JPH03226504A - Manufacture of high density titanium alloy powder sintered product - Google Patents

Abstract

PURPOSE:To make the density high and the metallurgical structure on surface layer fine and to improve fatigue characteristic of a product by executing cold isostatic pressing to mixed powder of Ti powder and the other alloy powder and successively, high temp. sintering, shot peening and hot isostatic pressing. CONSTITUTION:The Ti powder and metal powder or alloy powder of one or more kinds of Al, V, etc., are mixed so as to make the prescribed composition. After packing the mixed powder into a die, the cold isostatic pressing is execut ed. After executing the high temp. sintering to the obtd. formed body, the shot- peening is executed to seal holes on the surface and in the inner part. Successive ly, the hot isostatic pressing is executed to obtain the high density Ti alloy powder sintered product. As the other way, after executing the high temp. sintering treatment to the above formed body, the high density energy treatment with electron beam, etc., is executed, and successively, the hot isostatic pressing is executed.

Description

Detailed Description of the Invention (Field of Industrial Application) This book relates to a method for manufacturing titanium alloy sintered parts, particularly titanium alloy parts that have high density and excellent fatigue resistance by adopting the raw powder method. It is something.

(Conventional technology) Traditionally, parts with complex shapes such as automobile engine parts were made by cutting steel materials, but recently, in line with the demand for lighter weight and higher efficiency, this has been replaced by a cutting process. Development of various parts using titanium alloys is progressing.

However, conventional titanium alloy parts are manufactured by melting in a vacuum arc melting furnace, then undergoing processes such as forging, hot rolling, and heat treatment, and then being machined, and these processes are expensive. Due to its complexity and complexity, it was inevitably expensive to manufacture and lacked versatility.

Therefore, in recent years, near-net shape molding methods such as powder metallurgy methods have been used instead of conventional melting methods.

In this powder metallurgy method, a mixed powder that is mechanically mixed in advance to have a predetermined alloy component is filled into a flexible mold such as rubber so that it can be molded into a predetermined shape, and then cooled and left to stand. Compression molded into a predetermined shape using a hydraulic press (CI P),
Then, it is sintered at high temperature and then hot isostatically pressed (HI).
A method for manufacturing titanium alloy parts using the so-called raw powder method, which performs P), is being developed.

According to this method, since titanium powder, metal, or alloy powder is used without going through the expensive steps seen in the above-mentioned melting method, the additional component elements can be blended in any weight ratio, In addition, there is an advantage that elements that cannot be added due to solidification segregation or whose addition amount is limited in the melting method or the alloy powder method can be added.

However, in the raw powder method, since the mold (such as rubber) used during CIP is flexible, unevenness due to molding remains on the surface of the powder molded body, and this remains even after sintering and HIP. In addition, through-holes are partially formed on the surface of the powder compact after sintering, and pressure gas flows into these through-holes during the HIP process, so pressure acts inside the through-holes and seals the through-holes. Insufficient holes may remain as defects after HIP treatment, making the product unusable for parts requiring fatigue strength.

As a method for sealing a powder molded body, for example, as disclosed in JP-A-62-205201,
A method of shot blasting before IP has been proposed. Also, in Japanese Patent Application Laid-open No. 63-24320fi, HIP
Previously, irradiating a sintered material with an electron beam has been disclosed. The raw material powders disclosed in these publications are metal powders containing iron as a main component (in particular, the latter targets high-speed tool steel as an example), and do not disclose non-ferrous metal powders.

(Problem to be solved by the invention) Titanium alloy steel has high specific strength and excellent corrosion resistance and heat resistance, so it is gradually being applied to aircraft parts and automobile engine parts, and parts with complex shapes can also be developed using powder metallurgy. It is being done. The present invention employs the base powder method among powder metallurgy methods to manufacture parts of complex shapes from titanium alloys, and the conditions for molding into a specific shape and sintering are adjusted particularly as disclosed in the above-mentioned publication. By specifying it in relation to the titanium alloy, we eliminate the through holes remaining in the surface layer of powder sintered products, and provide a method for manufacturing titanium alloy parts with high density and excellent fatigue resistance. It is something to do.

(Means for Solving the Problem) The technical idea of the present invention is to melt the surface of the sintered body by irradiating cold plastic strain or high-density energy to the group of through-holes on the surface of the titanium alloy sintered body. High-density titanium alloy powder sintered product that undergoes pre-treatment to render defects harmless and then HIP treatment to induce recrystallization of the surface layer to refine the metal structure of the surface layer and improve the fatigue properties of the product. It is in the manufacturing method.

