used metals in cooling systems have been Na and eutectic BiPb, but, taking into consideration environmental protection and safety, Ga and its alloys seem more promising. Taking into account the absorption cross section of gallium, which is rather high at 2.2 barns per atom [4], and with the use of alloying elements such as Sn and Zn, with lower absorption cross sections of 0.63 and 1.10 barns per atom, respectively, the melting point will be reduced to below 21 °C at a certain ratio [3]. Reducing the melting point is possible because Sn and Zn form with Ga ternary eutectic [5], which has a great influence on the physical properties of the obtained alloys [6]. The thermal conductivity of pure gallium at 30 °C is 29 W/m K, much lower than for Sn and Zn (66 W/m K, and 116 W/m K, respectively [7]). The improved physical properties and reduced melting point of alloys allow the application of liquid metals as coolants in the rapidly-developing field of IT, which requires high PC performance capable of processing more data speedily [8]. Super computers need more power, transistors, etc., and a much higher ⇑ Corresponding author. E-mail address: [email protected] (T. Gancarz). https://doi.org/10.1016/j.matlet.2018.05.053 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
clock rate in order to complete tasks, which leads to the production of far more heat by the CPU and results in a shorter lifespan for the equipment. Heat removal by conventional thermal management methods such as air-cooling with fans [9–11], has either reached the limits of its practical applications, or will soon become impractical for emerging electronic components [8]. Therefore, continuous efforts are made to improve upon traditional methods and develop cooling systems for high power processors. The use of water or other conventional liquids has some limitations, as the low thermal conductivity of these fluids may reduce their effectiveness in heat transfer [8]. Liu and Zhou [12] proposed the use of liquid metal as fluid in computer cooling management systems, as such liquids can be pumped efficiently with silent, vibrationfree, low energy consumption, non-moving and compact magnetofluid dynamic pumps [13], which have great potential. This study focuses on the chemical reaction of liquid eutectic Ga-SnZn, as a potential liquid coolant, with Cu substrate. The obtained microstructure changes at interface are caused by the formation of the intermetallic layer. The kinetics of dissolving Cu substrate was determined with temperature and time of wetting, using the sessile drop method [14], with protective gas Ar (5N), for times of 24, 240 and 720 hours of contact, and at temperatures of 100, 105 and 250 °C. 2. Results and discussion The eutectic Ga-Sn-Zn proposed as more efficient for liquid cooling of electronic systems was investigate during wetting tests
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on Cu substrate, in order to better reflect the effect of time and temperature on the phenomena occurring at interface. Fig. 1 presents the microstructure of the Ga-Sn-Zn/Cu cross section, obtained at a temperature of 100 °C after 24, 240 and 720 h, respectively. EDS (see Table 1) and XRD analysis shows that the two phases b – CuGa2 and c – Cu9Ga4 are formed at the interface. The chemical composition, obtained by analysis is 34 and 51.6 (at. %) of Cu, and 66 and 38.4 (at. %) of Ga, respectively. After 24 h (Fig. 1a) the Cu is observed to have dissolved, and the CuGa2 phase is created at the interface, in accordance with the Cu-Ga phase diagram [15]. With increasing time (Fig. 1), a path of fast dissolving is created at the interface, and the thickness of the formed CuGa2 increases. After a longer time, Cu9Ga4, starts to occur as a very thin film between the CuGa2 and Cu substrate. As presented
Fig. 1. The microstructure after wetting of eutectic Ga-Sn-Zn alloy on Cu substrate at a temperature of 100 °C after a) 24 h, b) 240 h and 720 h.
