- Email: [email protected]
Thermodynamic characterization of solder Au–Ga alloys
Materials Chemistry and Physics 241 (2020) 122278
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Thermodynamic characterization of solder Au–Ga alloys Ana Kostov *, Lidija Gomidzelovic, Aleksandra Milosavljevic, Zdenka Stanojevic Simsic Mining and Metallurgy Institute Bor, Zeleni Bulevar 35, 19210, Bor, Serbia
H I G H L I G H T S
G R A P H I C A L A B S T R A C T
� Intermetal compound AuGa2 has higher microhardness compared to the dark phase of Ga. � Solder alloys Au–Ga have good misci bility regardless of the existence of AuGa2. � The content of gold is limited both by economic and technical reasons.
A R T I C L E I N F O
A B S T R A C T
Keywords: Au-Ga alloys Thermodynamics Characterization Solders Thermal analysis methods
Differential thermal analysis, Oelsen calorimetry as well as optical microscopy are used for thermodynamic characterization of Au–Ga solder alloys. Mechanical and electrical characteristic of the investigated alloys is done by measuring of hardness, micro hardness and electro conductivity. Obtained activities and activity coefficients at 873K are smaller than the unit, which means there is a negative deviation of the gallium activity from the Raoult law. Partial mixing and excess Gibbs’s energy of gallium is negative for all investigated alloys and do not reach 1800 J/mol for the excess energy and 4400 J/mol for the mixing energy which indicates good misci bility regardless of the existence of an intermetallic compound (AuGa2) in the alloy that microstructural analysis is shown. The obtained good miscibility is excellent for solder characteristics of the investigated alloys.
* Corresponding author. E-mail address: [email protected] (A. Kostov). https://doi.org/10.1016/j.matchemphys.2019.122278 Received 29 August 2017; Received in revised form 12 June 2019; Accepted 7 October 2019 Available online 10 October 2019 0254-0584/© 2019 Elsevier B.V. All rights reserved.
A. Kostov et al.
Materials Chemistry and Physics 241 (2020) 122278
the temperature range from 1050 to 1273 K, and for four alloy compo sitions xGa ¼ 0.2, 0.4, 0.6 and 0.8 in the work of Jendrzejczyk-Handzlik [20]. This study was supplemented with DTA experiments which were performed for three alloy compositions, namely 0.15, 0.25 and 0.40 gallium mole fraction. Results, taken together with the information existing in the literature, were used for the calculation of the optimized Au–Ga phase diagram by ThermoCalc software and calculations. The binary Au–Ga system of alloys was investigated as part of ternary systems of alloys such as Ag-Au-Ga [21,22] were DTA method is used for measurement of the enthalpies as one of the thermodynamic charac teristics and EMF measurements are used for thermodynamic properties at 1023–1348 K. The main reason for this investigation was the fact that the literature overview of Ag–Au-Ga system shows that the information about the liquid phase of this system does not exist at all. A few relative new literature data connected with Au–Ga system were related with research work of the author of this paper [23]. Since this is a relatively simple binary alloy system that is not sufficiently thermodynamically examined especially in the last ten years, although there is a certain numbers of literature data, in order to examine and define the characteristics of the alloys of this system Au–Ga, the authors carried out an analysis of this system in order to confirm the existence of an intermetallic compound AuGa2, the determination of thermodynamic values of the alloys in order to obtain solders suitable for the industrial application and give some new contribution to the results of the char acterization of this binary system of alloys. In addition to the thermodynamic analysis (DTA and Oelsen calo rimetry), the mechanical and electrical properties of the investigated alloys suitable for use as solder material are obtained. The hardness, microhardness and electrical conductivity of the tested alloys were determined. Also, by optical microscopy, the existence of the interme tallic compound AuGa2 is confirmed.
