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 v ol pet at the sintering temperature. Because of the excess liquid, the alloy densified easily and exhibited extensive liquid-solid separatio n 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 t ime. The microstructure of the settled region was quantified for volum e fraction of tungsten, grain size, connectivity, and settled solid an gle of repose. These results provide a basis for extending the microst ructural parameters to possible microgravity conditions. The grain gro wth rate constant varies with the inverse 2/3 power of the volume frac tion of liquid, possibly reflecting combined coalescence and solution- reprecipitation processes. This volume-fraction effect on the grain-gr owth-rate constant applies to several systems.