Microstructural Evolution During Materials Processing

9417326汤普森该研究计划创建分析模型来描述在快速连续加热过程中经历陡峭热梯度的金属合金中微观结构的演变，例如在焊件的热影响区。 该研究开发了在共晶温度及以上的微观组织演变的分析和数值解决方案。 微观结构演变的模型预测晶粒尺寸，沉淀物溶解，在加热过程中的液化，以及在冷却过程中的液体膜，形成沿着晶界的固化。 实验研究补充的分析和数值模型。 四个实验合金系统进行了研究：一个高纯度的金属（最小溶质阻力界面迁移）;一个二元固溶体合金（溶质阻力界面迁移）;一个两相二元合金没有固溶度（齐纳钉扎与最小溶质阻力）;和一个两相二元合金的溶解度（齐纳钉扎与溶质阻力）。 通过数据分析，验证了焊接热影响区热循环有限元热流模型的正确性。 在实验系统上进行了精心准备的钨极氩弧焊焊接。 测量了晶粒尺寸、沉淀物溶解和液膜厚度随热影响区位置的变化。 分析透射电子显微镜分析是在特别制备的样品上进行的，以突出沉淀溶解的微观结构。 分析的一个目标是生成界面和基质化学成分梯度的数据，用于与沉淀物溶解的分析模型进行比较。 %焊接组件的强度取决于焊缝金属和邻近焊缝的母材（称为焊缝热影响区）的强度。这项研究提供了一种预测微结构相关缺陷的方法，并提供设计信息，以避免其发生。***

9417326 Thompson This research program creates analytical models to describe the evolution of microstructure in metal alloys experiencing steep thermal gradients during rapid continuous heating, such as in the heat-affected zone of weldments. The research develops analytical and numerical solutions to microstructural evolution at and above the eutectic temperature. The models for microstructural evolution predict grain size, precipitate dissolution, liquation during heating, and solidification during cooling of liquid films that form along the grain boundaries. Experimental studies compliment the analytical and numerical models. Four experimental alloy systems are studied: a high purity metal (minimal solute drag on interface migration); a binary solid solution alloy (solute drag on interface migration); a two-phase binary alloy with no solid solubility (Zener pinning with minimal solute drag); and a two-phase binary alloy with solubility (Zener pinning with solute drag). A finite element heat flow model of the weld heat-affected zone thermal cycle is tested by the data analysis. Carefully prepared autogenous gas tungsten arc welds are made on the experimental systems. The grain size, precipitate dissolution, and liquid film thickness are measured as a function of position in the heat-affected zone. Analytical transmission electron microscopy analysis is performed on samples specially prepared to accentuate precipitate dissolution microstructures. A goal of the analysis is to generate data on interface and matrix chemical composition gradients for comparison to the analytical models of precipitate dissolution. %%% The strength of welded assemblies depends on the strength of the weld metal and base metal adjacent to the weld (referred to as the weld heat-affected zone). This research provides a means of predicting microstructure-related defects and provides design information to avoid their occurrence. ***