Design and Fabrication of Graded Materials with the Laser Engineered Net Shaping Process

这项研究的目的是开发设计和制造梯度过渡接头的方法，以避免不同焊缝的失效。渐变过渡接头将包括成分和合成性能的逐渐和可控的变化。这将大大减少或消除目前由成分和性能的急剧变化引起的不同焊缝中的故障。首先将使用结构优化例程确定属性中的最佳级配。然后，这些信息将被用于使用微结构建模和激光工程净成形(透镜)工艺来制造各种渐变过渡接头。将使用各种技术，包括光学/电子显微镜、显微硬度测试、高温拉伸测试和蠕变断裂分析，相对于行业标准接头评估这些接头的性能。然后，最优的分级接头将与常规接头一起安装到工业伙伴的发电厂中进行并排现场测试。随着对材料在不断增加的应力、温度和腐蚀环境下的性能提出更高的要求，连接不同材料的需求预计会增加。分级材料为连接不同的材料提供了巨大的潜力，但目前还没有设计这些节点以提高性能的方法。此外，不同类型的焊接故障目前具有重大的经济影响。例如，一次不同的焊接故障可能会使电力公司在停机时间内损失高达85万美元/天，并造成收入损失。如果成功，这项研究的结果将导致开发出可用于各种应用的分级材料的优化设计、制造和性能的方法。这些结果还将有助于更好地理解透镜加工中加工、结构和性能之间的复杂关系。最后，在发电应用中直接实施连接不同材料的技术将通过消除不同焊接故障而显著节省成本。

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.