JP3372358B2 - Manufacturing method of Ti alloy - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a Ti alloy capable of improving both strength and ductility.

[0002]

2. Description of the Related Art Ti, which is a group IVA metal element, has a high melting point and a high specific strength, and has the property of exhibiting corrosion resistance in all environments. Therefore, Ti alloys are nowadays used in the fields of the aerospace industry, which are inevitably used at high temperatures and also require high strength, or as structural materials for connecting rods of internal combustion engines, exhaust gas valves and the like. .

As an example, Ti which is an (α + β) alloy
There is a -6Al-4V alloy. This alloy has, for example, 4 % by mass of V for forming a β solid solution, and 6 % by mass of Al, which is an α-stabilizing element that improves the mechanical properties of Ti, and the balance is Ti and unavoidable. It is a composition composed of impurities, and a predetermined ductility is obtained by performing an aging treatment after the sintering treatment.

[0004]

By the way, the Ti-
Ti alloys such as 6Al-4V alloys are used as sintered alloys because of their low cost, but pores (sintered pores) are generated during the sintering process for obtaining the sintered alloys. Therefore, in actual use, the presence of the pores causes deterioration of the mechanical strength, and the mechanical strength varies variously depending on the shape and distribution of the pores. Due to this, the problem that sintered Ti alloys cannot be used as structural materials for members such as connecting rods and exhaust gas valves of internal combustion engines for which high speed durability is required, or as structural materials in the aerospace industry field is pointed out. Has been done.

The present invention solves this type of problem, and an object of the present invention is to provide a method for producing a Ti alloy which makes it possible to easily obtain a sintered Ti alloy having excellent ductility and strength.

[0006]

In order to solve the above-mentioned problems, the present invention provides 2 % by mass or more and 8 % by mass or less of Al powder, 2 % by mass or more and 6 % by mass or less of V powder, and 2 % by mass. % To 8 mass% Co and 1 mass% to 6 mass% Sn Co-Sn alloy powder, and 0.01 mass% to 0.3 mass% B based on the total weight. and a Cr-B-based metal compound powder is a step of the balance to form a mixed powder is Ti powder and unavoidable impurities, sintering process developing in the mixed powder, the mixed powder before
Is the temperature 15 ° C lower than the liquidus temperature of the Co-Sn alloy?
From the liquidus temperature to a temperature 15 ° C. higher than the liquidus temperature, and heating at a heating rate of 5 ° C./60 minutes to 250 ° C./60 minutes.

[0007]

[Detailed Description of Configuration] Obtained by the manufacturing method according to the present invention.
The Ti alloy was, alpha strength of the stabilizing an element Ti alloy, heat resistance and corrosion resistance of Al has an effect of improving (oxidation resistance) of 8 quality than 2% by weight, based on the total weight
It is blended so as to be less than the amount% . If Al is less than 2 wt%, the desired effects described above not express, also, 8 mass
This is because if the content exceeds 100 % , the Ti alloy becomes brittle due to the formation of an intermetallic compound of Ti ₃ Al.

V is in a composition range of 2 % by mass or more and 6 % by mass or less. V is a β-stabilizing element and has the effect of activating the precipitation from the β phase to the α phase and improving the strength by performing an aging treatment after the sintering treatment. If V is less than 2 % by mass , the desired effect is not exhibited, and if it exceeds 6 % by mass , only β-stabilization proceeds, so that the desired strength cannot be obtained.

Co has a composition range of 2 % by mass or more and 8 % by mass or less. Co is a eutectoid β-stabilizing element and a sintering promoting element, and has the effect of improving strength by increasing the addition amount. When Co is less than 2 % by mass , the desired effect is not exhibited, and when it exceeds 8 % by mass , a large amount of Ti—Co-based intermetallic compound precipitates, resulting in a decrease in ductility.

Sn has a composition range of 1 % by mass or more and 8 % by mass or less. Sn is a neutral element that forms a solid solution and stabilizes in both α-Ti and β-Ti phases, and due to solid solution strengthening due to the atomic radius difference between Ti and Sn, Ti increases with the addition amount. It has the effect of improving the strength of the alloy. In addition, Sn also has the effect of suppressing the material embrittlement due to ω-phase precipitation. When Sn is less than 1 % by mass , these desired effects are not exhibited, and when it exceeds 6 % by mass , the effects are saturated.

The Cr-B-based metal compound is a titanium alloy (α
It has the effect of promoting the refinement and densification of the + β) phase and improving the strength and ductility. The CrB-based metal compound, in a _{CrB 2, CrB, Cr 2 B} , Cr 5 B 2, any one or more, used alone or in combination, B
Is added in an amount of 0.01 % by mass or more and 0.3 % by mass or less based on the total weight. When B is less than 0.01 % by mass , the desired effect is not exhibited, and when it exceeds 0.3 % by mass , strength deterioration is caused.

