Multi-Scale Modeling and Experimentation on Liquid Phase Sintering in Gravity and Microgravity Environments

In this study, the compositions start with W-Ni-Cu-Mn powder mixtures. The solid-liquid ratio is adjusted via changes in the tungsten content from 70 to 90 wt %. Most of the tungsten remains solid during sintering. The liquid is formed from melting the mechanically alloyed Ni-Cu-Mn additive. The liquid dissolves up to 28 wt % tungsten at the sintering temperature, giving the desired semisolid system. In these experiments, changes are also made to the Ni:Cu ratio from 3:2 to 2:3 to slightly adjust the tungsten solubility. Seven cartridges with seven samples each are processed in microgravity. One cartridge is heated to the temperature where first significant densification occurs on Earth, 1180°C, and five of the cartridges are processed for progressively longer times at 1210°C. A seventh cartridge is for backup in case of an aborted run, otherwise it provides a replicate at 34 min at 1210°C. An early part of this research focused on developing a W-Ni-Cu-Mn alloy to allow lower sintering temperatures to accommodate downgraded furnace peak temperatures. The new alloys are tested using ground proof runs to gather ground data. Those results are contrasted with the microgravity data. Extensive testing is documented to show the experimental platform; tests involved thermal overload, vibration, equipment proofing, evaporation, transient runaway, and temperature verification trials. An early failure in the quartz ampoule led to redesign. Subsequent ground runs were conducted without failure. This report emphasizes the development of the experiments and details the densification and distortion data, and provides microstructure data. Modeling ideas were established early and awaited samples for verification. Much effort was directed to developing a time sequence whereby modeling data would be available for rheological variables associated with the solid-liquid-pore structures existing during sintering, namely extraction of the viscosity and strength variations during the 60 min of isothermal hold. The model is implemented in finite element analysis where stress on the sintering body is assessed using variations in the composition, component size, and gravity.