Table 1 The EDS analysis at the points marked in Figs. 1 and 2. at. % SnL 1 2 3 4 5 6 7 8 9 10 11 12
5.6 7.1 85.5
7.4
CuK
ZnK
GaK
33.4 11.2 3.6 33.7 1.1 33.7 34 5.4 34.5 51.6 58.7 31.7
1.3 1.5 3 1.6
65.3 81.7 86.3 64.7 13.4 65 66 85.2 64.4 38.5 35.8 68.3
1.3 2.0 1.1 9.9 5.5
in [16], the molten Ga dissolves Cu at sites where grain boundaries are more exposed and more deeply penetrated (see Fig. 1). The CuGa2 IMC created at the interface of the molten alloy and Cu susbtrate grows and continues to form as time increases. Next, a second Cu9Ga4 IMC starts to be created between this layer and the Cu substrate, forming a thin layer at the interface over increasing time. A similar microstructure for higher wetting temperatures of 150 and 250 °C after 720 h is observed (Fig. 2). The thickness of the CuGa2 phase increases, and at 250 °C the all Cu substrate is dissolved. Fig. 2b presents the two grey and dark grey regions, which correspond with Cu9Ga4 and CuGa2 (EDS presented in Table 1), and the visible contours of Cu substrate which show the last stage (thickness) of the Cu substrate before reactions are completed. Taking this into account, the IMCs formed at the interface do not block the dissolution of Cu substrate. However, as shown in a previous study of Ga on Cu [16], CuGa2 and Cu9Ga4, phases are observed at the interface, with Cu9Ga4 detected after 48 h as a continuous thin layer at 200, 220, 240, 280 and 300 °C. The proposed scheme of dissolution of Cu susbtrate by Ga in [16], shows that the liquid Ga, reacting with the Cu substrate, formed CuGa2 in the first stage of wetting, and that over time the Cu9Ga4 phase begins to be created. In our case, the scheme is the same, but the addition of Sn and Zn to Ga caused increasing dissolution of the Cu substrate. According to thermodynamic calculations [17,18], presented in Fig. 3, the c – Cu9Ga4 phase has lower Gibbs free energy compared to the b – CuGa2 phase. Taking into account the Cu-Ga system obtaining thermodynamic equilibrium, the c should occur. However, the additions of Sn and Zn caused increasing diffusion of Cu to Ga, which means higher dissolution of the Cu substrate and also higher diffusion of Ga to Cu. This means that there is no time for the Cu9Ga4 phase to stabilize and grow. Moreover, at higher wetting temperatures of 280 and 300 °C [16], the Cu9Ga4 phase is observed at the interface, which is in the with the Cu-Ga phase diagram, showing that the CuGa2 phase could exist below 254 °C. The dissolution of the Cu substrate and creation of IMCs at the interface are connected. This is shown in Fig. 4, which also demonstrates that the IMCs grew thicker as the reaction time and temperature increased. The IMC growth mechanism could be described as d ¼ kt n , where d is the mean thickness of the IMCs, k is the rate constant, t is the reaction time, and n is an exponent which can be used to determine the dominant kinetics of the system. For our study (see Fig. 4), the values of n were determined to be 0.60, 0.58 and 0.56 for reaction temperatures of 100, 150 and 250 °C, respectively, indicating a volume diffusion-controlled mechanism. This corresponded with the obtained line for received k values (5.25, 8.43 and 24.51 (1010 ms1)), which was used to calculate activation energy (Ea) based on the Arrhenius equation Ea , where k0, R and T represent the migration rate lnk ¼ ln ðk0 Þ RT
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T. Gancarz, K. Berent / Materials Letters 227 (2018) 116–119
Fig. 4. The thickness of the IMCs and Cu substrate during wetting test of eutectic Ga-Sn-Zn at temperatures of 100, 150 and 250 °C, after 24, 240 and 720 h.
Fig. 2. The microstructure after wetting of eutectic Ga-Sn-Zn alloy on Cu substrate after 720 h at temperatures of a) 150 °C and b) 250 °C.
