JPH05279707A - Sintered body which exhibits continuous change in composition and its production and its applied product - Google Patents

Abstract

PURPOSE:To provide the sintered body which exhibits a continuous change in compsn. and a change in characteristics and the process for production of such sintered body. CONSTITUTION:The sintered body which consists of a base phase and a liquid phase sintering and bonding phase and, the compsn. of which changes continuously in a uniaxially direction and the process for production of such sintered body. An example of the sintered body is the sintered body which has 93.5 to 98wt.% W content at one end of the uniaxial direction and 90 to 92.6wt.% at the other end and in which these contents gradually decrease continuously from one end toward the other. The process for production consists in maintaining the heating up speed at the time the temp. of the body to be sintered passes the liquid phase forming temp. and the temp. gradient in the body to be sintered respectively at specified temps. or above, then maintaining the respective parts of the body to be sintered at the liquid phase forming temp. for a short period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered body showing a continuous compositional change, a method for producing the same, and an applied product thereof.
More specifically, the present invention relates to an alloy sintered body of a refractory metal such as tungsten having a high rigidity / high specific gravity portion and a high toughness / high ductility portion, a method for producing the same, and an applied product thereof.

[0002]

2. Description of the Related Art Conventionally, a W-Ni-Fe-based sintered W alloy has been used for a core material and a quill which are required to have high rigidity / high specific gravity and high ductility at the same time. However, the high specific gravity and high ductility of the same alloy are in conflict with each other in terms of physical properties. That is, when the W content is increased, the specific gravity becomes high and the rigidity is improved, but the ductility is lowered. The opposite is true if the W content is reduced and the Ni or Fe content is increased.

When partial ductility is required, it is a general method to mix a powder having a small amount of W component into the part at the time of molding in the manufacturing process to manufacture a sintered body.
Japanese Patent Application Laid-Open No. 62-196306 is disclosed as a method for producing a W alloy having a composition difference between the surface layer and the inner surface of a sintered body. According to this method, since the W content in the outer peripheral portion is made higher than the W content in the core portion, powders having different compositions are filled so as not to mix with the outer peripheral portion and the core portion during the powder filling operation. In this method, it takes a lot of time to prepare powders having different compositions and to fill the powders so as not to mix them. Further, the obtained product also has a problem that a discontinuous portion is generated due to a rapid change in composition, and thus the product is easily broken near the portion.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sintered body such as a W alloy which shows a continuous composition change / characteristic change. Another object of the present invention is a rod-shaped or column-shaped alloy sintered body such as a core material, which has high rigidity at one end.
The purpose is to provide a sintered body having a high specific gravity and the other end having high ductility. Such a core material has a large penetrating force because the front part that collides with the object has high density and high rigidity, and has a high ductility in the rear part, which prevents cracking due to impact when fired. It becomes possible.

Further, an object of the present invention is to provide a method for easily producing a sintered body showing a continuous composition change, without the troublesome process of filling different composition powder at different positions. Is.

[0006]

The sintered body of the present invention comprises a base phase and a liquid phase sintered binder phase, and is characterized in that the composition continuously changes in a uniaxial direction.

Here, the base phase is a phase of a relatively high melting point substance that forms a solid phase skeleton during liquid phase sintering. The liquid-phase sintered binder phase is a phase composed of powder particles that melt during liquid-phase sintering or a eutectic phase by a solid-phase reaction, which has a melting point lower than that of the base-phase substance and serves to connect the base phases. It consists of a substance that is highly wettable with the base phase substance.

The term "composition continuously changes" means that the abundance ratio of the base phase and the liquid-phase sintered binder phase gradually changes in the state where no sharp change boundary is observed.

An example of the constituent material of the base phase has a melting point of 20.
High melting point ceramics of 00 ° C or higher, for example, WC, Mo
C, TiC, SiC, TaN, BN, Al ₂ O ₃ may be mentioned.

As another example of the constituent material of the base phase, a refractory metal having a melting point of 2000 ° C. or higher, such as W, Mo or Ta.
Is mentioned.

As an example of the constituent substance of the liquid phase, a melting point is 18
Metals having a temperature of 00 ° C. or lower (metals having a low melting point referred to in the present specification), for example, Ni, Fe, Co, Cu and Zn can be mentioned.

One preferred embodiment of the sintered body of the present invention is
The high melting point metal is tungsten, the low melting point metal is a metal containing nickel and iron, the tungsten content rate at one end in the uniaxial direction is 93.5 to 98% by weight, and the tungsten content rate at the other end is 87 to 92. The sintered body has a content of 6% by weight, and the content thereof gradually decreases from one end to the other end.

