Influence of Nanocrystalline ZrO2 Additives on the Fracture Toughness and Hardness of Spark Plasma Activated Sintered WC/ZrO2 Nanocomposites Obtained by Mechanical Mixing Method

摘要

The present study reports the formation of ultrafine hard particles of nanocomposite WC with different additions of ZrO2 powders (0.5 - 20 vol.%). The initial mixed powders of WC with the desired ZrO2 concentrations were mechanically mixed for 360 ks (end-product) under argon gas atmosphere at room temperature, using high energy ball mill. The end-product consists of average grain size of about 17 nm in diameter. The obtained nanocomposite powders were consolidated into fully dense compact, using spark plasma sintering (SPS) technique in vacuum. The experimental results revealed that the consolidation step, which was conducted at 1673 K with uniaxial pressure ranging from 19.6 to 38.2 MPa for short time (0.18 ks), does not lead to dramatic grain growth in the powders so that the consolidated nanocomposite bulk objects maintain their nanocrystalline behavior, being fine grains with an average size of 63 nm in diameter. The relative densities of consolidated nanocomposite WC/ZrO2 materials increase from 99.1% for WC-0.5% ZrO2 to 99.93% for WC-20% ZrO2. The indentation fracture toughness of the composites can be tailored between 7.31 and 19.46 MPa/m1/2 by controlling the volume fraction of ZrO2 matrix from 0.5% to 20%. The results show that the Poisson’s ratio increased monotonically with increasing the ZrO2 concentrations to get a maximum value of 0.268 for WC-20% ZrO2. In the whole range of ZrO2 concentrations (0.5 - 20 vol.%), high hardness values (20.73 to 22.83 GPa) were achieved. The Young’s modulus tends to decrease with increasing the volume fraction of the ZrO2 matrix to reach a minimum value of 583.2 GPa for WC-20% ZrO2. These hard and tough WC/ZrO2 nanocomposites are proposed to be employed as higher abrasive-wear resistant materials.