amount to 1.14 (107 ms1) and 16.9 (kJ/mol), respectively. The similar values of n were obtained in [16] for pure Ga on Cu substrate, where n for temperature 160 °C was 1 and 0.5 for the reactions at 200, 220 and 240 °C. An increasing constant rate with rising temperature was also observed, and the obtained activation energy was 23.8 (kJ/mol), which is in line with the value obtained in this study. Fig. 4 also presents the thickness of the Cu substrate, which corresponds to the dissolution of the Cu substrate with time and temperature. As was observed from microstructure examination for 100 and 150 °C, the IMC layer growth slightly dissolves the Cu substrate. A different character is observed for 250 °C, with a significant effect on the dissolution of the Cu substrate compared to the thickness of IMC layer formed at the interface. For a longer time of 720 h, the dissolution of all Cu substrate is observed. This effect could be connected with the formation of the IMC layers at the interface, as these are not impermeable layers what cause rapid diffusion of Ga to the Cu substrate as a consequence of the dissolution of the Cu substrate. An even faster dissolution effect could probably happen if the dissolution of the Cu substrate were connected with the grain boundary mechanism. Wetting phase transformation proceeds at GB [19,20], which could cause the detachment of all grains. However, according to the reactive wetting [21] observed in this study, in the beginning there is a reaction at the grain boundary, as a high energy place. The IMC layer starts to be formed at the interface and dissolution is controlled by the volume diffusion mechanism. 3. Conclusions
Fig. 3. The calculated Gibbs free energy of the Cu-Ga, and Cu-Zn phases using data from [17,18].
constant, universal gas constant, and absolute temperature, respectively. Then, the values of k0, and Ea were evaluated from the Arrhenius plot of ln k against 1/T as line dependences, which
To sum up, the present study shows that Cu substrate without any protective layer cannot be used in electronics devices with liquid metal cooling systems, based on eutectic Ga-Sn-Zn. Even at the lowest investigated temperature of 100 °C, 720 h was enough time to cause dissolution of the Cu substrate of 20 (lm). The same duration but increasing temperature shows even higher dissolution of 71 (lm) at 150 °C, and of the entire Cu substrate (250 (lm)) at 250 °C. Taking into account the high efficiency of liquid metals in cooling systems, a layer with high thermal conductivity should be applied to protect against reaction and dissolution of the Cu substrate. This will be the subject of further study in the near future.
T. Gancarz, K. Berent / Materials Letters 227 (2018) 116–119
Acknowledgment This work was financed by the National Science Centre Poland grant 2016/21/B/ST8/00324 ‘‘Design and physicochemical, thermal properties of low temperature metal alloys based on gallium” in 2017-2019. References [1] V.I. Rachkov, M.N. Arnoldov, A.D. Efanov, S.G. Kalyakin, F.A. Kozlov, N.I. Loginov, Yu I. Orlov, A.P. Sorokin, Therm. Eng. 61 (2014) 337–347. [2] T. Sawada, A. Netchaev, H. Ninokata, H. Endo, Prog. Nucl. Energy 37 (2000) 313–319. [3] S.H. Shin, J.J. Kim, J.A. Jung, K.J. Choi, I.C. Bang, J.H. Kim, J. Nuc. Mater. 422 (2012) 92–102. [4] P.R. Luebbers, W.F. Michaud, O.K. Chopra, ANL-93/31, Argonne National Laboratory, 1993. [5] W.F. Galo, T.C. Totemeier, Smithells Metals Reference Book, eight ed., Elsevier and ASM International, 2004. [6] K. Ma, J. Liu, Front. Energy Power Eng. China 1 (2007) 384–402.
