Structures, properties and responses to heat treatment of melt-spun Cu-La alloys

Copper alloys containing up to 15wt% La were prepared by melt spinning into ribbons of thickness between 30 to 100 μm. The melt-spun ribbons were heat treated for up to 2h and 800°C. Microstructures were of the typical Zone B type for Cu-1La and Cu-3La and of the Zone A/Zone B type for Cu-5La and Cu-8La ribbons. Only microstructures of the Zone A type was found in Cu-15La ribbon. The metastable extended solid solubility of La in Cu was evaluated by measurements of the lattice parameters of the supersaturated solid solution and significant extension from the equilibrium solid solubility was found. The secondary phase was identified by XRD and TEM as Cu₆La except Cu-15La ribbons in which the metastable Cu₅La and Cu₁₃La phases were also present. Results of TEM and XRD also showed the reduction in αCu grain size of the as-spun ribbons with alloying content, producing nano-sized αCu grain on the chill side of the ribbons. Both αCu and Cu₆La grains coarsened as a result of heat treatment for 2h at temperatures 600°C and above for all the compositions. The Hall-Petch plot of the annealed ribbons were also plotted and discussed.