Invar® Disk

Invar® Disk (Fe64/Ni36, UNS K93600) is the near-zero thermal expansion alloy in a ready-to-use precision circular geometry, offering a coefficient of thermal expansion of 1.7–2.0 × 10⁻⁶ K⁻¹ alongside a density of 8 g/cm³, modulus of 140–150 GPa, and tensile strength of 450–590 MPa in a dimensionally stable substrate suited to precision optical, metrological, and structural applications. The disk geometry directly suits its primary uses: optical mirror substrate blanks for telescope secondaries and laser cavity mirrors where thermal cycling between ambient and operating temperature would defocus or misalign a higher-CTE substrate; reference masses in absolute gravimetry where long-term dimensional stability under ambient temperature fluctuation is essential to measurement traceability; and structural spacers and mount elements in interferometric instruments, where the disc must hold separation distances constant across the environmental temperature range of the laboratory. The Curie temperature of 279 °C marks the upper service limit of the low-CTE behaviour, beyond which the magnetovolume effect responsible for the anomalous expansion dissipates. Below this limit and across the cryogenic range, the dimensional stability is maintained, supporting use in cryogenic dewar structural elements and superconducting magnet assembly components where thermal contraction mismatch between components is a design constraint. In research, Invar discs are used as precision substrate platforms for thin-film deposition trials, tribological test specimens, and reference samples in thermal expansion characterisation studies.