Influence of LaB6inoculant on the thermodynamics within the molten pool and subsequent microstructure development and cracking behavior of laser powder bed fused TiAl-based alloys

A LaB6particles decorated Ti48Al2Cr2Nb composite almost free of any cracks has been successfully fabricated by LPBF in this work. To better understand the role of LaB6inoculant in LPBF-fabricated γ-TiAl alloys, the effects of LaB6inoculant on the thermal behavior, microstructure evolution and crack sensitivity were investigated by simulation and experimental methods. Based on a single particle model, it was predicted that the addition of LaB6particle could induce a significant change in temperature gradient G. Due to the LaB6→La2O3in-situ transformation, the temperature field was severely perturbed, thus causing random Gorientations of the matrix surrounding the particle. Furthermore, based on the multi-particle model, predictions indicated that the 0.5 wt% LaB6inoculant led to a significant decrease of the Gmaxfrom 1.14× 107 °C/m to 6.9 × 106 °C/m but a little influence on solidification rate Rat solidified front, therefore contributing to a lower G/Rand resultant larger undercooling. In this condition, fine equiaxed grains with random orientations were expected to dominate in the solidified microstructure, which got well verified by the experiments where the maximum texture index dropped from 15.06 to 2.23 and the average grain size decreased from 16.13 ± 8.52 μm to 1.52 ± 1.10 μm due to the addition of LaB6inoculant. What's more, the LaB6inoculant also induced an apparent reduce in crack density from 7.02 ± 1.06 mm/mm2to 0.52 ± 0.12 mm/mm2and a rise in relative density from 97.65 ± 0.58% to 99.88 ± 0.10%, which could be mainly attributed to grain refinement, grain purification and texture attenuation.