Green microstructure effects on densification and distortion in liquid phase sintering

Abstract

Microstructure attributes such as solid volume fraction, dihedral angle, initial porosity, and initial pore size are important to densification and distortion control in liquid phase sintering (LPS). In our experiments, these parameters were varied to measure densification and distortion behavior during LPS using W–Ni–Cu alloys. Green compacts were formed using ethylene- bis-stearamide (EBS) as a pore-forming agent with the amount of polymer controlling the initial porosity. Different initial pore sizes were generated by varying the polymer particle size. Dihedral angle was varied by changing the Ni:Cu ratio in the alloys. Finally, the solid:liquid ratio was adjusted via the tungsten content. Dilatometry was employed to measure shrinkage and shrinkage rate during heating. Real time video imaging and quenching experiments isolated the sequence of densification and distortion events in LPS. Distortion was quantified using profiles determined with a coordinate measuring machine (CMM) to calculate a distortion parameter. Sintering results showed that at full densification, initial porosity and pore size have no observable effect on distortion for 80W–16Ni–4Cu alloy while distortion reduces with increasing solid volume fraction and dihedral angle. Microgravity experiments are proposed for further understanding of microstructure effects on densification and distortion in LPS.