The effect of internal hydrogen on a single-crystal nickel-base superalloy
- PDF / 3,028,015 Bytes
- 10 Pages / 630 x 792 pts Page_size
- 112 Downloads / 200 Views
I.
INTRODUCTION
BASEDon the superior performance of single-crystal superalloys under ambient conditions, their potential use in hydrogen-fueled engines is under consideration, tl] Many potential superalloys have been screened using notch tensile tests and other mechanical tests performed in hydrogen atmospheres designed to simulate service conditions. These tests provide valuable initial data but do not completely evaluate an aUoy's resistance to hydrogen embrittlement. A study was conducted to characterize more fundamentally the effect of hydrogen on single-crystal superalloys which, in service, can absorb H2 gas, presumably leading to embrittlement at lower temperatures. To simulate this condition, roomtemperature testing of specimens uniformly charged with hydrogen was performed utilizing PWA 1480 as a typical single-crystal superalloy. Others have more closely examined the effects of hydrogen in superalloys. Dollar and Bernstein le] conducted a study on internally charged CMSX-2 and found that hydrogen both reduced the tensile strain to failure and led to enhanced dislocation generation. A recent study by Hicks and Altstetter tal on IN* 718 and IN 625 also *IN is a trademark of Inco Alloys International, Inc., Huntington, WV.
showed a decreased ductility in uniformly charged specimens with evidence of higher amounts of localized plasticity. They argued that this localization of plasticity could explain their present results as well as many past results on these alloys. Similarly, Fritzmeier lal has observed localized plasticity due to hydrogen on several single-crystal
superalloys. This suggests that a hydrogen-enhanced locaiized plasticity (HELP) mechanism may explain many features of hydrogen embrittlement in superalloys.
II.
EXPERIMENTAL PROCEDURES
Single-crystal slabs made by TRW, Inc., Cleveland, OH, had the following composition (weight percent): A1
Co
Cr
Ta
Ti
W
Ni
4.83 5.35 10.43 11.86 1.29 4.07 balance Specimens were given a solution heat treatment at 1288 ~ for 4 hours followed by aging at 1080 ~ for 4 hours and 875 ~ for 32 hours. All specimens were aircooled to room temperature following each heat-treatment cycle. Mechanical testing and specimen preparation techniques have been explained elsewhere. [5] All hydrogencontaining specimens were gas-phase charged at Sandia National Laboratories, Livermore, CA, for 15 days at 350 ~ and at a pressure of 103.4 MPa followed by a rapid cool while still under pressure. These severe conditions were necessary to ensure a uniform hydrogen concentration due to the low diffusivity of hydrogen in PWA 1480. Hydrogen contents were analyzed by Luvak, Inc., Boylston, MA, using vacuum hot extraction at 900 ~
III.
RESULTS
A. Microstructure W.S. WALSTON, formerly Graduate Student, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, is Research Engineer, General Electric Aircraft Engines, Cincinnati, OH 45215. I.M. BERNSTEIN, formerly Chancellor, Illinois Institute of Technology, Chicago, IL, is Vice President for Arts,
Data Loading...
