Influence of directional solidification variables on the cellular and primary dendrite arm spacings of PWA1484

• Published in: Journal of materials science 2002-08, Vol.37 (16), p.3521-3532
• Main Authors: LI, L, OVERFELT, R. A
• Format: Article
• Language: English
• Subjects: Alignment; Applied sciences; Bridgman method; Cross-disciplinary physics: materials science; rheology; Crystal growth; Dendritic structure; Directional solidification; Exact sciences and technology; Flanges; Materials science; Metals. Metallurgy; Microstructure; Nickel base alloys; Nonuniformity; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Process parameters; Solidification; Superalloys
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1023/A:1016527509815

A series of directional solidification experiments have been performed to elucidate the effects of thermal gradient G and growth velocity V on the solidification behavior and microstructural development of the multicomponent Ni-base superalloy PWA 1484. A range of aligned as-cast microstructures were exhibited by the alloy: (i) aligned dendrites with well developed secondary and tertiary arms; (ii) flanged cellular dendrites aligned with the growth direction and without secondary arms; and (iii) cells with no evidence of flanges or secondary arms. The role of the imposed process parameters on the primary arm spacings that developed in the Bridgman-grown samples were examined in terms of current theoretical models. The presence of secondary arms increases the spacings between dendrites and leads to a greater sensitivity of λ1 on G−1/2V−1/4. The exponent of V was analyzed and found to depend upon the imposed gradient G. High withdrawal velocities and low thermal gradients were found to cause radial non-uniformity of the primary dendrite arm spacing. Such behavior was associated with off-axis heat flows.