The focus is on the manufacturing technology of titanium alloy powder sintered products using the raw powder method, which the inventor has researched for many years,
Surface modification technologies such as shot peening, electron beam irradiation, and laser beam irradiation. In other words, a mixed powder that has been mechanically mixed in advance to have a predetermined alloy composition is compacted into a predetermined shape using a mold press or cold isostatic press, and then vacuum sintered and HIPed. Eliminate residual through holes in the surface layer. To this end, the present invention eliminates residual through-holes in the surface layer of the product after HIP by previously treating the surface layer of the sintered titanium alloy semi-finished product with shot peening, electron beam irradiation, laser beam irradiation, etc. This is a method for manufacturing high-density titanium alloy powder sintered products that increases the density of the final product and also modifies and refines the surface metal structure to improve the fatigue properties of the product. That is, the present invention provides: (1) Filling a mold with a mixed powder of titanium powder and one or more metal powders or alloy powders so as to have a predetermined alloy composition, and performing cold isostatic pressing; After the molded body formed by this is subjected to high temperature sintering treatment, it is subjected to shot peening treatment using surface modification technology, and then subjected to hot isostatic pressing treatment. 2. The method of manufacturing a high-density titanium alloy powder sintered product according to claim 1, characterized in that a treatment (electron beam irradiation, laser beam irradiation) is performed, followed by hot isostatic pressing treatment.

In the present invention, as the titanium alloy, for example, AΩ
, V, Mo, Cr, Zr, Sn, Fe, etc., or a titanium alloy containing one or more of them.

In the present invention, metal powder refers to single powder such as A11 powder and alloy powder such as V4°Ai'6o.

In addition, Ti can be easily produced by mixing Ti with a mother alloy of commercially available alloy powder with a specific composition (α+β
) phase alloy system T i 69c+ A Q4 ', 6
V9 Gold or Ti 10%V-200FC!
396 A D Q The composition of the gold thread is a component system with little variation in quality.The present invention is not limited to this component system.

The size and shape of the raw material powder are preferably spherical with an average particle size of 100' or less in order to increase the packing density of the titanium alloy sintered body and to suppress the remaining of through holes on the surface. In addition, cold isostatic pressing is performed at 4000 kgf/cd or more, preferably 5000 kgf/c- for 15 minutes or more, and hot isostatic pressing is performed at a pressure of 4000 kgf/cd or more, preferably 5000 kgf/c- for 15 minutes or more, and hot isostatic pressing is performed in the two-phase temperature range of α and β of the mixed alloy component.
000 kg' f/cd or more, 15 minutes or more, the packing density is high, the number of through holes in the surface layer is reduced, the remaining bores (holes) inside the parts are eliminated, and a powder sintered product of high density titanium alloy is produced.

In the shot peening treatment, a steel ball is projected to crush the through holes and work harden the vicinity of the surface layer of the sintered body. To do this, a steel ball of about 500-1 or more is projected at 5 kg/c- or more for about 5 minutes to obtain a hardness of about 25 to 50 tIrm on the surface layer (
Desirably, the conditions are such that work hardening is achieved at 100 points with Hv500g). After the HIP treatment, the hardened layer is completed as a product with a finer metal structure from the surface to about 20 ts layer.

It is preferable that the surface refined metal structure has several α grains in an equiaxed position and has a hardness about 10 points higher than that of the base material.

As a result of sealing the surface and internal pores of the sintered body through shot peening treatment, it is possible to increase the density, refine the metal structure of the product, and obtain a highly reliable product with excellent fatigue properties. .

In addition, as a surface modification technology, heat sources such as gas, arc, and plasma have low energy density, so a large amount of heat is required to melt the surface of the sintered body, resulting in a coarse metal structure in the surface layer. This is not preferable because not only the above effects cannot be obtained, but also thermal deformation of the sintered body occurs.

Therefore, it is an important technical element to use a high energy density beam such as an electron beam or a laser beam to locally melt the surface layer of the sintered body with dwarf heat to refine the metal structure. For this purpose, the electron beam conditions are: acceleration voltage: 110 to 170 kV, and beam current: 5 to 50 mA.

Beam movement speed: 50mm ~ 3000ryu/akin
It is preferable to perform high-speed oscillation of the beam in a linear manner. In addition, the laser beam irradiation conditions were a laser beam output of 2.5 to 6 kW, 20
-13511111/' win speed, Ar atmosphere = 1
A condition of ~4 kg/e- is preferable.

