Fabrication and performance of binder jetting ceramic shells via PTSA powder modification and cyclic infiltration–leveling post-treatment

: Binder jetting (BJ) faces two key challenges for the investment casting of superalloys: poor powder flowability when mixed with liquid furan resin curing agents, and insufficient thermo-mechanical strength of the printed shells. This work develops a surface modification method by coating ceramic foundry sand with p-toluenesulfonic acid (PTSA) via an ethanol solution. With 0.4–0.6 wt.% PTSA, the modified powder achieves a 29–31° angle of repose, a green bending strength of 1.5 MPa, and a dimensional deviation within ±0.21 mm. A multi-cycle silica sol vacuum infiltration and sintering process is then applied: after two cycles, the room-temperature bending strength reaches 21.17 MPa and the 1500 °C bending strength reaches 7.35 MPa. To improve the poor inner surface roughness (Ra ≥ 19.07 μm) of the infiltrated shells, a combined leveling method (face-coat slurry + vibratory polishing) reduces Ra from 8.99 μm (directly coated) to 4.21 μm after 24 h, while the coating thickness decreases from 1.05 mm to 0.01 mm. Casting trials of an impeller shell using a Ni-based superalloy at 1550 °C demonstrate that the shells withstand the thermal and mechanical loads. This work provides a comprehensive material and process strategy – integrating powder surface engineering, post-infiltration strengthening, and inner surface leveling – to advance BJ technology toward high-performance ceramic shell manufacturing for investment casting.