1. Introduction Electronics as a business becomes more and more dominant. Today’s industry, transport, communications, home life, research and enter tainment cannot be imagined without the involvement of electronics. The number of electronic components and devices that are active is so large that the total amount of electronics produced becomes measurable with the amounts that other “heavier” industrial branches which deliver. That is why interaction with nature has become much more important and plays a vital role in the world economy and in the ecosystem. According to the European Union Guidelines for the Health and Environmental Protection of the European Union, all research is focused on the development of alloys and materials with optimal performance characteristics: optimal chemical composition, required melting point (depending on the type of applications), good wettability, good and controlled diffusivity in the surface layers of material, ductility, elec trical conductivity, mechanical strength, etc., with the removal or replacement of toxic elements such as lead, cadmium, beryllium, and other toxic and carcinogen elements. The goal is to obtain a material with features that ensure the reliability of the device in which the ma terial is installed, as well as functionality that will not affect the func tional characteristics. The phase balance of the Au–Ga binary system was examined by Weibke et al. [1], Owen et al. [2] Cook et al. [3] and Wallace et al. [4]. Based on their data, Moffatt [5] and Elliott et al. [6] draw an estimated phase diagram of this system. Enthalpy of mixings were determined by Bergman et al. [7], Beja [8], Predel et al. [9] Gather et al. [10] and Hayer et al. [11]. Enthalpy of formation of solid Au–Ga alloys was measured by Predel et al. by calo rimetry [9,12]. The gallium activity in the Au–Ga binary system was measured by Kameda and Azakami [13], using the EMS method, whereby they concluded that the values of the gallium activity showed a significant negative deviation from the Raoult law in the entire range of concen trations. Itagaki [14] examined the Au–Ga, Au–In, Au–Sn, Au–Sb, and Au–Te systems using calorimetry. In an effort to develop contact mate rials with a low melting point, Michikami and Yamaguchi [15] exam ined metallurgical properties (microstructure, hardness and electrical resistance) and contact properties of Au–Ga alloys. A critical evaluation of the thermodynamic data for the Au–Ga system using CALPHAD was performed by Liu et al. [16]. The intermetallic compound AuGa2 (58.5 wt% Au) is used in the jewelry industry as blue gold [17]. Based on the analysis of the literature data and its own research on the project [18], it was researching, and production of solder materials based on Au–Ga alloys. The Au–Ga alloys are used as new ecological solder material:
2. Experimental part The production technology of the investigated alloys consisted of the following phases: the production of alloys, the construction of a certain profile, the analysis of the required casting parameters and the defini tion of adequate technological solutions, the definition of cover agents and the dynamics of alloying, the definition of the minimum quantity of cast wire for the plastic deformation process, the semi-industrial experiment, ingots and profiles (chemical, metallographic, mechani cal, physical and technological), defining thermo-mechanical regime of plastic deformation and selection of devices, testing of finished products, analysis of results and repetition of experiments with possible correction of observed defects. The preloads of the selected compositions are made of pure metals (99.99%), blending in an electric resistance furnace. The samples of the alloys of the given composition were then made by melting the pre heating in the induction furnace, under an atmosphere of air, to 873K. The resulting samples were then heated at a temperature of 473K for an hour and cooled with an incandescent furnace at a cooling rate of 5 K/ min. In order to protect against oxidation, in all cases, a rug cover was used. The prepared samples of the selected alloy composition were sub jected to thermal, structural, mechanical and electrical tests. Differential Thermal Analysis (DTA) was done on Labsys Evo TG-DTA/DSC 1600 by Setaram Instrumentation. Oelsen calorimetry investigation was per formed by Oelsen calorimeter. Microstructural analysis of samples was performed by light optical microscopy (LOM), using a Reichert MeF 2 microscope (magnification up to 500�). The development of the struc ture was carried out with HNO3 þ HF solution (1:1). Recording of the structure was performed using a light optical microscope, at magnitudes 80–100 times depending on the size of the grain. The hardness was measured by universal hardness tester TH 160 INNOVATEST and microhardness was measured by PMT-3 apparatus. Electrical conduc tivity was performed by standard apparatus SIGMATEST 2.069
a) The content of gold is limited both by economic and technical rea sons, since we do not want too much gold in the alloy to excessively increase its melting point, as well as the price of the solder alloys itself, which would prevent its use. b) Highly gallium content alloys show a tendency to stratify, even in extreme cases, and galley extraction from the alloys at room tem perature, and with the increase in gallium content, a significant decline in the quality of the mechanical properties of the alloys has been observed. We obtained alloys with intermetallic compound AuGa2, which is confirmed by Liu, Guo, Li and Du [19]. In their paper, the Au–Ga system was critically assessed by means of CALPHAD technique. Based on the experimental data, the excess Gibbs energies of the solution phases were modeled with the Redlich–Kister equation and the intermetallic two compounds AuGa and AuGa2 were treated as stochiometric compounds. So, a set of self-consistent thermodynamic parameters of the Au–Ga system was obtained in Ref. [19]. Activities of gallium in the liquid Au–Ga alloys were determined in 2
A. Kostov et al.
Materials Chemistry and Physics 241 (2020) 122278
(Foerster) instruments for measured of electrical conductivity of metals.
Table 2 Characteristic temperatures of the Au–Ga alloy system.
3. Results and discussion For experimental research, seven alloys of the Au–Ga binary system were used, with a constant volume of 0.3 cm3. Compositions and masses of alloys examined are given in Table 1. Masses of samples in grams are calculated based on total volume of 0.3 cm3, percentage participation of elements in the alloy and relative atomic masses of the elements.
Alloy
Ga (% at)
Temperature (K)
A1 A2 A3 A4 A5 A6 A7
65 70 75 80 85 90 95
295 – 300 305 307 302 303
759 761 735 693 – 597 531
3.1. Differential Thermal Analysis Differential thermal analysis of the samples of the Au–Ga alloys were used for determining the characteristic temperatures of the alloys (melting temperatures). After the homogenization, the samples were heated to 1073 K at a heating rate of 10 K/min, whereby heating curves were obtained from which the characteristic temperatures were shown in Table 2. According to obtained DTA curves and defined characteristics tem peratures of alloys, the obtained data was put in the phase diagram of the Au–Ga alloys system. In Fig. 1, our obtained DTA experimental data are presented together with literature obtained data and showing the comparison of the ob tained DTA results with the data from the literature [5,6], which in dicates good mutual agreement. 3.2. Light optical microscopy Microstructural analysis of samples was performed using optical microscopy. The microstructure of the samples taken with the light optical microscope is presented in Fig. 2. Observing the microstructure of the investigated alloys, based on the phase diagram of the Au–Ga system (Fig. 1), it can be concluded that it consists of polygonal crystals of the AuGa2 intermetal compound embedded in a dark gallium base. The obtained intermetallic compound AuGa2 is also detected in Ref. [19] and confirmed our experimental results too. Fig. 1. Comparison of DTA results with literature data [5,6].