In this way, cold plastic strain or high-density energy is applied to the through-holes on the surface of the titanium alloy sintered body to perform pretreatment to render surface defects harmless, and then HIP treatment is performed to form the sintered body. By inducing refinement of the recrystallized structure of the surface layer, the surface metal structure is refined and the fatigue properties of the product are improved. For various parts that require fatigue properties, it is often only necessary to impart the fatigue properties to a limited portion of the part, and by applying the treatment of the present invention to the surface of molded products with complex shapes, it is possible to achieve excellent fatigue strength. It is possible to provide a method for manufacturing parts with

(Example 1) Two types of powder were prepared: a titanium powder consisting of 99.6% titanium, 0.09% oxygen, and 0.0005% or less of chlorine, and a mother alloy powder with a composition of 60% aluminum and 40% vanadium. .

A 10 mm'X200+D11' rod in the shape of a Ti-6%AM-4%V titanium alloy test piece was manufactured according to the following steps, and its properties were investigated.

First step: Titanium and master alloy powders were mechanically mixed at a weight ratio of 9:1.

Second step: The mixed powder obtained in the first step was filled into an elastic rubber mold having a predetermined shape.

3rd step: 4500 kg of powder filled into a rubber mold
/cd for 155 minutes.

4th step: The green compact is vacuumed at 10-'Torr, 120
Sintering treatment was carried out at 0'c for 2 hours.

Fifth step: In order to compare the sintered body without treatment (Test 1) and with the treatment, shot peening conditions were 0. A steel ball with a diameter of G (hardness Hv 590) was projected at a speed of 48 m/see. The projection time was set at two levels: 20 minutes (test 2) and 40 minutes (:lJt test 3). For electron beam irradiation (Test 4), the sintered body was inserted into an electron beam vacuum chamber with a vacuum level of 10-4 Torr, and the surface was melted (acceleration voltage: 2150 kV, beam current: 20 mA, beam movement speed: 1 m/'min).

In addition, the beam was oscillated into a line with a length of 25 mm by high-speed oscillation). In addition, beam irradiation was performed at a beam current of 1 OmA and other conditions were the same (Test 5).

For carbon dioxide laser beam irradiation, the sintered body was inserted into a laser beam vacuum chamber with a vacuum level of 10-'Torr, and the output was 4kW and the speed was 44m+s/mi to perform surface melting treatment.
thermal spraying in an Ar atmosphere of 2.0 kg/J (Test 6) and an output of 4 kV under the same other conditions (Test 7).

Note that the β transformation point of this alloy is 990°C.

Step 6: Ti-6%Al1-4 made by the conventional method (no pretreatment) and the method of the present invention! The sintered body of '6V alloy was inserted into a hot isostatic press furnace and heated at 920°C for 3 hours at 1000kg f/cd.
It was hot isostatically pressed.

Table 1 shows a comparison between the method of the present invention and the conventional method.

The surface sealing state of each metal was observed together with the observation of the metal structure of the cross section of the sample. The density was determined by the Archimedes method, and the relative density was calculated in advance using a standard sample with no surface through-holes or internal bores remaining and is shown in Table 1. The test conditions for fatigue strength are axial force, stress ratio R--1, frequency f-
20 Hz, in the atmosphere, at room temperature.

Table 1 As is clear from Table 1, as a result of the complete pore sealing treatment in all cases of the present invention, the remaining bores (holes) inside the parts are eliminated compared to the conventional method, and high-density It can be seen that a titanium alloy powder sintered product can be made and the fatigue strength (10' cycle number) is also improved.

(Example 2) Four types of powder: titanium powder consisting of 99.6% titanium, 0.09% oxygen, and 0.0005% or less of chlorine, and a mother alloy powder with a composition of BO% aluminum and 40% vanadium, and 85% vanadium. A master alloy powder containing 15% aluminum and a powder containing 100% iron were prepared.

Ti-10%y-2%Fe3%A according to the following steps
J7 titanium alloy test piece shaped rod 10mm-×200
m+*' was manufactured and its properties were investigated.

1st step: Titanium, master alloy AN 60V40. Vss
Ail l! , iron powder weight ratio 85:2.5:
Mechanical mixing was performed at a mixing ratio of 10.5:2.

Second step: The mixed powder obtained in the first step was filled into an elastic rubber mold having a predetermined shape.

