Compressive properties of zone-directionally solidified β-NiAl and its off-eutectic alloys with chromium and tungsten

The ordered intermetallic compound beta-NiAl and its pseudo-binary off-eutectic alloys with 1 at.% tungsten and 9.7 at.% chromium were directionally solidified (DS) in the 'floating-zone' mode, and tested for compressive strength and fracture behavior in the temperature range 300-800 K. The dual-phase structures created by the DS of ternary NiAl alloys led to improvements in both the compressive strength and the ductility. The room-temperature (300 K) 0.2% compressive yield strength (CYS) of DS NiAl(W) (623 MPa) is larger than the CYS of DS NiAl(Cr) (565 MPa) and DS NiAl (435 MPa). The CYS of the three alloys dropped with increasing test temperature, and at 800 K, the CYS values for the three materials were comparable (356, 315 and 344 MPa for NiAl, NiAl(W) and NiAl(Cr), respectively). All the DS alloys exhibited greater than near-zero ductility of polycrystalline beta-NiAl at room-temperature, with the fracture strain being the largest for the DS NiAl(Cr) (16.6%), followed by DS NiAl(W) (9.8%) and DS NiAl (7.33%). The strength and ductility data and fractography of test specimens suggest that ductile-phase toughening and second-phase strengthening are responsible for the observed improvements in the ductility and strength of NiAl. Limited tensile tests on the DS NiAl and DS NiAl(Cr) indicate that the CYS is greater than the tensile yield strength. (C) 2002 Elsevier Science B.V. All rights reserved.