Химико-металлургический синтез субмикронных порошков W + Ni со структурой “ядро (W) – оболочка (Ni)”

Abstract

The conditions for obtaining composite W + Ni powders with the core (W) –shell (Ni) structure and alloys based on them were studied in the work. W + Ni powders (5, 10, 20 wt.%) were obtained by the chemical-metallurgical method. The influence of nickel content, its precursor (nickel chloride or nitrate) and temperature treatment regime on the phase composition of the powders was studied. During the work, it was found that the nickel concentration does not affect the phase composition of the powder, however, 5 wt. % Ni is not enough to cladding all tungsten particles. A powder containing the least amount of impurities was obtained from nickel chloride after reduction annealing at 400 – 600 °C and from nickel nitrate after annealing at 550 °C. After annealing at 750 and 950 °C, the formation of the Ni4W intermetallic compound was observed, which may be due to the presence of oxygen and oxides on the surface of tungsten particles. An alloy based on 0.9 W + 0.1 Ni powder obtained from nickel chloride and annealed at 600 °C was produced by Spark Plasma Sintering at a temperature of 1050 °C and a pressure of 50 MPa. The phase composition of the central region of the obtained alloys did not change during the sintering process, however, the formation of the η1-phase Ni3W3C was observed on the surface, which is a product of the interaction of the initial powder with the graphite mold. The obtained alloys had a homogeneous microstructure; no traces of abnormal grain growth or formation of large γ-phase particles were observed. The Vickers hardness Hv10 of tungsten alloys sintered without isothermal holding was 5.6 ± 0.3 GPa, and the alloys sintered with 20-minute isothermal holding at 1050 °C — Hv10 = 4.9 ± 0.3 GPa.