Significantly improved sintering shrinkage of heavy calcium carbonate ceramic cores by binder jetting using Al powder additive

Abstract

In this study, the ceramic cores were printed with heavy calcium carbonate (HCC, CaMg(CO3)2) powder as raw material and Al powder as additive by binder jetting (BJ). The ceramic cores were impregnated with nano-ZrO2 dispersion solution and then sintered at high temperature to prepare the ceramic cores with low sintering shrinkage. The effects of different Al powder contents (20 wt%∼40 wt%) on the properties and sintering shrinkage of the ceramic cores were studied. It was found that with the increase of Al powder content (20 wt%∼40 wt%), the bending strength of the ceramic core gradually decreased from 35.82 MPa to 11.89 MPa, and the porosity continuously increased from 8.94 % to 46.4 %. The sintering shrinkage rate of the ceramic core also gradually decreased, and even slightly expanded. This is because the oxidation of the Al powder to Al2O3 produced a large volume expansion, and the Al2O3 reacted with the CaO and MgO generated by the decomposition of HCC to produce calcium hexaluminate (CA6), calcium dialuminate (CA2), MgAl2O4 (MA) and other substances, and these reaction processes also produced a certain volume expansion. When the amount of the Al powder was 40 %, the dimensional change rates of X, Y and Z axis of the ceramic core were 2.48 %, 2.35 % and −0.6 %, respectively. Compared with the ceramic core without Al powder, the sintering shrinkage rate decreased by 91.2 %, and the dimensional accuracy of the ceramic core was improved significantly. By observing the microstructure of the ceramic cores, it is found that various substances inside the ceramic core formed a network distribution structure, which achieved a good toughening effect and ensured that the ceramic core had a good bending strength under large porosity.