Microstructure evolution and properties of Cu–Ag microcomposites with different Ag content

Materials Science and Engineering A 435–436 (2006) 237–244

Microstructure evolution and properties of Cu–Ag microcomposites with different Ag content J.B. Liu a , L. Meng a,∗ , Y.W. Zeng b a

College of Materials Science and Chemical Engineering, Zhejiang University, Hangzhou 310027, China b Center of Analysis and Measurement, Zhejiang University, Hangzhou 310028, China Received 16 July 2006; accepted 28 July 2006

Abstract The Cu–Ag microcomposites containing 6, 12 and 24 wt.% Ag were prepared by cold drawing combined with intermediate heat treatments. The microstructure was observed and the tensile strength and electrical conductivity were determined at various draw ratios. The original ␣ dendrites, eutectic colonies and secondary precipitates evolve into filamentary bundles with tight arrangement of double phases during heavy cold drawing. The strength increases and the electrical conductivity decreases with draw ratio increasing. High Ag content produces high hardening rate, high tensile strength and low electrical conductivity. A continuous eutectic net can result in distinct strengthening and strong scattering. The strengthening in the Cu–6 wt.% Ag depends mainly on the strengthening of Cu matrix. The increased density of the interface between Cu matrix and eutectic colonies in the Cu–12 wt.% Ag with strong drawing strain creates an additional strengthening profit from the filamentary mixture. More Ag precipitates and higher interface density in the Cu–24 wt.% Ag result in earlier presence of the additional strengthening profit. The eutectic morphology has more important effect on the strength and conductivity in the Cu–Ag microcomposites than the eutectic volume fraction. © 2006 Elsevier B.V. All rights reserved. Keywords: Cu–Ag alloy; Microstructure; Tensile strength; Electrical conductivity

1. Introduction Cu–Ag microcomposites with filamentary structure of double phases are widely studied because there is an appropriate combination of mechanical strength and electrical conductivity [1–3]. These materials are primarily expected to be used in the magnetic windings of high field magnets, where high mechanical strength and excellent electrical conductivity are required to withstand Lorentz force and minimize Joule heating produced from strong exciting electrical current [4–6]. The attracted property of a tensile strength in excess of 1 GPa with a conductivity of (60–70)% IACS (International Annealed Copper Standard) has been realized in Cu–Ag microcomposites and further improvement are still expected to develop the magnetic design of high field magnets [7–9]. The filamentary structure of double phases in Cu–Ag alloys is generally produced by heavy drawing strain and intermediate heat treatment. The constituent concentration, drawing ratio and

∗

Corresponding author. Tel.: +86 57187951523; fax: +86 57187951171. E-mail address: [email protected] (L. Meng).

0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.07.125

heat treatment parameter strongly affect the properties [10–17]. In special, the Ag content is one of the important considered factors because the volume fraction of double phases, distribution aspect of filamentary structure and precipitation behavior of secondary particles are mainly dependent on the Ag content. A fabrication method of cold drawing combined intermediate heat treatment was developed for Cu–Ag microcomposites containing (2–60) at.% Ag [7]. The strength increased and gradually tended to saturate beyond (10–20) at.% Ag while the conductivity decreased with increasing Ag content and deformation degree. The evolution of microstructure during cold working was examined for Cu–Ag alloys containing (3–72) wt.% Ag [10]. The as-cast microstructure contained only Cu solid solution in the alloys with less than 6 wt.% Ag and primary Cu dendrites surrounded by a thin film of eutectic mixture in the alloys with more than 6 wt.% Ag. The volume fraction of eutectic colonies increased with Ag content increasing up to 100% at the eutectic composition about 72 wt.% Ag. These alloys with various Ag contents showed similar strengthening behavior during the initial stage of working and there was a second stage of additional hardening related to the refinement of Ag lamellae. The precipitation behaviors during aging treatment were compared

