Laser Engineered Net Shaping (LENS) is the tool by which graded transition joints are made from dissimilar alloys. LENS is a tool that uses a computer controlled laser system integrated with dual powder feeders. The dual powder feeders can be controlled independently so that the composition can be changed at various locations within the part for optimized mechanical and/or corrosion performance. The transition joints are produced by initially injecting a ferritic steel powder which is gradually graded into a stainless steel. In the graded transition, the compositional change from ferritic steel to stainless steel is spaced over 60 mm while it occurs over only 80 µm in the dissimilar metal weld joint. This smoothed compositional variation affects the mechanical properties in a similar fashion. The hardness profile generated in the graded transition joint is less severe and occurs over a much greater distance (60 mm) as compared to the dissimilar metal weld (80 µm). The smooth compositional and mechanical property variation produced in the graded transition joint improves the mechanical properties and corrosion resistance of the component and will enhance the lifetime of the graded transitions joints.
Dissimilar metal failures remain to be a significant problem to the power generation, oil, and gas industries. In the power generation industry alone, failures of dissimilar welds could cost a company $250,000 - $750,000 a day in lost revenue, repair/replacement costs, and down time. These transitions joints have the potential for significantly reducing and even eliminating the occurrence of these failures, thus providing the power generation industry with significant saving associated with forced plant outages. In addition, the fabrication of a functionally graded transition joint using LENS provides smooth microstructural and mechanical property transitions between dissimilar materials that then leads fewer weld failures.
This method can be used on multiple-material weld systems.
A US utility patent application has been filed: 20090208773