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 μm, 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 °C, the relative density of the alloy increased rapidly, and almost full densification WHA can be attained at 1250 °C. The microstructures of the WHAs produced contain three phases: W phase, γ-(Ni, Fe, W) binding phase and rich W phase. At 1000–1250 °C, the hardness of the alloys tends to first rise, reaching the maximum value of 72.2 HRA at 1100 °C, and then goes down. In the sintering temperature range from 1000 °C to 1250 °C, the bending strength continuously increases to a high value of 1334.6 MPa at 1250 °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 γ-(Ni, Fe, W) binding phase increases gradually with increasing sintering temperature. Above the temperature of 1200 °C, part W grains generate cleavage fracture.

► We fabricated fine-grained WHAs using SPS technology.
► The SPS method greatly improves the densification rate of the WHAs.
► The W grain growth is not obvious for SPS at temperature range of 1000–1250 °C.
► The variation of the hardness is not in agreement with that of the bending strength.
► The intergranular fracture is dominant for most fine-grained WHAs by SPS.