The balance of the above composition is the predominant T
i and a very small amount of unavoidable impurities. The unavoidable impurities include C, N, Fe, O _{2 and the} like.

[0013]

In the manufacturing method according to the present invention , the Co element and the Sn element are added as Co-Sn alloy powder. Therefore, since the liquid phase of the Co—Sn alloy powder is generated at a temperature equal to or lower than the sintering temperature, the sintered Ti alloy can be densified and the strength can be improved. In addition, Co element and Sn
When the elements are added as individual powders (elementary powders), the Sn element has a low melting point, so that Sn is melted out at a low temperature and flows out while leaving voids between the Ti particles. Therefore, there is no effect on the densification of the sintered Ti alloy. The Co element instantaneously forms a liquid phase due to the reaction between Ti and Co in the sintering process, but does not contribute to the densification between Ti particles.

Further, in the method for producing a Ti alloy according to the present invention, after each powder and the binder are mixed, CIP is performed.
A green compact is formed by a (cold isotropic working press) method or a hydraulic press method. Next, as shown in FIG. 1, the green compact is heated at a temperature rising rate of 5 ° C./60 minutes to 250 ° C./60 minutes within a liquidus temperature T _m ± 15 ° C. of the Co—Sn alloy. Further, the sintering process is performed at the sintering temperature T _s for the time t. Therefore, the liquid phase of the Co—Sn alloy is generated, and the densification is achieved by the rearrangement of the powder particles and the effect of promoting sintering.

Here, when the temperature is raised at a rate exceeding 250 ° C./60 minutes, the liquid phase of the produced Co--Sn alloy flows out, leaving voids between the Ti particles and densifying between the Ti particles. Cannot be achieved. On the other hand, if the temperature is raised at a rate of less than 5 ° C./60 minutes, densification is achieved by the generation of an appropriate amount of liquid phase and promotion of sintering, but it only lengthens the sintering cycle.

Further, although the liquidus temperature T _m can be expanded to a range of ± 15 ° C. or more, it is not efficient because it only lengthens the sintering cycle.

[0017]

The method for producing a Ti alloy according to the present invention will be described in detail below with reference to the accompanying drawings.

First, the Ti alloy according to the present example, the Ti alloy as a comparative example, and the Ti-based alloy used as the criterion for determining the physical properties.
6Al-4V alloys were produced and then the relative density (denseness), tensile strength and elongation (ductility) of each alloy was measured. Table 1 shows the experimental results of Examples 1 to 3 of the present invention and Comparative Examples 1 and 2.

[0019]

[Table 1]

The method for producing the Ti alloy of Example 1 will be described below. First, Ti powder, 3Al-4V alloy powder, and Cr
The liquidus temperature T _{m of the} B ₂ powder is lower than the sintering temperature (1260 ° C.), for example, about 1120 ° C. (66.7 mass% C
o-33.3 mass% Sn) alloy powder was added, and Ti-3 was added.
Component of Al-4V-4Co-2Sn-0.3CrB ₂
The composition was adjusted to obtain the desired mixed powder.

The mixed powder thus prepared is mixed in a V-shaped mixing frame for about 30 minutes and then mixed by a hydraulic press at about 6 ton / min.
It was compacted under a load of cm ² . This green compact is 11
After being heated at a temperature rising rate of 20 ° C./60 minutes in a temperature range of 20 ° C. ± 15 ° C., it was sintered. This sintering condition is
The temperature was 1260 ° C., the time was 14.4 Ksec, and the degree of vacuum was set to 10 ⁻³ Pa.

The method for producing the Ti alloy of Example 2 is substantially the same as that of Example 1, except that the temperature rising rate of the green compact in the temperature range of 1120 ° C. ± 15 ° C. is set to 60 ° C./60 minutes. Only the points differ.

The manufacturing method of the Ti alloy of Example 3 is the same as that of Examples 1 and 2 with respect to Ti powder, 3Al-4V alloy powder and CrB ₂ powder, but the liquidus temperature T _m is about 1120.
The (66.7 mass% Co-33.3 mass% Sn) alloy powder and the (30 mass% Co-70 mass% Sn) alloy powder of (degreeC) were added in the ratio of 1.2: 1. Ingredients / composition, powdering conditions, etc. are the same as in Examples 1 and 2, but 1120 ° C. ± 15
The temperature raising rate in the temperature range of ° C was set to 60 ° C / 60 minutes. A heat treatment diagram for the sintering of Examples 1 to 3 is shown in FIG.

