Effect of surface modification on the microstructure and sintering characteristics of tungsten nanopowders prepared by a wet chemical method

ABSTRACT In order to prepare high-performance tungsten alloys, surface modification of tungsten nanopowders prepared by a wet chemical method was carried out by acid pickling at room temperature. The low-temperature sintering characteristics of tungsten nanpowders before and after pickling was compared and analysed. The surface modification was carried out by pickling with a solution of hydrofluoric acid, concentrated nitric acid and ammonium fluoride at room temperature. After this surface treatment, uniformly distributed step-shaped defects formed on the surface of the tungsten nanopowders. After low-temperature sintering, the grain size of the tungsten alloy corresponding to the surface-modified powder precursor was reduced by 20% compared to the alloy using untreated powder as precursor. In addition, the step-shaped defects also increase the sintering activity of the pickled tungsten powder and promote its sintering densification, making the final density of pure tungsten sintered at 1600°C as high as 96.7%, and its hardness greatly increased to 521 HV0.2. The results show that room-temperature pickling and subsequent low-temperature sintering is a promising method for preparing high-performance nanotungsten alloys.