Metallurgical Analysis and Conservation of Turbine Blades from Recovered Apollo F-1 Engines

ABSTRACT

Turbine blades recovered from the Apollo Saturn V rocket F-1 engines were examined to determine an appropriate conservation protocol. Significant corrosion damage was observed in the turbine blades which appear to be made of a nickel based γ–γ′ superalloy. Pitting corrosion appears to have breached the surface of the turbine blades, and subsequently a form of dealloying corrosion preferentially attacked the γ′ phase. This corrosion left behind a thin network of interconnected γ phase, causing a severe loss of density of the blades and fragility of the blades. The particular alloy used for these turbine blades does not appear to be a known production alloy and may have been developed specifically for use in the F-1 rocket engines, with an increased concentration of refractory (Mo, Nb) elemental additions. The analytical results helped conservators determine a suitable treatment protocol for more than 400 blades and 100 fragments from four recovered turbines.

KEYWORDS:

• Space program
• superalloy
• turbine
• marine corrosion
• metallography

Acknowledgements

The authors acknowledge the substantial contributions to this project and paper from Dr. Timothy Foecke prior to his retirement from NIST, reviewers Dr. Dale Newbury, Dr. Mark Stoudt, Malcolm Collum, Greg Smith, and Studies in Conservation reviewers for helpful comments and suggested changes. As of the writing of this article some of the F-1 artifacts conserved during this project are on display at the Cosmosphere International Science Education Center & Space Museum in Hutchinson, Kansas USA; the Smithsonian National Air and Space Museum in Washington DC USA; and at the Museum of Flight in Seattle, Washington USA.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Pounds per square inch absolute (psia), or relative to a vacuum. There is an offset between psia and pounds per square inch gauge (psig), which is recorded relative to atmospheric pressures.

2 In many manufacturing records in the United States, niobium (Nb) may be listed as columbium (Cb).

3 Solid solution hardening is induced by replacing the base element with additional elements with slightly dissimilar atom sizes. This atomic arrangement blocks deformation and increases the strength of the material.

4 After the Greek ‘dendro’ meaning ‘tree’. Snowflakes might be the most familiar form commonly encountered, which are dendritic ice structures.

5 Using the tree analogy, dendrite arm spacing is akin to distance between branches. This parameter can be used to identify the growth mechanisms and energetics of the casting process, in a similar manner that trees and other plants can be identified by branching patterns.

6 Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by NIST, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.

7 Labeled as sample #10 in Creuziger and Foecke and data publication records.

8 The regions are not marked on Figure 5 as they were taken from a different sample.

9 Toughness is a metric for energy absorption in materials science that combines strength and ductility. In this case, the significant ductility of the γ phase makes it ‘tougher’ than the γ' phase, despite the strength of the γ phase being less than the γ' phase.

10 These inclusions were tentatively identified as carbides but did not have a significant C signature in Figure 9. C identification is not definitive as a carbon coating was required to make the sample surface conductive in the SEM.

11 This supposition is supported by informal discussions with Rocketdyne staff who visited during conservation.

Additional information

Funding

This work was supported by National Institute of Standards and Technology; Kansas Cosmosphere and Space Center.