JPH0310038A - Method for setting alloy components in ti alloy having excellent corrosion resistance - Google Patents

Abstract

PURPOSE:To permit the estimation of the corrosion resistance in Ti alloy and to improve the corrosion resistance with high reliability by determining the kind of elements for alloying into pure Ti and their amounts to be added so that the average bond order found from the bond order of the above elements and the atomic fractional rate of the elements is regulated to the value in the prescribed range. CONSTITUTION:The average bond order Bo of the alloy is found in the inequality I from the bond order (Bo)i between pure Ti and (i) element for alloying and the atomic fractional rate (xi) of the (i) element. Then, the kind of the elements for alloying and their amounts to be added are determined so that the average bond order Bo satisfy the inequality II or III according to the crystal structure (hcp or bcc) of the Ti alloy contg. the elements for each alloy. Furthermore, in the case where the crystal structure of the Ti alloy is regulated to (bcc), the kind of the elements for alloying and their amounts to be added are determined preferably by applying the inequality IV.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a method for setting the composition of additive elements for an alloy when manufacturing a Ti alloy with good corrosion resistance, and in particular to evaluating the corrosion resistance of a Ti alloy. The present invention relates to a method for setting alloy components that uses an average bond order of several hundred O as an index of .

[Conventional technology]

Ti has the characteristic of being easily passivated, but it is easily corroded in reducing environments such as hydrochloric acid and sulfuric acid, where the passive film is easily destroyed.For this reason, various alloying elements have traditionally been added to Ti. Therefore, Ti alloys with improved corrosion resistance have been developed. Development of this conventional Ti alloy,
In property management, the influence of alloying elements on one or more properties of the Ti alloy is determined through experiments and measurements, and the optimal alloy composition is determined based on these data.
The so-called trial-and-error method is commonly used.

[Point u while the invention is trying to solve the problem]

However, the conventional trial-and-error method requires a great deal of cost and time and is extremely inefficient, and is particularly difficult to implement with multi-component alloys. Further, when developing an alloy using an element, such as v, as a base metal, which has not been tested in many cases, an even larger amount of research and development investment is required. Furthermore, when this trial IW error method is used, the evaluation is inaccurate, which poses a major problem in improving the reliability and performance of materials.

The present invention was made in order to solve the above-mentioned conventional problems, and by obtaining a corrosion resistance index map in advance, predicting the corrosion resistance based on this, and conducting experiments only on alloys within a limited range, the corrosion resistance can be evaluated. The object of the present invention is to provide a method for setting the alloy composition of a Ti alloy with excellent corrosion resistance, which enables the development of an excellent Ti alloy and reduces investment in research and development.

[Means for solving the problem] The present inventors conducted various studies to solve the above problem, and
It has been found that the corrosion resistance of Ti alloys can be evaluated by using the bond order (hereinafter referred to as Bo) representing the magnitude of the bonding force between the base metal and the alloying element.

The present invention is based on the above knowledge, and the bond order (Bo) i of element i for alloy sealed in pure Ti and the atomic fraction χi of element i in the alloy are calculated by the following formula % formula % (). Find the bond order To. In the case of hCp, this average bond order number 100 is 3.513≦Bo≦4,000bc, depending on the crystal structure of the Ti alloy containing the alloying element.
In the case of c, the type of alloying element and its addition amount are determined so that 2.790≦100≦3.000, which is a method for setting the alloy composition of a Ti alloy with excellent corrosion resistance.

Further, when the crystal structure of the Ti alloy containing the alloying element is bcc, it is more preferable to determine the alloying element and its addition amount so that 2.860≦13o≦3.000.

Here, the above average bond degree 100 is 3.513 or less (h
c p -T i), 2.790 or less (bcc-TI
), the above-mentioned corrosion resistance improvement effect cannot be obtained, and the average bond order To is 4.000 or more (hcp-Ti
), 3.000 or more (bcc-Ti), it is not preferable because it becomes difficult to process even in hot conditions.

