Formation And Modification Of Surface Alloys By Excimer Laser Melting And Resolidification

Abstract

The use of pulsed lasers operating in the ultra-violet for the formation and modification of metal alloys opens a range of processing techniques which offer the precision of ion beam techniques but at much higher processing rates. In addition, excimer laser surface processing offers the possibility of new surface modification technologies. Most metals have low reflectivities in the uv, so laser light is coupled strongly to the surface. The short pulse length of these lasers, along with a shallow absorption depth, results in a heated zone which is also quite shallow, of the order of 1 micrometer. Modest fluences, of the order of 1 J-cm{sup {minus}2} are sufficient to melt this surface zone. Typical quench rates from the melt are of the order of 10{sup 10} K-sec{sup {minus}1}; high enough to produce amorphous phases in some materials. Mixing by liquid phase diffusion between layers of vacuum evaporated materials and zone refinement can result from multiple melt resolidification events. These techniques make available a large range of alloy compositions on engineering materials. The surface morphology of the processed layers is quite smooth with a surface finish less than 100 nm. Further processing prior to use is therefore not required for mostmore » applications. We have studied laser mixing of metals into engineering materials, both metal alloys and ceramics, the formation of ceramic structures on metals, the modification of alloys by surface zone refinement, and the mixing of binary and ternary multilayer structures. 25 refs., 6 figs., 2 tabs.« less