Strategies to reduce pores and cracks of molybdenum fabricated by selective laser melting

Selective laser melting (SLM) additive manufacturing process has been attractive to the fabrications of Mo and Mo alloys due to the advantage of fast near net shaping of complex shaped components. In order to reduce pores and cracks, by using high purity Mo powder, process parameter optimization, as well as La2O3 particle addition and post hot isostatic pressing (HIP) were applied. The results show that when the applied linear energy density is larger than 0.48 J/mm, the SLM samples can have continuous molten tracks. When the applied volumetric energy density is in the range of 250-280 J/mm3, small cubic SLM samples can have high relative densities larger than 99.7%. For large bulk SLM samples prepared with a volumetric energy density of 259 J/mm3, the addition of 0.9 wt% La2O3 can reduce the porosity from 0.76% to 0.63%. After HIP treatment, the highest relative density of 99.6% can be obtained for large bulk sample with La2O3 addition. Cracks are observed only at the surfaces of all samples, while no cracks can be seen in the inner parts. Moreover, after adding La2O3, the cracks at the surfaces are narrowed, and the crack number density is significantly reduced by >2 times.