LAUSR

ABSTRACT In this work, the powder of a Ni-based superalloy (EP741NP) was sieved into two batches, one with coarse powder (63–150 μm), and the other containing fine powder (25–63 μm). The effects of holding time, temperature, and vacuum level on the outgassing behaviours of these powders were investigated. The results indicated that the coarse and fine powders were most efficient at outgassing when holding at low temperatures (200–300°C) and vacuum for 4 and 24 h, respectively. Unde those conditions, 22% and 16% decreases in oxygen were recorded respectively. The structures and compositions of the oxides formed on the powders’ surfaces were analysed via thermodynamic calculations and by SEM/EDX/XPS. The porous surface oxide layers identified in both cases at 400°C/800°C in air mainly consist of aluminium oxide, with Cr and Ti, participated in the oxide formation.