Comparison of PM-HIP to Cast Alloy 625 for Nuclear ApplicationsAlexander Bullens1, Keyou Mao1, Esteban Bautista2, Janelle Wharry1

1Purdue University, 2California State University – North Ridge

Experimental MethodsIntroduction and Motivation

Results

References

Acknowledgements

Alloys produced by powder metallurgy with hot isostatic pressing (PM-HIP) have been used in the fossil fuels and aerospace industries for many years, but have not yet been introduced to nuclear applications [1,2]. Compared to traditional forged/cast metals, PM-HIP alloys can be produced with fewer defects and near-net shape. PM-HIP alloys have the potential to exhibit more advantageous mechanical properties, but more research needs to be done. Our research aims to study the differences between PM-HIP and forged/cast alloys under extreme conditions typical of nuclear applications [3]. The results of this study will contribute to the licensing of PM-HIP alloys to be used in nuclear applications.

PM-HIP Alloy 625 exhibits superior strength compared to its cast counterpart, mainly because of the refined grain size.

The PM-HIP (as well as the cast alloy) exhibit microstructural and mechanical integrity following 100 hour thermal aging at temperatures up to 800° C.

PM-HIP processed alloys have potential for being licensed for nuclear applications. Further research on these materials will need to be done to fully justify such licensing, including fully understanding the differences between PM-HIP and cast manufacturing methods.

The next step in our research is to investigate the samples that were heat treated for 1,000 hours and compare them to the 100 hour samples. Lastly, we would like to perform irradiation testing on these samples to see the differences in how radiation effects the degradation of the materials.

1. Conway, J., Hann, B., “Hot isostatic pressing of metal powders: A commercial success “High Pressure Technology -1999 (The ASME Pressure Vessels and Piping Conference), August 1, 1999 - August 5, 1999

2. Gandy, D., Siefert, J., Lherbier, L., Novotnak, D. “PM-HIP research for pressure retaining applications within the electricpower industry” ASME 2014 Small Modular Reactors Symposium, SMR 2014; Washington, DC; United States; 15 April2014 through 17 April 2014.

3. Jakobsson, K., Lardon, J., Pellegrini, C., Sundin, S. “High alloyed stainless steel PM material for demandingapplications”2014 World Congress on Powder Metallurgy and Particulate Materials, PM 2014, May 18, 2014 - May 22,2014.

The results from our chemical etching can be seen above, with the PM-HIP samples on top and the Cast samples on the bottom. We can also see the relationships between average grain size and heat treatment temperature along with hardness and heat treatment temperature.

From our results for 100 hours of annealing, the average grain size of the PM-HIP samples is consistently smaller than that of the cast samples at all heat treatment temperatures. We also observe that annealing does not cause a statistically significant change in grain size does outside of error bars.

PM-HIP samples exhibited higher hardness values than cast samples across all heat treatments, except at 800°C. However, neither PM-HIP nor cast specimens have a statistically significant change in hardness with annealing.

A special thank you goes out to all of the people who helped out on this project: Hao Wang, Priyam Patki, T. J. Novakowski, and Sophia Chun. Lastly, a thank you to the sponsors of my work: Purdue SURF, Department of Energy Nuclear Science User Facilities, and Purdue Nuclear Engineering.

Conclusions & Future Work

We received bars of Ni-base Alloy 625 that were manufactured by PM-HIP or casting. We cut each bar into smaller pieces to enable multiple annealing times and temperatures. We then heat treated the samples at 400°C, 600°C, and 800°C, for 100 hours in order to study the effect of temperature and time on the alloy. Annealed samples were mounted and mechanically polished with SiC paper then up through 1 μm diamond suspension. A chemical etchant, Adler’s Etchant, was used on each specimen so that the grain boundaries could be seen by optical microscopy. Lastly, microhardness testing was conducted on these samples to test the hardness of these samples.

PM-HIP

Cast

As Received

As Received

400 °C 600 °C 800 °C

400 °C 600 °C 800 °C

Cast

PM-HIP