Material characterization of nickel-based super alloys through

167 Pages·2017·3.89 MB·English

by  Pranaam Haldipur

Iowa State University Capstones, Theses and
Retrospective Theses and Dissertations
Dissertations
2006
Material characterization of nickel-based super
alloys through ultrasonic inspection
Pranaam Haldipur
Iowa State University
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Haldipur, Pranaam, "Material characterization of nickel-based super alloys through ultrasonic inspection " (2006).Retrospective Theses
and Dissertations. 1259.
https://lib.dr.iastate.edu/rtd/1259
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Material characterization of nickel-based super alloys
through ultrasonic inspection
by
Pranaam Haldipur
A dissertation submitted to the graduate faculty
in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY
Major: Materials Science and Engineering
Program of Study Committee:
R. Bruce Thompson, Major Professor
Brian Gleeson
David K. Hsu
Rohit Trivedi
Ronald A. Roberts
Lester W. Schmerr, Jr.
Iowa State University
Ames, Iowa
2006
UMI Number: 3217273
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Graduate College
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This is to certify that the doctoral dissertation of
Pranaam Haldipur
has met the dissertation requirements of Iowa State University
Signature was redacted for privacy.
Major Professor
Signature was redacted for privacy.
iii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS v
ABSTRACT vii
GENERAL INTRODUCTION 1
BACKGROUND OF NICKEL-BASED SUPER ALLOYS 4
INFLUENCE OF MICROSTRUCTURE ON UT INSPECTABILITY 8
SCATTERING INDUCED ATTENUATION IN POLYCRYSTALLINE MATERIALS
10
BACKSCATTERED GRAIN NOISE IN POLYCRYSTALLINE MATERIALS 12
DISSERTATION OUTLINE 14
REFERENCES 14
CHAPTER 1. VARIATION OF UT PROPERTIES IN NICKEL-BASED SUPER ALLOYS
AND THEIR RELATION WITH LOCAL MICROSTRUCTURE 19
BACKGROUND OF NICKEL-BASED SUPERALLOYS STUDIED 20
PRELIMINARY UT EXAMINATIONS OF THE BILLET
STRIP COUPONS 25
BACK-WALL TIME-OF-FLIGHT AND AMPLITUDE C-SCANS 26
C-SCANS OF BACKSCATTERED NOISE AMPLITUDE 33
CONCLUSIONS FROM PRELIMINARY MEASUREMENTS 41
DETAILED UT PROPERTY MEASUREMENTS 43
SUMMARY 69
REFERENCES 70
CHAPTER 2. GRAIN SIZE DETERMINATION, CORRELATION WITH ULTRASONIC
PROPERTIES AND ESTIMATION OF SINGLE-CRYSTAL ELASTIC CONSTANTS
FOR NICKEL-BASED SUPERALLOYS 75
METALLOGRAPHIC EXAMINATION OF GRAIN SIZE 76
GRAIN SIZING RESULTS 87
USING PURE NICKEL EQUIAXED MICROSTRUCTURES AS A MODEL SYSTEM
TO PROVIDE AN INITIAL THEORITICAL INTERPRETATION OF OUR DATA .. 95
CORRELATIONS BETWEEN UT PROPERTIES AND AVERAGE GRAIN
DIAMETERS 100
iv
ESTIMATION OF SINGLE-CRYSTAL ELASTIC CONSTANTS 104
APPLICATION TO NICKEL-BASED SUPER ALLOYS 124
SUMMARY 126
REFERENCES 126
CHAPTER 3. MULTIPLE SCATTERING EFFECTS IN NICKEL-BASED SUPER
ALLOYS 130
SINGLE SCATTERING NOISE MODEL 131
EXPERIMENTAL VALIDATION OF MULTIPLE SCATTERING
EFFECTS 133
SUMMARY 148
OVERALL CONCLUSIONS 149
REFERENCES 149
APPENDIX 152
V
ACKNOWLEDGEMENTS
I would first like to thank my advisor, Professor R. Bruce Thompson. I could not have
imagined having a better advisor and mentor for my PhD. His knowledge, perceptiveness,
encouragement and persistence have helped me in accomplishing this milestone. His
excellent guidance, support and physical insights have helped me in achieving a better
understanding of the scope of NDT and its applications. He always had the right words of
encouragement and thoughtfiilness at times when it was needed most. His kind personality
and approach to living a vibrant life are qualities I would definitely want to imbibe. His
encouragement and support all through this pivotal stage of my life cannot be expressed in
words.
I would also like to express my sincere gratitude to Dr. Frank J. Margetan. Being a
novice in the field of ultrasonics, I cannot imagine having a better person to help me in
understanding and achieving skill sets in ultrasonic NDE. His support and guidance in
dealing with every problem is most appreciated. He has always answered every question I
had with a smile and patience. Without his support accomplishing any of this would have
been so much harder.
I would also like to thank Dr. Lester W. Schmerr, Dr. David K. Hsu, Dr. Rohit Trivedi,
Dr. Brian Gleeson and Dr. Ronald A. Roberts for serving on my thesis committee and for
many helpful comments and guidance on my research.
Finally, I would also like to thank Mr. Dan Barnard and Mr. David Rehbein for their kind
assistance and guidance in carrying out experiments that with which I was not familiar. I
would also want to take this opportunity to thank every member of our research group in
expanding my knowledge and offering help at various stages. Only a few are named here: Dr.
Hak-Joon Kim, Dr. Linxiao yu, Dr. Anxiang Li, Dr. Y anming Guo, Dr. Jon Freidl and Dr.
Darrel Enyart.
vi
I would also like to thank all my friends at I SU whose companionship brought a lot of joy
and laughter. Not to forget all my friends, the "White House" gang as we called it, they
deserve a special recognition for making life in Ames so much more cherished.
I would especially like to express my deepest gratitude to my parents who have been a