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between the Cu–7 wt.% Ag and Cu–24 wt.% Ag [11,18]. Aging treatment increased the strength at starting drawing strain and the strain-hardening rate. During aging treatment, discontinuous precipitation was likely to occur in the alloys with low Ag content due to the existence of more high-angle grain boundaries of primary Cu dendrites while that was usually suppressed in the alloys with high Ag content due to the absence of high-angle grain boundaries or the complete enclosure of Cu dendrites by eutectic colonies. However, the microstructure evolution during cold drawing still needs further investigation since the co-deformation of Cu and Ag phases is very complex. More attentions should also be paid to the influence of Ag content on the strength and conductivity based on the microstructure investigation. In the present study, the Cu–Ag microcomposites containing 6, 12 and 24 wt.% Ag are prepared by heavy cold drawing and intermediate heat treatments. The microstructure is observed and the ultimate tensile strength and electrical conductivity are determined. The relation between microstructure and properties is discussed for the filamentary composites evolved from original isolated eutectic, discontinuous eutectic and continuous eutectic in three tested alloys, respectively. 2. Experimental The starting materials are metallic silver and electrolytic copper with at least 99.99% purity. The tested Cu–Ag alloys with the Ag contents 6, 12 and 24 wt.% were melted in a vacuum induction furnace and cast into rod ingots with 23.0 mm diameter in a copper mold. The ingots were homogenized at 700 ◦ C for 2 h and at 720 ◦ C for 2 h followed by furnace cooling. The homogenized ingots were turned off to 21.5 mm diameter in order to remove surface defects. Cold drawing was performed at ambient temperature. Drawing reduction is presented in terms of the logarithmic strain by η = ln(A0 /A) and referred as draw ratio, where A0 and A are the original and final cross-section area of the drawn specimens. The drawing process was interrupted at η = 1.3, 2.0 and 2.8 for intermediate annealing for 1 h at 400, 380 and 360 ◦ C, respectively. Optical microscopy, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were employed to observe the microstructure. The constituent concentration was determined by an energy-dispersive spectrometer of X-ray system (EDS) operating at 20 kV. Eutectic spacing was determined using standard stereographic intercept procedure [19]. The ultimate tensile strength was determined at ambient temperature with a strain rate of 2.0 × 10−4 s−1 . The electrical conductivity was measured at ambient temperature by the direct current four-probe technique. 3. Results and discussions

␣ dendrites besides small eutectic colonies dispersed between ␣ dendritic arms since the alloy has a low Ag content. The eutectic proportion rises with Ag content increasing. The eutectic colonies display extended branches in the Cu–12 wt.% Ag and continuous net-like structure surrounding ␣ dendrites in the Cu–24 wt.% Ag. The average spacing of ␣ dendritic arms is 13, 10 and 6 ␮m in the Cu–6 wt.% Ag, Cu–12 wt.% Ag and Cu–24 wt.% Ag, respectively. This observation on the change of the spacing of ␣ dendritic arms is slightly different from that in Ref. [10], where the spacing changed insignificantly with the Ag content from 7.5 to 35 wt.%. The reduced spacing of dendritic arms in the as-cast microstructure with high Ag content in our investigation can be attributed to the decreased pouring temperature or the quick freezing rate since the alloys with higher Ag contents have lower melting points. Moreover, it is possible that there was an extended constitutional supercooling layer in front of the liquid–solid boundary during solidification of the high Ag alloys, which should result in more secondary branches or smaller spacing of primary ␣ dendritic arms. The as-cast microstructure can be distinguished more clearly in Fig. 2. The eutectic colonies in the Cu–6 wt.% Ag should mainly be formed during non-equilibrium freezing process since 6 wt.% Ag is lower than the solid solubility limit (7.9 wt.% Ag) of Ag solute in Cu matrix at the eutectic temperature. The nonequilibrium eutectic fails to display the lamellar mixed structure of double phases or seems to show a divorced eutectic morphology since the amount and scale of non-equilibrium eutectic colonies are rather small in the alloy. In the alloys Cu–12 wt.% Ag and Cu–24 wt.% Ag, the lamellar mixture of double phases can be observed in larger eutectic colonies or thicker eutectic area. A small amount of non-equilibrium eutectic should also be included in the colonies and some thin eutectic colonies also tend to show the divorced morphology. The constituent concentration in ␣ dendrites and eutectic colonies in the as-cast microstructure is given in Table 1. The Ag concentration in ␣ dendrites in the Cu–12 wt.% Ag and Cu–24 wt.% Ag is obviously higher than that in the Cu–6 wt.% Ag. This indicates that non-equilibrium freezing results in a high supersaturation in Cu matrix in the as-cast alloys with the Ag contents higher than the solid solubility limit of Ag solute in Cu matrix. Moreover, the Ag concentration in eutectic colonies also slightly increases with Ag content increasing. Some secondary precipitates appear in ␣ dendrites of the homogenized alloys (Fig. 3). The precipitates should be formed during the furnace cooling after homogenization. For the homogenized Cu–6 wt.% Ag, the precipitates have a low volume fraction and a random distribution due to low degree of superTable 1 EDS test results of the constituent concentration (wt.%) in the as-cast microstructure Alloy

