Fracture Behavior of W-Ni-Fe Heavy Alloys

Heavy alloys were liquid phase sintered from compacts of mixed W, Ni, and Fe powders. The alloy compositions ranged from 93 to 97 wt pct W, with the Ni:Fe ratio maintained at 7:3. Sintering was performed under hydrogen in the 1465 to 1485 °C temperature range, giving full density within the first 15 minutes. The room temperature strength and ductility showed major degradation with sintering times in excess of two hours. Tensile tests and bend tests have been performed to isolate the fracture mode and the property determining features. Initial cracking occurs at the tungsten-tungsten grain boundaries and in the tungsten grains. These latter cracks propagate through the structure to give eventual failure. The ductility to failure is shown to be governed by the strength of the tungsten-matrix interface. The maximum elongation depends on the contiguity, which in turn is set by the alloy composition. Formerly a Postdoctoral Fellow at RPI under a fellowship from the Korea Science and Engineering Foundation