Chemical Reduction

A primary source of titanium powder is "sponge fines," so called because of their origin and appearance (Fig. 1). Sponge fines are small irregular particles of nominally pure titanium produced during the production of titanium sponge from titanium tetrachloride. The commercial production of titanium metal involves the chlorination of natural or synthetically produced rutile, TiO2, in the presence of carbon (Ref 1). The resulting titanium tetrachloride is reduced to metallic titanium by the Kroll process using magnesium (Ref 2) or by the Hunter process using sodium (Ref 3). Most of the remnant chloride is removed by vacuum distillation or by water leaching. The final sponge fines typically contain 0.12 to 0.15 wt% Cl. The inherent chloride content of conventional sponge fines can lead to incomplete densification and limited fatigue properties. A typical screen analysis and chemical composition of sponge fines produced by sodium reduction are given in Tables 1 and 2, respectively. Table 3 gives tensile properties of Ti-6Al-4V compacts produced from sponge fines and aluminum-vanadium master alloy.

Table 1 Screen analysis of sodium reduced titanium sponge fines

Mesh

size (U.S.)

Particle, .'''m

Weight percent retained

+80

+177

0

-80

+100

-177

+149

0.1

-100

+140

-149

+105

11.2

-140

+200

-105

+74

32.9

-200

+230

-74

+64

5.0

-230

+325

-64

+45

23.3

-325

-45

Table 2 Typical chemical analysis of Hunter process titanium sponge fines sinter compacted Ti-6Al-4V produced from these fines and Al-V master alloy powder

Element

Analysis, wt%

Sponge fines

Sintered compact

Al

6.2

V

4.1

O

0.13

0.24

N

0.03

0.016

H

0.07

0.002

C

0.02

0.02

Fe

0.02

0.18

Na

0.10

0.10

Cl

0.13

0.12

Table 3 Typical tensile properties of Ti-6Al-4V compacts made from blended sponge fines and Al-V master alloy powder

Material

0.2%

yield strength

Tensile

strength

Elongation, %

Reduction of

MPa

ksi

MPa

ksi

area, %

Cold isostatic press and hot isostatic press

827

120

917

133

13

26

Press and sinter

868

126

945

137

15

25

Wrought mill annealed

923

134

978

142

16

44

MIL-T9047 (min)

827

120

896

130

10

25

Sponge fines from the Hunter process. Source: Ref 1

Sponge fines from the Hunter process. Source: Ref 1

Fig. 1 Sponge fines made by the Hunter process

Commercially pure (CP) titanium is also being produced in Russia from titanium dioxide by reduction with calcium hydride (Ref 4) as follows:

0 0

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