3.1. Microstructural evolution The microstructure of the as-cast alloys containing different Ag content consists of pro-eutectic ␣ dendrites and eutectic colonies (Fig. 1). The Cu–6 wt.% Ag is primarily composed of

Cu–6 wt.% Ag Cu–12 wt.% Ag Cu–24 wt.% Ag

Cu matrix

Eutectic

Cu

Ag

Cu

Ag

96 91 89

4 9 11

27 24 22

73 76 78

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Fig. 1. Optical microstructure of the as-cast alloys: (a) Cu–6 wt.% Ag, (b) Cu–12 wt.% Ag and (c) Cu–24 wt.% Ag.

saturation in the as-cast alloy with low Ag content. For the homogenized Cu–12 wt.% Ag and Cu–24 wt.% Ag, the precipitates have a relatively high volume fraction and a regular arrangement due to high degree of supersaturation in the as-cast alloys with middle or high Ag content (Table 1). The average diameter of the typical secondary precipitates observed in TEM is about 100 nm and the average spacing about 200 nm (Fig. 4). The selected area diffraction pattern (SADP) indicates that phases Cu and Ag have a cube-on-cube orientation relationship (1 0 0)Cu //(1 0 0)Ag and 0 1 1Cu //0 1 1Ag [20]. There exists steady elongation and refinement of the eutectic colonies and ␣ dendrites in the alloys drawn to η = 1.4 (Fig. 5). The eutectic colonies in the Cu–6 wt.% Ag and Cu–12 wt.% Ag are elongated from original separated islands to bars. The eutectic colonies in the Cu–24 wt.% Ag still keep original netlike structure but the net walls and net holes are elongated along

the drawing direction. The secondary precipitates should also be elongated and refined but they are too fine to be distinguished by optical microscopy. The eutectic colonies and ␣ dendrites in the alloys with a much higher draw ratio evolve into filamentary bundles (Fig. 6). The bundles shown on transverse section are basically made up of eutectic fibers and secondary Ag whiskers. Island- or netlike morphology can still be kept after heavy drawing for the alloys with different Ag content. The microstructure on longitudinal section of the three alloys is characterized with fine fibers arranged regularly. Filaments in the Cu–6 wt.% Ag show a more incompact and inhomogeneous distribution than those in other alloys. The eutectic filamentary bundles in the Cu–12 wt.% Ag and Cu–24 wt.% Ag tend to develop into the ribbons. The evolution behavior of the eutectic colonies and secondary precipitates during cold drawing is illuminated in Fig. 7

Fig. 2. FESEM microstructure of the as-cast alloys: (a) Cu–6 wt.% Ag, (b) Cu–12 wt.% Ag and (c) Cu–24 wt.% Ag.

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Fig. 3. FESEM microstructure of the homogenized alloys: (a) Cu–6 wt.% Ag, (b) Cu–12 wt.% Ag and (c) Cu–24 wt.% Ag.

