An interaction between a stainless steel (AISI 316) substrate holder and an Al 2011 substrate occurred during plasma nitriding at similar to575 degreesC. The interaction layer formed was similar to100 mum thick, with a hardness of 850 HV and was composed of Al, Cu, Fe, Ni and Cr, suggesting diffusion from the steel holder into the Al substrate. Prior to the plasma treatment the hardness of the Al substrate was 122 HV. While some interaction occurs on heating in the absence of plasma, the presence of plasma under otherwise identical conditions significantly enhances this interaction. The application of a sample voltage bias did not affect the formation of this layer. However, on plasma treatment at lower temperatures (500 degreesC), no layer was formed. (C) 2002 Elsevier Science B.V. All rights reserved.