Rapidly Solidified High‐Strength Invar 36 Prepared by Planar‐Flow Melt Spinning

Invar 36 combines an exceptionally low coefficient of thermal expansion (CTE) with limited hardness, which restricts its use in mechanically demanding precision applications. Here, planar‐flow melt spinning was used to refine the microstructure without changing the nominal alloy composition. Four combinations of wheel speed (20 and 40 m s −1 ) and nozzle–wheel gap (0.30 and 0.60 mm) were investigated in five repeated runs, producing local ribbon thicknesses of 20–160 μm. X‐ray diffraction confirmed a single‐phase face‐centered‐cubic austenitic structure in both the as‐cast alloy and the wheel side of a 30 µm ribbon, while changes in relative peak intensities were consistent with processing‐induced texture. Electron backscatter diffraction (EBSD) revealed a heterogeneous coarse‐grained as‐cast microstructure and an average grain size of approximately 1 μm in the 30 μm ribbon cross‐section. Microhardness increased from approximately 180 HV for the as‐cast alloy to approximately 590 HV for the 20 µm ribbon. Nanoindentation showed a smaller change in indentation modulus, from approximately 140 to 132 GPa. The CTE of the 30 μm ribbon was 3.1 × 10 −6 /°C over 25–150 °C, compared with 2.2 × 10 −6 /°C for the as‐cast alloy. These results demonstrate that melt spinning can markedly increase the hardness of Invar 36 through microstructural refinement, although the accompanying changes in thermal and elastic response must be considered.