JPH07109017B2 - Heat resistant Ti alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a heat-resistant Ti alloy excellent not only in hot workability but also in high-temperature strength characteristics.

[Prior Art] Ti alloy is indispensable as a material for chemical devices and aircraft because of its excellent mechanical properties and corrosion resistance, and its small specific gravity and light weight. However, there is a drawback that the strength decreases in a high temperature range exceeding 600 ° C, and for example, the Vickers hardness (hereinafter sometimes referred to as Hv) at 800 ° C is usually only about 50. Therefore, the heat resistance temperature for structural members is limited to about 600 ° C, and the high temperature strength was extremely insufficient. Therefore, TiAl (Ti-50 at% Al) intermetallic compounds are being developed in order to improve such defects, and strength properties that are the same as those in the normal temperature range can be obtained up to a temperature range of about 800 ° C. ing.

[Problems to be Solved by the Invention] However, the above intermetallic compounds are not without drawbacks.
The biggest problem is that the hot workability is low. Therefore, attempts have been made to avoid such inconveniences by using powder metallurgy or the like, but there are many problems that have not yet been solved.

The present invention has been made in view of such circumstances, and an object thereof is to provide a heat-resistant Ti alloy capable of obtaining sufficient strength characteristics and hot workability even in a high temperature range of 800 ° C or higher.

[Means for Solving Problems] The Ti alloy of the present invention comprises four inventions.
Of the invention has a relationship that the Al content and the total content (M) of the eutectoid β-phase stabilizing element (hereinafter sometimes simply referred to as M element) satisfy all of the following formulas (a) to (c). Yes, balance is Ti
And the inevitable impurities.

3 (Al) +2 (M) ≧ 45%… (a) 2 (Al) +5 (M) ≦ 145%… (b) 3 (Al) + (M) ≦ 120%… (c) Next According to the invention, in the above-mentioned first invention, Sn and / or Zr is substituted for a part of the Al content (Al ') within a range satisfying the following formula (e).

A third aspect of the invention is that the alloy composition of the first aspect further includes a solid solution type β-phase stabilizing element (hereinafter may be simply referred to as N element) in a total content (N) represented by the following formula: It is added in a range satisfying (d).

0 <(N) ≦ (Al) (D) Further, in the fourth invention, in the third invention, Sn and / or Sn within a range in which a part (Al ′) of the Al content satisfies the above formula (e). It is replaced by Zr.

[Operation] Some intermetallic compounds have the property that the strength increases as the temperature rises as long as they are within a certain temperature range. The present invention utilizes the effect of improving the high temperature strength by such an intermetallic compound. That is Ti
When Al is added to the Al to precipitate the α ₂ phase (Ti ₃ Al), the high temperature strength is improved. Further, when the M element is added to Ti, an intermetallic compound is formed between the Ti and the M element to improve the high temperature strength.

Moreover, in these intermetallic compounds, unlike the above-mentioned known TiAl-based intermetallic compounds, by adjusting the amount of the additional element, it is possible to obtain excellent hot workability in the high temperature region as is apparent in the examples described later. I found that it can be adjusted to. However, as the precipitation amount of the intermetallic compound increases, the amount of these compounds formed at the grain boundary also increases, resulting in grain boundary destruction and deterioration in hot workability. Therefore, in order to maintain good high temperature strength without deteriorating hot workability, it is necessary to limit the amounts of Al and M added. The formulas (a) to (c) are defined from such a viewpoint, and the reasons for setting these formulas will be described below.

3 (Al) +2 (M) ≧ 45% (B) This formula is determined from the viewpoint of improving high temperature strength.

When 12% or more of Al is added to Ti, Ti ₃ Al precipitates, but according to the study by the present inventors, it is necessary to add 15% or more of Al alone to obtain sufficient high temperature strength. It was found that there is (see FIG. 1 of the Example described later). Further, with respect to the M element alone, sufficient high temperature strength was obtained with the addition amount of 22.5% (see FIG. 1). Next, even if the amount of Al added is less than 15%, the required high-temperature strength can be obtained by simultaneously adding the M element together. For example, if the added amount of (Al): 5%, (M): 15% The strength was sufficient (see FIG. 1). (A)
The formula is obtained from such experimental results.

Next, 2 (Al) +5 (M) ≦ 145% (B) and 3 (Al) + (M) ≦ 120% (C) are determined from the viewpoint of maintaining hot workability. That is, the maximum allowable addition amount for maintaining the required hot workability is
Al was 40%, and M element was about 30% in the operating temperature range of ordinary equipment, that is, 1200 ° C or less, although it varied depending on the hot working temperature (see Fig. 1). When both Al and M were added, the maximum allowable addition amount of M was 15% at (Al): 35%. The above equations (b) and (c) are obtained from such experimental results.

