Melting Behavior of Al/Pb/Sn/Al Multilayered Thin Films
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SOLID thin films are finding more and more technological applications. In this context, the thermal stability of the thin films is a major concern for the future development.[1] The modern applications require the thickness of the solid thin film in nanometric range. As the thickness of the films deceases to nanometric scale, the underlying surfaces as well as interfacial area become too large.[2–5] Therefore, the thermal stability of such a low-dimensional system against phase transformation relative to their bulk counterpart is of critical concern.[6,7] The phase transformation behavior of thin films can effectively be understood by studying the melting and solidification behavior. It is well known that the melting point of any low-dimensional solids such as free nanoparticle is considerably lower relative to the equilibrium melting point whereas the embedded nanoparticle exhibits superheating that has been explained by experimental and theoretical approaches.[1,8–12] It has also been reported that the melting point of the nanoscaled thin films decreases with the reduction of the film thickness.[4,13] Novel technological applications demand further reduction of the film thickness and thus make the thermal stability of these nanostructured material a major obstacle for potential usage.[2] TherePATAN YOUSAF KHAN and M. MANOLATA DEVI, Ph.D. Students, and KRISHANU BISWAS, Associate Professor, are with the Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India. Contact e-mail: [email protected] Manuscript submitted April 6, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
fore, there is a need to devise novel strategies to improve thermal stability of the thin films. There have been few reports in the literature on such strategies.[2,7] Lu et al. have shown that it is possible to achieve even superheating in thin films with epitaxial interfaces by suppression of the melt growth during melting.[7] By confining Pb thin films in Al layers using repeated cold rolling of sandwiched Al/Pb/Al as well as magnetron sputtering, these authors have reported maximum superheating of 80 K (or 80 C) for 6 nm Pb layers sandwiched between Al layers. Huge superheating is explained by suppression of the melt growth between the epitaxial layers during melting.[2,5] It has been suggested that the role of the epitaxial interfaces in case of Al/Pb/ Al multilayer thin film is mainly to suppress the melt growth.[1] The present investigation is primarily aimed to probe this effect on alloys. As the alloy thin films are more widely used in various technological applications, it is worth to understand the effect and devise strategies to make these thin films thermally stable. Therefore, the multilayered thin films of Pb/Sn in Al have been prepared by accumulated roll bonding (ARB) process to study the effect of increased interfacial area on the phase transformation of Pb/Sn sandwiched layers. It is to be noted that ARB is one of the severe plastic deformation (SPD) techniques, normally utilized to fabricate mate
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