Nathan Klingbeil (Advisor), Joy Gockel (Committee Member), Raghavan Srinivasan (Committee Member)
Master of Science in Materials Science and Engineering (MSMSE)
Laser based additive manufacturing of Ti-6Al-4V components is under consideration for aerospace applications. The mechanical properties of the finished components depend on their microstructure. Process mapping compares process variables such as heat source power, heat source travel speed, material feed rate, part preheat temperature and feature geometry to process outcomes such as microstructure, melt pool geometry and residual stresses. In this work, the microstructure of two-dimensional pads, multilayer pads, thin walls, and structural components at the steady state location was observed. A method for measuring β grain widths that allows for the calculation of standard deviations, confidence intervals, and variances in grain size was developed. This represents an improvement over the commonly used line-intercept method. The method was used to compare variability of β grain widths across different part geometries. It was found that thin wall parts have the highest β width variability and that the width of the β grains varies more towards the top of multi-layered samples than towards the bottom. Experimental results for α and β grain size across multiple deposit geometries are presented that offer new insight into the effect of process variables on microstructure. β grain widths are also compared for different deposit geometries with the same power, velocity, and feed rate. Single layer pad geometries were found to have the smallest β grain widths, multi-layer pads had larger β grain widths, and thin wall samples had the largest β grain widths. Trends in α width with Vickers hardness were also considered in the context of thermal gradient measurements. Hardness maps were created for the structural component samples. Optical microscopy was used to observe a layering effect in structural component samples. It was found that light and dark bands had different Vickers microhardness values.
Department or Program
Department of Mechanical and Materials Engineering
Year Degree Awarded
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