Submicron coating strategy overcomes densification bottlenecks in liquid-phase sintering of immiscible WCu bimetallic systems

Tungsten‑copper (WCu) composites had received attention due to their high melting point (W) and excellent conductivity/thermal conductivity (Cu), and were widely used in high-temperature electrical contact materials. However, their intrinsic immiscibility limited the achievement of densification via conventional powder metallurgy, yielding sintered densities of only 85–92 % of theoretical values. This study proposed a submicron coating engineering strategy to address this challenge. By chemically precipitating and hydrogen-reducing a CuSO₄ precursor, submicron W coatings were constructed on micron-sized W particles (4–5 μm). After calcination at 450 °C and hydrogen reduction at 900 °C, the coated composite powders were liquid-phase sintered at 1300 °C for 2 h, achieving a relative density of 97.8 %, which significantly surpassed the value of conventional methods (84.9 %). Microstructural analysis revealed that the submicron coatings prolonged the particle rearrangement phase by isolating micron-sized W grains, while the high surface activity of submicron particles enhanced interfacial diffusion, synergistically optimizing densification. The sintered body without impurity phase exhibited an electrical conductivity of 54.7 % IACS (comparable to 56.0 % for infiltration products), a 73 % hardness increase (179.8 HB). This strategy overcame the densification bottlenecks in immiscible systems by regulating interparticle interactions and offered a universal solution for analogous systems (e.g., MoCu, WAg).