POROSITY AND ARGON CONCENTRATION IN GAS-ATOMIZED GAMMA-TIAL POWDER AND HOT ISOSTATICALLY PRESSED COMPACTS

The porosity, the pore size distribution and the Ar-concentration of d ifferent powder particle size fractions of Ar gas atomized gamma-TiAl alloy powder is analysed. While the porosity is found to increase stro ngly (32-45 mu m: 0.05%; 250-355 mu m: 0.9% volume porosity), the Ar-c oncentration only varies little with increasing powder size fraction ( 32-45 mu m: 0.5 +/- 0.15 mu g g(-1) Ar; 250-355 mu m: 1.2 +/- 0.15 mu g g(-1)). The reason for this different behaviour is the decrease of t he Ar gas pressure inside the pores with increasing pore diameter (7 m u m pore diameter: similar to 0.17 MPa; 100 mu m pore diameter: simila r to 0.03 MPa). The Ar-concentration of hot isostatically pressed gamm a-TiAl powder, size fraction 0-250 mu m, is 0.45 +/- 0.1 mu g g(-1). T his Ar-content can not be further reduced by choice of distinct powder particle size fractions. (C) 1998 Elsevier Science S.A. All rights re served.