3.3. Hardness measurement
porosity of the dark phase made it impossible to obtain a visible print.
Within the characterization of the investigated alloys, the hardness was measured by the Brinell method for only three samples, because they are suitable for solder materials production. The obtained results are presented in Fig. 3. Fig. 3 shows the change in the hardness of the alloy depending on the contents of the gallium. It can be noted that with the increase in gallium content in the alloy, the hardness value de creases, approaching the hard gallium hardness (HB ¼ 6).
3.5. Electrical conductivity measurement The results of the measurement of electrical conductivity of samples suitable as solder materials are given in Fig. 4. The highest gold content has the highest value of electrical con ductivity 6.057 MS/m, and then electrical conductivity decreases with increasing gallium content up to xGa ¼ 0.85. After this minimum, con ductivity shows a slow trend in the rise in values for the investigated alloys, which corresponds to the electrical conductivity of pure gallium of �7.1 MS/m.
3.4. Microhardness measurement When testing microhardness (again for three samples of alloys A2, A4 and A6), a load of 50 g was used for all samples and all the present phases. The results of the microhardness measurement of the investi gated alloys are presented in Table 3. The obtained microhardness values show that the light phase (AuGa2) has a higher microhardness compared to the dark phase (Ga). In the case of the A6 alloy, the high
3.6. Oelsen calorimetry The cooling curves for the Au–Ga alloys system, recorded according to the described procedure of Oelsen’s calorimetry [24], were used to construct enthalpy isotherms, based on the temperature change of the calorimeter and for the temperature interval 350–1000 K, and obtained results are given in Fig. 5. In accordance with the thermodynamic bases set by Oelsen [24], planimetry graphic was performed which allowed further quantitative thermodynamic analysis. The results of Oelsen’s quantitative thermo dynamic analysis of the Au–Ga binary system of alloys are given in Tables 4 and 5. The activity values, partial molar quantities for the gallium in the Au–Ga system of alloys at a temperature of 873 K. were obtained by the
Table 1 Composition and mass of the tested Au–Ga alloys. Alloy
Ga (% at)
xGa
xAu
mGa (g)
mAu (g)
A1 A2 A3 A4 A5 A6 A7
65 70 75 80 85 90 95
0.65 0.70 0.75 0.8 0.85 0.90 0.95
0.35 0.30 0.25 0.20 0.15 0.10 0.05
1.2095 1.2934 1.3761 1.4577 1.5381 1.6175 1.6958
1.8402 2.8122 1.2961 1.0297 0.767 0.5078 0.2522
3
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Materials Chemistry and Physics 241 (2020) 122278
Fig. 3. Change in the hardness of the samples depending on the gal lium content.
a)
Table 3 Results of the measurement of the microhardness of the tested Au–Ga alloys. Alloy A2 A4 A6
Hμ Light phase
Dark phase
139,7 136,4 131,3
28,7 33,3 –
b)
Fig. 4. The dependence of electrical conductivity on the composition.
Oelsen calorimetry method. The obtained activity coefficients are smaller than the unit and amount value goes in the interval from 0.783 to 0.968, which means we can conclude that there is a negative devia tion of the gallium activity from the Raoult law. Also, activities of the investigated alloys are less than unit and goes in the interval from 0.548 to 0.919. Partial excess and mixing Gibbs’s energy of gallium is negative for all investigated alloys and do not reach 1800 J/mol for the excess energy and 4400 J/mol for the mixing energy. These values indicate good miscibility regardless of the existence of an intermetallic com pound (AuGa2) in the investigated obtained alloys that microstructural analysis is shown.
c) Fig. 2. The microstructure of the tested Au–Ga alloys: a) A2 (100x), b) A4 (80x), c) A6 (80x). 4