119
[7] D. Zivkovic, L. Balanovic, D. Manasijevic, T.H. Grguric, D. Cubelac, A. Mitovskia, Int. J. Mater. Res. 104 (2013) 26–34. [8] A. Dobosz, Y. Plevachuk, V. Sklyarchuk, B. Sokoliuk, T. Gancarz, Fluid Phase Equilibr. 465 (2018) 1–9. [9] F.J. Disalvo, Science 285 (1999) 703–706. [10] R.R. Schmidt, E.E. Cruz, M.K. Iyengar, J. Res. Dev. 49 (2005) 709–723. [11] K. Ebrahimi, G.F. Jones, A.S. Fleischer, Renew. Sustain. Energy Rev. 31 (2014) 622–638. [12] J. Liu, Y.X. Zhou, A computer chip cooling method which uses low melting point metal and its alloys as the cooling fluid, China Patent, 02131419.5, 2002. [13] A. Miner, U. Ghoshal, Appl. Phys. Lett. 85 (2004) 506–508. [14] T. Gancarz, J. Pstrus, K. Berent, J. Mater. Eng. Perform. 25 (2016) 3366–3374. [15] B. Massalski, Editor-in-Chief; H. Okamoto, P.R. Subramanian, L. Kacprzak, Editors. ASM International, Materials Park, Ohio, USA. December 1991. [16] S.-K. Lin, C.-L. Cho, H.-M. Chang, J. Electron. Mater. 43 (2014) 204–211. [17] T. Gancarz, Mater. Letter. 171 (2016) 187–190. [18] J.-B. Li, L.N. Ji, J.K. Liang, Y. Zhang, J. Luo, C.R. Li, G.H. Rao, CALPHAD 32 (2008) 447–453. [19] B.B. Straumal, P. Zieba, W. Gust, Int. J. Inorg. Mater. 3 (2001) 1113–1115. [20] S.G. Protasova, O.A. Kogtenkova, B.B. Straumal, P. Zieba, B. Baretzky, J. Mater. Sci. 46 (2011) 4349. [21] N. Eustathopoulos, R. Voytovych, J. Mater. Sci. 51 (2016) 425–437.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Featured Letter
The applications of Cu substrate in liquid metal cooling systems Tomasz Gancarz a,⇑, Katarzyna Berent b a b
Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 30-059 Krakow, Poland AGH University of Science and Technology, Academic Centre for Materials and Nanotechnology, 30-059 Krakow, Poland
a r t i c l e
i n f o
Article history: Received 4 May 2018 Received in revised form 10 May 2018 Accepted 11 May 2018
Keywords: Interface Wettability Intermetallic layer Chemical reaction Liquid metal Microstructure
a b s t r a c t Advances in electronics and nuclear energy have led to devices producing greater heat and therefore requiring more efficient cooling systems. The proposed liquid metal based on eutectic Ga-Sn-Zn meets such expectations. First, however, the materials which are used for storage and mostly applied in electronics, such as Cu, should be examined. The investigated liquid/Cu substrate couples were crosssectioned and subjected to scanning electron microscopy to observe interfacial microstructure changes. The created intermetallic Cu-Ga phase layer at the liquid/Cu substrate interface was identified by x-ray diffraction analysis, and the kinetics of the formation and growth of the IMC layer were determined. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction The application of liquid metals for cooling allow smaller and more efficient cooling systems. Various liquid metals are used as primary coolants in fast breeder reactors (LMFBR) in Gen-IV nuclear energy systems [1–3]. The advantage to using liquid metals in cooling systems is that it is easier to recycle spent fuels from nuclear power plant operations. So far, the mostly commonly used metals in cooling systems have been Na and eutectic BiPb, but, taking into consideration environmental protection and safety, Ga and its alloys seem more promising. Taking into account the absorption cross section of gallium, which is rather high at 2.2 barns per atom [4], and with the use of alloying elements such as Sn and Zn, with lower absorption cross sections of 0.63 and 1.10 barns per atom, respectively, the melting point will be reduced to below 21 °C at a certain ratio [3]. Reducing the melting point is possible because Sn and Zn form with Ga ternary eutectic [5], which has a great influence on the physical properties of the obtained alloys [6]. The thermal conductivity of pure gallium at 30 °C is 29 W/m K, much lower than for Sn and Zn (66 W/m K, and 116 W/m K, respectively [7]). The improved physical properties and reduced melting point of alloys allow the application of liquid metals as coolants in the rapidly-developing field of IT, which requires high PC performance capable of processing more data speedily [8]. Super computers need more power, transistors, etc., and a much higher ⇑ Corresponding author. E-mail address: [email protected] (T. Gancarz). https://doi.org/10.1016/j.matlet.2018.05.053 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
