Seripta METALLURGICA Vol. 23, pp. 1281-1284, 1989 Pergamon Press plc Printed in the U.S.A. All rights reserved ON THE NICKEL-RICH NICKEL-GERMANIUM SOLID SOLUTION I. Rama Brahman+, A.K. Jena+ and M.C. Chaturvedi # + Department of Metallurgical Engineering Indian Institute of Technology,Kanpur, India # Department of Mechanical Engineering University of Manitoba, Winnipeg, Canada R3T 2N2 (Received February 22, 1989) (Revised May 16, 1989) Introduction The nickel-rich nickel-germanium solid solution has large solubility for germanium (1). Unusual variations of the properties of the solid solution are suggested by the lattice parameters reported by Pearson and Thomson (2). However, lattice parameters reported by two other investigators (3,4) suggest other possibilities. Pearson and Thomson (2) show that the lattice parameter increases with germanium content at first with decreasing rate and later with increasing rate, whereas according to Lecocq (3) the lattice parameter increases at first with increasing rate and later with decreasing rate. Klement (4), on the other hand, reports linear variation of lattice parameter with composition. In this investigation the unusual behaviour of the solid solution has been examined in terms of its lattice parameter and microhardness. Nickel-germanium alloys containing 1.95, 4.94, 8.03, 10.92 and 14.35 at%Ge were prepared by arc melting 99.99% pure nickel and germanium in water cooled copper hearths under purified argon atmosphere using a nonconsumable tungsten electrode. One alloy containing 17.1 at%Ge was also prepared by induction melting. The alloys were sealed in quartz tubes under vacuum and homogenized at ll00"C. Metallographic and X-ray measurements after several cycles of annealing confirmed homogeneity of the alloys. For ageing and strain relieving the specimens were also sealed under vacuum in quartz tubes. Metallographic specimens were etched in a solution of nitric acid, glacial acetic acid and water in the ratio 2:1:1 by volume. The specimens were examined and some of the phases present in the specimens were analysed by SEM. The microhardness values were determined in a Leitz microhardness tester with a load of 10g. The average of at least ten measurements made at the grain centres was calculated. Lattice parameters of the alloys were determined from the diffractometer tracings obtained with strain relieved powder samples. Silicon was used as the standard. The values of 'a' were obtained by Nelson-Riley extrapolation. All measurements were made at 21+-1"C. Results and Diseq~sion Corcmosition Dependence of Lattice Parameter: The lattice parameters of the alloys are listed in Table 1. The lattice parameter of pure nickel, 3.5239 x 1010m, measured in this investigation is in excellent agreement with literature values of 3.5238 x 1010m (2), 3.52415 x lO10m (5,6), 3.52405 x 1010m (7) and 3.52375 x 1010m (8). Fig. 1 shows that the lattice parameter of the solid solution increases initially with decreasing rate and at higher concenu'ations of germanium with increasing rate. Although such behaviour is unusual, this is supported by the results of Pearson and Thomson (2). The lattice parameters reported by Lecocq (3) are generally lower. The results of Klement (4) obtained with splat-cooled alloys may not have high accuracy. TABLE 1. Lattice Parameters of Nickel-rich Nickel-Germanium Solid Solution at 21"C. Composition, at%Ge 0.00 1.95 4.94 8.03 10.92 14.35 Lattice Parameter, 1010m 3.5239 3.5298 3.5346 3.5400 3.5454 3.5556 1281 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc