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.

Keywords

• arc cladding
• MoSi2
• La2O3
• microstructure
• wear resistance
• fracture toughness