Note that the bond order (Bo) i of element i above is determined by the molecular orbital method (
Discrete-VariaLional(DV)
It can be determined by the Xα cluster method). This DV-Xα cluster method is a molecular orbital calculation method performed using an aggregate (cluster) model of several to several dozen atoms.

FIG. 9 shows the cluster model used by the inventor in the above calculation, and FIG. 9 (4) shows a close-packed hexagonal lattice (hcP), MT
+,, cluster model, and Fig. 9 1bl is a body-centered cubic lattice (b CC), MT l +a cluster model. However, in the figure, ◯ indicates TI, and ◯ indicates alloying element M.

In each of the above figures, the interatomic distance is set from the lattice constant,
The electronic structure of a cluster (molecule) is defined by SlaL
However, unlike the usual method, the secular equation is solved self-consistently using the Xα potential proposed by Er). , find the electron energy eigenvalues and eigenfunctions.

This cluster method differs from the band calculation method in that it allows us to investigate local electronic states. By examining the electronic state around the alloying element using the cluster model shown in FIG. 9, it is possible to determine a parameter representing the alloying effect, that is, the bond order Bo between the Ti base metal and the alloying element M. This bond order Bo is determined by calculating the overlapping integral of the respective atomic orbits of the base metal Ti and the alloying element M for all base metal lXTi atoms around the alloying element M in the cluster in Figure 9. . In the case of a multi-component alloy, the bond order (Bo) of element i in alloying element M is determined by the above formula.
The average bond order Bo, which is the average value of i, is determined.

Note that the corrosion resistance of the Ti alloy can also be evaluated by using the d-orbital energy level (hereinafter referred to as Md) of the alloying element M in the base metal.

In this case, two new electron levels, 1g and Ltg, based on the alloying element M appear at the d''9 electron level calculated by the cluster containing the alloying element M. The average of these two In the case of a multi-element alloy, use the average (t[Md) calculated from the Md of each i element in the alloying element M.

In addition, the present inventors have determined the phase stability index t using 13o-%d.
Figure 1 has been developed and has already been applied for (Japanese Unexamined Patent Application Publication No. 62-50
In this application, an index diagram was created to predict harmful phases when excessive elements are added in order to improve the mechanical properties of alloys.
The present invention uses W o -TX d to create an index diagram showing the corrosion resistance of Ti alloys.

[Effect]

In this invention, it has been discovered that the corrosion resistance of Ti alloys is related to the magnitude of the bonding force between the base metal and the alloying element, and the bond order representing this bonding force is used as a parameter indicating corrosion resistance. , by calculating the above bond order from the f1 class of alloying elements or the amount added
It becomes possible to estimate the corrosion resistance of the alloy. This makes it possible to limit the scope of trial-and-error tests for determining the optimal alloy composition to a narrow range, and it is only necessary to conduct experiments on alloys within this range, which requires significantly less cost, effort, and effort than conventional methods. The time can be reduced, and the corrosion resistance of the Ti alloy can be improved with high reliability.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Examples described below are hcp-7i or bcc-T, respectively.
This was done to find the optimal range for the average bond order of several hundred for i. In the first example, a sulfuric acid solution was used as a corrosive solution in the polarization measurement and immersion test for setting the optimal range. In the second example, a hydrochloric acid solution was used as the corrosive solution. Further, in each example, as a specific example 1, the above polarization measurement etc. were carried out in a corrosive solution at 70°C, and as a specific example 2, a corrosion rate measurement was carried out in a corrosive t8W! i,
An example of what was done inside is shown.

First, a specific example 1 of the first embodiment will be explained in detail using FIGS. 1 to 9.

First, the relationship between the amount of alloying elements added and To,'id was investigated.

