Consolidation behavior of L1(2) phase (Al+12.5 at. %Cu)(3)Zr powder with nanocrystalline structure during CIP and subsequent sintering

Abstract

The mechanically alloyed (Al + 12.5 at.% Cu)(3)Zr powders were consolidated by cold isostatic pressing (CIP) and subsequent sintering. Effects of CIP pressure and sintering temperature on the stability of metastable L1(2) phase and nanocrystalline structure were investigated. Before sintering, the powders were CIPed at 138, 207, 276, and 414 MPa. The relative densities of the CIP compacts were not greatly affected by the CIP pressure. However, the L1(2) phase of the specimen CIPed at pressures greater than 276 MPa was partially transformed into D0(23). The optimum consolidation conditions for maintaining L1(2) phase and nanocrystalline microstructure were determined to be CIP at 207 MPa and sintering at 800degreesC for 1 h for which the grain size was 34.2 nm and the relative density was 93.8%. Full density specimens could be prepared by sintering above 900degreesC, however, these specimens consisted of L1(2) and D0(23) phases. The grain sizes of all the specimens were confirmed by TEM and XRD, and were found to be less than 40 nm. This is one of the smallest grain sizes ever reported in trialuminide intermetallic compounds. (C) 2004 Elsevier B.V. All rights reserved.