AE714 Course Project : Hydrogen Embrittlement of Nickel – Response to waves

1. AE714 Course Project: Hydrogen Embrittlement of Nickel – Response to waves Aswath Narayanan R AE714 Atomistic Modeling

2. INTRODUCTION Subsurface hydrogen embrittlement crack initiated at a non-metallic inclusion. Ref. www.hghouston.com Hydrogen Embrittlement in carbon steel, zinc plated part. Ref. www.vikingeng.net AE714 Atomistic Modeling

3. Where it is critical? • Cast and wrought nickel-base alloys are the workhorse materials for the "hot components" of gas turbine engines, and will probably continue to be for some time to come.* • The major reasons are that such alloys have high strength in the temperature range up to 20000 F. They also have generally good oxidation resistance. Ref. N I C K E L - B A S E ALLOYS FOR AEROSPACE A P P L I C A T I O N S John C. Freche AE714 Atomistic Modeling

4. Previous Studies • Previous studies suggest that Hydrogen increases the stress at the grain boundaries and hence cause the weakening of the material. • Despite extensive study, the mechanism(s)of hydrogen embrittlement have remained unclear. Several candidate mechanisms have evolved, each of which is supported by sets of experimental observations. AE714 Atomistic Modeling

5. Behavior of Hydrogen atoms in Nickel • Potential used : EAM potential for NI-H • where F is the embedding energy which is a function of the atomic electron density rho, phi is a pair potential interaction, and alpha and beta are the element types of atoms I and J. (From LAMMPS manual). • EAM potential is used for metals since it is conceptually similar to the multi body type of bonding in metals. AE714 Atomistic Modeling

6. Sample input from an Ultrasound Transducer. AE714 Atomistic Modeling

7. Input to model – Hanning Pulse • It is used to simulate a real time Ultrasound Signal. • Has a narrow band- is focused around the central frequency. AE714 Atomistic Modeling

8. Results FFT OF OUTPUT TIME DOMAIN OUTPUT AE714 Atomistic Modeling

9. Phase of the output response-FFT • The effect of the Hydrogen atoms in the lattice is expected to change the phase of the reflected signal. • However, due to problems with FFT, the peak occurs at zero frequency. AE714 Atomistic Modeling

10. Stress Wave propagation STRESS CONTOURS DISPLACEMENT CONTOURS AE714 Atomistic Modeling

11. Wavelet Transforms and Future work • It is difficult to obtain the frequency spectrum using FFT’s , as the band over which the output is to be Fourier Transformed is not trivially obtained in this case. • Further, the effect of anisotropy and dispersion on wave propagation will also be attempted. AE714 Atomistic Modeling

12. References • [1] http://www.uni-saarland.de/fak8/wwm/research/phd_barnoush/hydrogen.pdf • [2] Hydrogen embrittlement of nickel DH Lassila – 1985 • [3] Hydrogen embrittlement of nickel T Matsumoto, HK Birnbaum - Name: Trans. Jpn. Inst. Met., Suppl, 1980 • [4] Hydrogen Embrittlement of Nickel B Kolachev - Izv. VUZ Tsvetn. Metall. • [5] The intergranularembrittlement of nickel by hydrogen: The effect of grain boundary segregation R. M. Latanision and H. Opperhauser • [6] Semiempirical, Quantum Mechanical Calculation of Hydrogen Embrittlement in Metals Murray S. Daw and M. I. Baskes • [7] The influence of hydrogen on the plastic deformation ductility, and fracture of nickel in tension T. Boniszewski and G. C. Smith AE714 Atomistic Modeling

13. Thank You!!! AE714 Atomistic Modeling