The intense heat sources associated with laser processing of materials often affect the microstructure of the part being processed. For example, in laser beam welding, the resulting high cooling rates tend to produce brittle microstructures in high hardenability materials. Such materials are normally pre-heated before welding and may also be subjected to post-weld heat treatment. Conventional pre-heating and post-weld heat treatment are often either too expensive or impractical to use. Such heat treatments reduce productivity and may affect other parts of the material. To eliminate these problems, the researcher's will investigate the split-beam laser welding concept, where the laser beam will be split into two, resulting in a dual heat source. The leading minor source will pre-heat the material while the major source will be used for the actual welding. This pre-heat by the leading source will achieve the lower cooling rate induced by conventional pre-heating in a single step. Such control of microstructure by splitting of the laser beam can be extended to other materials processing applications such as surface heat treatment. The work will include a thermal analysis of the problem, followed by (and to a large extent parallel with) an extensive experimental program both to verify the analyses, and to elucidate the potential benefits of the split-beam laser materials processing concept. The experimental task will constitute the bulk of the research project.
