Professor René Wasserman Award 2010 - Favez Denis

"For an outstanding contribution in the field of joining dissimilar materials by laser welding, that combines experimental investigations at multiple scales and an in-depth analysis of phase transformations and processes."

Soudage laser or-acier : métallurgie et procédé.

In jewelry manufacturing, joining dissimilar materials is usually achieved by brazing or soldering. These methods have however several disadvantages, including undesired phases transformations of the base metals during heat treatment. An alternative technology is laser beam welding. A laser beam is able to melt locally the interface without affecting the bulk microstructure. With this method, however, a thorough understanding of the solidification microstructure is required.
In this project, the process of laser welding an 18 carat yellow gold to a superaustenitic stainless steel has been studied and developed. First, a fundamental metallurgical analysis of the gold-steel system was carried out, partially based on the peritectic Au-Fe elemental system, using Differential Thermal Analysis (DTA) and directional solidification in a Bridgman-type furnace. By combination of these observations, the microstructure formation in gold-steel welds could be explained. Following this, a concept for gold-steel welding has been proposed and successfully tested.
This thesis has also shown that a fundamental metallurgical approach is a powerful tool for complex welding development. It allows not only to develop a viable industrial solution, but also to acquire a knowledge that can be used to expand the process to other materials or different geometries.