strong pillar of support and who continue to give of themselves so that their children will
prosper. Their boundless love and affection continue to amaze me. I have always aspired to
imbibe the ethics and principles that my father has stood by all through his life and he has
always been an immense source of inspiration. My mother deserves special mention for her
caring guidance, unconditional love and for being a friend I could talk to all through my life.
I would also like to thank my sister for guiding me in all walks of life.
Last but not the least, my sincere gratitude to all my teachers who shaped my life and
make me the person I am today.
vii
ABSTRACT
Nickel-based super alloys are widely used in aircraft engine components, mainly in turbine
disks and the high-pressure compressor. Extensive data on the mechanical properties of these
alloys is available. However, fundamental data relating micro-structural features to ultrasonic
properties, in turn controlling the inspectability, are not available. Understanding the
sensitivity of flaw detection depends on establishing such a relationship between the
ultrasonic properties and microstructure of the super alloys. Knowledge of these relationships
would facilitate improvements in current Ni billet inspections as well as provide data for
analysis of the Probability of detection (POD) of the inspections for various defect types.
INCONEL 718 (IN718) and Waspaloy are two classes of the nickel-based super alloys
currently being investigated. Backscattered noise is caused by the scattering of sound at grain
boundaries. Such "grain noise" carries useful information about the metal microstructure, but
it interferes with the detection of echoes from small or subtle defects. A single scattering
model has been found to be very effective in simulating the effects of backscattered noise on
the ultrasonic inspection of billets and forgings engine alloy materials. The work on this
dissertation is focused on evaluating the effectiveness of the single scattering model in
predicting backscattered noise in the nickel-based alloys. Attenuation, grain size and single-
crystal elastic constants are important input parameters that need to be evaluated for making
the predictions of noise levels. Determination of these quantities on a number of nickel-based
super alloy samples is reported and studied how noise levels predicted with the current single
scattering model compare with the direct measurements of noise on the same samples. The
deviations observed will provide a guide to future improvements in the model.
In Chapter 1, experimental investigations of the relationships between ultrasonic
properties (velocity, attenuation, and backscattered grain noise) and the microstructure are
reported. The variation of the ultrasonic properties along different inspection directions and
along the billet diameter has been studied. The attenuation measurements were carried out by
three different techniques in order to establish that measured attenuation is mainly due to
scattering at grain boundaries. The backscattered noise measurements were analyzed to
extract a material parameter, the noise Figure-of-Merit (FOM), a measure of the noise
generating capacity of the local microstructure. The experimental studies showed how both
the attenuation and FOM varied with position in IN718 and Waspaloy specimens. A close
relationship was established between the measured attenuation and the Noise FOM, a result
consistent with classical theories for backscattering and attenuation but inconsistent to
observations in titanium.
Chapter 2 describes a quantitative study of the relationship of the experimental
observations reported in Chapter 1 to the predictions of classical theories, which require as
input the single-crystal elastic constants of the grains and the grain size. Detailed
metallography was carried out in order to deduce precise grain size at different locations in
the billet coupons. The single crystal elastic constants for these alloys are unknowns and an
effort to infer the single-crystal elastic constant of the nickel-based super alloys from
ultrasonic measurements (coupled with grain size measurements) is reported. The proposed
strategy was first validated on polycrystalline copper and then applied to model-base super
alloys.
In Chapter 3, a detailed study of the accuracy of the single scattering model to predict
the grain noise generated by the microstructure was carried out. The backscattered grain
noise theory is based on the single scattering assumption. The goal was to determine the
frequency-dependent FOM parameter that is a measure of the noise-generating capacity of
the microstructure. The basic assumptions of the Independent Scatterer Noise Model are, if
the radiation pattern of the transducer is well modeled, and if the microstructure does not
vary with inspection depth, then the FOM values deduced from the noise data should be
independent of the time gate used in the analysis. The measured results were compared to the
predictions of the single scattering theory to test if the model assumptions are justified. In
general, the good agreements between theory and experiment implied that the single
scattering model is a good approximation. However in one of the nickel-based super alloy