Effect of annealing and process parameters on microstructure and properties of DC Magnetron Sputtered Ni-Zr alloy thin f
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Effect of annealing and process parameters on microstructure and properties of DC Magnetron Sputtered Ni-Zr alloy thin films Bibhu P. Sahu, Rahul Mitra Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, 721302, West Bengal, India
ABSTRACT Ni-Zr alloy thin films were processed by DC magnetron sputtering of high purity Ni and Zr targets in ultrahigh vacuum at ambient temperature, with the substrate being subjected to either 0 V or -60 V bias. Some of the as-deposited films were annealed in vacuum at 700oC for 1 h. Surface profilometer and atomic force microscope were used to measure the film thickness and surface roughness, respectively. X-ray diffraction and cross-sectional TEM analysis have shown dispersion of nano-sized Ni3Zr dispersed in nanocrystalline Ni matrix. Nano-indentation and scratch tests conducted at 2 mN load have shown variation of hardness, Youngs modulus, scratch resistance, and coefficient of friction with substrate bias and annealing due to changes in grain size and surface roughness. INTRODUCTION Thin films of Ni-Zr alloy have been found to be attractive because of the possibility of their growth with both crystalline and amorphous structure depending on the composition. A recent study by Turnow and co-workers [1] has shown that the binary Ni-Zr alloy thin films prepared by dc magnetron sputtering possess amorphous structure for compositions having 16-93 at. % Ni. Magnetron co-sputtering of multiple targets for deposition of alloy thin films has now become most convenient way of processing, because it allows a wide range of compositions to form. Here, the desirable purity of the films is easily achieved by use of high purity targets and Ar gas for sputtering. The Ni-Zr alloy films have been investigated for application in fuel cells, biomedical industries, stressed atomic force microscopy probes, and most importantly in nuclear reactor engineering, as well as for hydrogen storage and separation [2]. The amorphous Ni-Zr alloy films have been found to undergo crystallization on annealing at temperatures in the range of 650-750oC [3]. Crystallization of these films leads to the formation of Ni-Zr based binary intermetallic phases like Ni3Zr, which possess higher hardness, as well as greater resistance to both wear and corrosion compared to that of pure Ni, and therefore could be used as nanocomposite protective coatings [4, 5]. Furthermore, nanocrystallinity of the Ni-Zr alloy films is preferred for better hydrogensorption properties, and use for hydrogen storage [6]. The scope of the present study includes processing of nanocrystalline Ni-Zr alloy films by dc magnetron co-sputtering of high purity Ni and Zr targets with or without substrate bias, annealing of the as-deposited films at 700oC, study of microstructure using scanning and transmission electron microscopy, as well as evaluation of surface roughness, nanoindentation hardness, Youngs modulus, and scratch resistance.
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