A. Kostov et al.
Materials Chemistry and Physics 241 (2020) 122278
Fig. 5. Diagram of enthalpy isotherms for temperature interval 350–1000 K. Table 4 Results of Oelsen’s thermodynamic analysis for the Au–Ga alloys. Alloy
xGa
I (cm2)
II(cm2)
ΔI
ΔII
muk
J1
J2
ΔSMid
J1- ΔSMid
J1- ΔSMid
ΔIV
Px
-RlnaGa
aGa
γGa
A1 A2 A3 A4 A5 A6 A7
0.65 0.7 0.75 0.8 0.85 0.9 0.95
111 99.8 91 101.4 98.1 102 100.6
3 12 5 3.5 4.7 5 3.8
/ 0.60 0.90 1.20 1.10 1.10 0.70
/ 0.30 0.50 0.70 0.80 0.80 0.50
0.0267 0.0265 0.0263 0.0261 0.0260 0.0258 0.0256
/ 1.0109 1.5270 2.0502 1.8924 1.91 1.22
– 0.5055 0.8484 1.1960 1.3763 1.39 0.87
– 5.0790 4.6755 4.1606 3.5146 2.7029 1.6505
–
–
–
– 3.08 1.88 1.56 1.31 1.00 0.65
– 5.00 3.50 2.50 2.00 1.20 0.70
– 0.548 0.656 0.740 0.796 0.866 0.919
– 0.783 0.875 0.925 0.936 0.962 0.968
873K
Alloy
xGa
aGa
γ Ga
A1 A2 A3 A4 A5 A6 A7
0.65 0.70 0.75 0.80 0.85 0.90 0.95
– 0.548 0.656 0.740 0.796 0.866 0.919
– 0.783 0.875 0.925 0.936 0.962 0.968
GMGa(J/mol)
GEGa (J/mol)
–
–
4365 3055 2182 1659 1048 611
4.5735 3.8271 2.9646 2.1383 1.3171 0.7785
2.00 2.80 2.60 2.20 1.70 1.00
characteristic temperature of melting in the investigated systems are obtained. The obtained DTA results are compared with the data from the literature and shown good mutual agreement. Microstructural analysis of investigated samples was performed by light optical microscopy and showed that alloys are consisted of polygonal crystals of the AuGa2 intermetal compound embedded in a dark gallium base. The obtained AuGa2 intermetal compound confirmed literature data connected with the existing of the intermetallic compound in the investigated system of alloys. Also results of hardness and microhardness measurements and electrical conductivity measurements are given for the alloys which are suitable for solder production. It can be noted that with the increase of gallium content in the alloy, the hardness value decreases, approaching the hard gallium hardness. The obtained microhardness values show that the light phase (AuGa2) has a higher microhardness compared to the dark phase (Ga). Electrical conductivity of investigated alloys showed the highest gold content has the highest value of electrical conductivity of 6.057 MS/m and electrical conductivity decreases with
Table 5 Thermodynamic values of gallium for the Au–Ga alloys. T(K)
4.0681 3.1485 2.1103 1.6222 0.7975 0.4297
1776 967 563 479 283 239
4. Conclusions In this paper are presented results of experimental investigation of thermal, structural, mechanical, electrical and thermodynamic charac teristics of Au–Ga system alloys. According to DTA measurements the 5
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Materials Chemistry and Physics 241 (2020) 122278
increasing gallium content Thermodynamic properties obtained by Oelsen calormetry, indicate that gallium shows good miscibility with gold in all investigated alloys, because obtained activities and activity coefficients are smaller than the unit, which have a negative deviation of the Raoult law. Obtained results should contribute to a better knowledge of Ga–Au based system of alloys properties because there are not a lot of the data in the literature. Obtained results are also useful for deter mining alloys characteristic and their used as solders.
[5] W.G. Moffatt, N.Y. Schenectady, The Handbook of Binary Phase Diagrams, General Electric Comp, 1982. [6] R.P. Elliott, F.A. Shunk, Bull. Alloy Phase Diagrams 2 (1981) 356. [7] C. Bergman, J.P. Bros, M. Carbonel, M. Gambino, M. Laffitte, Rev. Int. Hautes Temp. Refract. 8 (1971) 205. [8] R. Beja, Th�ese, Univ. Aix-Marseille, France, 1969. [9] B. Predel, D.W. Stein, Acta Metall. 20 (1972) 515. [10] B. Gather, R. Blachnik, J. Chem. Thermodyn. 16 (1984) 487. [11] E. Hayer, K.L. Komarek, M. Gaune-Escard, J.P. Bros, Z. Metallkde. 81 (1990) 233. [12] B. Predel, D.W. Stein, Acta Metall. 20 (1972) 681. [13] K. Kameda, T. Azakami, J. Jpn. Inst. Metals 40 (10) (1976) 1087. [14] K. Itagaki, J. Jpn. Inst. Metals 40 (10) (1976) 1038. [15] O. Michikami, Y. Yamaguchi, Rev. Electr. Commun. Lab. 22 (1–2) (1974) 191. [16] J. Liu, C. Guo, C. Li, Z. Du, J. Alloy. Comp. 508 (1) (2010) 62. [17] www.gold.org/discover/sciindu/GTech/2000_30/colgold.pdf. [18] Project No TR34005, Titled: Development of Ecological Knowledge-Based Advanced Materials and Technologies for Multifunctional Application, Period of Realization 2011-2017, Financial Support of Ministry of Education, Science and Technological Development of the Republic Serbia. [19] J. Liu, C. Guo, C. Li, Z. Du, J. Alloy. Comp. 508 (1) (2010) 62–70. [20] D. Jendrzejczyk-Handzlik, J. Phase Equilibria Diffusion 38 (3) (2017) 305–318. [21] D. Jendrzejczyk-Handzlik, J. Chem. Thermodyn. 107 (2017) 114–125. [22] D. Jendrzejczyk-Handzlik, Thermochim. Acta 662 (2018) 126–134. [23] L. Gomidzelovic, D. Zivkovic, N. Talijan, V. Cosovic, Lj Balanovic, Materials Testing 54 (5) (2012) 347–350. [24] W. Oelsen, E. Schurmann, H.J. Weigt, O. Oelsen, Archiv fur das Eisenhuttenwesen 27 (1956) 487–511.
