Thin single crystal copper specimens (thickness ~250 nm) containing coherent iron particles (diameter 40–50 nm) have been bombarded with argon ions (5, 80, and 330 keV). During this process some of the iron particles transform to martensite. The transformation was observed near the exposed surface and sometimes also close to the other surface but never in between. This is interpreted in terms of mechanical waves starting from the impact area. Journal of Applied Physics is copyrighted by The American Institute of Physics.