Pulsed YAG laser welding of ODS alloys

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Abstract
The probelm of joining ODS alloys by welding for high temperature use has limited their application in industry. To date, all wedling processes employed have resulted in loss of dispersoid through agglomeration or slagging off and the development of grain boundaries perpendicular to the existing structure of the material. Pulsed laser welds of ODS INCOLOY alloy MA 956 have been examined for morphology and distribution of dispersoid by x‐ray and transmission electron microscopy. The results indicate that the dispersoid remains suspended in the alloy without agglomeraaing or floating out of the fusion zone. Grain boundary formation perpendicular to the existing structure can also be corrected by use of the laser beam and proper joint design. Due to the strong preferred orientation of the ODS alloys, the fusion zone in a laser weld solidifies epitaxially from the side walls of the weld cavity to within a narrow zone of the weld centerline, which is comprised of equiaxed grains. If the weld cavity is oriented properly, the epitaxial growth will orient the grains parallel to the base metal structure. The only grain boundaries to form perpendicular to the base metal structure will be those equiaxed grains which form at the weld centerline. Properly oriented pulsed YAG laser welds of ODS alloys have resulted in retention of a large portion of the high temperature properties of the base alloy.

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