Figure 1 shows how To and ud of the alloy are on the index diagram when using the cluster model of hcp-7+ in Figure 9 (8), using Ti as the base metal, and adding the various alloying elements shown. For example, when adding Z' or Hf to pure Ti, @o, pd changes upward and to the right as the amount of addition increases from the position of Ti shown in the figure.On the other hand, when adding AI Figure 2 shows that using the cluster model of bζc-Ti in Figure 9 t), using TI as the base metal, and adding the various alloying elements shown in the figure, the alloy 100, For example, when Mo is added, it changes to the upper left from the position of Ti, and when V and Cr are added, it changes almost to the left.

Furthermore, when Fa, Co, and Ni are added, To and Md change downward compared to pure Ti.

Next, binary h c p -T i alloy (α coalescence &),
a: pure Ti, b two Ti 10wL%A1 (hereinafter,
(using atomic %), c: Tl-2Affi, d
:T 1-2Nb, e : Ti-2Ta, r : Ti-
10Hf, g: T 1-10zr (D) Each alloy was melted and subjected to polarization measurements and immersion tests in a sulfuric acid solution at 70°C.

Figure 3 shows g:Ti-IQZ' as an example of polarization measurement.
Figure 4 shows the relationship between the bond order Bo and the current density of the active dissolution peak of the binary phase alloy.
Third. As is clear from Figure 4, Z'' is an element that reduces the current density of the active t8 melting peak, and
, Ta, and Hr also decreased the 1i current density of the active dissolution peak. On the other hand, Aj increased the current density at the active peak. Also, from this test, it was found that regardless of the alloy system, the bond order B
A quantitative relationship is recognized between e and the t current density of the active dissolution peak, and the alloy system with a large bond order Bo has an active i' of 8%.
It was found that the f-peak current density was low.

This suggests that Bo is an important parameter for evaluating the corrosion resistance of hcp-Ti alloys. From the same figure, it can be seen that when BO≧3.513 or more, the corrosion resistance is improved compared to pure Ti.

As a result, if the T1 alloy is HCP Kozo, taking into account that it is difficult to process even in hot when 3o is 4.000 or more as mentioned above, the bond order is 3.513≦3.513≦
It can be set within the range of Bo≦4.000.

In addition, Figure 5 shows the relationship between corrosion loss and Bo in the immersion 71 test, and it is clear from the figure that alloy systems with higher Bo have better corrosion resistance, and this also reflects the results shown in Figure 4 of the C book. It corresponds to

Next, a similar study will be described for a binary bcc-Ti alloy (β alloy) to which Fe, V, Cr, and Mo are added in a range of 11 to 22 aL%.

Figure 6 shows the results for Ti-11Mo as an example of scratching measurements, and Figure 7 shows the relationship between the bond order BO of these binary β-phase alloys and the current density of the generated melting peak. As is clear from Figure 7, a quantitative relationship is observed between the bond order BO and the tfL density of the active dissolution peak. This is not related to the type of alloy system, and the current density at the active melting peak is low in alloy systems with large BO.This shows that Bo is an important parameter for evaluating the corrosion resistance of BCC-Ti alloys as well. This suggests that It can be seen that when Bo≧2.790 or more, the corrosion resistance can be improved more than that of pure Ti.

As a result, when the Ti alloy is bcc+Ma, considering the above-mentioned workability, that is, the fact that when BO is 3.000 or more, it is difficult to work even under hot conditions, the bond order ■O is set to 2.790≦B
It can be set in the range of o≦3.000.

In addition, Fa, V, and Mo are elements that shift the corrosion potential (cathode reaction) toward the no-pull side, and Mo in particular shifts the corrosion potential significantly as shown in Figure 6, showing passivity in the natural immersion state. . The elements that shift these corrosion potentials are Tf in FIG.

- [d Change Md to the left from the position of Ti on the diagram.

From this, the ld level is related to the corrosion potential and %T
It can be seen that along with O, it is a useful parameter for evaluating corrosion resistance. Further, the 'IJIB diagram shows the relationship between corrosion loss in the immersion test and Bo.

It can be seen from the figure that the alloy system with a large Bo content has good corrosion resistance, and this corresponds to the results shown in Fig. 7.

