Characterization of Invar Syntactic Foams Obtained by Spark Plasma Sintering

This study presents the synthesis of sintered composite foams based on the Invar alloy (64Fe-36Ni), using hollow spherical particles from a nickel superalloy (NiCrSiB) in order to generate porosity. The Invar powder was obtained by mechanical alloying (MA), and the NiCrSiB hollow spherical particles were incorporated into the composite at 20 vol %. The sintering was realized using the spark plasma sintering (SPS) process in an argon atmosphere at 600 °C and 5 MPa, with 10 s holding time. The porous structures were structurally characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The coefficient of linear thermal expansion (CTE) of the Invar/NiCrSiB syntactic foams was found to be 2.52 × 10−6 °C−1 in the 25–150 °C temperature range and 19.68 × 10−6 °C−1 in the 150–400 °C range.