Acknowledgements The research presented in this paper has been done in the frame of the projects: “Development of ecological knowledge-based advanced materials and technologies for multifunctional application” No TR34005 financed by Ministry of Education, Science and Technological Development of the Republic of Serbia. References [1] [2] [3] [4]
F. Weibke, E. Hesse, Z. Anorg. Allg. Chem. 240 (1939) 289. E.A. Owen, E.A.O. Roberts, J. Inst. Met. 71 (1945) 213. C.J. Cooke, W. Hume-Rothery, J. Less Common. Met. 10 (1966) 42. W. Wallace, W.J. Kitchingman, J. Less Common. Met. 17 (1969) 263.
6
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Thermodynamic characterization of solder Au–Ga alloys Ana Kostov *, Lidija Gomidzelovic, Aleksandra Milosavljevic, Zdenka Stanojevic Simsic Mining and Metallurgy Institute Bor, Zeleni Bulevar 35, 19210, Bor, Serbia
H I G H L I G H T S
G R A P H I C A L A B S T R A C T
� Intermetal compound AuGa2 has higher microhardness compared to the dark phase of Ga. � Solder alloys Au–Ga have good misci bility regardless of the existence of AuGa2. � The content of gold is limited both by economic and technical reasons.
A R T I C L E I N F O
A B S T R A C T
Keywords: Au-Ga alloys Thermodynamics Characterization Solders Thermal analysis methods
Differential thermal analysis, Oelsen calorimetry as well as optical microscopy are used for thermodynamic characterization of Au–Ga solder alloys. Mechanical and electrical characteristic of the investigated alloys is done by measuring of hardness, micro hardness and electro conductivity. Obtained activities and activity coefficients at 873K are smaller than the unit, which means there is a negative deviation of the gallium activity from the Raoult law. Partial mixing and excess Gibbs’s energy of gallium is negative for all investigated alloys and do not reach 1800 J/mol for the excess energy and 4400 J/mol for the mixing energy which indicates good misci bility regardless of the existence of an intermetallic compound (AuGa2) in the alloy that microstructural analysis is shown. The obtained good miscibility is excellent for solder characteristics of the investigated alloys.
* Corresponding author. E-mail address: [email protected] (A. Kostov). https://doi.org/10.1016/j.matchemphys.2019.122278 Received 29 August 2017; Received in revised form 12 June 2019; Accepted 7 October 2019 Available online 10 October 2019 0254-0584/© 2019 Elsevier B.V. All rights reserved.
A. Kostov et al.
Materials Chemistry and Physics 241 (2020) 122278
the temperature range from 1050 to 1273 K, and for four alloy compo sitions xGa ¼ 0.2, 0.4, 0.6 and 0.8 in the work of Jendrzejczyk-Handzlik [20]. This study was supplemented with DTA experiments which were performed for three alloy compositions, namely 0.15, 0.25 and 0.40 gallium mole fraction. Results, taken together with the information existing in the literature, were used for the calculation of the optimized Au–Ga phase diagram by ThermoCalc software and calculations. The binary Au–Ga system of alloys was investigated as part of ternary systems of alloys such as Ag-Au-Ga [21,22] were DTA method is used for measurement of the enthalpies as one of the thermodynamic charac teristics and EMF measurements are used for thermodynamic properties at 1023–1348 K. The main reason for this investigation was the fact that the literature overview of Ag–Au-Ga system shows that the information about the liquid phase of this system does not exist at all. A few relative new literature data connected with Au–Ga system were related with research work of the author of this paper [23]. Since this is a relatively simple binary alloy system that is not sufficiently thermodynamically examined especially in the last ten years, although there is a certain numbers of literature data, in order to examine and define the characteristics of the alloys of this system Au–Ga, the authors carried out an analysis of this system in order to confirm the existence of an intermetallic compound AuGa2, the determination of thermodynamic values of the alloys in order to obtain solders suitable for the industrial application and give some new contribution to the results of the char acterization of this binary system of alloys. In addition to the thermodynamic analysis (DTA and Oelsen calo rimetry), the mechanical and electrical properties of the investigated alloys suitable for use as solder material are obtained. The hardness, microhardness and electrical conductivity of the tested alloys were determined. Also, by optical microscopy, the existence of the interme tallic compound AuGa2 is confirmed.
