An investigation of surface modification due to the deposition of silicon onto molybdenum

This thesis reports on experiments to form a molybdenum disilicide (MoSi₂) layer on the surface of molybdenum. A 3 kW CO₂ laser was utilized to melt the surface of the molybdenum, where a powder feeder was employed to spray silicon powder into the melt pool created by the laser. A matrix of experiments was performed to find the optimal conditions for the deposition of silicon to create a MoSi₂ layer. From these experiments it was concluded that the translation velocity of the processing laser and the amount of silicon being deposited onto the molybdenum surface are crucial parameters. The addition of silicon to the melt pool increased the cross sectional area of the fusion zone, as compared to a laser radiated surface without the addition of silicon. The addition of silicon at translation velocities of 500 and 750 (mm/min), caused a substantial increase of both the fusion zone and molybdenum-silicon areas, compared to translation velocities from 1000 to 2000 (mm/min). The surface modification experiments produced molybdenum-silicon regions varying in percent concentrations from 1 wt. % silicon to cladding layers containing 99 wt. % silicon. Different phases of molybdenum-silicon were present including Mo₃Si, Mo₅Si₃ and a small region of MoSi₂.