Preparation of fine-grained tungsten heavy alloys by spark plasma sintered W–7Ni–3Fe composite powders with different ball milling time

Abstract

The fine-grained tungsten heavy alloys (WHAs) with grain size of about 1–3μm were successfully prepared by spark plasma sintered W–7Ni–3Fe composite powders with different high-energy ball milling (HEBM) time. This study analyzes the effects of HEBM time not only on the composite powders but on the microstructure and mechanical properties of WHAs. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to investigate the microstructure and phase evolution rules of powders and alloys, respectively. The γ-(Ni, Fe, W) is not observed in XRD patterns of the ball milled powders. With prolonging HEBM time, the W phase diffraction peak becomes increasingly wider, and its intensity continues to decline. However, the completely amorphous structures are not formed even after HEBM 40h. The relative density of the WHAs prepared by HEBM assisted SPS technique decreases gradually with increasing the ball milling time. For the WHAs sintered in 1150°C for 8min, the W grains grow finer and the content of the γ-(Ni, Fe, W) binding phase greatly increases with prolonging the HEBM time. Meanwhile, over 5h of HEBM time, the bending strength continuously decreases and the hardness slightly increases. The intergranular fracture of the W grains is the main bending fracture mode in all the WHAs. The microporous of different sizes are distributed on the bending fracture and progressively increased with prolonging the ball milling time.