The W alloy of this embodiment has a W content of 87-9.
8% by weight. W content is 87% by weight (hereinafter simply referred to as%)
If it is less than this, the liquid phase at the time of sintering becomes too much and the shape of the sintered body is broken. Also, the specific gravity becomes low. W content is 98%
If it exceeds, the liquid phase at the time of sintering becomes too small and the sintered density decreases. The portion having a W content of 93.5 to 98% is a portion having high rigidity and high specific gravity, and the portion having a W content of 87 to 92.6% is a portion having high ductility and high toughness.

Nickel and iron become a liquid phase during sintering and play the role of a sintering aid. The total content is preferably 2 to 10%. The relative ratio of nickel and iron content is Ni: Fe
= 5: 5 to 8: 2 is preferable. Liquidus in this composition range,
Since the temperature of the solidus line is the lowest and the area of the solid-liquid coexisting phase is narrowed, it is possible to efficiently sinter. Further, instead of Ni and Fe, Co is 5% to improve ductility.
You may make it contain below.

Other impurities include C, O, P, S and N.
a, K, Ca, Mo, Si and the like. The total content thereof is preferably 0.01% or less.

The W alloy sintered body of this embodiment is preferably rod-shaped or columnar. This is because the composition change in the uniaxial direction tends to occur. The rod-like shape or the columnar shape means that the length in the longitudinal direction is longer than the length (width) in the perpendicular direction, for example, the ratio of the lengths (aspect ratio) is 2 or more.

The method for producing a sintered body showing a continuous compositional change according to the present invention includes a rate of temperature increase when the temperature of the object to be sintered passes through the liquid phase generation temperature in the liquid phase sintering step, and the inside of the object to be sintered. By keeping the temperature gradient above a certain value and raising the temperature, and then by holding each part of the body to be sintered above the liquid phase formation temperature for a short time, the liquid-phase sintered binder phase is uniaxially oriented in the sintered body. It is characterized by moving.

The temperature rising rate, temperature gradient and holding time can be appropriately selected according to the specific composition of the sintered body and the required composition gradient.

One aspect of the present invention is a method for producing a tungsten alloy gradient composition sintered body, which comprises the following steps. (A) A step of mixing a high melting point metal powder and a low melting point metal powder to prepare a powder mixture (B) A step of compression-molding the obtained powder mixture to obtain a molded body (C) The obtained molded body Is heated to a temperature of 1,400 ° C. or lower to obtain a pre-sintered body. (D) The obtained pre-sintered body is heated to a temperature above 1,400 ° C. until the liquid phase formation temperature of the low melting point metal is reached. Temperature rising rate is 5 ° C
Per minute or more, and the temperature gradient in the sintered body when the liquid phase formation temperature is reached is maintained at 1 ° C./mm or more, and the temperature is raised to the liquid phase sintering temperature (E) Liquid phase formation temperature or more While holding the sintered body at (sintered body temperature-liquid phase formation temperature) x time integral value is 250 to 5,
Process of maintaining temperature and keeping temperature in the range of 000 ℃ ・ minute

The production method, particle size, pretreatment conditions and the like of the powder of this embodiment are not particularly limited, but preferred powders are hydrogen-reduced W powder having a particle size of 3 to 10 μm and carbonyl Ni.
Powder, carbonyl Fe powder.

The compression molding method of this embodiment is also not particularly limited, and a uniaxial compression method, an isotropic compression method, an extrusion method and the like can be applied. The relative density of the molded body is 50 to 8
0% is preferable. If it is less than 50%, the strength is low and it is easily deformed or broken. Those over 80% are difficult to make by ordinary methods.

The purpose of pre-sintering is to increase the density while reducing the powder surface. The temperature is 800-1
It is 400 ° C. If the temperature is lower than 800 ° C., the reduction of the powder surface becomes insufficient and the sinterability deteriorates, so that pores may remain even after the main sintering and defects may occur. If the temperature exceeds 1400 ° C, the sintered body will be almost densified during the pre-sintering, and the liquid phase will not move during the main sintering, which will be described later, and the composition difference will not occur.

The pre-sintering is preferably performed in a reducing atmosphere. A hydrogen atmosphere is preferable as an example of the reducing atmosphere. This is because hydrogen can sufficiently reduce the powder surface and is not trapped as residual pores during sintering.

