production and characterization of porous titanium alloys

224 Pages·2007·8.75 MB·English

PRODUCTION AND CHARACTERIZATION OF POROUS TITANIUM ALLOYS

A THESIS SUBMITTED TO
THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES
OF
MIDDLE EAST TECHNICAL UNIVERSITY

BY

ZİYA ESEN

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY
IN
METALLURGICAL AND MATERIALS ENGINEERING

OCTOBER 2007
Approval of the thesis:

‘’PRODUCTION AND CHARACTERIZATION OF POROUS
TITANIUM ALLOYS’’

submitted by ZİYA ESEN in partial fulfillment of the requirements for the degree
of Doctor of Philosophy in Metallurgical and Materials Engineering, Middle
East Technical University by,

Prof. Dr. Canan Özgen
Dean, Graduate School of Natural and Applied Sciences

Prof. Dr. Tayfur Öztürk
Head of Department, Metallurgical and Materials Engineering

Prof. Dr. Şakir Bor
Supervisor, Metallurgical and Materials Engineering, METU

Examining Committee Members

Prof. Dr. İbrahim Günal
Department of Physics, METU

Prof. Dr. Şakir Bor
Metallurgical and Materials Engineering, METU

Assoc. Prof. Dr. Kadri Aydınol
Metallurgical and Materials Engineering, METU

Assoc. Prof. Dr. Nuri Durlu
Mechanical Engineering, TOBB ETU

Assist. Prof. Dr. Arcan Dericioğlu
Metallurgical and Materials Engineering, METU

16.10.2007
Date :
I hereby declare that all information in this document has been obtained
and presented in accordance with academic rules and ethical conduct. I also
declare that, as required by these rules and conduct, I have fully cited and
referenced all material and results that are not original to this work.

Name, Last name : Ziya Esen

Signature :

iii
ABSTRACT

PRODUCTION AND CHARACTERIZATION OF
POROUS TITANIUM ALLOYS

Esen, Ziya
Ph.D., Department of Metallurgical and Materials Engineering
Supervisor: Prof. Dr. Şakir Bor

October 2007, 211 pages

In the present study, production of titanium and Ti6Al4V alloy foams has
been investigated using powder metallurgical “space holder technique” in which
magnesium powder were utilized to generate porosities in the range 30 to 90 vol. %.
Also, sintering of titanium and Ti-6Al-4V alloy powders in loose and compacted
condition at various temperatures (850-1250oC) and compaction pressures
(120-1125 MPa), respectively, were investigated to elucidate the structure and
mechanical properties of the porous cell walls present due to partial sintering of
powders in the specimens prepared by space holder technique. In addition,
microstructure and mechanical response of the porous alloys were compared with
the furnace cooled bulk samples of Ti-6Al-4V-ELI alloy subsequent to betatizing.
It has been observed that the magnesium also acts as a deoxidizer during
foaming experiments, and its content and removal temperature is critical in
determining the sample collapse.
Stress-strain curves of the foams exhibited a linear elastic region; a long
plateau stage; and a densification stage. Whereas, curves of loose powder sintered
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samples were similar to that of bulk alloy. Shearing failure in foam samples
occurred as series of deformation bands formed in the direction normal to the
applied load and cell collapsing occured in discrete bands.
Average neck size of samples sintered in loose or compacted condition were
found to be different even when they had the same porosity, and the strength was
observed to change linearly with the square of neck size ratio.
The relation between mechanical properties of the foam and its relative
density, which is calculated considering the micro porous cell wall, was observed to
obey power law. The proportionality constant and the exponent reflect the structure
and properties of cell walls and edges and macro pore character.

Keywords: Powder metallurgy, Space Holder, Titanium and Ti6Al4V alloy Foam,
Mechanical Properties, Heat Treatment

v
ÖZ

GÖZENEKLİ TİTANYUM ALAŞIMLARININ
ÜRETİMİ VE KARAKTERİZASYONU

Esen, Ziya
Doktora, Metalurji ve Malzeme Mühendisliği Bölümü
Tez Yöneticisi: Prof. Dr. Şakir Bor

