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«by Peng Chen A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Mechanical Engineering) in ...»

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MANUFACTURING OF POROUS SURFACES WITH MICRO-SCALE

FEATURES FOR ADVANCED HEAT TRANSFER

by

Peng Chen

A dissertation submitted in partial fulfillment

of the requirements for the degree of

Doctor of Philosophy

(Mechanical Engineering)

in The University of Michigan

2008

Doctoral Committee:

Professor Jun Ni, Chair

Professor Elijah Kannatey-Asibu Jr.

Professor John Halloran Assistant Professor Gap-Yong Kim © Peng Chen All rights reserved 2008

DEDICATION

……… to the memory of my dear uncle Mr. Ximing Tang who gave me the first and best lessons of scientific thinking and introduced me to the world of engineering when I was young. His encouragement until the last moment of his life, and his memories ever since, have been the best source of motivation for completion of this work. To the memory of a great teacher and man whose thoughts were always ahead of his time…….

ii

ACKNOWLEDGEMENTS

It is Professor Jun Ni whom I wish to thank for his guidance and financial support through the course of my graduate studies. Particularly, I appreciate the faith he put in me and my knowledge that made me work enthusiastically hard, if not only, to prove that he did not believe in me in vane. It was through intellectual interactions with him that, now I realize how much, I grew up as an engineer, researcher and a person.

Especially, I would like to express my appreciation to Professor Gap-Yong Kim for standing by me in all my attempts in completing my graduate studies and being my perfect role model.

I would like to thank my mother Mrs. Youwen Tang and my father Mr. Jinfa Chen for their undivided love. Without their encouragement I could not have succeeded. I am grateful to my uncle Mr. Shuyu Tang and my aunt Mrs. Hong Zhang for their support. My sincere thanks to my sister Xueling Chen and her husband for not only being supportive family members but being my best friends with whom I always enjoyed spending time and sharing my experiences.

I would like to thank my dissertation committee members for their useful comments and guidance. My special thanks to Steven Emanuel for his technical support.

Last but not least, I would like to thank my dearest Wei Zhao for her love, understanding and encouragement.

iii

TABLE OF CONTENTS

DEDICATION

ACKNOWLEDGEMENTS

LIST OF FIGURES

LIST OF TABLES

CHAPTER 1

INTRODUCTION

1.1 Motivation

1.2 Research Framework and Objectives

1.2.1 Forming of Porous Micro-features using Cold Compaction and Incomplete Sintering Method

1.2.2 Forming of Porous Micro-features and Particle/Substrate Bonding using Hot Compaction

1.2.3 Discrete Element Modeling of the Pressure Assisted Sintering Process......... 10

1.3 Dissertation Organization

CHAPTER 2

FORMING OF POROUS MICRO-FEATURES USING COLD COMPACTION

AND INCOMPLETE SINTERING METHOD

2.1 Introduction

2.2 Literature Review

2.2.1 Deformation Behavior of Powders in Cold Compaction

2.2.2 Sintering Process

2.2.3 Computational Modeling of Cold Powder Compaction

2.3 Experimental Investigation

2.3.1 Experimental Set-up and Procedures

2.3.2 Experimental Results and Discussion

2.4 Cold Compaction Simulation

2.4.1 Material Modeling for Compaction Simulation

iv 2.4.2 FEA Validation: a Case Study on Compaction of Zirconia Powder............... 48 2.4.3 FEA Modeling: Compaction of Copper Powder into Micro-features............. 52

