X-RAY-DIFFRACTION STUDY OF RESIDUAL-STRESS MODIFICATION IN CU/W SUPERLATTICES IRRADIATED BY LIGHT AND HEAVY-IONS

The effect of low temperature ion irradiation on the residual stress state was studied as a function of the ion fluence in Cu/W superlattices prepared by ion beam sputtering. The residual stress tensor in tungsten layers is completely determined from X-ray diffraction data using the ''sin2psi method''. In the as-prepared state, the Cu/W superlattices are strongly strained, and we find in-plane compressive stresses as high as 6.4 GPa in tungsten layers. Relaxation of the stress state is observed after low temperature ion irradiation with increasing dose. This phenomenon is almost complete for doses as low as 0.1-0.2 dpa, and appears related to atomic rearrangement in the elemental layers rather than interfacial mixing. The role of the incident particle mass is also evidenced. Per dpa, heavy ion irradiation (Kr) induces the strain relaxation more quickly than light ions (He).