Ekim 2007, 211 sayfa

Bu çalışmada, boşluk yapıcı olarak magnezyum tozu kullanılan toz
metalurjisi yöntemi ile % 30-90 arasında gözenek içeren köpüksü titanyum ve Ti-
6Al-4V alaşımının üretilebilirliği araştırılmıştır. Ayrıca, boşluk yapıcı kullanılarak
üretilmiş köpüklerin kısmi sinterlenmiş hücre duvarlarının yapısını ve mekanik
özelliklerini belirlemek için titanyum ve Ti-6Al-4V alaşım tozlarının gevşek
durumda değişik sıcaklarda (850-1250oC) ve değişik presleme basınçlarında
(120-1125 MPa) sinterlenmesi araştırılmıştır. Buna ek olarak, gözenekli alaşımların
iç yapısı ve mekanik davranışları betalaştırma sonrası yavaş soğutulan hacimli
Ti-6Al-4V alaşım numuneleri ile karşılaştırılmıştır.
Köpük üretiminde kullanılan magnezyumun titanyumun oksitlenmesini
engellediği, magnezyum miktarı ile uzaklaştırma sıcaklığının numunelerin çökme
oranını belirleme yönünden önemli olduğu gözlenmiştir.
Üretilen köpüklerin gerilim-gerinim eğrileri doğrusal elastik, plato ve
yoğunlaşma bölgelerinden oluştuğu, gevşek durumda sinterlenen numunelerin
eğrilerinin ise hacimli numunelere benzerlik gösterdiği belirlenmiştir. Köpüklerde
vi
kesme kopması, uygulanan yüke dik yöndeki deformasyon bantlarının oluşumu ile
meydana gelmiş ve farklı bantlarda hücrelerin çökmesi ile gerçekleşmiştir.
Aynı gözenek miktarına sahip gevşek ve preslenmiş durumda sinterlenmiş
numunelerde ortalama boyun bölge kalınlıklarının farklı olduğu ve bu
numunelerinin dayançalarının boyun bölge kalınlık oranının karesi ile doğru orantılı
olarak değiştiği belirlenmiştir.
Üretilen köpüklerin mekanik özellikleri ile mikro gözenekli hücre duvar
yapısı dikkate alınarak hesaplanan göreceli yoğunluk arasındaki ilişkinin üssel
olarak değiştiği görülmüş, elde edilen empirik denklemlerdeki üs ve oran
katsayılarının hücre duvarlarının yapısı ile özelliklerini ve köpüklerdeki makro
gözenek özelliklerini yansıttığı sonucuna varılmıştır.

Anahtar Kelimeler: Toz Metalurjisi, Boşluk Yapıcı, Titanyum and Ti6Al4V Köpük,
Mekanik Özellikler, Isıl İşlem

vii
To my Family
viii
ACKNOWLEDGMENTS

I wish to express my deepest gratitude to my supervisor Prof. Dr. Şakir Bor
for his firm guidance, his helpful suggestions, prompt feedbacks, endless patience
advice, criticism, encouragements and close collaboration throughout the research.
This dissertation could not have been completed without his support.

I am grateful to Ebru Saraloğlu for her never ending support, encouragement
and help throughout the entire period of the study.

I am also grateful to Dr. Elif Tarhan and Dr. Kaan Pehlivanoğlu for their
precious helps, advice, valuable support and encouragement during the development
of the study.

I am indebted to my colleagues and friends; Tufan Güngören, Tarık
Aydoğmuş, Hasan Akyıldız and Gül İpek Nakaş for their help and patience.
Additional thanks go to various friends for their support and encouragement.

Special thanks to my family for their supports. Finally, thanks to all the
technical staff of the Metallurgical and Materials Engineering Department for their
suggestions, help and comments during this study.

This thesis study has been financially supported by M.E.T.U Resesarch Fund
and by TÜBİTAK through the projects BAP-2005-03-08-05 and 104M121,
respectively.
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TABLE OF CONTENTS

ABSTRACT………………………………………………………………...... iv
ÖZ…………………………………………………………………..………… vi
DEDICATION................................................................................................. viii
ACKNOWLEDGEMENTS..………………………………………......…… ix
TABLE OF CONTENTS………………………………………..…......…… x
CHAPTER
1. INTRODUCTION…………………………………...…...………...... 1
2. THEORY…………………………………………….....…………….. 6
2.1. Cellular Materials: Properties, Applications and Production
Methods...................................................................................... 6
2.1.1. General............................................................................... 6
2.1.2. Properties and Applications of Metallic Foams….…… 8
2.1.3. Production Methods of Cellular Metallic Materials...... 11
2.2. Powder Metallurgy....................................................................... 14
2.2.1. General............................................................................... 14
2.2.2. Pre-consolidation Powder Handling…..……………..... 14
2.2.3. Powder Consolidation....................................................... 15
2.2.4. Sintering............................................................................. 17
2.2.4.1. Solid State Sintering.......................................... 18
2.2.4.2. Liquid Phase Sintering...................................... 21
2.2.4.3. Transient Liquid Phase Sintering.................... 22
x