JPS5919981B2 - W-based high toughness sintered alloy - Google Patents

Description

[Detailed description of the invention] The present invention relates to a W-based sintered alloy having high toughness.

Traditionally, W-based sintered alloys have mainly been used for their high specific gravity, high modulus of elasticity, and radiation shielding effect, but in recent years, it has been thought that the high melting point of W can be used to apply them to heat-resistant materials such as die-casting molds. There is.

The problem with heat-resistant materials is that thermal shock and pressure are applied at the same time, such as in die-casting mold parts.
They often break brittle, and there are restrictions on the dimensions and shapes that can be used.

The present invention provides a high-toughness W-based sintered alloy with improved toughness and oxidation resistance, and a method for producing the same.

The W-based sintered alloy according to the present invention has W particles and Fe-Ni-Cu.
It consists of a binder phase consisting of Cr, which generates a liquid phase during the sintering process, and which surrounds the W particles.

The toughness of an alloy with such a structure is determined by the following factors: the W particles and the binder phase have sufficient wettability and strong interfacial strength, the binder phase itself has high toughness, and the W particles This is determined by the fact that it does not grow coarse during the sintering process.

The W-based sintered alloy according to the present invention contains 85 to 95% by weight of W and Cr.
0.5 to 3% by weight, the balance being Cu, Fe, and Ni
Consists of ingredients.

The composition range of Cu, Fe, and Ni in the W+Cr-containing Cr balance is shown in the shaded area A-B- of the Fe-Ni-Cu composition diagram in Figure 3.
This is the range surrounded by C-D-E-F-A.

In the figure, Cu/F at points A, B, C, D, E, and F
The elNi ratio is as follows.

A; Cu/Fe=60/40 B: Cu/Fe/Nj=15/40/
15C; Cu/Fe/Ni = 15/4/
15D; Cu/Fe/N1=85/4/10E;
Cu/Fe/Ni = 85/5/10F:
Cu/Fe/Ni = 60/5/35Cu
-The amount of Fe in the Fe-Ni combination is 4% or more, 40
% or less, the Cu amount is preferably 15% or more and 85% or less when Fe is less than 5%, and 15% or more and less than 60% when Fe is 5% or more and 40% or less.

The reason why the amount of W was limited to 85% or more was to maintain the heat resistance and high strength of the W-based alloy.If it exceeds 95%, the amount of the binder phase becomes too small and there are many contact areas between the W particles. This is because the toughness decreases.

An example is shown in FIG.

The W particles become coarse during sintering to form a polyhedron, and each surface serves as a contact surface between the W particles.

The toughness is extremely low as shown in Table 1 A612.

The first effect of adding Cr is to prevent coarsening of W particles during liquid-phase sintering, to configure the binder phase into a network, and to provide high toughness.

A specific example is shown in FIG.

FIG. 2 is an impact fracture diagram of the alloy of Table 1/162.

The mesh-like distribution of the binder phase prevents the W particles from becoming coarse, and disperses impact energy, for example.

Furthermore, it becomes possible to obtain high toughness by inhibiting the growth of cracks propagating through the binder phase.

The second effect of adding Cr is to improve the oxidation resistance of the binder phase.

The reason why the amount added is 0.5% or more is that if it is less than 0.5%, not only the second effect but also the first effect cannot be exhibited.

If it exceeds 3%, the toughness of the binder phase decreases and the sinterability also decreases.

The effect of Cu in the W-based sintered alloy of the present invention is to generate a liquid phase at a relatively low temperature during the sintering process, facilitating sintering and improving the wettability between the binder phase and W particles. .

However, if the amount of CuO in the binder phase is too large, the heat resistance strength will be reduced.

Therefore, the amount of Cu is limited to the above range.

Although the amount of Cu was limited in relation to the amount of Fe, Fe is an essential constituent element in the W-based sintered alloy of the present invention.

The first effect is that it facilitates the addition of Cr.

Since Cr is easily oxidized, it is necessary to pay close attention to the sintering atmosphere and the grinding and mixing process. If Cr2O3 is formed, not only will Cr not be alloyed, but the toughness will be significantly reduced due to the presence of oxides.

However, when a master alloy powder of Fe or Fe--Ni is used as in the present invention, the above-mentioned problems are almost eliminated and the effects of Cr can be fully exhibited.

Further, by utilizing the sigma phase generated in Fe-Cr and Fe-Ni-Cr systems, a Cr master alloy powder can be easily obtained by grinding or the like.

Therefore, the Fe amount is related to the Cr addition J amount in Cu-F
4% or more is required when e-Ni is combined with silk.

The second effect of Fe is to cause Cr to form a solid solution in the binder phase.

As a result, it becomes possible to improve the oxidation resistance of the W-based sintered alloy.