2.5 Conclusions

CHAPTER 3

FORMING OF POROUS MICRO-FEATURES AND PARTICLES/SUBSTRATE

BONDING USING HOT COMPACTION

3.1 Introduction

3.2 Literature Review

3.2.1 Uni-axial/uni-directional hot pressing (hot die compaction)

3.2.2 Powder forging (P/F, P/M forging, P/M hot forming)

3.3 Forming of Porous Micro-features Using Hot Compaction

3.3.1 Experimental Setup and Procedures

3.3.2 Experimental Results and Discussions

3.4 Thermal Analysis of the Hot Compaction System

3.4.1 Finite Element Modeling of the Heat Transfer Process

3.4.2 Results and Discussions

3.5 Particle/substrate bonding produced by hot compaction

3.5.1 Experimental Setup and Procedures

3.5.2 Experimental Results and Discussions

3.6 Conclusions

CHAPTER 4

DISCRETE ELEMENT MODELING OF THE PRESSURE ASSISTED

SINTERING PROCESS

4.1 Introduction

4.2 Literature Review

4.2.1 Computational Modeling of Sintering Processes

4.2.2 Summary of Computational Modeling Techniques for Sintering.................. 101

4.3 Numerical Modeling of Hot Compaction (Network Model)

4.3.1 Formulation of the Numerical Model

4.3.2 Modeling of Unit Problem and Validation

4.3.3 Modeling of Multi-particle Problem with Boundary Conditions.................. 107





4.4 Conclusions

CHAPTER 5

SUMMARY AND CONTRIBUTIONS

5.1 Summary

5.1.1 Forming of Porous Micro-features using Cold Compaction and Incomplete Sintering Method

v 5.1.2 Forming of Porous Micro-features and Particle/Substrate Bonding using Hot Compaction

5.1.3 Discrete Element Modeling of the Pressure Assisted Sintering Process....... 121

5.2 Contributions

5.3 Recommendations for the Future Work

APPENDIX

APPENDIX: Matlab Source Code for Discrete Element Model Simulation................. 126 BIBLIOGRAPHY

–  –  –

Figure 1-1 The potential of various surface modifications to enhance pool boiling (Liter and Kaviany 2001)

Figure 1-2 Overview of the various production methods for porous metallic materials (Liu and Liang 20001; Davies and Zhen 1983; Banhart 2001; Banhart 2000).. 5 Figure 1-3 Proposed fabrication method: powder pressing and powder rolling (cold/hot) 6 Figure 1-4 Illustration of the entire fabrication process

Figure 2-1 Basic powder forming process steps

Figure 2-2 Deformation behavior of powders in cold compaction (Cocks 2001)............ 16 Figure 2-3 The evolution of microstructure during sintering (German 1994).................. 18 Figure 2-4 Two categories of transport (German 1994)

Figure 2-5 Continuum models (Zavaliangos 2002)

Figure 2-6 Micromechanical models (Zavaliangos 2002)

Figure 2-7 Representation of powder yielding surfaces of continuum model (PM Modnet Computer Modeling Group 1999)

Figure 2-8 2D sketch of the contact geometry between two spherical particles (Cundall and Strack 1979)

Figure 2-9 Simplified calculation scheme of DEM (Cundall and Strack 1979)............... 27 Figure 2-10 Experimental set-up and punch/die set (Kim et al. 2007)

Figure 2-11 Microchannel dimensions and measured data (courtesy of Gap-yong Kim) 33 Figure 2-12 Laser measurement system (BIM)

Figure 2-13 Copper powder

–  –  –

Figure 2-16 Magnified side view of successfully formed micro-protrusions

Figure 2-17 Magnified side view of unsuccessfully formed micro-protrusions............... 38 Figure 2-18 SEM of the compact surface

Figure 2-19 Pore size distribution at different cold compaction force

Figure 2-20 Hardness of the cold compacted part compressed using different force....... 40 Figure 2-21 Hardness of part sintered at different temperatures

Figure 2-22 Porosity of formed micro-features with various aspect ratios

Figure 2-23 Hardness of formed micro-features with different aspect ratios

Figure 2-24 Porosity of formed micro-features sintered at different temperatures.......... 45 Figure 2-25 Cross-sectional views of the bump1 before and after sintering

Figure 2-26 The DPC model (PM Modnet Computer Modelling Group 1999)............... 46 Figure 2-27 Densification behavior of the zirconia powder (Kim et al. 2000)................. 49 Figure 2-28 Illustration of the FEA model

Figure 2-29 Die compaction process

Figure 2-30 Simulation validation (relative density distribution)

Figure 2-31 Geometry and dimension of the die (symmetric view)

Figure 2-32 Material properties used in ABAQUS (Martin et al. 2002; Park et al. 1999;

Vyal and Laptev 2002)

Figure 2-33 Compaction simulation validation

Figure 2-34 Shape and density of the powder compact before and after compaction...... 55 Figure 3-1 Schematic of four conventional hot consolidation processes (German 1996) 59 Figure 3-2 Forging modes and stress conditions on pores for: a) re-pressing; b) upsetting (James 1994)

Figure 3-3 Experimental setup: a) compaction assembly (front view); b) compaction assembly (top view); c) compaction assembly (section view); d) whole setup 66

–  –  –

Figure 3-5 Die insert #2

Figure 3-6 Die insert #3

Figure 3-7 Hot compacted part: a) successfully formed micro-features; b) magnified cross-sectional view (insert #1)

