FABRICATION HIGH HOMOGENEOUS TI-32MO ALLOY FOR …

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.

27282930313233

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

西部超导

Western Superconducting Technologies Co., Ltd

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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

20212223242526272829303132

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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Result of X-ray analysis for BT16

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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.

西部超导


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