in order to indicate the microstructure evolution from as-cast aspect to filamentary bundles more clearly. Since both of Cu and Ag belong to face-centered cubic structure and have the same slip system, they have similar stress–strain and work hardening behavior [12]. During cold drawing, ␣ dendrites and eutectic colonies are co-deformed and elongated along drawing direction. The eutectic colonies undergo axisymmetric deformation during cold working and therefore their morphology on transverse section has an insignificant change except shrinking during deformation. The eutectic spacing dependent on draw ratio is given in Fig. 8 for the tested alloys. The eutectic spacing in the Cu–6 wt.% Ag is remarkably larger than that in the Cu–12 wt.% Ag since the Ag content in the former is so low that only small eutectic colonies disperse between the ␣ dendritic arms (Fig. 1a). The eutectic spacing in the Cu–24 wt.% Ag is the smallest in all tested alloys since there is sufficient eutectic to form a contin-

uous net surrounding the ␣ dendritic arms (Fig. 1c). With draw ratio increasing, the difference of the eutectic spacing between three alloys decreases and tends to eliminate in strong strain range because all structural components in the microstructure have evolved into the filamentary morphology and the eutectic filamentary bundles can hardly be identified clearly from the fiber mixture. 3.2. Ultimate tensile strength The variation of ultimate tensile strength with draw ratio is shown in Fig. 9. With draw ratio increasing, the strength increases for the tested alloys. The Cu–24 wt.% Ag shows obvious hardening rate and high tensile strength since the alloy with high Ag content has a continuous net-like structure and small eutectic spacing. It is worth notice that low Ag alloy Cu–6 wt.% Ag exhibits the approximate strengthening to the middle Ag alloy Cu–12 wt.% Ag in the range of η < 4.5. However, the Cu–12 wt.% Ag has higher hardening rate than the Cu–6 wt.% Ag as η > 4.5. The strength of Cu–Ag microcomposites could be expressed using the composite model considering the strengthening contribution from Cu matrix and Ag fiber [10]: σcom = fCu (σwhCu + σCugrain ) + fAg (σwhAg + σAgfiber )

Fig. 4. TEM image and corresponding SADP of the homogenized Cu–12 wt.% Ag.

(1)

where fCu and fAg are the volume fractions of Cu and Ag phases, σ whCu and σ whAg are the strengths from work hardening of the Cu and Ag phases, and σ Cugrain and σ Agfiber are the strengths from structure refining. Two stages of the strengthening mechanism can be considered to be responsible for the change of hardening rate with draw ratio for the Cu–Ag microcomposites with different Ag content in present work. During the initial stage of working, Cu matrix and eutectic structure have sufficient scale to retain the dislocation substructure. The strengthening contributed from Ag phase in the Cu–6 wt.% Ag and Cu–12 wt.% Ag could be neglected

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Fig. 5. Optical microstructure on longitudinal section of the alloys drawn to η = 1.4: (a) Cu–6 wt.% Ag, (b) Cu–12 wt.% Ag and (c) Cu–24 wt.% Ag.

Fig. 6. FESEM microstructure of the alloys drawn to η = 6.0: (a) Cu–6 wt.% Ag on transverse section, (b) Cu–12 wt.% Ag on transverse section, (c) Cu–24 wt.% Ag on transverse section, (d) Cu–6 wt.% Ag on longitudinal section, (e) Cu–12 wt.% Ag on longitudinal section and (f) Cu–24 wt.% Ag on longitudinal section.

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Fig. 7. Schematic microstructure evolution of eutectic colonies and secondary precipitates during drawing for the tested alloys.

Fig. 8. Eutectic spacing dependent on draw ratio for the tested alloys.

Fig. 9. Ultimate tensile strength dependent on draw ratio of the tested alloys.