A rubber mold for a CIP test piece was prepared so that the product would be an io++ui- fatigue test piece after HIP.

3rd step: 4500 kg of powder filled into a rubber mold
/C- for 155 minutes.

4th step: The green compact is vacuumed at 10-'Torr, 130
Sintering treatment was carried out at 0'C for 3 hours.

Fifth step: In order to compare the sintered body with no treatment (test 10) and with treatment, the sintered body was inserted into a shot peening projection device under shot peening conditions, and a steel ball with a diameter of 0.5 ms (hardness Hv 550 ) 47m
/see was projected for 15 minutes (Test 8). In addition, for electron beam irradiation, the sintered body was inserted into an electron beam vacuum chamber with a vacuum level of In-'Torr, acceleration voltage: 160 kV, beam current + 23
+IIA, beam movement speed: 1 m/1n, and surface melting treatment was performed while oscillating the beam linearly at high speed (Test 9).

The β transformation point of this alloy is 790°C.

Sixth step: The sintered bodies made by the conventional method (no pretreatment) and the method of the present invention are inserted into a hot isostatic press furnace, and heated at 760°C for 3 hours at 1050 kg f.
/c- hot isostatically pressed.

Table 2 shows a comparison between the method of the present invention and the conventional method.

The surface sealing state of each metal was observed together with the observation of the metal structure of the cross section of the sample. The density was determined by the Archimedes method, and the relative density was calculated in advance using a standard sample with no surface through-holes or internal bores, and is shown in Table 2. The test conditions for fatigue strength in the table are axial force, stress ratio R--1, frequency f-20Hz, atmosphere, and room temperature.

Table 2 As is clear from Table 2, as a result of the complete pore sealing treatment in all cases of the present invention, the remaining bores (holes) inside the parts are eliminated compared to the conventional method, and high-density It can be seen that a titanium alloy powder sintered product is produced and the fatigue strength (107 cycles) is also improved.

(Example 3) Two types of powder were prepared: a titanium powder consisting of 99.6% titanium, 0.09% oxygen, and 0.0005% or less of chlorine, and a master alloy powder having a composition of 60% aluminum and 40% vanadium.

Ti-6%Aj7-4%V titanium alloy automotive connecting rod 25I11×801m1′w× according to the following process
220 mm' was manufactured and its characteristics were investigated.

First step: Titanium and master alloy powders were mechanically mixed at a weight ratio of 9:1.

2nd step: The mixed powder obtained in the 1st step was filled into an elastic rubber mold of a predetermined shape.

3rd step: 4000 kg of powder filled into a rubber mold
/CI for 155 minutes.

Fourth step, vacuum the green compact at tflO-'Torr, 12
Sintering treatment was performed at 50°C for 3 hours.

Fifth step: Insert the sintered body into a shot peening projection device under shot peening conditions, and insert a 47 m steel ball (hardness Hv 550) with a diameter of 0.5.
/see was projected for 15 minutes. For comparison, a conventional method without pretreatment was included.

Sixth step: The Ti-6%Al-4%V alloy sintered bodies made by the conventional method (no pretreatment) and the method of the present invention were inserted into a hot isostatic press furnace and heated at 920°C for 3 hours. , hot isostatically pressed at 100,100 O/cd. When a physical fatigue test was conducted on a connecting rod for an automobile, the method of the present invention was found to have an approximately 25% improvement in fatigue strength compared to the conventional method.

(Effects of the Invention) As explained above, the present invention allows parts with complex shapes to be manufactured from titanium alloy, and by irradiating the sintered alloy member with high-density energy such as shot blasting, EB, laser, etc. Then, by applying HIP treatment, a titanium alloy with a relative density of 100% is obtained.In other words, it is light and has high specific strength, which is the characteristic of titanium, and has excellent corrosion resistance and heat resistance, as well as high density and fatigue resistance. You can get excellent parts.

sub-agent

Claims (2)

[Claims] (1) A molded body made by filling a mold with a mixed powder made by mixing titanium powder and one or more metal powders or alloy powders to have a predetermined alloy composition, and performing cold isostatic pressing. A method for producing a high-density titanium alloy powder sintered product, which comprises subjecting it to high-temperature sintering, followed by shot blasting, and then hot isostatic pressing. (2) After high-temperature sintering of the molded body, high-density energy (electron beam irradiation, laser beam irradiation)
2. The method for producing a high-density titanium alloy powder sintered product according to claim 1, further comprising performing a treatment and then a hot isostatic pressing treatment.