The type of M element used in the present invention is not particularly limited, but for example, Mn, Cr, Fe, Co, Ni, Cu, Zn or
Si etc. are illustrated. However, Mn, Cr and Fe are most preferable, and Ni and Co are next preferable, in consideration of the effect of addition, solubility and cost.

Next, N element, which is a solid solution type β-phase stabilizing element, does not form an intermetallic compound when added to Ti, but has an action of expanding the β-phase region in the matrix. Hot workability is improved. However, the added amount increases and β
As the phase region expands, the strength characteristics decrease, especially
The degree of strength reduction in the high temperature range of about 800 ° C is remarkable. Therefore, it is necessary to limit the amount of N element added to a range in which high temperature strength is maintained. According to the experiment, the amount of N element added
When the addition amount of Al is exceeded, the decrease in high temperature strength tends to be remarkable (see Hv column of Example 4 Tables 8 and 9 described below), and even when the strength decrease is not significant, N If the added amount of the element is excessive, the specific gravity of the alloy becomes large, which is not preferable. From this point of view, the following formula 0 <(N) ≦ (Al) (d) is defined. The type of N element in the present invention is not particularly limited, but V, Mo, Nb, Ta, etc. are exemplified.

Next, Sn and Zr coexist with Al in the Ti alloy,
And an intermetallic compound is formed between them and the same effect as the addition effect of Al. Therefore, Sn and / or Zr can be added instead of a part of the added amount of Al. In this case, the quantitative relationship between Sn and Zr, which are substituted by 1 atomic% of Al, is Al = Sn.
/ 3, Al = Zr / 6. As a result, the quantitative relationship of the content (Al ') of Al that replaces Sn and / or Zr is defined as (Al') = (Sn) / 3 + (Zn) / 6 (d).

As with Sn and Zr, Hf can be added instead of Al.

Examples will be described below, but the present invention is not limited to the following examples, and it is within the technical scope of the present invention to appropriately change the design in view of the gist of the preceding and the following.

[Examples] Example 1 Fe, Cr and Mn were selected as the M element and mixed with Ti and Al.
120 g of the original alloy was melted by the tungsten arc melting method, and 11
Hot rolled at 50 ° C. The processing rate was 25% per pass, and reheating was performed for each pass, and the final rate was 75%.

In order to evaluate the hot workability as a qualitative material, the state of cracking on the surface and inside of the material after rolling is judged visually or by an optical microscope, and it is considered good until surface cracking occurs.
Those that could crack inside were not allowed. For alloys with good hot workability, high-temperature strength up to 800 ° C was measured [corresponding to a value of approximately 1/3 of tensile strength (Kgf / mm ² ) Vickers hardness (Hv)].

Fig. 1 shows the test results of hot workability and high-temperature strength characteristics (hereinafter, both may be simply referred to as characteristics) Ti-Al-M3.
It is shown as an elemental composition diagram (the balance: Ti). The symbols ◎, ○ and other symbols in the figure are based on Table 1.

In FIG. 1, the relational expression of the contents of Al and M element shows the limit line of high temperature strength [formula (a)] and the limit line of hot workability [formulas (b) and (c)]. It was found that both the high temperature strength property and the hot workability were excellent within the range surrounded by the three limit lines. By the way, as the M element, F
All of e, Cr, and Mn showed almost the same effect of addition, and although there were some differences in hardness, the range of appropriate addition amount was the same.

It is to be noted that more preferable addition conditions for achieving extremely high temperature strength and hot workability are 2.5% <(Al) ≦ 35% 2.5% <(M) ≦ 15% (Al) + (M) ≧ 20% 2 (Al) +5 (M) ≦ 145% are all satisfied, and more preferable addition conditions are 5% ≦ (Al) ≦ 35% 5% ≦ (M) ≦ 15% (Al) + (M) ≧ It was found that 20% (Al) +4 (M) ≦ 75% was all satisfied.

Example 2 Ni, Co, Si, Cu, and Zn were selected as M elements, and a Ti-Al-M ternary alloy was melted and hot rolled in the same manner as in Example 1 to evaluate the characteristics. The evaluated alloy composition is shown by a circle in FIG. 2 (the balance: Ti). The results are shown in Tables 2-6. The following second
In Table 11, the symbols ◎, ○ and × in the column of hot workability mean the following, respectively.

◎… No surface cracks ○… Surface cracks ×… Internal cracks Also, A in each remarks column of Tables 2 to 7 and 10 below.
And B respectively mean A: Inventive Example B: Comparative Example.

From Tables 2 to 6, it was found that the characteristics of Ni, Co, Si, Cu and Zn were also good if the expressions (a) to (c) were satisfied.

Example 3 Several kinds of M elements were added in combination and the characteristics of a soluble and hot rolled Ti alloy were evaluated. The results are shown in Table 7.