since fAg , compared with fCu , is very small in both alloys according to the strengthening mechanism of dislocation model. The strength is mainly contributed from strain hardening in Cu matrix or σ com is mostly dependent on σ whCu and σ Cugrain . Therefore, the Cu–6 wt.% Ag and Cu–12 wt.% Ag have the approximate strength since σ whCu and σ Cugrain in the Cu–6 wt.% Ag are similar to those in the Cu–12 wt.% Ag. Obviously high Ag content or continuous eutectic structure results in significantly fine ␣ dendritic arms or high σ Cugrain in the Cu–24 wt.% Ag than in the Cu–6 wt.% Ag and Cu–12 wt.% Ag. Moreover, relatively high volume fraction of Ag phase in the Cu–24 wt.% Ag produces a notable strengthening effect of phase mixture. σ Agfiber should be greater than σ Cugrain since the Ag phase has smaller scale than Cu dendrites while the value of σ whAg has been thought to be similar to that of σ whCu [10]. Therefore, the Cu–24 wt.% Ag exhibits higher strength level than the Cu–6 wt.% Ag and Cu–12 wt.% Ag. The elongated grains are too fine in diameter to maintain a steady dislocation substructure when the drawing strain reaches a sufficiently high level. Most dislocations can be absorbed to the grain boundary and phase interface [8,12]. The change of strengthening mechanism from dislocation model to interface obstacle model results in the presence of the second strengthening stage in high drawing strain range. The strengthening effect of the microcomposites in the second strengthening stage is mainly from the structure refining or σ com enhancing is mainly due to the increases of σ Cugrain and σ Agfiber . The Cu–12 wt.% Ag has smaller dendritic spacing and more phase interfaces than the Cu–6 wt.% Ag. This implies that there should be higher σ Cugrain and σ Agfiber in the former. Therefore, the Cu–12 wt.% Ag shows higher hardening rate or strength level than the Cu–6 wt.% Ag in the second strengthening stage. There are much smaller dendritic spacing and much higher interface density in the Cu–24 wt.% Ag than in the Cu–12 wt.% Ag and Cu–6 wt.% Ag. Therefore, the strengthening effect of

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Fig. 10. Electrical conductivity dependent on draw ratio of the tested alloys.

structure refining should be much significant in the Cu–24 wt.% Ag and results in high tensile strength and early appearance of the second strengthening stage. 3.3. Electrical conductivity The electrical conductivity of the tested alloys dependent on draw ratio is shown in Fig. 10. The increase of draw ratio results in the decrease of electrical conductivity for all tested alloys due to the increase of electronic scattering from lattice distortion or internal fault structure. The electrical conductivity and decaying tendency of the Cu–6 wt.% Ag are approximate to those of the Cu–12 wt.% Ag although the volume fraction of Ag phase in both alloys is different. However, the Cu–24 wt.% Ag with a continuous net-like eutectic shows an evidently low conductivity and relatively rapid decline with draw ratio increasing. The electrical resistivity of the two-phase microcomposites could be assumed as a combination of the individual resistivity of each phase [21,22]. In the present analysis, the contribution of two structure components, Cu matrix and Ag fiber, to the measured resistivity of the Cu–Ag microcomposites can be evaluated using a parallel-circuit model [21,22]: 1 ρCuAg

=

1 − fAg fAg + ρCu ρAg

(2)

where ρCu and ρAg are the electrical resistivities of Cu matrix and Ag fiber. It has been deduced that the electronic conduction in the microcomposites is primarily controlled by electronic transmission in Cu matrix [21]. The Cu–6 wt.% Ag and Cu–12 wt.% Ag can show an approximate electrical conductivity since both alloys have continuous Cu matrix or similar electron transmission in Cu matrix. The electronic transmission in the Cu matrix should be more difficult in the Cu–24 wt.% Ag than in other alloys since the Cu matrix separated by continuous netlike eutectic in the Cu–24 wt.% Ag has small dendritic spacing and contains a larger amount of Ag precipitates. Therefore, the Cu–24 wt.% Ag shows a low conductivity.