Next, a second specific example of the first embodiment will be explained.

Here, 40%t(! SO4″fP!1! i8
The corrosion rate of the bcc-Ti alloy was measured in liquid.

The Ti-35Mo-3Nb alloy, which is a conventional material, is an alloy that is said to have extremely good corrosion resistance, but because of the large amount of Me added, it has poor workability.

On the other hand, as shown in Table 1, the alloy of the present invention, in which Zn and Hf are added so that Be≧2.860, has good workability and exhibits super corrosion resistance that exceeds that of conventional materials. Ta.

In this way, it has a bccii structure, and Bo≧2.860
It can be seen that the Ti alloy has super corrosion resistance.

As a result, in the case of the bcc structure, the range of bond order 100 can be further set to the optimal range of 2.860≦Bo≦3.000.

Next, a second embodiment of the present invention will be described.

The major difference from the first example is that the scratching measurement and immersion test were conducted using salt f11f8 solution instead of the sulfuric acid solution as the corrosive solution.

This result shows that the T1 alloy prepared by the alloy composition setting method of the present invention also has excellent corrosion resistance against chlorine.

(Specific Example 1 of Second Example) First, a decentralized measurement was performed using a hydrochloric acid solution for a, b, f, and H of the above-mentioned α alloys. The results are shown in Figure 1O, and Figure 11 shows the relationship between the current density of the active melting peak in the hydrochloric acid solution and the bond order Bo for the α alloy 1M described above.
-g are all shown. As is clear from these figures, there is a quantitative relationship between the bond order Bo and the current density of the active dissolution peak, which is related to the alloy system.
It was found that the current density at the active melting peak was low in alloy systems with a large o. This suggests that BO is an important parameter for evaluating the corrosion resistance of hcp-Ti alloys. From the same figure, it can be seen that when BO≧3.513 or more, the corrosion resistance against chlorine is also improved compared to pure Ti.

As a result, when the Ti alloy has an hcp structure, taking into account that it is difficult to process even in hot conditions when 13o is 4.000 or more as mentioned above, the bond order of several hundred is 3.513
It can be set within the range of ≦Bo≦4.000.

More salt! ! α alloys a and b were immersed in two solutions.
In addition to f and g, the test was also conducted for T i -2Z r.

The results are shown in FIG. 12. From the same figure, it can be seen that the alloy system with a large Bo content has good corrosion resistance, which corresponds to the results shown in FIG. 11.

Next, two-element BCC-Ti alloy (β alloy), specifically Ti-8Co and Ti-12Cr.

Anodic polarization measurements were performed on pure Ti, Ti-22V, Ti-8Mo, Tl-8Ni, and Tl-8Co.

Ti-12Fe, Ti, Ti-12Cr, Ti-8N
i, TiTi-1l was subjected to cathode content Bii measurement using hydrochloric acid t8 solution. The results are shown in Figure 13 (11) and ('b), respectively, and Figure 14 shows these two results.
Bond order Bo of original β element phase alloy and if of active melting peak
It shows the relationship with f density. From these figures, there is no relationship with the type of alloy system, and B.

A relationship is observed in which the electric vX density of the active dissolution peak is low for alloy systems with a large value. From this, BO is bcc
It is suggested that -Ti alloy is also an important parameter for evaluating corrosion resistance. and BO≧2.7
It can be seen that when it is 90 or higher, the corrosion resistance against chlorine can also be improved compared to pure Ti.

As a result, when the Ti alloy has a bcc structure, considering the above-mentioned workability, that is, the fact that it is difficult to work even in hot conditions when π0 is 3.000 or more, the bond order 100 is set to 2.790≦100≦3. It can be set in the range of 000.

Also in this second embodiment, Fe, Co, and Mo are used.

