Mechanical Activation of Nb75Al Powder Mixtures with Different Process Control Agents

Abstract

The behavior of different process control agents (PCAs) during mechanical activation of Nb75Al powder mixtures was investigated. Mechanical activation by high-energy ball milling was carried out on a shaker mill (SPEX®8000) for 1 hour. Each PCA (Stearic acid, ethanol and methanol) was added to the powder charge in two proportions (1 and 2 wt%). Shape and microstructure of activated powders (aggregates) were analyzed by scanning electron microscopy. Milled powder mixtures were uniaxially pressed in cylindrical compacts that were further vacuum reacted at a constant heating rate (30°C/min) in order to produce NbAl3 intermetallic compound. The temperature of the samples was monitored by an S-type thermocouple. The results show that the shape and the microstructure of the milled powders were strongly affected by the type and quantity of PCAs, therefore changing the reaction behavior and the densification of the produced pellets. Although ethanol was more effective to control aggregate size, best densification results were attained with 2 wt% of stearic acid.