Effect of In-Situ Alloying with Si on the Microstructure of a Novel Ti-5Cu Alloy Manufactured by Laser Powder Bed Fusion

The present work aims to explore the influence of Si addition on the microstructure of a novel Ti-5Cu alloy produced by the Laser Powder Bed Fusion (L-PBF) technique, under an in-situ alloying strategy. For this purpose, Ti–5Cu and Ti–5Cu–1Si samples were manufactured under the same volumetric energy density (VED), i.e., 50.26 J/mm3. The findings revealed that incorporating 1 wt% Si into the Ti-5Cu alloy converted the prior β columnar and equiaxed grains with an average size of 41 μm and 22 μm, respectively, to finer equiaxed prior β grains within the Ti-5Cu-1Si microstructure, which featured with an average size of about 8 μm. Greater tendency for columnar to equiaxed transition and a notable grain refinement with Si addition were linked to a greater constitutional supercooling zone created by the rejection of Si solute atoms in front of the solidification front. Comparison of the solidification ranges for Ti-5wt%Cu and Ti-1wt%Si alloys plotted by PANDAT software revealed that Si has a more severe impact on the solidification range than Cu, making it a potentially better option for inducing columnar to equiaxed transition. Incorporating 1% Si to the Ti-5Cu alloy increased the growth restriction factor from 35 to 60 K, resulting in an almost 3-fold reduction in grain size. Addition of Si to the Ti-5Cu alloy also significantly refined the average length of α lath from about 4 μm to about 1.7 μm in the microstructure of Ti–Cu–Si alloys.