Effect of MeV ion irradiation on the coefficient of thermal expansion of Fe–Ni Invar alloys: A combinatorial study

The effect of low-dose MeV ion irradiation on the thermal conductivity and coefficient of thermal expansion (CTE) of Fe–Ni alloys has been studied over the entire composition range using a combinatorial method. With our experimental precision of ±5%, the thermal conductivity of Fe–Ni alloys is unchanged by 2.3MeVAr+ irradiation at a fluence of 1.2×1014ionscm-2. The CTE of Fe–Ni Invar alloys with Ni concentrations between 30 and 37 at.% increases significantly upon 2.3MeVAr+ irradiation. At the Invar composition of Fe65Ni35Fe65Ni35, the CTE increases from 0.5×10-6K-1 before ion irradiation to 4.3×10-6K-1 after irradiation for an ion fluence of 1.2×1014ionscm-2 or, equivalently, 0.1 displacements per atom. We attribute this increase in CTE to changes in atomic short-range order created by ion irradiation.