A Study of the Kinetics of Phase Transformations in Nb-Ti-Al Alloys
Abstract
The solidification pathways, subsequent solid-state transformations and the liquidus sulface in the Nb-Ti Al system have been examined as part of a larger investigation of phase equilibria in Nb-Ti-Al intermetallic alloys. Fifteen alloys ranging in composition from 15 to 40 at. % Al, with Nb to Ti ratios of 4:l, 2:1,1.5:1,1:1 and 1:1.5 were prepared by arc-melting, and the as-cast microstructures were characterized by optical microscopy, microhardness, x-ray diffraction, differential thermal analysis, back-scattered electron imaging, electron probe microanalysis and transmission electron microscopy. The results indicate that the range of primary 3 solidification is much wider than that indicated in previously reported liquidus surfaces, both experimental and calculated Differential thermal analysis bas identified the existence of a 3 to y + 7transformation in three alloys where it was previously thought not to exist: confirmation was provided by high temperature vacuum heat treatments in the single-phase 3 region followed by rapid quenching. The location of the boundary between the 3, -Y and 6 primao solidification fields has been redefined. A massive /J--- 6 transformation, which was observed in the east microstructure of a Nb-25Ti-25AI alloy, was repeatable through cooling following homogenization. A 3--- > S+ cY eutectoid-like transformation in the 25 at. % Al alloys, was detected by differential thermal analysis and evaluated through microstructure analysis of heat treated samples. Trends in the 3phase with variations in composition were established for both lattice parameters and microhardness.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 19, 2000
- Accession Number
- ADA382042
Entities
People
- Joseph C. Mishurda
- Keith J. Leonard
- Vijay K. Vasudevan
Organizations
- University of Cincinnati