Abstract Close-Coupled Gas Atomization (CCGA) is often used to produce spherical metal powders with a wider Particle Size Distribution (PSD) (10 – 500 µm) compared to that required by the main Additive Manufacturing processes (10 – 105 µm). This work presents an accuracy evaluation of a mathematical model based on the Lubanska equation to predict the d50 for CCGA. Atomization experiments of 316L steel were conducted to evaluate the tip diameter and atomization gas pressure effects on PSD and, the d50 experimental results were used as the reference to the mathematical model evaluation. The mathematical model accuracy could be improved by: (i) considering the backpressure phenomenon for the metal flow rate calculation, since it was an important inaccuracy source; (ii) reviewing the tip diameter effect, which had a lower impact on d50 than that predicted by the Lubanska equation. The atomization gas pressure was the most influential parameter on d50 and d90 and the increase of the gas pressure led to a significant reduction in PSD and, consequently, increased yield.

Experimentos de solidificação direcional foram realizados em um forno do tipo Bridgman para remoção de carbono e impurezas metálicas contidas no silício. Para remoção de carbono, a solidificação se deu pela extração do molde da zona quente para a zona fria do forno, enquanto que, para remoção de impurezas metálicas, a solidificação foi conduzida pelo resfriamento do forno sem a movimentação do molde. Nos experimentos para remoção de carbono, uma velocidade de extração do molde de 5 µm/s resultou em lingote com macroestrutura colunar de grãos alinhados ao seu eixo central e macrossegregação de carbono e partículas de SiC para o topo do lingote. No entanto, na velocidade de 80 µm/s, a macroestrutura consistiu de grãos colunares e alinhados na direção radial com partículas de SiC encontradas em todo o lingote, mesmo havendo maiores concentrações de carbono no topo do lingote, o que mostra uma macrossegregação menos severa. No experimento de remoção de impurezas metálicas, uma macroestrutura de grãos colunares alinhados ao eixo central do lingote foi obtida e os perfis de concentração de impurezas mostraram que houve macrossegregação para o topo do lingote

Directional solidification experiments were carried out in a Bridgman furnace to remove carbon and metallic impurities from silicon. For carbon removal, solidification was achieved by extracting the mold from the hot into the cold zone of the furnace, while for the removal of metallic impurities, solidification occurred by cooling the furnace with a motionless mold. In the experiments of carbon removal, a mold extraction rate of 5 µm/s results in an ingot with columnar grain structure aligned in the ingot axial direction and a macrosegregation of carbon and SiC particles to the ingot top regions. However, at a mold extraction rate of 80 µm/s, the grain structure consisted of columnar grains aligned in the radial direction and SiC particles were observed throughout the ingot, showing lower macrosegregation with a carbon concentration still larger at the ingot top. In the metallic impurities removal experiment, an ingot with a columnar grain structure aligned in the ingot axial direction was obtained and the concentration profiles showed significant metallic impurities macrosegregation to the ingot top.