Microstructure manipulations to attain densification without distortion during liquid phase sintering.

摘要

Liquid phase sintering provides a means for net-shape manufacturing, but there is a common concern about shape distortion during densification. In the present work, a theory is created to achieve densification without distortion by manipulating microstructure and its evolution during sintering.; The microstructure parameters considered in this study are solid volume fraction, dihedral angle, green porosity, and green pore size. These parameters were varied to measure densification and distortion behavior during liquid phase sintering using W-Ni-Cu alloys. Green compacts were formed using ethylene-bis-stearamide 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 volume fraction was adjusted via the tungsten content. Dilatometry was employed to measure shrinkage and shrinkage rate during heating. Distortion was quantified using final compact profiles determined with a coordinate measuring machine to calculate a distortion parameter.; Sintering results showed that solid volume fraction and dihedral angle are dominant factors on densification and distortion during liquid phase sintering. Distortion decreased with increasing solid volume fraction and dihedral angle, both contributing to a higher solid contiguity. Densification decreased with increasing green porosity and pore size, while initial pore structure did not show observable effects on distortion in situations of fast densification where full density is achieved.; Real time video imaging and quenching results verified that densification and distortion are sequential events in liquid phase sintering with densification occurring first. In gravity, distortion is inhibited until pores are closed and the compact is nearly fully densified.; Based on the experimental results, some processing strategies emerge that achieve densification and prevent distortion in liquid phase sintering. Microgravity experiments are proposed for further understanding of microstructure effects on densification and distortion in liquid phase sintering.