CARACTERÍSTICAS MICROESTRUTURAIS DOS METAIS-DUROS A BASE DE WC COM FASE LIGANTE ALTERNATIVAS Co/Ni/Co-Ni FABRICADOS PELA TÉCNICA DE MANUFATURA ADITIVA PBF-LB/M

: The objective of this work is to present the microstructural characterization of WC-30Co, WC-30Ni and WC-30(Co,Ni) alloys, with high content of binding phase (30% by weight), produced by the additive manufacturing technique Laser powder bed fusion (L-PBF). The cemented carbides specimens were manufactured from the conventional powder metallurgy mixture and produced without polymeric binders and without grinding, to preserve the ceramic and metallic particulate sizes. One of the great challenges of this work was the dry flowability of the WC mixtures with the metallic phases Co, Ni and their combination (Co, Ni), where the need to develop a vibrating device to allow the flow and at the same time the compressibility arose. of metallic powders, made by a roller compactor, which may have improved the reduction of residual porosity, the apparent density and the minimization of microcracks of the samples manufactured by the L-PBF technique. In direct sintering (L-PBF) for WC-30Co and WC-30(Co, Ni) alloys with energy density greater than 400 J/mm 3 , the eta-  phase appeared in the Co-based samples, due to the presence of oxygen (250 to 350 ppm) in the system. WC-30(Co, Ni) alloys with alternative ligand phase showed fewer cracks in samples generated by different levels of power factors (W) as a function of laser scanning speed (mm/s). The ideal substrate for the PBF-L technique should be of the same addition material, but in this work, for reasons of cost and feasibility, an AISI 1020 steel substrate was used, with a different thermal expansion coefficient, and this may have contributed for the increase of residual stresses and generation of cracks in some samples. Binary and ternary equilibrium diagrams were used to predict, after direct sintering and rapid cooling, the appearance of the phases combined with WC. The cemented carbides with alternative ligand phase Ni and (Co, Ni) seem to be more promising, as they showed few cracks in most specimens and the apparent porosity was less than 15 µm, when compared to the WC samples. WC-30Co alloys containing cobalt (allotropic) showed many cracks, low porosity and high presence of eta-  phase, mainly for energy densities above 300 J/mm 3 , in specific and isolated regions, contributing to thermal stresses and resulting in microcracks.