Surface Modification of Molybdenum by Iron-Powder Pack Treatment

Abstract

Molybdenum sheets were embedded in mixtures of iron, graphite and alumina powders and heated at 1073–1373 K for 1.8–14.4 ks in a nitrogen flow. This process is a new surface modification technique called “Iron-powder pack (IPP) treatment”. The amount of alumina added as an anti-sintering agent was fixed in the powder mixtures, and the volume ratio of iron, graphite and alumina powders was varied from 0:10:2 to 6:4:2. An XRD pattern of the surface of the molybdenum sheet heat-treated at 1273 K for 3.6 ks using a 0:10:2 mixture had some small peaks for α-Mo₂C. However, it could be identified by optical microscopy and scanning electron microscopy. On the other hand, the use of mixtures containing iron powder led to the formation of an α-Mo₂C layer. When IPP treatment using a 4:6:2 mixture was carried out at 1273 K for 3.6 ks, the α-Mo₂C layer with a thickness of approximately 14 µm formed on the molybdenum surface. The layer began to be observed at a heating temperature of 1073 K, and grew toward the inside of the molybdenum via the diffusion of carbon from the powder mixture. The sheet covered with the thick α-Mo₂C layer showed a surface hardness of approximately HV = 1500.

Fig. 3 Optical micrograph of a cross section of a molybdenum sheet heat-treated at 1273 K for 3.6 ks in a nitrogen flow using a 4:6:2 mixture of iron, graphite and alumina powders.