Solidification of Nb-bearing superalloys. Part 1: Reaction sequences
- Lehigh Univ., Bethlehem, PA (United States)
- Sandia National Labs., Albuquerque, NM (United States)
The solidification reaction sequences of experimental superalloys containing systematic variations in Fe, Nb, Si, and C were studied using differential thermal analysis (DTA) and microstructural characterization techniques. The reaction sequences responsible for microstructural development were found to be similar to those expected in the Ni-Nb-C ternary system and commercial superalloys of comparable composition. The solute-rich interdendritic liquid generally exhibited two eutectic-type reactions at the terminal stages of solidification: L {r_arrow} ({gamma} + NbC) and L {r_arrow} ({gamma} + Laves). The Ni- base alloys with a high C/Nb ratio represented the only exception to this general solidification sequence. This group of alloys terminated solidification with the L {r_arrow} ({gamma} + NbC) reaction and did not exhibit the {gamma}/Laves constituent. At similar levels of solute elements (Nb, Si, and C), the Fe-base alloys always formed more of the {gamma}/Laves eutectic-type constituent than the corresponding Ni-base alloys. Silicon additions also increased the amount of the {gamma}/Laves constituent that formed in the as-solidified microstructure, while C additions promoted formation of {gamma}/NbC. The influence of Nb was dependent on the C content of the alloy. When the C content was low, Nb additions generally promoted formation of {gamma}/Laves, while Nb additions to alloys with high C led to formation of the {gamma}/NbC constituents. The results of this work are combined with quantitative analyses for developing {gamma}-Nb-C pseudoternary solidification diagrams in a companion article.
- Research Organization:
- Sandia National Laboratory
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 290255
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 11 Vol. 29; ISSN 1073-5623; ISSN MMTAEB
- Country of Publication:
- United States
- Language:
- English
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