CA1043133A - Titanium alloy - Google Patents

Abstract

ABSTRACT

A titanium base alloy consisting essentially by weight of 0.5% to 2.0% nickel, 0.1% to 0.8% molybdenum, up to 0.2% maximum iron, balance titanlum for use in equipment for processing hot brine solutions such as desalination units, salt evaporators, chlorine cells and the like.

Description

~043133 Our invention relates generally to a novel titanium base alloy exhibiting good corrosion resistance. More particularly, the titanDum base alloys of our invention have good corrosion resistance in hot brine environ-ments at temperatures on the order of 375UF.
The known titanium base alloys and commerically pure titanium present a significant problem when used in equipment for processing hot brine solutions such as desalination units, salt evaporators and chlorine cells. In the past, equipment used in hot brine environments made of un-alloyed titanium and titanium base alloys has failed due to the corrosive effects of the hot brine solution. A known titanium base alloy which can withstand the corrosive attack of hot brine solutions is a titanium base alloy containing 0.2% palladium. However, while this titanium base alloy including palladium successfully resists corrosion in desalination units and other equipment for processing hot brine solutions, it is impractical ~ to use this alloy due to the high cost and limited availability of palladium.
; We have invented a novel titanium base alloy containing molybdenum : and nickel wherein the iron content does not exceed 0.2% by weight which has excellent corrosion resistance to hot brine solutions and is not unduly expensive.
Accordingly the present invention provides a titanium base alloy consisting essentially by weight of about 0.6% to 0.9% nickel, 0.2% to 0.4%
molybdenum, up to 0 2% maximum iron, balance titanium, said alloy being - characterized by good corrosion resistance in hot brine environments.
Each of siliconand aluminum may be present as incidental impurities in the preferred composition range in amounts up to 0.1% and the normal titanium base alloy interstitials may be present.
A specific alloy falling within the scope of our invention which has excellent properties contains 0.3% molybdenum, 0.8% nickel, up to 0.1% maximum iron and the balance titanium and incidental impurities.
It is preferred that the alloys according to our invention contain ~ : , ~ ;~

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no more than 0.1% iron, but it has been determined that an alloy containing ~ -up to 0.2% iron will have good corrosion resistance in hot brine solutions -so long as molybdenum and nickel are present in the alloy in the proper amounts. It is ' .~. ~.

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~43133 believed that a Ti-Mo-Ni alloy with no iron will exhibit better corrosion resistance than the same alloy with iron, but an average iron content of about 0.09% is inherently present as an impurity in the titanium sponge from which our alloy is melted. Iron may be tolerated in our alloy up to a maximum of about 0. 2% and compen-sation made for the iron.
To determine the effect of iron on the corrosion rate of titanium and titanium base alloys, a number of tests were carried out on samples having different amounts of iron. Both un-10 alloyed titanium and titanium base alloys having compositionswithin the ranges of our invention were tested. Additionally, a Ti-0.2Pd alloy was tested as a base for comparison. These com-positions and the corrosion rates thereof are reported in Table I. ;~
TABLE I

Corrosion (MpY) Composition 5%HC1 1%H2SO4 Heat %Fe %Mo %NiBoilingBoiling 1401 1. 0 - - 640 990 1409 .50 - - 600 707 1986 . 40 - - 436 -Ti-50A . 09 - - 246 707 1952 .02.3 .8 12 84 4978 . 05 .3 .8 16 109 1953 . 10 .3 . 8 20 198 1751 .20. 3 . 8 98 212 1954 . 30 . 3 .8 340 404 Ti-.2Pd . 09 - - 3 6 .,' :
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-A comparison of the compositions and the corrosion rates in :
Table I clearly shows that an increase in the iron content has a -~
' deleterious effect on the corrosion rate of both unalloyed titanium and on the Ti-Mo-Ni alloy of our invention. The corrosion rates ^
in Table I show a substantial advantage for our alloy when the iron ,, content of the alloy is no greater than 0. 2%. Further tests were ,'"~ made on alloys having varying molybdenum and nickel contents ~:
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,-......... with different amounts of iron in 5% boiling hydrochloric acid and ~ :
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' 1~343133 It will be seen from a consideration of the data in Table 11 that the corrosion rates are generally higher when the iron content of the alloy exceeds 0. 2%, and such is clear for the alloys having compositions within the ranges of our invention.
Additionally, the data for heats E and F shows that the molybdenum and nickel act synergistically to provide substantially improved corrosion resistance over an alloy containing only molybdenum or only nickel. In heats E and F both the nickel and the molyb-denum are present in amounts within the preferred composition ranges of our invention.
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In order to determine the effect of molybdenum on the corrosion rate of our titanium base alloys, a large number of heats were melted wherein the nickel content was maintained constant while the molybdenum content was varied along with different iron contents. The compositions and the corrosion rates thereof are shown in Table III.