clock rate in order to complete tasks, which leads to the production of far more heat by the CPU and results in a shorter lifespan for the equipment. Heat removal by conventional thermal management methods such as air-cooling with fans [9–11], has either reached the limits of its practical applications, or will soon become impractical for emerging electronic components [8]. Therefore, continuous efforts are made to improve upon traditional methods and develop cooling systems for high power processors. The use of water or other conventional liquids has some limitations, as the low thermal conductivity of these fluids may reduce their effectiveness in heat transfer [8]. Liu and Zhou [12] proposed the use of liquid metal as fluid in computer cooling management systems, as such liquids can be pumped efficiently with silent, vibrationfree, low energy consumption, non-moving and compact magnetofluid dynamic pumps [13], which have great potential. This study focuses on the chemical reaction of liquid eutectic Ga-SnZn, as a potential liquid coolant, with Cu substrate. The obtained microstructure changes at interface are caused by the formation of the intermetallic layer. The kinetics of dissolving Cu substrate was determined with temperature and time of wetting, using the sessile drop method [14], with protective gas Ar (5N), for times of 24, 240 and 720 hours of contact, and at temperatures of 100, 105 and 250 °C. 2. Results and discussion The eutectic Ga-Sn-Zn proposed as more efficient for liquid cooling of electronic systems was investigate during wetting tests
117
T. Gancarz, K. Berent / Materials Letters 227 (2018) 116–119
on Cu substrate, in order to better reflect the effect of time and temperature on the phenomena occurring at interface. Fig. 1 presents the microstructure of the Ga-Sn-Zn/Cu cross section, obtained at a temperature of 100 °C after 24, 240 and 720 h, respectively. EDS (see Table 1) and XRD analysis shows that the two phases b – CuGa2 and c – Cu9Ga4 are formed at the interface. The chemical composition, obtained by analysis is 34 and 51.6 (at. %) of Cu, and 66 and 38.4 (at. %) of Ga, respectively. After 24 h (Fig. 1a) the Cu is observed to have dissolved, and the CuGa2 phase is created at the interface, in accordance with the Cu-Ga phase diagram [15]. With increasing time (Fig. 1), a path of fast dissolving is created at the interface, and the thickness of the formed CuGa2 increases. After a longer time, Cu9Ga4, starts to occur as a very thin film between the CuGa2 and Cu substrate. As presented
Fig. 1. The microstructure after wetting of eutectic Ga-Sn-Zn alloy on Cu substrate at a temperature of 100 °C after a) 24 h, b) 240 h and 720 h.
Table 1 The EDS analysis at the points marked in Figs. 1 and 2. at. % SnL 1 2 3 4 5 6 7 8 9 10 11 12
5.6 7.1 85.5
7.4
CuK
ZnK
GaK
33.4 11.2 3.6 33.7 1.1 33.7 34 5.4 34.5 51.6 58.7 31.7
1.3 1.5 3 1.6
65.3 81.7 86.3 64.7 13.4 65 66 85.2 64.4 38.5 35.8 68.3
1.3 2.0 1.1 9.9 5.5
in [16], the molten Ga dissolves Cu at sites where grain boundaries are more exposed and more deeply penetrated (see Fig. 1). The CuGa2 IMC created at the interface of the molten alloy and Cu susbtrate grows and continues to form as time increases. Next, a second Cu9Ga4 IMC starts to be created between this layer and the Cu substrate, forming a thin layer at the interface over increasing time. A similar microstructure for higher wetting temperatures of 150 and 250 °C after 720 h is observed (Fig. 2). The thickness of the CuGa2 phase increases, and at 250 °C the all Cu substrate is dissolved. Fig. 2b presents the two grey and dark grey regions, which correspond with Cu9Ga4 and CuGa2 (EDS presented in Table 1), and the visible contours of Cu substrate which show the last stage (thickness) of the Cu substrate before reactions are completed. Taking this into account, the IMCs formed at the interface do not block the dissolution of Cu substrate. However, as shown in a previous study of Ga on Cu [16], CuGa2 and Cu9Ga4, phases