The epitaxial growth of nickel-copper surface alloys on a copper substrate is studied by high energy ion scattering. Nickel has been deposited by decomposition of nickel carbonyl on the (100) surface of copper at an elevated temperature. The composition of the grown overlayers is measured by glancing angle Rutherford backscattering spectroscopy. The morphology is investigated by ion channeling. The samples are studied after exposure as well as after subsequent annealing. In addition, LEED and AES are used as complementary techniques. It is found that an overlayer with a thickness of about ten monolayers is a surface alloy: it contains about equal amounts of well mixed nickel and copper. The strain in this surface alloy is equal to the strain expected for pseudomorphic layer growth. A much thicker overlayer contains only a few percent copper and has grown epitaxially; however, there are many defects present at the interface. The strain in this surface alloy exceeds the equilibrium strain, but this excess disappears by annealing. The thick surface alloy is broken apart into separate regions, which causes rapid interdiffusion during annealing.@en