MICROSTRUCTURE OF THE GRAVITATIONALLY SETTLED REGION IN A LIQUID-PHASE SINTERED DILUTE TUNGSTEN HEAVY ALLOY

A dilute tungsten heavy alloy consisting of 50W-35Ni-15Fe (wt pet) was liquid phase sintered at 1500 degrees C for times ranging from 30 to 960 minutes. This alloy corresponds to a nominal solid content of 20 vol pet at the sintering temperature. Because of the excess liquid, the alloy densified easily and exhibited extensive liquid-solid separation due to the density difference between the phases. The solid content at the compact bottom ranged from 45 to 70 vol pet over position and time. The microstructure of the settled region was quantified for volume fraction of tungsten, grain size, connectivity, and settled solid angle of repose. These results provide a basis for extending the microstructural parameters to possible microgravity conditions. The grain growth rate constant varies with the inverse 2/3 power of the volume fraction of liquid, possibly reflecting combined coalescence and solution-reprecipitation processes. This volume-fraction effect on the grain-growth-rate constant applies to several systems.