Experimental research and first-principles calculation of the effects of La₂O₃ on the microstructure and properties of the MoSi₂ coating using arc-cladding

Abstract The poor room-temperature toughness of MoSi 2 hinders its application as a structural material. A thorough analysis was conducted using arc cladding experiments and first-principles calculations to investigate the effect of La 2 O 3 on the mechanical properties of the MoSi 2 coating. The ductility of La 2 O 3 (Poisson’s ratio v > 0.26; B/G > 1.75) was demonstrated by the first-principles calculation, which enhanced the fracture toughness of MoSi 2 . The bulk modulus, shear modulus, Young’s modulus, and Vickers hardness of La 2 O 3 were calculated through Voigt-Ruess-Hill approximations. The findings of the experiment indicated that the pure MoSi 2 coating consisted of MoSi 2 and Mo 5 Si 3 phases with cellular dendritic crystals. When the MoSi 2 coating was added with La 2 O 3 , the microstructure of the coating became denser and finer. La 2 O 3 reacted with SiO 2 , which formed La 2 Si 2 O 7 phases. When the La 2 O 3 content was 3, 5, 7, and 9 wt%, the average hardness of the coatings with La 2 O 3 was 9.73, 16.78, 29.98, and 52.67% more than that of the pure MoSi 2 coating, respectively. The MoSi 2 coating was added with 7 wt% La 2 O 3 had the highest fracture toughness, approximately twice as high as the pure MoSi 2 coating. This was attributed to the fact that La 2 O 3 could disperse the main stress of cracks and inhibit their propagation. Furthermore, the MoSi 2 coating added with 7 wt% La 2 O 3 had the flattest wear surface and the lowest wear loss.