Thermal and mechanical properties of sintered machinable LaPO4–ZrO2 composites

Monazite-type LaPO4 was synthesized using the wet precipitation and mechanochemical reaction methods. Mixtures of xLaPO4–(1−x)ZrO2 (x=0–1) were dry-pressed to disks or plates and cold isostatically pressed (CIP) at 100 MPa for 10 min and then sintered at temperature between 1500 and 1600°C for 1, 3, and 5 h in air, respectively. Relative densities larger than 96.8% (x≤0.4) and 92% (x=0.5–1) were achieved. It was found that these composites with x≥0.25 and single-phase LaPO4 were machinable, that is, they could be cut and drilled using conventional tungsten carbide metal-working tools. The drilling rates were measured by applying a fixed load of 49 N to the drill at 6400 rpm. X-ray diffraction results showed that the LaPO4 did not react with ZrO2, at least at 1600°C in air. The linear thermal expansion coefficient, thermal conductivity, bending strength, and Young’s modulus of the sintered composites were measured.