Metallurgical and Materials Transactions A

, Volume 33, Issue 6, pp 1795–1804

Tree-ring formation during vacuum arc remelting of INCONEL 718: Part I. Experimental investigation

  • X. Xu
  • R. M. Ward
  • M. H. Jacobs
  • P. D. Lee
  • M. McLean
Article

Abstract

In the production of turbine discs, the final wrought structure is critically dependent on aspects of the ingot grain structure produced by vacuum arc remelting (VAR) prior to cogging and forging. Variations in the as-cast grain structure in the nickel-based superalloy INCONEL 718 were investigated, focusing upon regions where strings of equiaxed grains interrupt a predominately columnar-dendritic structure. These features, termed “tree rings,” form concentric circles that can be observed visually on etched transverse sections of the VAR ingot. These structures are of interest because they correlate with perturbations in control of the process and have also been associated with the occurrence of defects. This article describes an experimental study of these tree rings, which both characterizes them and investigates possible mechanisms for their formation. Fluctuations in the macroscopic heat, mass, and momentum transfer, which can increase the grain nucleation at the mushy zone front (similar to a columnar-to-equiaxed transition), were considered to be the most likely of the mechanisms hypothesized. In a second article, a multiscale mathematical model is developed to quantify these concepts and to determine whether they account for the features observed.

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Copyright information

© ASM International & TMS-The Minerals, Metals and Materials Society 2002

Authors and Affiliations

  • X. Xu
    • 1
  • R. M. Ward
    • 2
  • M. H. Jacobs
    • 2
  • P. D. Lee
    • 3
  • M. McLean
    • 3
  1. 1.IMMPETUSThe University of SheffieldSheffieldUnited Kingdom
  2. 2.the IRC in Materials ProcessingUniversity of BirminghamBirminghamUnited Kingdom
  3. 3.the Department of MaterialsImperial College of Science, Technology and MedicineLondonUnited Kingdom

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