Bonding of Molybdenum by Immersion Process in Fused Salts

Abstract

Bonding of the molybdenum was carried out by immersion in fused mixture of boric acid, potassium borate, magnesium powder and an activator. In this process, boron supplied by the fused boric acid and potassium borate formed a boride layer on the molybdenum surface. The composition, structure, thickness, and hardness of the molybdenum boride, and the wear resistance of the bonded molybdenum were investigated. X-ray analysis showed that the composition of the molybdenum boride layers formed by immersion boriding were MoB (δ-MoB) and Mo₂B₅. Boride layers formed by immersion at 1000°C for 5h were about 25μm thick, and had knoop hardness numbers of from 2900 to 3400. The apparent activation energy obtained was 80.1kcal/mol for the formation of molybdenum boride at temperatures from 900 to 1000°C. Borided molybdenum showed greater wear resistance than did unborided molybdenum within the limits of this experiment.