1. Introduction Electronics as a business becomes more and more dominant. Today’s industry, transport, communications, home life, research and enter tainment cannot be imagined without the involvement of electronics. The number of electronic components and devices that are active is so large that the total amount of electronics produced becomes measurable with the amounts that other “heavier” industrial branches which deliver. That is why interaction with nature has become much more important and plays a vital role in the world economy and in the ecosystem. According to the European Union Guidelines for the Health and Environmental Protection of the European Union, all research is focused on the development of alloys and materials with optimal performance characteristics: optimal chemical composition, required melting point (depending on the type of applications), good wettability, good and controlled diffusivity in the surface layers of material, ductility, elec trical conductivity, mechanical strength, etc., with the removal or replacement of toxic elements such as lead, cadmium, beryllium, and other toxic and carcinogen elements. The goal is to obtain a material with features that ensure the reliability of the device in which the ma terial is installed, as well as functionality that will not affect the func tional characteristics. The phase balance of the Au–Ga binary system was examined by Weibke et al. [1], Owen et al. [2] Cook et al. [3] and Wallace et al. [4]. Based on their data, Moffatt [5] and Elliott et al. [6] draw an estimated phase diagram of this system. Enthalpy of mixings were determined by Bergman et al. [7], Beja [8], Predel et al. [9] Gather et al. [10] and Hayer et al. [11]. Enthalpy of formation of solid Au–Ga alloys was measured by Predel et al. by calo rimetry [9,12]. The gallium activity in the Au–Ga binary system was measured by Kameda and Azakami [13], using the EMS method, whereby they concluded that the values of the gallium activity showed a significant negative deviation from the Raoult law in the entire range of concen trations. Itagaki [14] examined the Au–Ga, Au–In, Au–Sn, Au–Sb, and Au–Te systems using calorimetry. In an effort to develop contact mate rials with a low melting point, Michikami and Yamaguchi [15] exam ined metallurgical properties (microstructure, hardness and electrical resistance) and contact properties of Au–Ga alloys. A critical evaluation of the thermodynamic data for the Au–Ga system using CALPHAD was performed by Liu et al. [16]. The intermetallic compound AuGa2 (58.5 wt% Au) is used in the jewelry industry as blue gold [17]. Based on the analysis of the literature data and its own research on the project [18], it was researching, and production of solder materials based on Au–Ga alloys. The Au–Ga alloys are used as new ecological solder material:
2. Experimental part The production technology of the investigated alloys consisted of the following phases: the production of alloys, the construction of a certain profile, the analysis of the required casting parameters and the defini tion of adequate technological solutions, the definition of cover agents and the dynamics of alloying, the definition of the minimum quantity of cast wire for the plastic deformation process, the semi-industrial experiment, ingots and profiles (chemical, metallographic, mechani cal, physical and technological), defining thermo-mechanical regime of plastic deformation and selection of devices, testing of finished products, analysis of results and repetition of experiments with possible correction of observed defects. The preloads of the selected compositions are made of pure metals (99.99%), blending in an electric resistance furnace. The samples of the alloys of the given composition were then made by melting the pre heating in the induction furnace, under an atmosphere of air, to 873K. The resulting samples were then heated at a temperature of 473K for an hour and cooled with an incandescent furnace at a cooling rate of 5 K/ min. In order to protect against oxidation, in all cases, a rug cover was used. The prepared samples of the selected alloy composition were sub jected to thermal, structural, mechanical and electrical tests. Differential Thermal Analysis (DTA) was done on Labsys Evo TG-DTA/DSC 1600 by Setaram Instrumentation. Oelsen calorimetry investigation was per formed by Oelsen calorimeter. Microstructural analysis of samples was performed by light optical microscopy (LOM), using a Reichert MeF 2 microscope (magnification up to 500�). The development of the struc ture was carried out with HNO3 þ HF solution (1:1). Recording of the structure was performed using a light optical microscope, at magnitudes 80–100 times depending on the size of the grain. The hardness was measured by universal hardness tester TH 160 INNOVATEST and microhardness was measured by PMT-3 apparatus. Electrical conduc tivity was performed by standard apparatus SIGMATEST 2.069
a) The content of gold is limited both by economic and technical rea sons, since we do not want too much gold in the alloy to excessively increase its melting point, as well as the price of the solder alloys itself, which would prevent its use. b) Highly gallium content alloys show a tendency to stratify, even in extreme cases, and galley extraction from the alloys at room tem perature, and with the increase in gallium content, a significant decline in the quality of the mechanical properties of the alloys has been observed. We obtained alloys with intermetallic compound AuGa2, which is confirmed by Liu, Guo, Li and Du [19]. In their paper, the Au–Ga system was critically assessed by means of CALPHAD technique. Based on the experimental data, the excess Gibbs energies of the solution phases were modeled with the Redlich–Kister equation and the intermetallic two compounds AuGa and AuGa2 were treated as stochiometric compounds. So, a set of self-consistent thermodynamic parameters of the Au–Ga system was obtained in Ref. [19]. Activities of gallium in the liquid Au–Ga alloys were determined in 2
A. Kostov et al.
Materials Chemistry and Physics 241 (2020) 122278
(Foerster) instruments for measured of electrical conductivity of metals.
Table 2 Characteristic temperatures of the Au–Ga alloy system.
3. Results and discussion For experimental research, seven alloys of the Au–Ga binary system were used, with a constant volume of 0.3 cm3. Compositions and masses of alloys examined are given in Table 1. Masses of samples in grams are calculated based on total volume of 0.3 cm3, percentage participation of elements in the alloy and relative atomic masses of the elements.
Alloy
Ga (% at)
Temperature (K)
A1 A2 A3 A4 A5 A6 A7
65 70 75 80 85 90 95
295 – 300 305 307 302 303
759 761 735 693 – 597 531
3.1. Differential Thermal Analysis Differential thermal analysis of the samples of the Au–Ga alloys were used for determining the characteristic temperatures of the alloys (melting temperatures). After the homogenization, the samples were heated to 1073 K at a heating rate of 10 K/min, whereby heating curves were obtained from which the characteristic temperatures were shown in Table 2. According to obtained DTA curves and defined characteristics tem peratures of alloys, the obtained data was put in the phase diagram of the Au–Ga alloys system. In Fig. 1, our obtained DTA experimental data are presented together with literature obtained data and showing the comparison of the ob tained DTA results with the data from the literature [5,6], which in dicates good mutual agreement. 3.2. Light optical microscopy Microstructural analysis of samples was performed using optical microscopy. The microstructure of the samples taken with the light optical microscope is presented in Fig. 2. Observing the microstructure of the investigated alloys, based on the phase diagram of the Au–Ga system (Fig. 1), it can be concluded that it consists of polygonal crystals of the AuGa2 intermetal compound embedded in a dark gallium base. The obtained intermetallic compound AuGa2 is also detected in Ref. [19] and confirmed our experimental results too. Fig. 1. Comparison of DTA results with literature data [5,6].