As is clear from Table 7, even in the case of a Ti alloy in which a plurality of M elements are added in combination, the addition amount of which satisfies the above expressions (a) to (c) is either hot workability or Hv hardness. Also turned out to be good.

Example 4 Mn or Cr was added as an M element and V was added as an N element.
The properties of the Ti alloy obtained by adding Mo and Mo were evaluated. The results are shown in Tables 8 and 9. A and B in the remarks column of these tables
Means A: present invention (N added) B: comparative example (N added).

As is clear from Tables 8 and 9, V and Mo improve the hot workability, but when the addition amount is excessive, the high temperature strength is significantly reduced. However, it was found that the examples of the present invention satisfying the above formulas (A) to (D) had excellent hot workability, substantially improved Hv, and only a slight decrease in Hv.
Further, V and Mo had the same effect on hot workability and high temperature strength characteristics, even if one of V and Mo was added alone or both of them were added at the same time.

Example 5 Targeting Mn additive, Sn and / or
The characteristics when Zr was added were evaluated. The results are shown in Table 10. The Al equivalent in Table 10 and Table 11 described later means the sum of the value of the added Sn and Zr amounts converted into the Al amount based on the above equation (e) and the actually added Al amount.

As is clear from Table 10, when a part of Al is replaced with Sn and / or Zr, all the examples of the present invention satisfying the above formulas (a) to (c) and (e) show good characteristics. It was

Example 6 Targeting Mn, V and Mo additives, a part of Al is Sn and / or
The characteristics when substituting for Zr were evaluated. The results are shown in Table 11.

As is apparent from Table 11, even if a part of Al was replaced with Sn and / or Zr based on the formula (e), there was almost no difference in the characteristics.

[Advantages of the Invention] Since the present invention is configured as described above, heat-resistant Ti that does not impair hot workability and has significantly improved high-temperature strength characteristics compared to conventional Ti alloys and TiAl-based intermetallic compounds It is now possible to provide alloys.

[Brief description of drawings]

FIG. 1 is a diagram showing hot workability and high temperature strength characteristics in each composition (remainder: Ti) of Ti-Al-M (M: Mn, Cr, Fe) alloys,
Fig. 2 is a diagram showing the composition (remainder: Ti) of the sampled material for the hot workability and high temperature strength property test of Ti-Al-M (M: Ni, Co, Cu, Zr, Si) alloys. is there.

Claims (4)

[Claims] 1. An Al content [hereinafter expressed as (Al), where (A
l) means atomic%] and the total content of eutectoid β-phase stabilizing elements [hereinafter expressed as (M), where (M) means atomic%], but the following formulas (a) to ( A heat resistant Ti alloy characterized by satisfying all of the above (3) and the balance being Ti and inevitable impurities. 3 (Al) +2 (M) ≧ 45%… (B) 2 (Al) +5 (M) ≦ 145%… (B) 3 (Al) + (M) ≦ 120%… (C) 2. The Al content (Al) and the total content of the eutectoid β-phase stabilizing element (M) are in a relationship satisfying all of the following expressions (a) to (c), and the following expression ( Al within the range of (e)
A heat-resistant Ti alloy, characterized in that a part of the content (Al ') is replaced by Sn and / or Zr, and the balance consists of Ti and unavoidable impurities. 3 (Al) +2 (M) ≧ 45%… (B) 2 (Al) +5 (M) ≦ 145%… (B) 3 (Al) + (M) ≦ 120%… (C) [Wherein (Sn) and (Zr) represent atomic% of Sn and Zr, respectively] 3. Al content (Al), total eutectoid β-phase stabilizing element content (M) and total solid solution type β-phase stabilizing element total content [hereinafter referred to as (N), However, (N) means atomic%] is a relationship satisfying all of the following formulas (a) to (d), and the balance is Ti and unavoidable impurities. 3 (Al) +2 (M) ≧ 45%… (B) 2 (Al) +5 (M) ≦ 145%… (B) 3 (Al) + (M) ≦ 120%… (C) 0 <(N) ≤ (Al) ... (d) 4. The Al content (Al), the total eutectoid β-phase stabilizing element content (M), and the total solid solution type β-phase stabilizing element content (N) are expressed by the following formula (a): ) To (d) are all satisfied, and a part (Al ′) of the Al content is replaced by Sn and / or Zr within a range that satisfies the following formula (e):
A heat-resistant Ti alloy characterized by the balance being Ti and inevitable impurities. 3 (Al) +2 (M) ≧ 45%… (B) 2 (Al) +5 (M) ≦ 145%… (B) 3 (Al) + (M) ≦ 120%… (C) 0 <(N) ≤ (Al) ... (d) [Wherein (Sn) and (Zr) represent atomic% of Sn and Zr, respectively]