fabrication high homogeneous ti-32mo alloy for …
TRANSCRIPT
FABRICATION HIGH HOMOGENEOUS TI-32MO ALLOY FOR TITANIUM
MASTER ALLOY IN AEROSPACE APPLICATION
Baoquan Fu, Hailong Xu, Yi Feng, Xianghong Liu, Yong Feng, Pingxiang Zhang
Western Superconducting Technologies Co.,Ltd, 710023, Xi’an, P.R.China
Abstract:
A new method to fabricate high homogeneous Ti-32Mo master alloy is introduced by
this paper. Triple VAR method is used and gets a high homogeneous ingot. The
Chemical Analysis, SEM and X-RAY are used to analysis the composition uniformity of
Ti-32Mo alloy. The results indicate that the difference of molybdenum element is smaller
than 2%. It can be satisfied the requirement for special -titanium alloy for aerospace
application. The impurity elements are also very low. The BT16 alloy which is a key
material for aerospace rivet is used to verify the quality of Ti-Mo master alloy. The
molybdenum content of BT16 alloy which adds the Ti-32Mo master alloy has also very
homogeneous. It is indicate that this master alloy can be used to special -titanium alloy
for aerospace application.
Key words: Ti-30Mo; master alloy; aerospace application; -titanium alloy; VAR;
homogeneous
1. Introduction
Titanium and titanium alloys have became one of the most attractive materials due to
their light weight, high specific strength, corrosion resistance, biocompatibility and
mechanical properties. -titanium alloy has good elevated temperature properties and
resistance to oxidation [1,2]
, it widely used to aerospace application. The molybdenum is
usually added to -titanium alloy (such as Ti-10Mo-8V-1Fe-3.5Al (TB3), Ti-15Mo-2.7Nb-
3Al-0.25Si (-21S) and Ti-3.0Al-4.5V-5.0Mo (BT16) et.al.) as a stabilized -phase
element [3]. All those alloys have the same characteristics which are high Mo content
and few Al content. But molybdenum has very high melting point than titanium. It is very
difficult to directly add in titanium alloys which have relatively high molybdenum content.
The normal Al-65Mo (GFE) alloys can not satisfy these alloys requirement for high
molybdenum content and few aluminum. It is necessary to produce high homogeneous
Ti-32Mo alloy as titanium master alloy. The common melting method for Ti-32Mo alloy
is combination method of skull furnace and VAR furnace or powder metallurgy method.
The rates of final products are usually very low and the chemical elements are also very
difficult to control for combination method [4]. The powder metallurgy method is easy
lead in oxidized impurity elements. This paper reports a new method to fabricate high
homogeneous Ti-32Mo alloy. Triple VAR method is used and gets a very high
homogeneous ingot. The SEM and X-RAY are used to analysis the composition
uniformity of Ti-32Mo alloy. One big commercial BT16 ingot is used to verify the quality
of Ti-32Mo master alloy.
2. Experiment procedure
The VAR furnace form WST was used to fabricate the Ti-32Mo alloy by triple melting.
High-purity titanium and molybdenum as raw material were used to ensure the low
impurity of final product. And the Ti-32Mo ingot which diameter was 360mm was
prepared by Western Superconducting Technologies Co.,Ltd. The figure 1 was the
procedure of Ti-32Mo master alloy.
Sponge
TitaniumPure Nb
Preparing Electrode
Welding
Electrode
Triple VAR Melting
Machine
Sampling
Figure 1 Procedure of Ti-32Mo fabrication
In order to verify the quality of Ti-32Mo master alloy, the Ti-3.0Al-4.5V-5.0Mo (BT16)
alloy which used to rivet material for aircraft was prepared. The Ti-32Mo master alloy
was obtained by machining the Ti-32Mo ingot. The 3ton BT16 ingot was prepared by
VAR.
The main chemical elements from different parts of ingot were analyzed by Chemical
Laboratory of NIN. The scanning electron microscope (SEM) was used to analyzed the
microscopic homogeneous of ingot. The X-ray used to observe the segregation of
molybdenum element.
3. Results and discussion
The fabrication procedures of Ti-32Mo alloy are very simple comparing with other
methods. The main procedures are operated in vacuum condition and the
contamination and oxidized are avoided. It is very easy to control the quality of Ti-32Mo
ingot. At the same time, the cost of preparing of Ti-32Mo alloy is also deceased
apparently for no waste material comparing the combination method.
3.1 Result of macroscopic homogeneous analysis
The chemical composition of Mo elements and impurities are analyzed on the ingot
longitudinal direction from five positions. The figure 2 indicates the sample places. The
table 1 showed the results of chemical composition analysis on ingot longitudinal
direction.
