Microstructure and mechanical properties of a MoSi2-Mo5Si3 eutectic composite processed by laser surface melting

Abstract

Laser surface melting (LSM) of a single-crystal substrate of a MoSi2-Mo5Si3 eutectic composite has been performed to check the feasibility of mechanical property improvement through microstructure refinement and seeded growth of the eutectic composite on top of the seed composite single crystal by additive manufacturing processes using scanned laser beam. LSM is proved to be capable of obtaining a eutectic composite maintaining the eutectic script-lamellar microstructure as well as crystallographic orientations of the substrate single crystal. The eutectic script-lamellar microstructure is considerably refined from several micrometers (the substrate) to several tenths nanometers (43 ± 7 nm) after LSM processing while maintaining the orientation relationship. Due to the microstructure refinement, the hardness increases by about 38% from 11.60 ± 0.04 GPa (substrate) to 15.96 ± 0.42 GPa (LSMed region) and the fracture toughness increases by about 34% from 3.8 ± 0.3 MPa m1/2 (substrate) to 5.1 ± 1.5 MPa m1/2 (LSMed region).