However, the reason why the amount of Fe is limited to 40% or less is because if it exceeds 40%, the sinterability decreases and it becomes difficult to obtain a dense alloy with few defects.

The method for producing the W-based sintered alloy of the present invention will be described below with reference to Examples, including W powder with an average particle size of 3 to 4μ, electrolytic Cu powder, carbonyl Ni powder, carbonyl Fe powder, and Fe-42,
325, which is obtained by crushing a Si-→ phase compound obtained by heat treating a 5% Cr, Fe-17, 5% Ni-44, 5% Cr alloy.
Using powders with a mesh size or less, they were blended to have the composition shown in Table 1, mixed and ground in a ball mill, and then subjected to hydrostatic pressure at 3 j□H/Cr? Molded with L, 30mmφXIO□
It was made into a u+ molded body.

A part of the molded body is 12mrrt x 55mm, 6r
Cut into a specimen of nm x 33ii, 1,250°
30 ml in a hydrogen stream at various temperatures from C to 1,450 C.
n~60ml1n was sintered.

A 10 mm x 50 mrrt impact test piece with a notch and a 5 mm x 30 mm transverse rupture strength test piece were prepared from the sintered body, and the Charpy impact value and transverse rupture strength were measured respectively.

Further, these test pieces were appropriately cut out and the high temperature hardness was measured.

It is clear from Table 1 that the alloy of the present invention exhibits high toughness and high hardness.

The table also compares the oxidation resistance of the conventional alloy and the alloy of the present invention.

For the oxidation resistance test, the material was heated in air at 600°C for 100 hours, and the oxidation weight gain was measured.

From this result, it is clear that the oxidation resistance is significantly improved by the addition of Cr.

In order to evaluate the performance of the W-based sintered alloy of the present invention as a heat-resistant material, the alloy according to the present invention shown in Table 1 was
A test piece of ×3071Lm was prepared and
An experiment of forced cooling and forced heating, each held at a temperature of about 30 seconds, was conducted and surface cracks were observed, but no cracks were observed after repeating the test about 10,000 times.

As mentioned above, the W-based sintered alloy of the present invention has strong bonding strength between the binder phase and W particles, and the addition of Cr prevents the growth and coarsening of the W particles, resulting in high toughness and oxidation resistance. It can be manufactured using normal sintering methods and is a useful material as a heat-resistant material.

[Brief explanation of drawings]

Figure 1 shows the impact fracture surface of a conventional material magnified 1000 times. FIG. 2 shows the impact fracture surface of the material of the invention magnified 500 times. FIG. 3 is a composition diagram showing the composition range of the FeNi-Cu alloy that is the remainder of the alloy of the present invention.

Claims (1)

[Claims] 1 W85-95% by weight, Cr 0.5-3% by weight, the balance being three components of Cu, Fe, and Ni, composition diagram A-B-C-D- shown in Figure 3. Range surrounded by E-F-A, where A: Cu/Fe=6o/40 B: Cu/Fe,/'Ni=15/4o
/15C: Cu/Fe/Ni = 15/4/
1 sD: Cu/Fe/N i = 85/
4/10E: A W-based high toughness sintered alloy characterized by a ratio of Cu/Fe/N1=s515/10 F: Cu/Fe/N1=s515/35. 2 The amount of Fe in the combination of Cu, Fe, and Ni is 4%
The W-based high toughness sintered alloy according to claim 1, wherein the W-based high toughness sintered alloy is 40% or less. 3 The amount of Cu in the CutFeyNi combination is F
If e is 4% or more and Fe is less than 5%, 15% or more 85%
Below, if Fe is 5% or more and 40% or less, 15% or more6
The W-based high toughness sintered alloy according to claim 1, which has a content of less than 0%. . 4 85 to 95% by weight of W, 0.5 to 3% by weight of Cr, and the remainder consists of components of Cu, Fe, and Ni, and is surrounded by the composition diagram A-B-C-D-E-F-A shown in Figure 3. where A: Cu/Fe=60/40 B: Cu/Fe/Ni = 15/40/1
5C: Cu/Fe/Ni = 15/4/1
5D: Cu/Fe/'N i = 85/4
/l OE: Cu/Fe/Ni = 85/
5/10F: Cu/Fe/Ni = 60/
A W group characterized by molding and sintering a mixed powder consisting of a mixed powder with a ratio of 5/35, in which Cr is a powder obtained by grinding Fe-Cr or Fe-Ni-Cr sigma phase compound. High toughness sintered alloy manufacturing method. 5. The method for producing a W-based high-toughness sintered alloy according to claim 4, wherein the sintering is carried out at a temperature of 1250 to 1450° C. at which constituent powders other than W begin to react and form a liquid phase.