Enhanced compressive strength and tailored microstructure of selective laser melted Ti-46.5Al-2.5Cr-2Nb-0.5Y alloy with different boron addition

The microstructures and compressive properties of Ti-46.5Al-2.5Cr-2Nb-0.5Y alloy with varied boron (B) addition processed by selective laser melting (SLM) had been systematic studied. With increasing the B content from 0 to 2 wt%, the average grain size of SLM-processed Ti-46.5Al-2.5Cr-2Nb-0.5Y/B composites decreased from 16.64 µm to 5.66 µm, meanwhile, the {0001} texture index and high angle grain boundaries (HAGBs) increased from 10.78 and 87.9% to 22.69 and 94.4%. The phase evolution mechanism of Ti-46.5Al-2.5Cr-2Nb-0.5Y/B composites during the SLM process can be summarized as: firstly, β and B phases precipitated out from the liquid phase, then the β phase transformed to α phase and part of the α phase transferred to γ phase, later, some new phases of TiB₂ and AlB₂ emerged by the diffusion mechanism of B, Ti and Al atoms, and then the β and α phases orderly transformed to B₂ and α₂, lastly, the γ, B₂, B, TiB₂, AlB₂ phases in a range of several hundred nanometers were randomly distributed within the α₂ matrix. Due to the grain refinement strengthening mechanism, the compressive strength and strain of Ti-46.5Al-2.5Cr-2Nb-0.5Y/B parts increased to the maximum of 1610.53 MPa and 5.17%.