Invar-type nanocrystalline compacts obtained by spark plasma sintering from mechanically alloyed powders

Invar36 (Fe₆₄Ni₃₆) and Invar-Cu (Fe₅₉Ni₃₆Cu₅) nanocrystalline compacts were successfully obtained by spark plasma sintering from mechanically alloyed powders. The coefficient of thermal expansion (CTE) was determined for both Invar36 and Invar-Cu compacts. For Invar36 powder, the lattice parameter value is constant up to 250 °C, while for the Invar-Cu powder, the value of lattice parameter changes for the temperatures that exceed 160 °C. Both Invar36 and Invar-Cu nanocrystalline compacts were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and dilatometry. The value of CTE is very low for both Invar36 compact (α = 0.6 × 10⁻⁶/°C) and Invar-Cu (α = 5.2 × 10⁻⁶/°C) up to Curie temperature (T _C), in agreement with in situ (high-temperature X-ray diffraction—HT-XRD) analyses of Invar-type powders.