Up Middle Bottom
Up-Middle Middle-Bottom
Figure 2 Sampling position
Table 1 Chemical composition analysis results for longitudinal direction
TiMo Chemical Composition%
Si Fe Mo H C O N
Dete
ction
Po
sition
Up 0.04 0.02 33.16 0.002 0.01 0.10 0.004
Up-Middle 0.04 0.02 32.94 0.01
Middle 0.04 0.04 32.26 0.01 011 0.004
Middle-Bottom 0.04 0.06 32.11 0.01
Bottom 0.04 0.03 31.59 0.001 0.01 0.12 0.013
Standard(smaller) 0.15 0.30 30~34 0.015 0.10 0.15 0.05
All chemical composition can satisfy the requirements of standard of Ti-32Mo alloy
from the table 1. The molybdenum average value is 32.41%. The maximum deviation of
average value and each place composition value for molybdenum is 0.82%. The relative
value which is a ratio of deviation value and average value is only 2.5%. The ingot
chemical composition can be regarded homogeneous if the relative value is smaller
than 5% in general thinking at same ingot. So the longitudinal homogeneous of this Ti-
Mo ingot are very good.
The figure 3 indicates that the Mo content of different cross section parts. Three cross
sections chemical compositions of ingot are analyzed form up, middle and bottom. Five
points Mo content are tested and compared. The figure 4 is the sample positions.
26272829303132333435
Up Middle Bottom
1
2
3
4
5
Figure 3 The Mo content on different cross section parts of Ti-30Mo ingot
Figure 4 The sampling position
The distribution of Mo elements at each section part is homogeneous. The chemical
composition range is only 1%. The progressively increase rule of Mo content is very
apparently from up to bottom part. This phenomenon is caused by the Mo distribution
coefficient K. The content of one element will be increased from the up to bottom part of
ingot if the value of K larger than 1[5]. The table 2 shows the typical distribution
coefficient K values in titanium alloy.
2 1 3
4
5
Table 2 Distribution coefficient K of elements in titanium
Element V Al Fe Mo Sn Cu Si Ni
K 0.5 0.4 0.3 >1 0.3 0.2 0.2 0.05
The figure 4 shows the relationship of homogeneous properties and times of melting.
Five different samples are getting from once, second and triple ingot. The sample
position for each ingot is same with figure 2. The results indicate that the triple melting is
necessary. The best homogeneous properties are getting from triple melting.
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Mo content of
First Melting
Mo content of
second
melting
Mo content of
triple
melting
up
up-middle
middle
middle-bottom
bottom
Figure 4 Relationship of Mo contents with times of melting
3.2 The result of microscopic homogeneous analysis
The microscope homogeneous is analyzed by energy dispersive x-ray spectroscopy
(EDX). The sample method is same with figure 4. There are 15 samples from different
position. Nine points Mo contents for each sample are tested by EDX. Figure 5 is the
microscopic homogeneous analysis results. The range fluctuate is a little big than
macroscopic homogeneous analysis results. However, it is also a very good result.
20212223242526272829303132
up middle bottom
1
2
3
4
5
Figure 5 Microscopic homogeneous analysis in Ti-32Mo ingot
3.3 Result of X-ray analysis
The molybdenum has very high melting point and density than titanium. It is very easy
to produce the segregation of Mo element. X-ray photographic technology is used to
find the high density segregation usually. The principle of this technology is that different
atomic number of metal element will lead different contrast grade under the x-ray
negative film. Figure 6 shows the x-ray photograph for different position of ingot. No
any Mo element segregation is found in Ti-32Mo ingot from the bottom to up. It is
indicate that the Ti-32Mo ingot is very homogeneous.
Up Middle Bottom
Figure 6 X-ray photograph for different position in Ti-32Mo ingot
3.4 Application of Ti-32Mo alloy in BT16 ingot
One big ingot of BT16 (Ti-3.0Al-4.5V-5.0Mo) was fabricated by triple VAR to verify the
quality of Ti-32Mo alloy. The ingot size is 3000kg and diameter is 620mm. Figure 7
shows the chemical composition of BT16 ingot.
Up Up-Middle Middle Middle-Bottom Bottom
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Mo, wt%
Position
Standard
Range
Figure 7 The Mo composition of BT16 ingot
It is very homogeneous for main elements and impurities form bottom to up. Figure 8 is
the x-ray photograph in Bt16 ingot. The BT16 ingot is forged and drawn to 6mm wire.
The ultrasonic test indicates that no any defect is found. At same time, the noise of
ultrasonic is also very low. It is proved that BT16 alloy which fabricated by Ti-32Mo
master alloy is very homogeneous. It can be used to aerospace application.
Up Bottom
Figure 8 X-ray photograph of BT16 ingot
4. Conclusion
The chemical composition of Ti-32Mo master alloy ingot is very homogeneous by triple
VAR melting. The chemical and EDX analysis indicate that the Mo content is changed
only 2%~3%. No any Mo segregation is found in Ti-32Mo ingot by X-ray photograph. It
is proof that the VAR method can solve Mo segregation problems. This master alloy is
added to BT16 alloy to verify the quality of Ti-32Mo ingot. A very homogenous big BT16
ingot is got. The results show that this master alloy can be used to special -titanium
alloy for aerospace application.
