Effects of Ni addition on the microstructure and properties of nanostructured copper–germanium alloys
Graphical abstract
Highlights
► The effects of Ni on the structural evolution of nanocrystalline Cu–Ge alloys were investigated. ► Ni addition resulted in diminishing the crystallite and particle sizes during mechanical alloying. ► Ni addition resulted in postponing the nanocrystallization transition during heat treatment. ► Excellent thermal stability was demonstrated at high temperatures. The mechanism was proposed.
Introduction
Over the past two decades, copper–germanium alloys have received a great deal of attention on account of their outstanding semiconducting properties, which is an indispensable property required for electrical and electronic applications. Recently, it has become increasingly important to develop novel semiconducting and dielectric materials with enhanced performance [1], [2], [3], [4], [5], [6], [7], [8], [9]. The most facile and practicable method for developing the new alloys of interest is adding alloying elements to the binary Cu–Ge alloys. Depending principally on the desired properties and functionalities, a variety of alloying elements have been utilized in the ternary Cu–Ge-X alloys including Sn [10], Mn [10], [11], [12], Fe [12], [13], [14], Co [12], Ni [12], [15], [16], [17], [18], Ag [19], [20], [21], Al [22], Te [23], Se [24], Si [25], [26], Tl [27], Ga [28], Tm [29], Au [30] and Ce [31]. Among these elements, transition metals like Ni are significant mainly due to their properties such as compatibility, relatively low cost, and availability.
Ternary Cu–Ge–Ni alloys were first investigated by Bochvar et al. [16] and Burkhardt and Schubert [17] on a partial isothermal section at 500 °C. Cockayne and Raynor [12] assessed the effect of Ni addition on the lattice constants of the ζ−Cu5Ge phase. Recently, Cornish and Watson reviewed all previous studies on this ternary system [15]. However, no further systematic study is reported in the literature on Cu–Ge–Ni alloys, especially on the effects of adding Ni to nanocrystalline Cu–Ge alloys. As an attempt to establish a promising direction for further developments in the field, the present research work was designed to explore the effects of Ni on the microstructure and various properties of nanostructured copper–germanium alloys.
Section snippets
Materials processing
High purity elemental powders of Cu, Ni, and Ge with average particle sizes of 10, 10 and 5–20 μm, respectively, were subjected to high energy ball milling in a Fritsch P6 planetary ball mill using 10 mm WC balls and vial to form the Cu84Ge16−xNix (x = 0, 1, 3 and 5 wt.%) compositions. We will refer to the four alloys by their nominal Ni addition throughout the current article, as presented in Table 1. A ball to powder ratio (BPR) of 10:1 was maintained and milling speed was kept at 300 rpm for
XRD studies
The XRD patterns of the four study alloys after different MA times are presented in Fig. 1 (a–d) in which the diffraction peaks of the initial materials can be clearly seen. According to this Figure, the diffraction peaks weakened and broadened gradually with milling time. However, as shown in all the XRD patterns, the intensity of Ni and Ge elements diminished more rapidly than those of Cu, which can be attributed to the negligible solubility of Ni in Ge structure, whereas Ge can be highly
Conclusion
In this study, adding Ni to binary Cu–Ge alloys by means of MA, and the subsequent annealing were investigated. It was found that increasing Ni content in the alloys leads to such consequences as suppressing the formation of the intemetallic phase during MA, reducing the driving force for nanocrystallization during subsequent annealing, and decreasing the crystallite size of the alloys; hence, the high thermal stability of the Ni containing Cu–Ge nanostructured alloys prepared. Furthermore, it
Acknowledgement
ARK would like to thank Asma Rezaei for her valuable contribution to this project.
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Present address. School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran.