JPS62109937A - Corrosion resistant titanium alloy containing nb and mo - Google Patents

Abstract

PURPOSE:To obtain a Ti alloy showing superior corrosion resistance in any environment including an environment contg. a nonoxidative acid at a relatively low cost by specifying a composition consisting of Mo, Nb and Ti. CONSTITUTION:This Ti alloy having superior corrosion resistance consists of 15.5-50.0wt% Mo, 1.0 - <20.0wt% Nb and the balance essentially Ti. The alloy maintains a stable passive film and shows superior corrosion resistance in an environment contg. a nonoxidative acid such as hydrochloric acid or sulfuric acid as well as in an environment contg. an oxidative acid such as nitric acid and an environment contg. a neutral chloride such as seawater without using an expensive alloying element such as Pd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a titanium alloy that exhibits excellent corrosion resistance not only in a neutral chloride environment but also particularly in a non-oxidizing acid environment.

<Prior art and its problems> When titanium first began to be produced on an industrial scale, its light and strong characteristics were utilized, and titanium was mainly used in the aerospace industry. Recently, it has come to be widely used as a material for chemical industrial equipment, thermal/nuclear power generation equipment, seawater desalination equipment, etc. However, although titanium generally has excellent corrosion resistance, it only demonstrates its high corrosion resistance in an oxidizing acid environment such as nitric acid or in a neutral chloride environment such as seawater. Corrosion resistance in non-oxidizing acid environments, which are commonly found in many countries, was extremely unsatisfactory. In other words, in a non-oxidizing acid environment such as hydrochloric acid or sulfuric acid, the passive film (a thin oxide layer) that maintains titanium's corrosion resistance becomes unstable and active dissolution occurs. .

Therefore, for the purpose of use in such a non-oxidizing acid environment, T
i-Pd alloys have been developed and have come into widespread use, especially in environments containing hydrochloric acid. This is a small amount (
This method takes advantage of the phenomenon that when Pd (approximately 0.2% by weight) is added, the hydrogen overvoltage is significantly lowered, and the natural potential is shifted to the passive state region of pure titanium.

However, this Ti--Pd alloy is relatively expensive, and therefore its use is inevitably limited. In addition, Pd has a problem in that there are many uncertainties in terms of stable supply because the birthplace of Pd is unevenly distributed.

<Means to Solve the Problems> From the above-mentioned viewpoint, the present inventors have devised a method that has sufficiently satisfactory corrosion resistance even in a non-oxidizing acid environment.
J, In order to provide a new low-cost titanium alloy to replace the -Pd alloy, we have developed a new technology that specifically states that ``the corrosion resistance of titanium is due to the passive film formed on its surface, which consists of oxides.
In a non-oxidizing acid solution, this titanium oxide film is destroyed and can exist stably.Therefore, active dissolution occurs across the entire surface, increasing the corrosion rate. Recognizing that "if it exists stably, there will be no deterioration in corrosion resistance," we conducted research aimed at further stabilizing the oxide passive film in titanium materials. In this case, the passive film formed on the titanium surface is strengthened and the corrosion resistance in non-oxidizing acid solutions is improved, but in this case, if a specific amount of Nt is added together with Mo, the passive film becomes even more stable. corrosion resistance in non-oxidizing acid solutions as well as in neutral chloride environments has dramatically improved, making it possible to improve the corrosion resistance of expensive Ti-Pd.
The results showed that the oxidation of the alloys exceeded that of the alloys.

This invention was made based on the above knowledge, and a titanium alloy is made of: Mo: 15.5 to 50.0% (hereinafter, the component ratio is based on weight), Nb: 1.0% By containing less than 20.0% of the above and having a chemical composition in which the remainder is substantially Ti, it is characterized by providing excellent corrosion resistance that is unaffected by the environment. be.

Here, the reason why the composition of the titanium alloy of the present invention is numerically limited as described above will be explained.

(a) M.

Mo has the effect of strengthening the passive film on the surface of the titanium alloy and improving corrosion resistance, and is also an element that dissolves in environmental fluids and becomes molyfdate ions, which exhibits an inhibitory effect. Moreover, by making it coexist with a specific amount of Nb, it further stabilizes the above passive film and has the effect of dramatically improving the corrosion resistance of titanium alloys, especially in non-oxidizing acid environments. . however,
If the content is less than 15.5%, the desired effect cannot be obtained in the above action, and in particular, the expected synergistic effect will not appear even if Nb coexists with a specific amount of Nb.

On the other hand, even if Mo is contained in an amount exceeding 500%, the effect of adding it will be saturated, and oxidizing agents (e.g. ferric chloride etc.)
Corrosion resistance will deteriorate in an environment where these coexist. Therefore, the Mo content was determined to be 15.5 to 500%.

(bl Nb The Nb component is particularly coexisting with Mo having a modulus of 15.5 or higher to significantly form a passive film on the surface of the titanium alloy.

It has the effect of stabilizing the alloy and dramatically improving the corrosion resistance of the alloy, but the content is 1. If the content is less than ○, the desired effect cannot be obtained from the above action, and on the other hand, even if the content is 200 or more, the synergistic effect created by coexistence with a specific amount of MO will not be exhibited as expected, and the expensive Nb The Nb content was determined to be 10% or more and less than 200% because the uniformity of the amount would impair the low cost characteristics of the titanium alloy of the present invention.

Next, the present invention will be explained using examples and comparing with comparative examples.

<Example> First, commercially available industrial pure titanium plates (JI type 32) and Ti
-0.2% Pd alloy plate (ASTM Grade 7
) was prepared, and a plate material of a titanium alloy having a composition of 5+ as shown in Table 1 was also prepared. The titanium alloy plate material was prepared by blending a predetermined amount of Nb powder and MO powder into a pure titanium sponge, and performing triple arc melting using a W electrode in an Ar gas atmosphere with a purity of 9999% to a thickness of 20mm x 8mm. ou
@X After melting a 100myn long square ingot,
This was forged, hot rolled and cold rolled to a thickness of 4wn (
Width: 50 mx) and then annealed.

Next, from each of these materials, 2 to 5 pieces are rolled in parallel to the rolling direction.
A strip-shaped test piece of M thickness x 10 width x 40 length was taken, and ≠
After polishing with 320 Emery Harbor and degreasing and cleaning with acetone, a corrosion test was conducted in a non-oxidizing acid environment.

For the corrosion test, [5 sulfuric acid solution] and [5
% hydrochloric acid - 1% ferric chloride aqueous solution] and bring it to a boil. Two test pieces were immersed in each flask, and after 18 hours, they were taken out and washed with water before and after the test. Find the weight change and calculate the corrosion rate Cji/m2・
h) was adopted.

The results of the corrosion tests conducted in this manner are also shown in Table 1.

As is clear from the results shown in Table 1, the alloy of the present invention exhibits excellent corrosion resistance in a non-oxidizing acid environment, and even in an oxidizing-resistant acid environment containing an oxidizing agent, there are no practical problems. Shows no corrosion resistance. It can be seen that all comparative alloys whose component compositions deviate from the conditions specified in the present invention have inferior corrosion resistance in either or both of a non-oxidizing acid environment and a non-oxidizing acid environment containing an oxidizing agent. .

From these results, it is clear that the titanium alloy according to the present invention will exhibit extremely excellent performance for parts used in environments where hydrochloric acid or sulfuric acid condenses at temperatures below the dew point. be.

In this case, there is also the advantage that it can be used with peace of mind because there is no significant deterioration in corrosion resistance even in an environment containing an oxidizing agent.

Note that the titanium alloy of the present invention contains Sl, v%M1Zr,
It was also confirmed that the corrosion resistance is not adversely affected even if Sn or the like is added alone in an amount of 5% or less. Furthermore, since the titanium alloy of the present invention contains Mo, it goes without saying that it can be strengthened by solid solution strengthening or other heat treatments.

<Overall Effects> As explained above, according to the present invention, it is possible to provide a relatively inexpensive titanium alloy that exhibits excellent corrosion resistance in any environment including a non-oxidizing acid environment, This brings about extremely useful effects industrially, such as making it possible to further improve the performance and reliability of equipment and equipment used in corrosive environments.

Claims (1)

[Claims] It is characterized by containing Mo: 15.5 to 50.0%, Nb: 1.0% to less than 20.0%, and the remainder substantially consisting of Ti. Titanium alloy with excellent corrosion resistance.