Thermal Stability and Grain Growth Kinetics of Ultrafine-Grained W with Various Amount of La₂O₃ Addition

In this study, ultrafine-grained W alloys with various amount of La₂O₃ addition (0.5 ~ 5.0 wt pct) have been prepared by pressureless sintering. The influence of the addition of La₂O₃ particles on the grain growth of ultrafine-grained W alloys have been studied. The results showed that the addition of La₂O₃ particles can significantly decrease the grain growth rate, but it seems counterintuitive that the ultrafine-grained W alloy with 2.0 wt pct La₂O₃ addition, rather than 5.0 wt pct, has the smallest grain size (1.23 μm) after annealing at 1900 °C for 6 h. To reveal the abnormal grain growth behavior, the inhibition effect of the size and distribution of La₂O₃ particles on grain growth was analyzed, suggesting that the excessive addition of La₂O₃ particles can cause an abnormal increase in grain size duo to the large fraction of intergranular particles, the small-particle spacing and the high mass transfer rate at the grain boundary.