Reference:
[1] Xie Huiru, The research and development of titanium alloy in China, Rare Metals
Letters, 2007,26(8):7~9
[2] Zhao Yue et.al., The structure and hydrogen uptake properties in Ti-Mo alloy,
Journal of Metals, 2003,39(1):89~93
[3] Yu Zhengtao et.al., Effect of alloy elements, processing and heat treatment for
mechanical properties and microstructure of -titanium alloy for biological application,
Journal of Rare Metals, 2007,31(4):417~419
[4] Cheng Jinwei et.al., Research state of titanium melting technology and theory, The
paper of 9th special casting and nonferrous alloy annual conference, 2001(02)
[5] Handbook of nonferrous metal processing, metallurgy industrial press
Corresponding Author: Fu, Baoquan, 1972.8, Doctor, Senior Engineer, Email:
[email protected], Tel: +86-029-8652-4696
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Outline
Introduction
Experiment Procedure
Homogeneous Analysis for Ti-32Mo Alloy
Application in BT16
Conclusion
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-titanium alloy is start to application in aerospace.
The characters -titanium:
Introduction
Good elevated temperature
properties
Resistance to oxidation
High molybdenum content
Typical -titanium alloy:
Ti-10Mo-8V-1Fe-3.5Al (TB3)
Ti-15Mo-2.7Nb-3Al-0.25Si (-21S)
Ti-3.0Al-4.5V-5.0Mo (BT16)
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The conventional master alloy(such as Al65Mo)can not
satisfied the requirement of this alloy.
The common melting method for Ti-32Mo alloy:
Combination method
Powder metallurgy method
The defects of common melting method:
Low rates of final products
Easy to lead oxidized impurity
Triple VAR method is developed by WST.
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Experiment and Procedure
Electrode Prepare
V
A
RFinish Ingot
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Homogeneous Analysis of Ti-32Mo Alloy
How to judgment one ingot is homogenous?
Three Steps:
1. Research the element distribution of longitudinal
direction
2. Research the element distribution of radial
direction
3. Research the main element segregation
IF R(which is deviation value /average value)<=5%, we
can think about the alloy is homogenous.
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The Homogeneous Analysis of Ti-32Mo Alloy
Size:360mm Weight:500kg
Mo Fe Si C N O H
T 33.16 0.02 <0.04 0.01 0.004 0.10 <0.001
T_M 32.94 0.02 <0.04 0.01
M 32.26 0.04 <0.04 0.01 0.004 0.11 0.001
M-B 32.11 0.06 <0.04 0.01
B 31.59 0.03 <0.04 0.01 0.013 0.12 <0.001
Stand
ard30~3
4
≤0.3
0
≤0.15 ≤0.10 ≤0.05 ≤0.15 ≤0.015
Chemical composition results of
longitudinal position
Average Mo :32.41% Deviation:0.82% R=2.5%
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26
27
28
29
30
31
32
33
34
35
Up Middle Bottom
1
2
3
4
5
21 3
4
5
Mo content on different cross section parts of Ti-32Mo ingot
The sampling position
The distribution of Mo elements at each section part is
homogeneous. The chemical composition range is only 1%.
R =1.5%
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Radial distribution for Mo
R1 R2 R3 R4 R5
头 33.37 33.51 33.69 32.75 32.67
中 34.56 34.06 33.93 34.45 34.56
尾 33.25 33.89 34.02 33.91 33.31
31.5
32
32.5
33
33.5
34
34.5
R1 R2 R3 R4 R5
Up
32.5
33
33.5
34
34.5
35
35.5
R1 R2 R3 R4 R5
Middle
32.5
33
33.5
34
34.5
R1 R2 R3 R4 R5
Bottom
R1
R2
R3
R4
R5
Radial distribution for Mo
R=4%
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For radial direction: No apparently regularity
Top:The molybdenum content is decrease from the
side to center.
Middle:The molybdenum is very homogenous.
Bottom:The molybdenum is homogenous.
Macroscopic homogenous for Mo content on different position of Ti-32Mo
ingot
For longitudinal direction:
The molybdenum content is increase from the up to
bottom of ingot. It shows that molybdenum is
negative segregation element.
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Mo content of First
Melting
Mo content of
second melting
Mo content of
triple melting
up
up-middle
middle
middle-bottom
bottom
Relationship of Mo contents with times of melting
The triple melting is necessary.
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Result of microscopic homogeneous analysis
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up middle bottom
1
2
3
4
5
The range fluctuate is a little big than macro homogeneous
analysis results.
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Result of X-ray analysis
No any Mo element segregation is found in TiMo ingot from
the bottom to up.
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It is very homogenous for Mo content form up to bottom.
Ti-32Mo Application for BT16
Up Up-Middle Middle Middle-Bottom Bottom
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Mo, wt%
PositionStandard
Range
Size:620mmWeight:3000kg
Ti-3.0Al-4.5V-5.0Mo
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Microstructure of BT16 bar
Side Center
The very fine and homogeneous microstructure also indicate
very homogenous chemical composition for BT16 ingot.
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Conclusion
The chemical composition of Ti-32Mo master alloy ingot is
very homogeneous by triple VAR melting.
The chemical and SEM analysis indicate that the Mo
content is changed only 2%~3%.
No any Mo segregation is found in Ti-32Mo ingot by X-ray
photograph.
The BT16 results show that this master alloy can be used
to special -titanium alloy for aerospace application.