Interdendritic Fluid Flow Effects on Single Crystal Grain Defects
Abstract
This research project has been investigating the phenomenon of grain defect formation in nickel-base superalloys. Cylindrical samples of the nickel-based multicomponent alloy PWA 1484 were produced by Howmet Corporation. Utilization of this alloy enabled the application in this research of previous data on this alloy on dendrite arm spacings and thermophysical properties. Samples were re-solidified under carefully controlled laboratory conditions to modify the solidification length scales (mushy zone lengths and dendritic spacings) and the density differences within the mushy zone during solidification. The primary dendrite arm spacings that developed in the Bridgman-grown samples were examined in terms of current theoretical models of the effects of process parameters. Low thermal gradient conditions necessitated modifying the theoretical relationship for primary dendrite arm spacings by the factor 1+F(PHI), where((f(phi)) is a function of the ratio of radial-to-longitudinal thermal gradients (Gr/GL). Validated computational models of the directional solidification process showed that the mushy zone isotherms were flat for these conditions. In addition, for the range of thermal gradients and solidification velocities investigated (^ 5-50 deg C/cm and 0.0005 - 0.01 cm/sec, respectively), no samples exhibited channel segregates or freckle grain defects, in agreement with industrial experience for flat mushy zone isotherms.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 26, 2000
- Accession Number
- ADA384209
Entities
People
- R. A. Overfelt
Organizations
- Auburn University