AE714 Atomistic Modeling

AE714 Course Project: Hydrogen Embrittlement of Nickel – Response

to waves

Aswath Narayanan R

AE714 Atomistic Modeling

INTRODUCTION

Hydrogen Embrittlement in carbon steel, zinc plated part.Ref. www.vikingeng.net

Subsurface hydrogen embrittlement crack initiated at a non-metallic inclusion. Ref. www.hghouston.com

AE714 Atomistic Modeling

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

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

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

Sample input from an Ultrasound Transducer.

AE714 Atomistic Modeling

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.

0 0.5 1 1.5 2 2.5 3

x 10-16

-0.025

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

TIME (ps)

AM

PLIT

UD

E

-5 -4 -3 -2 -1 0 1 2 3 4 5

x 1017

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

X: 1e+016Y: 0.5

FREQUENCY (HZ)

AM

PLIT

UD

E/W

EIG

HTS

AE714 Atomistic Modeling

Results

-5 -4 -3 -2 -1 0 1 2 3 4 5

x 1017

0

2

4

6

8

10

12

14

16

18

20

FREQUENCY (Hz)

AM

PLIT

UD

E

FFT OF OUTPUT

0 0.5 1 1.5 2 2.5 3 3.5

x 104

-50

-40

-30

-20

-10

0

10

TIME STEPS

AM

PLIT

UD

E O

F F

IRS

T L

AY

ER

TIME DOMAIN OUTPUT

AE714 Atomistic Modeling

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

Stress Wave propagation

LAYERS

TIM

E S

TE

PS

2 4 6 8 10 12 14 16 18 20

0.5

1

1.5

2

2.5

3

x 104

STRESS CONTOURS

LAYERS

TIM

E S

TEP

S

2 4 6 8 10 12 14 16 18 20

0.5

1

1.5

2

2.5

3

x 104

DISPLACEMENT CONTOURS

AE714 Atomistic Modeling

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

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 intergranular embrittlement 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

Thank You!!!