Ni is an element that shifts the corrosion potential (cathode reaction) toward the no-pull side (see Figure 13 (bl)), and Mo in particular causes a large shift in the corrosion potential as shown in Figure 6, making it passive in the natural immersion state. These elements that shift the corrosion potential change ld to the left from the position of Ti on the 100-1d diagram in Figure 2. From this, the Md level is related to the corrosion potential, and the To It can be seen that this is a useful parameter for evaluating corrosion resistance.

Further, an immersion test using a salt el Fe solution was conducted on a β alloy containing Fe, V, Cr, Co, and Mo in a range of 11 to 22 at% (see Figure 15).
As shown in the figure, the larger the BO, the better the corrosion resistance, which corresponds to the results shown in FIG.

(Specific Example 2 of Examples of 'l!, 2) Table 2 shows the results of measuring the corrosion rate of a BCC-Ti alloy in a 409 HCZ boiling solution. , and 100≧2.8600T1 alloy is found to have super corrosion resistance even when sealed in chlorine.

Table 1 Table 2 [Effects of the Invention] As described above, according to the method for setting the alloy composition of the T1 alloy with excellent corrosion resistance according to the present invention, the bond order (Bo) of the i element for alloying with respect to pure Ti and the i Since the alloying element class iI and the amount added are determined so that the average bond order Bo determined from the atomic fraction χi of the element is a value within a predetermined range, the effect of improving corrosion resistance can be predicted and It is only necessary to conduct experiments on alloys of
This has the effect of reducing labor and time and improving the corrosion resistance of the Ti alloy.

[Brief explanation of the drawing]

1 to 9 are diagrams for explaining the alloy composition setting method according to the first embodiment of the present invention, and FIG.
A diagram showing the effect of alloying elements on corrosion resistance in p-Ti alloy, Figure 2 is a diagram showing the effect of alloying element on corrosion resistance in bcc-Ti alloy, Figure 3 is a polarization curve diagram of Tl 10Zr alloy, Figure 4 is a corrosion resistance index diagram showing the active dissolution peak current of hcp-Ti alloy.
Corrosion resistance index diagram showing corrosion loss of alloy, Figure 6 is T i
-11Mo alloy polarization curve diagram; Figure 7 is a corrosion resistance index diagram showing active dissolution peak current of BCC-Ti alloy; Figure 8 is a corrosion resistance index diagram showing corrosion loss of BCC-Ti alloy;
Figures fal and (bl are hCp-"l"i, respectively. Figs. is a diagram showing the first
Figure 0 is an anode decentralization curve diagram of hap-Ti alloy, male 11
The figure is a corrosion resistance index diagram showing the active dissolution peak current of hcp-Ti alloy, Figure 12 is a corrosion resistance index diagram showing corrosion loss of hcp-Ti alloy, and Figure 13 (4) is an anode polarization curve diagram of bcc-Ti alloy. , Fig. 13 fbl is a 7-F polarization curve diagram of the bcc-Ti alloy, Fig. 14 is a corrosion resistance index diagram showing the active dissolution peak current of the bcc-Ti alloy, and Fig. 15 is a diagram showing the corrosion weight loss of the bcc-Ti alloy. It is a corrosion resistance index diagram.

Claims (1)

[Claims] (1) Bond order (Bo) between pure Ti and i-element for alloying
From i and the atomic fraction χi of element i, the following formula @B@o=Σ
The average bond order @B@o of the alloy is determined according to χi(Bo)i, and the average bond order @B@o is determined in the following range depending on the crystal structure (hcp or bcc) of the Ti alloy containing each alloying element. 3.513≦@B@o≦4.000 (for hcp)2
．． A method for setting alloy components of a Ti alloy with excellent corrosion resistance, characterized in that the types and amounts of alloying elements are determined so that 790≦@B@o≦3.000 (in the case of bcc). (2) The crystal structure of the Ti alloy containing each alloying element is bcc
In the case of , the above average bond order @B@o is 2.860@B
2. A method for setting alloy components of a Ti alloy with excellent corrosion resistance as claimed in claim 1, wherein the types and amounts of alloying elements are determined so that @o≦3.000.