Article

Metallurgical and Materials Transactions A

, Volume 40, Issue 7, pp 1701-1709

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Sodium Borohydride Reduction of Aqueous Silver-Iron-Nickel Solutions: a Chemical Route to Synthesis of Low Thermal Expansion–High Conductivity Ag-Invar Alloys

  • E.A. SterlingAffiliated withDepartment of Mechanical Engineering and Materials Science, Franklin W. Olin College of Engineering
  • , J. StolkAffiliated withDepartment of Mechanical Engineering and Materials Science, Franklin W. Olin College of Engineering Email author 
  • , L. HaffordAffiliated withDepartment of Mechanical Engineering and Materials Science, Franklin W. Olin College of Engineering
  • , M. GrossAffiliated withDepartment of Chemical Engineering, Bucknell University

Abstract

Thermal management is a critical concern in the design and performance of electronics systems. If heat extraction and thermal expansion are not properly addressed, the thermal mismatch among dissimilar materials may give rise to high thermal stresses or interfacial shear strains, and ultimately to premature system failure. In this article, we present a chemical synthesis process that yields Ag-Invar (64Fe-36Ni) alloys with a range of attractive properties for thermal management applications. Sodium borohydride reduction of an aqueous Ag-Fe-Ni metal salt solution produces nanocrystalline powders, and conventional powder processing converts this powder to fine-grained alloys. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy, thermomechanical analysis, and electrical conductivity measurements; thermal conductivity is estimated using the Wiedemann–Franz law. Sintering of Ag-Fe-Ni powders leads to the formation of two-phase silver-Invar alloys with low coefficients of thermal expansion (CTEs) and relatively high electrical conductivities. A sample of 50Ag-50Invar exhibits a CTE of 8.76 μm/(m· °C) and an estimated thermal conductivity of 236 W/(m·K). The Ag-Invar alloys offer thermodynamic stability and tailorable properties, and they may help address the need for improved packaging materials.