Microstructure and mechanical properties of fine-grained W-7Ni-3Fe heavy alloy by spark plasma sintering

The present study utilizes the spark plasma sintering (SPS) to produce fine-grained W-7Ni-3Fe heavy alloys (WHAs) with W grain sizes of less than 5 mu m, and discusses the effects of sintering temperature on the microstructures and mechanical properties of the alloy. At the lower sintering temperature range of 1000-1100 degrees C, the relative density of the alloy increased rapidly, and almost full densification WHA can be attained at 1250 degrees C. The microstructures of the WHAs produced contain three phases: W phase, gamma-(Ni, Fe, W) binding phase and rich W phase. At 1000-1250 degrees C, the hardness of the alloys tends to first rise, reaching the maximum value of 72.2 HRA at 1100 degrees C, and then goes down. In the sintering temperature range from 1000 degrees C to 1250 degrees C, the bending strength continuously increases to a high value of 1334.6 MPa at 1250 degrees C. The good mechanical properties of the alloys could be attributed to grain refinement strengthening and solid solution strengthening. The bending fracture of the alloy mainly displays the features of intergranular fracture at the lower sintering temperature, and the ductile tearing of gamma-(Ni, Fe, W) binding phase increases gradually with increasing sintering temperature. Above the temperature of 1200 degrees C, part W grains generate cleavage fracture. (C) 2012 Elsevier B.V. All rights reserved.