are observed at the interface, with Cu9Ga4 detected after 48 h as a continuous thin layer at 200, 220, 240, 280 and 300 °C. The proposed scheme of dissolution of Cu susbtrate by Ga in [16], shows that the liquid Ga, reacting with the Cu substrate, formed CuGa2 in the first stage of wetting, and that over time the Cu9Ga4 phase begins to be created. In our case, the scheme is the same, but the addition of Sn and Zn to Ga caused increasing dissolution of the Cu substrate. According to thermodynamic calculations [17,18], presented in Fig. 3, the c – Cu9Ga4 phase has lower Gibbs free energy compared to the b – CuGa2 phase. Taking into account the Cu-Ga system obtaining thermodynamic equilibrium, the c should occur. However, the additions of Sn and Zn caused increasing diffusion of Cu to Ga, which means higher dissolution of the Cu substrate and also higher diffusion of Ga to Cu. This means that there is no time for the Cu9Ga4 phase to stabilize and grow. Moreover, at higher wetting temperatures of 280 and 300 °C [16], the Cu9Ga4 phase is observed at the interface, which is in the with the Cu-Ga phase diagram, showing that the CuGa2 phase could exist below 254 °C. The dissolution of the Cu substrate and creation of IMCs at the interface are connected. This is shown in Fig. 4, which also demonstrates that the IMCs grew thicker as the reaction time and temperature increased. The IMC growth mechanism could be described as d ¼ kt n , where d is the mean thickness of the IMCs, k is the rate constant, t is the reaction time, and n is an exponent which can be used to determine the dominant kinetics of the system. For our study (see Fig. 4), the values of n were determined to be 0.60, 0.58 and 0.56 for reaction temperatures of 100, 150 and 250 °C, respectively, indicating a volume diffusion-controlled mechanism. This corresponded with the obtained line for received k values (5.25, 8.43 and 24.51 (1010 ms1)), which was used to calculate activation energy (Ea) based on the Arrhenius equation Ea , where k0, R and T represent the migration rate lnk ¼ ln ðk0 Þ RT
118
T. Gancarz, K. Berent / Materials Letters 227 (2018) 116–119
Fig. 4. The thickness of the IMCs and Cu substrate during wetting test of eutectic Ga-Sn-Zn at temperatures of 100, 150 and 250 °C, after 24, 240 and 720 h.
Fig. 2. The microstructure after wetting of eutectic Ga-Sn-Zn alloy on Cu substrate after 720 h at temperatures of a) 150 °C and b) 250 °C.
amount to 1.14 (107 ms1) and 16.9 (kJ/mol), respectively. The similar values of n were obtained in [16] for pure Ga on Cu substrate, where n for temperature 160 °C was 1 and 0.5 for the reactions at 200, 220 and 240 °C. An increasing constant rate with rising temperature was also observed, and the obtained activation energy was 23.8 (kJ/mol), which is in line with the value obtained in this study. Fig. 4 also presents the thickness of the Cu substrate, which corresponds to the dissolution of the Cu substrate with time and temperature. As was observed from microstructure examination for 100 and 150 °C, the IMC layer growth slightly dissolves the Cu substrate. A different character is observed for 250 °C, with a significant effect on the dissolution of the Cu substrate compared to the thickness of IMC layer formed at the interface. For a longer time of 720 h, the dissolution of all Cu substrate is observed. This effect could be connected with the formation of the IMC layers at the interface, as these are not impermeable layers what cause rapid diffusion of Ga to the Cu substrate as a consequence of the dissolution of the Cu substrate. An even faster dissolution effect could probably happen if the dissolution of the Cu substrate were connected with the grain boundary mechanism. Wetting phase transformation proceeds at GB [19,20], which could cause the detachment of all grains. However, according to the reactive wetting [21] observed in this study, in the beginning there is a reaction at the grain boundary, as a high energy place. The IMC layer starts to be formed at the interface and dissolution is controlled by the volume diffusion mechanism. 3. Conclusions
Fig. 3. The calculated Gibbs free energy of the Cu-Ga, and Cu-Zn phases using data from [17,18].