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Electrical resistance is mainly produced from electronic scattering at internal interfaces between Cu matrix and Ag phase [21]. With draw ratio increasing, the interface interval reduces or the interface density increases with the diameter of Cu and Ag fibers decreasing. Therefore, the electrical conductivity decreases due to increased contribution of interface scattering in the tested alloys. Moreover, much more phase interfaces in the Cu–24 wt.% Ag result in obvious decaying tendency of electrical conductivity. The electrical conductivity and strength in the Cu–12 wt.% Ag are similar to those in the Cu–6 wt.% Ag although there are more eutectic colonies in the former. This indicates that the eutectic volume fraction plays an insignificant effect on the microcomposite properties. However, the electrical conductivity and strength in the Cu–24 wt.% Ag are distinctly different with those in the Cu–12 wt.% Ag due to continuous net-like eutectic morphology. This implies that the eutectic morphology can play a more important role on the microcomposite properties than the eutectic amount. 4. Conclusions With Ag content increasing from 6 to 24 wt.% in the Cu–Ag filamentary microcomposites, the eutectic morphology changes from discontinuous islands to a continuous net and the precipitation morphology changes from random distribution to regular arrangement. During heavy cold drawing, the eutectic colonies are evolved into filamentary bundles with tight arrangement of double phases and the secondary precipitates into fine whiskers. With draw ratio increasing, the strength increases and the electrical conductivity decreases in the alloys. High Ag content in the alloys produces high tensile strength and work hardening rate but low electrical conductivity. In special, there exist distinct strengthening profit and electronic scattering effect when the Ag content is high enough to produce a continuous eutectic structure. The strengthening of the Cu–6 wt.% Ag depends mainly on the hardening of Cu matrix. The increased density of the interface between Cu matrix and eutectic colonies in the Cu–12 wt.% Ag produces an additional strengthening profit from the filamentary mixture in the range of strong drawing strain. Much more Ag precipitates and much higher interface density in the Cu–24 wt.% Ag result in the additional strengthening profit appearing at lower drawing strain. The effect of eutectic morphology on the strength and conductivity is more important than the eutectic volume fraction in the Cu–Ag microcomposites with the Ag contents (6–24) wt.%. Acknowledgement The project is supported by the National Natural Science Foundation of China (Grant No. 50371076). References [1] Y. Sakai, K. Inoue, H. Maeda, Acta Mater. 43 (1995) 1517–1522. [2] Y. Sakai, H.J. Schneider-Muntau, Acta Mater. 45 (1997) 1017–1023.

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[3] M. Motokawa, H. Nojiri, S. Mitsudo, Y. Inamura, IEEE Trans. Magn. 32 (1996) 2534–2537. [4] M. von Ortenberg, O. Portugall, N. Puhlmann, H.U. Mueller, M. Barczewski, G. Machel, M. Thiede, Physica B216 (1996) 158–161. [5] H. Maeda, K. Inoue, T. Kiyoshi, T. Asano, Y. Sakai, T. Takeuchi, K. Itoh, H. Aoki, G. Kido, Physica B216 (1996) 141–145. [6] J.E. Crow, D.M. Parkin, H.J. Schneider-Muntau, N.S. Sullivan, Physica B216 (1996) 146–152. [7] Y. Sakai, K. Inoue, T. Asano, H. Wada, H. Maeda, Appl. Phys. Lett. 59 (1991) 2965–2967. [8] S.I. Hong, M.A. Hill, Acta Mater. 46 (1998) 4111–4122. [9] S.I. Hong, M.A. Hill, Y. Sakai, J.T. Wood, J.D. Embury, Acta Mater. 43 (1995) 3313–3323. [10] A. Benghalem, D.G. Morris, Acta Mater. 45 (1997) 397–406.

[11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]

W. Gr¨unberger, M. Heilmaier, L. Schultz, Z. Metallkd. 93 (2002) 58–65. G. Frommeyer, G. Wassermann, Acta Metall. 23 (1975) 1353–1360. L. Zhang, L. Meng, J.B. Liu, Scripta Mater. 52 (2005) 587–592. L. Zhang, L. Meng, Mater. Sci. Technol. 19 (2003) 75–79. L. Zhang, L. Meng, Mater. Lett. 58 (2004) 3888–3892. J.B. Liu, L. Meng, Mater. Sci. Eng. A418 (2006) 320–325. W.B. Lee, E.H. Yoon, S.B. Jung, J. Mater. Sci. Lett. 22 (2003) 1751–1754. A. Gaganov, J. Freudenberger, W. Gr¨unberger, L. Schultz, Z. Metallkd. 95 (2004) 425–432. E.E. Underwood, Quantitative Sterology, Addison-Wesley, 1970. K. Han, A.A. Vasquez, Y. Xin, P.N. Kalu, Acta Mater. 51 (2003) 767–780. L. Zhang, L. Meng, Scripta Mater. 52 (2005) 1187–1191. J.D. Verhoeven, H.L. Downing, L.S. Chumbley, E.D. Gibson, J. Appl. Phys. 63 (1989) 1293–1301.