Surface Alloying in Stainless Steel and Ni--20Fe by Pulsed Laser Irradiation

Surface alloys have been produced by pulsed laser irradiation of thin metal overlayers (Au and Mo) on austenitic stainless steel and Ni--20Fe. The structure and composition of the surface alloys have been characterized by Rutherford backscattering and ion channeling. The stainless-steel alloy has a thin surface layer with nonsubstitutional Au or Mo on top of the substitutional alloy. Metastable solid solutions of Au are formed with concentration levels as high as 5 at.% in stainless steel and 28 at.% in Ni--20Fe. The laser alloying process involves surface melting and, in some cases, the formation of approx 1- mu m-high ridges. The quality of the epitaxial regrowth, as seen in the channeling spectra, ranges from good to very poor. Dechanneling in the alloyed surface has a complex behavior and is dependent on the energy density used for the irradiation. It is also important whether or not the irradiation is carried out in air or in flowing helium. The use of flowing He instead of air has a striking reverse effect on the two alloy systems; it reduces the lattice disorder of alloys formed by Au and stainless steel, while an increase in disorder is seen when Au is alloyed with Ni--20Fe. 19 ref.--AA