Microstructural modification of Ti–6Al–4V by using an in-situ printed heat sink in Electron Beam Melting® (EBM)

Unidirectional heat transfer during additive manufacturing (AM) processes results in anisotropy of microstructure and mechanical properties in fabricated components. In the present study, the influence of in-situ printed heat sinks on the microstructure of Ti–6Al–4V was investigated. Different numbers of heat sinks were designed and produced by the Electron Beam Melting® (EBM) process. The coupons were characterized by an optical microscope, scanning electron microscope, tensile and hardness tests, and fracture analysis. An increase in the number of heat sinks was accompanied by a reduction in grain thickness. While elongated grains still formed in all coupons, due to the dominant heat transfer along the buildup direction. The refinement of microstructure was confirmed by a reduction in the average thickness of α-lath from 1.73 μm in the coupon with no heat sink to 1.01 μm in the coupon with the highest number of the heat sinks. The ultimate tensile strength and hardness were increased by increasing the number of heat sinks. The results of fractorgraphy suggested that coupons with the maximum number of heat sinks (5-HS) showed a more ductile fracture. Also, digital reconstruction of the fracture surface showed that the unmelted powder particles had an influence on the crack initiation.

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