Here, when the Co--Sn alloy powder is added, a desired alloy component is obtained from the relationship between the sintering temperature and the liquidus formation temperature (liquidus temperature T _m ) only with a single Co--Sn alloy powder. You may not get it. Therefore, as described above, C
A desired alloy component is obtained by adding and adjusting a plurality of alloys having different components with an o-Sn alloy powder. At that time, the liquidus temperature T _m of the Co—Sn alloy changes as the mass% of Sn is changed, as shown in FIG. Therefore, it is desirable to select a Co-Sn alloy powder having different added components and the same liquidus temperature T _m to obtain a desired alloy component.

It is easily assumed that such an alloy preparation method can be applied to an alloy system of Fe and Ni and Sn which are transition elements of the same family as Co.

In Comparative Example 1, Co powder and Sn powder were added to Ti powder, 3Al-4V alloy powder and CrB ₂ powder, and then compacted and fired under the same conditions as those in Example 2 above. Tied up. Further, Comparative Example 2 is Ti-6Al-4V.
It is an alloy and was manufactured by adding 6Al-4V alloy powder to Ti powder. The mixing conditions, powder compacting conditions, etc. are the same as in Example 1.

As a result, in Examples 1 to 3, the mechanical strength and the relative density were improved as compared with Comparative Examples 1 and 2. In particular, the relative density was remarkably improved, so that the sintered Ti alloy was densified. Therefore, as a structural material for members such as connecting rods and exhaust gas valves of internal combustion engines that can effectively secure mechanical strength and high speed durability, or as a structural material in the aerospace industry field, sintering The effect that the Ti alloy can be effectively used was obtained.

Next, the same manufacturing method as in Example 1 was adopted, and an experiment was conducted to detect changes in the relative density of each Ti alloy obtained by variously changing the rate of temperature rise in the temperature range of 1120 ° C. ± 15 ° C. went. The results are shown in FIG. 4, and it was found that the control of the heating rate near the liquidus temperature T _m affects the relative density. In particular, at a temperature rising rate of 180 ° C./60 minutes or less, a relative density of 99% or more is obtained.
Even at a heating rate of 50 ° C./60 minutes or less, a relative density of 98% or more, that is, Comparative Examples 1 and 2 or more was obtained.

Further, FIG. 5 shows the results of fatigue tests conducted using the Ti alloy of Example 1 and the Ti alloys of Comparative Examples 1 and 2. From this, it was determined that Example 1 was superior to Comparative Examples 1 and 2 in terms of fatigue strength as well.

In each of the examples, the rate of temperature rise is limited to within at least ± 15 ° C. of the liquidus temperature T _m of the Co—Sn alloy. You can also However, if this range is widened, the sintering cycle is only lengthened, which is not efficient.

[0031]

As described above, the production of the Ti alloy according to the present invention
According to the manufacturing method , the following effects can be obtained.

Since the Co--Sn alloy powder is added, a liquid phase is generated at a temperature equal to or lower than the sintering temperature, the sintered Ti alloy is densified, and both ductility and strength can be improved. This has the effect of preventing fatigue failure of the Ti alloy and making it suitable for use in internal combustion engines and the like.

[Brief description of drawings]

FIG. 1 is a heat treatment diagram of sintering in a method for producing a Ti alloy according to the present invention.

FIG. 2 is a relationship diagram between mass% of Co—Sn alloy and liquidus temperature.

FIG. 3 is a heat treatment diagram of sintering in the method for producing a Ti alloy according to Examples 1 to 3.

FIG. 4 is a diagram showing the relationship between the temperature rising rate and the relative density.

5 is an explanatory diagram of fatigue tests of Example 1 and Comparative Examples 1 and 2. FIG.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C22C 1/00-49/14

Claims (2)

(57) [Claims] 1. An Al powder of 2 % by mass or more and 8 % by mass or less,
2 mass% or more and 6 mass% or less of V powder and 2 mass% or more and 8 mass%
Mass% or less of Co and S of 1 mass% or more and 6 mass% or less
and a Co—Sn alloy powder consisting of n and a Cr—B based metal compound powder containing 0.01 % by mass or more and 0.3 % by mass or less of B with respect to the total weight, and the balance being Ti powder and forming a mixed powder is inevitable impurities, sintering process developing in the mixed powder, the mixed powder, the C
Liquid from a temperature 15 ° C lower than the liquidus temperature of the o-Sn alloy
5 within the range of 15 ℃ higher than the phase line temperature
C./60 minutes to 250 [deg.] C./60 minutes of heating at a heating rate. 2. The method according to claim 1 , wherein the mixed powder has a temperature 15 ° C. lower than a liquidus temperature of the Co—Sn alloy.
Temperature range from 15 ° C to 15 ° C above the liquidus temperature
The method for producing a Ti alloy is characterized in that heating is performed at a heating rate of 5 ° C./60 minutes to 180 ° C./60 minutes.