The liquidus formation temperature of one W alloy of this embodiment is about 1430 ° C. (1430-1440 ° C.). The temperature of the main sintering (liquid phase sintering) is about 1500 ° C (1450 to 16 ° C).
Around 00 ° C). An important point is that a temperature gradient is provided in the material when passing through the liquid phase formation temperature during the main sintering temperature rise, and the sintering time is kept constant for a certain period of time. This temperature rising rate needs to be 5 ° C./min or more. If it is less than this, the sintering proceeds during the temperature rise to densify and the difference in composition does not occur.

The action when a composition difference occurs in the sintered body of the present invention will be described. When the temperature of the high temperature part in the sintered body becomes higher than the liquid phase formation temperature, the liquid phase of low melting point component is generated,
It becomes a sintering aid and the sintering proceeds rapidly. for that reason,
The same portion is densified while containing the liquid phase, but next to the same portion, there is also a portion where the temperature is low and the liquid phase is not generated, that is, a portion having connecting holes. The liquid phase in the high temperature portion moves to the low temperature side along the connecting holes due to the capillary force as a driving force.
Due to this action, some parts of the sintered body have a large amount of liquid phase components, while other parts have a small amount of liquid phase components.

The temperature gradient in the sintered body of this embodiment is 1 ° C. /
mm or more, preferably 1.5 ° C./mm or more, more preferably 2 ° C./mm or more. If it is less than 1 ° C./mm, the liquid phase is less likely to move and it is difficult to obtain a composition difference.

During the main sintering, the time for holding the sintered body above the liquid phase formation temperature must be short. The liquid phase is
This is because the W powder can move freely, so that if the time during which the sintered body is at or above the liquid phase formation temperature in a wide range becomes long, the composition difference applied during the temperature rise gradually returns to the average. This averaging phenomenon tends to occur when the sintering temperature is high. The integrated value of (sintered body temperature-liquid phase generation temperature) × time (minutes) while the sintered body is held at the liquid phase generation temperature or higher is 250 to
By setting the temperature to 5000 ° C./minute, averaging of the composition can be avoided. This integrated value is the area surrounded by the diagonal lines in FIG. That is, the temperature was the temperature of the sintered body and the value obtained by subtracting the liquidus formation temperature from the temperature of the sintered body during the period from when the liquidus temperature was exceeded when the temperature was raised to when the liquidus temperature was exceeded when the temperature was lowered. It is a value obtained by integrating the product with time (minutes).

While the temperature is being maintained, it is not possible to keep the temperature of the portion that has previously become higher, but the lower temperature portion does not reach the liquid phase formation temperature.
In some cases, the temperature of the entire sintered body (or the entire sintering furnace) cannot be lowered. For example, if the length of the sintered body is 100 mm and the temperature gradient is raised at 3 ° C./mm in one direction, the temperature difference in the sintered body becomes 300 ° C. If the heating rate is 5 ° C./minute, it takes 60 minutes to raise the temperature by 300 ° C. In the meantime, if the previously heated portion is kept at a high temperature for a long time, the holding time may be too long.

Therefore, it is necessary to lower the temperature of only the portion of the sintered body previously heated in the temperature raising step, in parallel with the operation of raising or holding the temperature of the portion which is heated later. In order to carry out such an operation, it is preferable to use a sintering furnace provided with a mechanism for moving the sintered body in a furnace having a temperature difference depending on the place. Alternatively, it is also possible to use a device capable of moving and heating the sintered body from one end to another end while moving the heating zone of the furnace.

[0030]

Example: W powder (average particle size 5 μm), Ni powder (5 μm)
) And Fe powder (7 μm in the same amount) with 93: 4.9: 2.1.
The ingredients were blended in a ratio of (weight ratio) and mixed by a V-type mixer. The liquid phase formation temperature in this composition was 1430 ° C.

600 g of the obtained mixed powder was filled in a rubber mold having a diameter of 30 mm and a length of 120 mm. CIP molding it under the conditions of pressure of ² Ton / m ^{2 and} time of 60 seconds to give a density of 11.5 g / cm ^3.
A molded body of was obtained. Then, the molded body is 800, 1100,
Pre-sintering was performed for 1 hour under each condition of 1400 ° C. The obtained pre-sintered body was heated at a maximum temperature of 1500 ° C. in a heating furnace having heat zones set to three kinds of temperature rising patterns (A, B, C), and the preheating rate was from 1.5 mm / min to 10 mm / min. The main sintering was performed by moving in the longitudinal direction at a speed. The 1500 ° C. holding time was changed to 10, 33, and 50 minutes.

