An improved gas nozzle for laser surface alloying

An experimental research project was undertaken to characterize the flow field surrounding the molten metal during laser alloying. In addition, an objective of this project was to design a protective gas nozzle system for laser alloying that would control the entrainment of the outside gas, provide a gentle pressure to the molten metal and not adversely effect the alloying process.; Existing nozzle geometries were selected for evaluation in a water tunnel simulation. The water tunnel simulation visualized a complex, three-dimensional oblique flow field, which was created by the Nd:YAG's optics/gas delivery package being configured 15 degrees from normal to the work surface to prevent reflection back into the optics. From the water tunnel simulation two geometries were characterized in gas trials with argon, nitrogen and helium gases. A convergent (conic) geometry and divergent geometry were evaluated by measuring the pressure field and oxygen content impinging on an instrumented flat plate. A divergent nozzle geometry was used in creating laser alloyed surfaces, and those surfaces were examined for oxygen content.; The water tunnel simulation provided general knowledge about the oblique jet impingement flowfield (with its recirculation zones and entrainment patterns), nozzle geometry selection (the 7 degree simple divergent), and the revelation about the unsteady swirling motion feeding into the nozzle entrance and proceeding through the entire flowfield. The water tunnel results suggest that possible improved protection of the molten metal can be achieved by changing the processing direction of the laser beam, providing a shroud gas around the jet, and improving the flow quality before the nozzle entrance. The gas trials verified the flow patterns seen in the water tunnel simulation, and provided more specific flowfield details (impingement pressure profiles and percent oxygen profiles) with three gases helium, argon, and nitrogen. The laser alloy surfaces created were analyzed by Scanning Auger Microprobe, which could not provide definitive percent oxygen measurement.