[en] The unidirectionally solidified microstructure of the Ni--Nb eutectic alloy consists of alternate lamellae of Ni₃Nb (delta) and Ni--Nb solid solution (γ) phases. Nb has a solubility limit in γ phase that decreases with temperature, suggesting the possibility of obtaining additional delta phase and strength via precipitation processes. To this end, the microstructure, γ phase lattice parameter and microhardness of the aligned composite were examined in the as-grown, solution treated (ST), and ST + aged conditions. Little precipitation was found after a ten hour 1000⁰C aging treatment in the as-grown ingots. However, approximately 12 vol percent of Widmanstatten delta precipitates--[111]/sub γ/ habit planes--was produced after a 1220⁰C solution treatment followed by short time aging at 1000⁰C. Considerable precipitation was found also after longer time aging at 800⁰C. Lattice parameter measurements indicate the γ phase to be in a metastable, supersaturated condition. Upon ST + aging, the γ lattice parameter decreases slightly, reflecting the Nb loss associated with delta precipitation. The remaining solubility of Nb in γ is compared with previously reported results. The microhardness of the composite was determined as a function of heat treatment and found to increase with increasing vol percent of delta (original lamellae + precipitates). A significant precipitation hardening effect was noted for the ST + 800⁰C aging treatment with hardness measurements suggesting a substantial increase in yield strength