The objective of this research is to develop methods for designing and fabricating graded transition joints for avoiding failures in dissimilar welds. The graded transition joints will consist of gradual and controlled changes in composition and resultant properties. This will significantly reduce or eliminate failures in dissimilar welds that are currently caused by very sharp changes in composition and properties. The optimal gradation in properties will first be determined using structural optimization routines. This information will then be utilized to fabricate various graded transition joints using microstructural modeling and the Laser Engineered Net Shaping (LENS) process. The performance of these joints will be evaluated relative to the industry standard joints using a variety of techniques, including light/electron microscopy, microhardness testing, high temperature tensile testing, and creep-rupture analysis. Optimal graded joints will then be installed into the power plants of the industrial partner along with conventional joints for side-by-side field testing.
The need to join dissimilar materials is expected to increase as more demand is placed on the performance of materials under conditions of increasing stress, temperature, and corrosive environment. Graded materials offer significant potential for joining dissimilar materials, but methods for designing these joints for improved performance are not yet available. In addition, dissimilar weld failures currently carry significant economic impact. For example, a single dissimilar weld failure can cost an electric power company up to $850,000/day in down time and lost revenue. If successful, the results of this research will lead to development of methods for optimizing the design, fabrication, and performance of graded materials that can be used in a variety of applications. The results will also lead to an improved understanding of the complex relationships between processing, structure, and properties in LENS processing. Lastly, the direct implementation of the technology for joining dissimilar materials in power generation applications will provide significant cost savings by eliminating dissimilar weld failures.
