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Crystallographic texture evolution in electron beam melting additive manufacturing of pure Molybdenum...

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Materials & Design
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Additive manufacturing (AM) technologies offer novel opportunities for processing difficult to cast refractory materials. Unlike casting, which necessitates a large melt, AM only requires selective melting of small volumes which unlocks new opportunities for processing of high temperature refractories. Electron beam melting (EBM) AM is particularly attractive as the rapidly moving electron beam can be utilized to heat the powder bed which mitigates against some process induced cracking mechanisms. Molybdenum is a promising material for future nuclear energy technologies such as fusion. A great deal of prior work has been done to investigate laser based processing of molybdenum but little EBM focused work currently exists. In this work we investigate EBM processed molybdenum and observe sharp {001}, {111}, and mixed {001} & {111} crystallographic fibers in the build direction. The apparent preference between these build direction fibers is dependent on the imposed energy density and this is likely explained by the weld pool shape. Detailed microscopy reveals that the observed columnar grains consist of much finer equiaxed low angle boundary subgrans suggesting large process induced stresses leading to appreciable plastic deformation. The implications resulting from this work are that molybdenum may be processed crack-free via EBM AM and that fiber-switching may be controlled, and exploited, towards fabricating components with optimized performance.