3.3. Hardness measurement
porosity of the dark phase made it impossible to obtain a visible print.
Within the characterization of the investigated alloys, the hardness was measured by the Brinell method for only three samples, because they are suitable for solder materials production. The obtained results are presented in Fig. 3. Fig. 3 shows the change in the hardness of the alloy depending on the contents of the gallium. It can be noted that with the increase in gallium content in the alloy, the hardness value de creases, approaching the hard gallium hardness (HB ¼ 6).
3.5. Electrical conductivity measurement The results of the measurement of electrical conductivity of samples suitable as solder materials are given in Fig. 4. The highest gold content has the highest value of electrical con ductivity 6.057 MS/m, and then electrical conductivity decreases with increasing gallium content up to xGa ¼ 0.85. After this minimum, con ductivity shows a slow trend in the rise in values for the investigated alloys, which corresponds to the electrical conductivity of pure gallium of �7.1 MS/m.
3.4. Microhardness measurement When testing microhardness (again for three samples of alloys A2, A4 and A6), a load of 50 g was used for all samples and all the present phases. The results of the microhardness measurement of the investi gated alloys are presented in Table 3. The obtained microhardness values show that the light phase (AuGa2) has a higher microhardness compared to the dark phase (Ga). In the case of the A6 alloy, the high
3.6. Oelsen calorimetry The cooling curves for the Au–Ga alloys system, recorded according to the described procedure of Oelsen’s calorimetry [24], were used to construct enthalpy isotherms, based on the temperature change of the calorimeter and for the temperature interval 350–1000 K, and obtained results are given in Fig. 5. In accordance with the thermodynamic bases set by Oelsen [24], planimetry graphic was performed which allowed further quantitative thermodynamic analysis. The results of Oelsen’s quantitative thermo dynamic analysis of the Au–Ga binary system of alloys are given in Tables 4 and 5. The activity values, partial molar quantities for the gallium in the Au–Ga system of alloys at a temperature of 873 K. were obtained by the
Table 1 Composition and mass of the tested Au–Ga alloys. Alloy
Ga (% at)
xGa
xAu
mGa (g)
mAu (g)
A1 A2 A3 A4 A5 A6 A7
65 70 75 80 85 90 95
0.65 0.70 0.75 0.8 0.85 0.90 0.95
0.35 0.30 0.25 0.20 0.15 0.10 0.05
1.2095 1.2934 1.3761 1.4577 1.5381 1.6175 1.6958
1.8402 2.8122 1.2961 1.0297 0.767 0.5078 0.2522
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Fig. 3. Change in the hardness of the samples depending on the gal lium content.
a)
Table 3 Results of the measurement of the microhardness of the tested Au–Ga alloys. Alloy A2 A4 A6
Hμ Light phase
Dark phase
139,7 136,4 131,3
28,7 33,3 –
b)
Fig. 4. The dependence of electrical conductivity on the composition.
Oelsen calorimetry method. The obtained activity coefficients are smaller than the unit and amount value goes in the interval from 0.783 to 0.968, which means we can conclude that there is a negative devia tion of the gallium activity from the Raoult law. Also, activities of the investigated alloys are less than unit and goes in the interval from 0.548 to 0.919. Partial excess and mixing Gibbs’s energy of gallium is negative for all investigated alloys and do not reach 1800 J/mol for the excess energy and 4400 J/mol for the mixing energy. These values indicate good miscibility regardless of the existence of an intermetallic com pound (AuGa2) in the investigated obtained alloys that microstructural analysis is shown.
