Influence of LaH2 on oxidation characteristics and irradiation melting characteristics of a tungsten coating fabricated by atmospheric plasma spraying

In this work, as a kind of rare earth hydrides, 1.5 wt.% LaH2 powder was introduced into a tungsten powder and then processed by atmospheric plasma spraying (APS) to form a coating. The oxidation characteristics and laser irradiation melting characteristics of the tungsten coatings with or without LaH2 addition were investigated and compared. The results showed that the coatings exhibited typical splat/lamellar microstructure. WO3, which was distributed between lamellar layers or in splats, formed in the APS-W coating by the oxidation reaction between W and O2. The introduction of LaH2 in the tungsten-based coating led to forming WO2 by a deoxidization of WO3. La2O3 with a morphology of long strip, which was distributed mainly between lamellar layers and had a filling effect on the pores, formed in the APS-W/LaH2 coating by the oxidation reaction between La/LaH2 and WO3/O2. The oxide/oxygen content and the porosity of the APS-W/LaH2 coating were apparently lower than those of the APS-W coating; and the relative density and thermal conductivity of the former were higher than those of the latter. The trends of the crack to form in the APS-W/LaH2 coating were lower than that in the APS-W coating when the two types of coatings were irradiated by a laser. The coarse elongated tungsten grains formed in laser irradiation melting sample for the APS-W coating. But the fine equiaxial tungsten grains formed in laser irradiation melting sample for the APS-W/LaH2 coating, which was mainly the result of the pinning effect of the re-precipitated spherical La2O3 particles on the re-crystalline tungsten grain boundaries. The ability of the APS-W/LaH2 coating to resist high heat loading was greater than that of the APS-W coating.