constant, universal gas constant, and absolute temperature, respectively. Then, the values of k0, and Ea were evaluated from the Arrhenius plot of ln k against 1/T as line dependences, which
To sum up, the present study shows that Cu substrate without any protective layer cannot be used in electronics devices with liquid metal cooling systems, based on eutectic Ga-Sn-Zn. Even at the lowest investigated temperature of 100 °C, 720 h was enough time to cause dissolution of the Cu substrate of 20 (lm). The same duration but increasing temperature shows even higher dissolution of 71 (lm) at 150 °C, and of the entire Cu substrate (250 (lm)) at 250 °C. Taking into account the high efficiency of liquid metals in cooling systems, a layer with high thermal conductivity should be applied to protect against reaction and dissolution of the Cu substrate. This will be the subject of further study in the near future.
T. Gancarz, K. Berent / Materials Letters 227 (2018) 116–119
Acknowledgment This work was financed by the National Science Centre Poland grant 2016/21/B/ST8/00324 ‘‘Design and physicochemical, thermal properties of low temperature metal alloys based on gallium” in 2017-2019. References [1] V.I. Rachkov, M.N. Arnoldov, A.D. Efanov, S.G. Kalyakin, F.A. Kozlov, N.I. Loginov, Yu I. Orlov, A.P. Sorokin, Therm. Eng. 61 (2014) 337–347. [2] T. Sawada, A. Netchaev, H. Ninokata, H. Endo, Prog. Nucl. Energy 37 (2000) 313–319. [3] S.H. Shin, J.J. Kim, J.A. Jung, K.J. Choi, I.C. Bang, J.H. Kim, J. Nuc. Mater. 422 (2012) 92–102. [4] P.R. Luebbers, W.F. Michaud, O.K. Chopra, ANL-93/31, Argonne National Laboratory, 1993. [5] W.F. Galo, T.C. Totemeier, Smithells Metals Reference Book, eight ed., Elsevier and ASM International, 2004. [6] K. Ma, J. Liu, Front. Energy Power Eng. China 1 (2007) 384–402.
119
[7] D. Zivkovic, L. Balanovic, D. Manasijevic, T.H. Grguric, D. Cubelac, A. Mitovskia, Int. J. Mater. Res. 104 (2013) 26–34. [8] A. Dobosz, Y. Plevachuk, V. Sklyarchuk, B. Sokoliuk, T. Gancarz, Fluid Phase Equilibr. 465 (2018) 1–9. [9] F.J. Disalvo, Science 285 (1999) 703–706. [10] R.R. Schmidt, E.E. Cruz, M.K. Iyengar, J. Res. Dev. 49 (2005) 709–723. [11] K. Ebrahimi, G.F. Jones, A.S. Fleischer, Renew. Sustain. Energy Rev. 31 (2014) 622–638. [12] J. Liu, Y.X. Zhou, A computer chip cooling method which uses low melting point metal and its alloys as the cooling fluid, China Patent, 02131419.5, 2002. [13] A. Miner, U. Ghoshal, Appl. Phys. Lett. 85 (2004) 506–508. [14] T. Gancarz, J. Pstrus, K. Berent, J. Mater. Eng. Perform. 25 (2016) 3366–3374. [15] B. Massalski, Editor-in-Chief; H. Okamoto, P.R. Subramanian, L. Kacprzak, Editors. ASM International, Materials Park, Ohio, USA. December 1991. [16] S.-K. Lin, C.-L. Cho, H.-M. Chang, J. Electron. Mater. 43 (2014) 204–211. [17] T. Gancarz, Mater. Letter. 171 (2016) 187–190. [18] J.-B. Li, L.N. Ji, J.K. Liang, Y. Zhang, J. Luo, C.R. Li, G.H. Rao, CALPHAD 32 (2008) 447–453. [19] B.B. Straumal, P. Zieba, W. Gust, Int. J. Inorg. Mater. 3 (2001) 1113–1115. [20] S.G. Protasova, O.A. Kogtenkova, B.B. Straumal, P. Zieba, B. Baretzky, J. Mater. Sci. 46 (2011) 4349. [21] N. Eustathopoulos, R. Voytovych, J. Mater. Sci. 51 (2016) 425–437.