c) Fig. 2. The microstructure of the tested Au–Ga alloys: a) A2 (100x), b) A4 (80x), c) A6 (80x). 4
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Materials Chemistry and Physics 241 (2020) 122278
Fig. 5. Diagram of enthalpy isotherms for temperature interval 350–1000 K. Table 4 Results of Oelsen’s thermodynamic analysis for the Au–Ga alloys. Alloy
xGa
I (cm2)
II(cm2)
ΔI
ΔII
muk
J1
J2
ΔSMid
J1- ΔSMid
J1- ΔSMid
ΔIV
Px
-RlnaGa
aGa
γGa
A1 A2 A3 A4 A5 A6 A7
0.65 0.7 0.75 0.8 0.85 0.9 0.95
111 99.8 91 101.4 98.1 102 100.6
3 12 5 3.5 4.7 5 3.8
/ 0.60 0.90 1.20 1.10 1.10 0.70
/ 0.30 0.50 0.70 0.80 0.80 0.50
0.0267 0.0265 0.0263 0.0261 0.0260 0.0258 0.0256
/ 1.0109 1.5270 2.0502 1.8924 1.91 1.22
– 0.5055 0.8484 1.1960 1.3763 1.39 0.87
– 5.0790 4.6755 4.1606 3.5146 2.7029 1.6505
–
–
–
– 3.08 1.88 1.56 1.31 1.00 0.65
– 5.00 3.50 2.50 2.00 1.20 0.70
– 0.548 0.656 0.740 0.796 0.866 0.919
– 0.783 0.875 0.925 0.936 0.962 0.968
873K
Alloy
xGa
aGa
γ Ga
A1 A2 A3 A4 A5 A6 A7
0.65 0.70 0.75 0.80 0.85 0.90 0.95
– 0.548 0.656 0.740 0.796 0.866 0.919
– 0.783 0.875 0.925 0.936 0.962 0.968
GMGa(J/mol)
GEGa (J/mol)
–
–
4365 3055 2182 1659 1048 611
4.5735 3.8271 2.9646 2.1383 1.3171 0.7785
2.00 2.80 2.60 2.20 1.70 1.00
characteristic temperature of melting in the investigated systems are obtained. The obtained DTA results are compared with the data from the literature and shown good mutual agreement. Microstructural analysis of investigated samples was performed by light optical microscopy and showed that alloys are consisted of polygonal crystals of the AuGa2 intermetal compound embedded in a dark gallium base. The obtained AuGa2 intermetal compound confirmed literature data connected with the existing of the intermetallic compound in the investigated system of alloys. Also results of hardness and microhardness measurements and electrical conductivity measurements are given for the alloys which are suitable for solder production. It can be noted that with the increase of gallium content in the alloy, the hardness value decreases, approaching the hard gallium hardness. The obtained microhardness values show that the light phase (AuGa2) has a higher microhardness compared to the dark phase (Ga). Electrical conductivity of investigated alloys showed the highest gold content has the highest value of electrical conductivity of 6.057 MS/m and electrical conductivity decreases with
Table 5 Thermodynamic values of gallium for the Au–Ga alloys. T(K)
4.0681 3.1485 2.1103 1.6222 0.7975 0.4297
1776 967 563 479 283 239
4. Conclusions In this paper are presented results of experimental investigation of thermal, structural, mechanical, electrical and thermodynamic charac teristics of Au–Ga system alloys. According to DTA measurements the 5
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increasing gallium content Thermodynamic properties obtained by Oelsen calormetry, indicate that gallium shows good miscibility with gold in all investigated alloys, because obtained activities and activity coefficients are smaller than the unit, which have a negative deviation of the Raoult law. Obtained results should contribute to a better knowledge of Ga–Au based system of alloys properties because there are not a lot of the data in the literature. Obtained results are also useful for deter mining alloys characteristic and their used as solders.
[5] W.G. Moffatt, N.Y. Schenectady, The Handbook of Binary Phase Diagrams, General Electric Comp, 1982. [6] R.P. Elliott, F.A. Shunk, Bull. Alloy Phase Diagrams 2 (1981) 356. [7] C. Bergman, J.P. Bros, M. Carbonel, M. Gambino, M. Laffitte, Rev. Int. Hautes Temp. Refract. 8 (1971) 205. [8] R. Beja, Th�ese, Univ. Aix-Marseille, France, 1969. [9] B. Predel, D.W. Stein, Acta Metall. 20 (1972) 515. [10] B. Gather, R. Blachnik, J. Chem. Thermodyn. 16 (1984) 487. [11] E. Hayer, K.L. Komarek, M. Gaune-Escard, J.P. Bros, Z. Metallkde. 81 (1990) 233. [12] B. Predel, D.W. Stein, Acta Metall. 20 (1972) 681. [13] K. Kameda, T. Azakami, J. Jpn. Inst. Metals 40 (10) (1976) 1087. [14] K. Itagaki, J. Jpn. Inst. Metals 40 (10) (1976) 1038. [15] O. Michikami, Y. Yamaguchi, Rev. Electr. Commun. Lab. 22 (1–2) (1974) 191. [16] J. Liu, C. Guo, C. Li, Z. Du, J. Alloy. Comp. 508 (1) (2010) 62. [17] www.gold.org/discover/sciindu/GTech/2000_30/colgold.pdf. [18] Project No TR34005, Titled: Development of Ecological Knowledge-Based Advanced Materials and Technologies for Multifunctional Application, Period of Realization 2011-2017, Financial Support of Ministry of Education, Science and Technological Development of the Republic Serbia. [19] J. Liu, C. Guo, C. Li, Z. Du, J. Alloy. Comp. 508 (1) (2010) 62–70. [20] D. Jendrzejczyk-Handzlik, J. Phase Equilibria Diffusion 38 (3) (2017) 305–318. [21] D. Jendrzejczyk-Handzlik, J. Chem. Thermodyn. 107 (2017) 114–125. [22] D. Jendrzejczyk-Handzlik, Thermochim. Acta 662 (2018) 126–134. [23] L. Gomidzelovic, D. Zivkovic, N. Talijan, V. Cosovic, Lj Balanovic, Materials Testing 54 (5) (2012) 347–350. [24] W. Oelsen, E. Schurmann, H.J. Weigt, O. Oelsen, Archiv fur das Eisenhuttenwesen 27 (1956) 487–511.
Acknowledgements The research presented in this paper has been done in the frame of the projects: “Development of ecological knowledge-based advanced materials and technologies for multifunctional application” No TR34005 financed by Ministry of Education, Science and Technological Development of the Republic of Serbia. References [1] [2] [3] [4]
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