Cerium dioxide (CeO2), yttrium oxide (Y2O3), and lanthanum oxide (La2O3) are the three most common rare earth oxides that alloy with molybdenum (Mo). All three improve both the ductility and high-temperature strength of Mo. However, lanthanum molybdenum (Mo-La alloy), created by combining lanthanum and molybdenum in their liquid state, exhibits the best performance. For example, the longitudinal ductility of Mo-La alloy plate is at least 20%, and as much as 46%, more significant than that of pure molybdenum plate.
The Effect of La2O3 in Enhancing the Ductility of Lanthanum Molybdenum
There are two primary reasons for the excellent ductility of lanthanum molybdenum.
Fine-sized, uniformly dispersed La2O3 particles inhibit the growth of intergranular microcracks during the Mo-La deformation process, which is completed at a smooth, gradual pace. These fine particles also ensure short crystal slips between each two of the alloy’s atomic planes, limiting dislocation pile-up during deformation.
La2O3 also reduces the adverse effects that C, N, and O impurities have on molybdenum ductility by decreasing the size of Mo-La grains. The concentration of impurities is thus reduced due to the enlarged area of the grain boundary. The finer grain structure also results in more surface area where impurities may deposit, further reducing their concentration on the grain boundaries.
The Effect of La2O3 in Enhancing the Strength of Lanthanum Molybdenum
La2O3’s fine-sized particles also significantly enhance the yield strength of molybdenum by acting as a “pinning agent,” in accordance with the theory of the Orowan strengthening mechanism. These tiny particles impede the dislocation movement that occurs during deformation by “pinning” it at the boundaries of Mo-La crystalline grains and along their strong slip bands. This effect of La2O3 boosts lanthanum molybdenum’s strength to resist the dislocation movement stresses.