Figure 3-8 Interconnected porous structure of the formed micro-features (insert #1)..... 71 Figure 3-9 Effects of design factors on the hardness: a) response surface; b) main effect plot

Figure 3-10 Effects of design factors on the porosity: a) response surface; b) main effect plot

Figure 3-11 Magnified cross-sectional view (insert #2)

Figure 3-12 Interconnected porous structure of the formed micro-features (insert #2)... 77 Figure 3-13 Successfully formed micro-protrusions with different taper angles (insert #3)

Figure 3-14 FEA model: a) cross-sectional view; b) boundary conditions

Figure 3-15 Heat flux input for different target temperatures: a) 400 °C; b) 450 °C; c) 500 °C

Figure 3-16 Validation of the simulation with experiment

Figure 3-17 Temperature distribution of the powder: a) 400 °C; b) 450 °C; c) 500 °C... 85 Figure 3-18 Copper substrate with scratched surface

Figure 3-19 Particle/substrate bonding made by hot pressing

Figure 3-20 Microscopic pictures of the bonding interface

Figure 3-21 Reference for the tape test (ASTM D3359)

Figure 3-22 Specimen cutting for tape test: a) Compression cutting; b) Specimen made;

c) Cutting block

Figure 3-23 Three-point bending test

Figure 4-1 Model for the neck growth problem (Hwang and German 1984)

–  –  –

Figure 4-3 Comparison of modeling techniques for powder sintering process.............. 102 Figure 4-4 Illustration of the 2-particle pressure assisted sintering model

Figure 4-5 Comparison between simulation and experiment results

Figure 4-6 Effects of temperature and force on r/R

Figure 4-7 Illustration of the 10-particle model

Figure 4-8 Frame analysis of the ten-particle system

Figure 4-9 Calculation scheme for multi-particle pressure assisted sintering problem...111 Figure 4-10 Neck radius during pressure assisted sintering (350 ºC, 10N)

Figure 4-11 Relative center approaching (350 ºC, 10N)

Figure 4-12 Neck radius during pressure assisted sintering (384 ºC, 10N)

Figure 4-13 Neck radius during pressure assisted sintering (422 ºC, 10N)

Figure 4-14 Relative center approaching (384 ºC, 10N)

Figure 4-15 Relative center approaching (422 ºC, 10N)

–  –  –

Table 2-1 F-test to determine the effect of the sintering temperatures on the hardness... 42 Table 2-2 Material properties of zirconia powder (Kim et al. 2000)

Table 3-1 Tool materials properties (CES Selector)…..……………..…………………..64 Table 3-2 Experimental design and results

Table 3-3 Material properties used in simulation

Table 4-1 Constant n and m in Equation 5-4 (Hwang and German 1984)

Table 4-2 Material property of copper (Swinkels and Ashby 1981)

Table 4-3 Axial interaction force between particles

–  –  –

Nowadays, the manufacturing industry has been challenged to further reduce the size of their products, due to government regulations and consumer demands for lightweight, power-efficient and portable devices. However, the performance of highly integrated devices and systems experiencing high heat loads is often limited by the internal heat generation and the associated undesirable elevated temperature levels.

Examples of such circumstances can be found in electronic systems, automotive, residential and industrial equipment, which all require cooling units to sustain certain low level temperatures to ensure the expected efficiency and performance. Furthermore, the trend of increasing integrated, compact and miniaturized devices leads to even higher heat loads and compel interdisciplinary research efforts to develop advanced heat exchangers that are compact, small, efficient and inexpensive (Chen et al. 2006).

Advanced heat transfer technology in recent years has been highly dependent upon the improvement of two phase heat transfer in tubes, where phase transformation from liquid to vapor phase significantly increases the level of thermal energy transfer

–  –  –

device while maintaining relatively low material temperatures. Methods to improve two phase heat transfer can be grouped as active and passive techniques. Active techniques include mechanical aids, surface vibration, fluid vibration, and the addition of electrostatic fields. Passive techniques include surface treatments, roughening and modification of the surface, surfaces extension, displaced enhancement, swirl flow techniques, alteration of surface tension, and the inclusion of additives to the coolant.

–  –  –

Several recent heat transfer studies indicated that porous surfaces with nano/micro-scale features lead to heat transfer efficiency improvements up to 180-300% (Kunugi et al. 2004; Liter and Kaviany 2001). Figure 1-1 presents a map of the potential

–  –  –



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