In Dynamic Recoil Mixing (DRM) a film of constant thickness is sputtered on to a substrate by using a broad low energy (lkeV) ion beam and is subsequently bombarded by a high energy (10 key) ion beam. During the bombardment process a dynamic balance is maintained between the backsputtering and the deposition of the film, thus providing an ‘unlimited’ source of the dopant material. In this way very high surface dopant concentrations may be achieved which otherwise cannot be reached by more conventional ion beam mixing techniques. Furthermore, by choosing reactive ion species, films of novel chemical compositions may be produced. This technique has been employed to produce silicon nitride films on polished commercial mild steel samples. Measurements of knoop hardness of these films indicate an increase of over 200% whilst the wear and friction properties have shown considerable improvement. Conventionally sputtered silicon films of similar thickness, recoil mixed silicon using argon, or implantation of 10 keV argon and nitrogen to similar doses, indicate only a modest change in tribological characteristic compared to the reactive mixed films.