SHAPE DISTORTION IN LIQUID-PHASE-SINTERED TUNGSTEN HEAVY ALLOYS

Shape retention during liquid phase sintering is a major concern at hi gh liquid contents, or large density differences between the solid and the liquid phases. This study demonstrates the role of microstructura l parameters in controlling the bulk dimensional changes that occur du ring liquid phase sintering of tungsten heavy alloys (WHAs). Tungsten- nickel-copper alloys containing 80 wt pet tungsten, the balance contai ning Ni and Cu in the ratio 6:4, 7:3, or 8:2, were sintered at tempera tures between 1400 degrees C and 1500 degrees C. Compact distortion wa s quantified using a coordinate measuring machine and related to the m icrostructural parameters, such as solid volume fraction, grain size, dihedral angle, grain contiguity, and connectivity. Supplementary expe riments were performed on W-Ni, W-Cu, and Mo-Cu alloys to compare the role of microstructural parameters in controlling distortion. A low so lid solubility and a small grain size coupled with a high dihedral ang le and connectivity restrict distortion. Based on the experimental obs ervations and stereological relations, the critical solid content requ ired to maintain structural rigidity is related to specific combinatio ns of dihedral angle and grain connectivity.