Effect of two-step reduction on ZrC size and dispersion

• Various ZrC powders were produced by a one-step (OSR) and two-step reduction (TSR).
• TSR stoichiometry produces ZrC0.91–ZrC0.97.
• TSR1513 shows agglomerates of <1 μm, which consist of particle size of 30 nm.
• The average TSR1513 particle size was the smallest among the W–ZrC samples.
• This improves the Vickers hardness.

A two-step carbothermal reduction process produced zirconium carbide particles with less aggregation and smaller ZrC grains than those produced by one-step reduction. Reduction at 1500 °C for 10 min (1st step) and then at 1300 °C for 30 min (2nd step) produced significantly smaller agglomerations (1–8 μm) and particles (33 nm) than those produced using other reduction processes, which were 2–200 μm and >1 μm, respectively. The first high-temperature step allowed effective reduction, while the subsequent cooler step inhibited grain growth and agglomeration. The resulting ZrC particles showed a stoichiometric composition of ZrC0.97 through control of the carbon content. A sintered W–ZrC composite made using the two-step-reduced ZrC was harder and showed a more homogeneous dispersion of ZrC in the tungsten matrix than a composite made using one-step sintered ZrC.