Table 1 shows the results of chemical composition analysis of the front and rear ends of the products 1 to 6 of the present invention thus obtained. Comparative Examples 7 to 10 in the table are W alloy sintered bodies produced in the same manner as in the Example except that the sintering conditions were deviated from the manufacturing method of the present invention. Comparative Example 7
Indicates that the pre-sintering temperature is too high, 8 indicates that the holding time of the main sintering is too long, 9 indicates that the temperature rising rate is too slow, and 10 indicates that the temperature gradient of the sintered body is too small. ..

[0033]

[Table 1]

In each of Examples 1 to 6, a difference in composition was apparent at the front and rear ends of the sintered body. However, in Comparative Examples 7 to 9, no difference in composition appeared. It should be noted that the sintered bodies obtained in both Examples and Comparative Examples were 100% dense. The heating furnace patterns A, B, and C shown in the table are temperature patterns of the sintering furnace (FIG. 1).
Indicates.

[0035]

As is apparent from the above description, the present invention has the following effects. It is possible to manufacture a sintered body whose composition continuously changes in a uniaxial direction by a simple method without performing laborious work such as preparation of different composition powder and partial filling. It is possible to obtain a sintered body such as a W alloy having one end having high density and high rigidity, the other end having high ductility and high toughness, and having no composition change boundary in the middle. Therefore, there is an advantage in that it is possible to avoid the breakage due to the concentration of stress on the high density and high rigidity portion of the composition change boundary.

[Brief description of drawings]

FIG. 1 is a graph showing a temperature pattern of a sintering furnace used in a method for producing a W alloy sintered body according to an example of the present invention and a comparative example. A and B show the temperature pattern of the example of the present invention, and C shows the temperature pattern of the comparative example.

Claims (9)

[Claims] 1. A sintered body comprising a base phase and a liquid-phase sintered binder phase, the composition of which continuously changes in a uniaxial direction. 2. The sintered body according to claim 1, wherein the base phase is made of a high melting point ceramic or a high melting point metal, and the liquid phase sintered binder phase is made of a low melting point metal. 3. The high melting point ceramic is tungsten,
Carbide, nitride of molybdenum, tantalum or titanium,
The sintered body according to claim 2, which is one or more ceramics selected from carbonitrides or borides, and the low melting point metal is one or more metals selected from nickel, iron and cobalt. 4. The high melting point metal is one or more metals selected from tungsten, molybdenum and tantalum, and the low melting point metal is one or more metals selected from nickel, iron and cobalt. The sintered body described. 5. The high melting point metal is tungsten, the low melting point metal is a metal containing nickel and iron, and the tungsten content at one end in the uniaxial direction is 93.5 to 98 wt%, and the tungsten content at the other end. Is 87-92.6% by weight
The sintered body according to claim 4, wherein the content rate is continuously reduced from one end to the other end. 6. The sintered body according to claim 5, which has a rod shape or a column shape. 7. A core material made of the sintered body according to claim 6. 8. In the liquid phase sintering step, the rate of temperature rise and the temperature gradient in the body to be sintered when the temperature of the body to be sintered passes through the liquid phase generation temperature are each kept above a certain value, and then the temperature is raised. 2. The sintered body according to claim 1, wherein the liquid phase sintered binder phase is uniaxially moved in the sintered body by holding each part of the sintered body at a liquid phase generation temperature or higher for a short time. Manufacturing method. 9. (A) a step of mixing a high melting point metal powder and a low melting point metal powder to prepare a powder mixture; (B) a step of compression-molding the obtained powder mixture to obtain a molded body; C) a step of heating the obtained compact to a temperature of 1400 ° C. or lower to obtain a pre-sintered body; (D) the pre-sintered body obtained above 1400 ° C. in a liquid phase formation temperature of a low melting point metal. Up to 5 ℃ /
And (E) the liquid phase formation temperature while maintaining the temperature gradient in the sintered body when the liquid phase formation temperature reaches the liquid phase formation temperature at 1 ° C./mm or more; and (E) the liquid phase formation temperature. The integrated value of (sintered body temperature-liquid phase formation temperature) × time while holding the sintered body is 250 to 50
6. The method for producing a sintered body according to claim 4 or 5, further comprising the step of maintaining the temperature and decreasing the temperature while maintaining the temperature in the range of 00 ° C / minute.