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TABLE ILI

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:; Corrosion (MpY) Composition 5%HC11%H2SO4 Heat %Fe %Mo %Ni Boiling Boiling 1956 .25 - .8 674 1106 - 1902 .02 - .8 125 850 ::
1957 .25 .1 .8 21 276 :
1953 . 10 .3 .8 20 198 ; ~ .
1987 .10 .6 .8 51 176 ' 10 1751 .20 .3 .8 98 212 ;:~ 1954 . 30 .3 .8 340 404 ! ` ~
~; 1984 . 30 .6 .8 172 293 1955 .40 .3 .8 391 488 1985 .40 .6 .8 152 350 r ', 1958 .25 .2 .8 172 266 1959 .25 . 4 .8 24 222 `' ' 1960 .25 . 5 .8 96 87 ~, i 1983 .23 .6 .8 61 193 .. -- <.2 - 2. 0 64 277 ~., ;~ 20 1704 .2 .3 2.0 8 0 Uncoded . The test results in Table III generally show that a small in-- crease in molybdenum results in a decrease in the corrosion rate in an alloy having the same iron and nickel contents.
; Additionally, a comparison of the corrosion rates for the first three heats and the last two heats shows that the molybdenum ` -8-., ~
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and the nickel act synergistically in lowering the corrosion rate.
To determine the effect of nickel on the corrosion rate, a number of titanium base alloy heats were melted containing varying amounts of nickel with a constant 0.3% molybdenum and with different iron contents. The compositions and the corrosion rates are shown in Table IV.
TABLE IV

Corrosion (MpY) Composition 5%HC11%H2So4 Heat %Fe %Mo %NiBoilingBoiling 2180 <.1 .3 .3 241 -2179 <.1 .3 .5 39 2181 <.1 .3 .7 0.5 -2182 <. 1 .3 .9 0.5 _ --* .2 . 3 - 18S 502 , 1615 .2 .3 .2 211 400 -1616-1701** .2 . 3 . 5 192 375 , 1751 .2 . 3 .8 98 212 1702 .2 .3 1.0 43 188 1703 .2 . 3 1.5 5 118 1704 .2 .3 2.0 8 - --- < .2 ~ 2. 0 64 277 Uncoded ** Average - Two Samples These test results show that from 0.5% to 2. 0%
nickel has a beneficial effect on corrosion resistance so long as molybdenum is present.

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1~431;~3 -It is known that the addition of nickel to titanium base alloys will enhance the corrosion resistance, but we have determined that more than 2. 0% nickel renders titanium base alloys very brittle and difficult to fabricate and to weld. This is : shown in Table V where the nickel and molybdenum contents were ; varied in the different heats and mechanical tests were conducted at room temperature.

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~43~33 It will be seen from Table V that the heats having higher nickel and molybdenum contents have relatively poorer ductility. While an increase in the nickel and molybdenum ; contents will improve the corrosion resistance of our alloy, it is necessary to understand that increased amounts of these elements :. , .
has an adverse effect upon the fabricability of the alloy. This will ;~
be seen from the weld bend data in Table V.
Fabricability studies show that as nickel in-creases from 0. 3% to 1. 0%, edge checking of the specimens in-creases proportionately and strip cold rollability under tension -~
decreases to a point where edge loss and coil rupture make the alloy impractical to cold roll. For this reason, we limit the maximum nickel content of our alloy to about 1. 0% when final processing is cold rolling. However, for sections which are not to be cold rolled such as plate, our alloy may have a nickel con-tent up to 2. 0%.
Table VI shows elevated temperature properties of unalloyed titanium and two titanium base alloys. The com-positdon of heat 4978 is in accorda=ce with our invendon.

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The alloy of our invention has acceptable prop-erties whereas the alloy having iron in excess of 0. 2% has relatively -poorer ductility.
The thermal stability of an alloy in accordance with our invention is shown in Table VII. After exposure at 600F
for 200 hours the alloy exhibited good stability.
TABLE VII

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Heat Test Condition (Ksi) (Ksi) 4978 Room Temperature 74 60 33 4978 6000F - 200 Hrs. 79 60 32 * 1 in. gage length To illustrate the crevice corrosion resistance of a Ti-0. 3Mo-0. 8Ni alloy as compared with Ti-50A (unalloyed tita-- nium) and Ti-0.2Pd alloy, samples of the three compositions (all compositions included 0.1% nominal Fe) were submerged in saturated sodium chloride solution at 350F for 500 hours. The samples were removed, sandblasted and weighed. It was deter-mined that the alloy of our invention and the Ti-0.2Pd alloy had no 20 measurable weight loss whereas Ti-50A had lost 57 milligrams.
Various compositions were tested to determine the hydrogen uptake efficiency. The compositions and the uptake efficiencies are shown in Table VIII.
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TABLE VIII
' Composition Heat %Fe%Mo %Ni HUE Avg. %
1952 .02.3 .8 1.3 1953 .10.3 .8 .0 1954 .30. 3 . 8 . 7 . :
1955 .40.3 .8 2.2 ; 1956 .25 - .8 1.0 1957 .25. 1 .8 . 7 : -1958 .25.2 .8 .4 1959 .25.4 .8 . 1 ..
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Ti-. 2Pd - - - 1. 0 Ti-50A - - ~ 4-~ Ti-2Ni - - - 85. 0 ~
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position of our invention are generally acceptable and are far superior to a Ti-2Ni alloy. '~

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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A titanium base alloy consisting essentially by weight of about 0.6% to 0.9% nickel, 0.2% to 0.4% molybdenum, up to 0.2% maximum iron, balance titanium, said alloy being characterized by good corrosion resistance in hot brine environments.

2. A titanium base alloy as set forth in claim 1 having up to 0.1%
maximum iron, balance titanium.

3. A titanium base alloy as set forth in claim 1 having 0.8% nickel, 0.3% molybdenum, up to 0.1% maximum iron, balance titanium.